Perspectives on transport pathways of microplastics across the Middle East and North Africa (MENA) region

Introduction

The pervasive occurrence of MPs both globally and within the MENA region has become a major environmental concern due to their ubiquitous presence across all biomes¹. MPs are defined as polymer particles sized from 1 µm to 5 mm with various shapes such as fibers, fragments, and films which can be classified into primary MPs that are intentionally manufactured in such small sizes, and secondary MPs which can be formed through the breakdown of plastic products, especially when they enter natural habitats^2,3,4,5.

MPs are by-products arising from a variety of human activities, including industrial production, agricultural activities, sewage disposal, and the breakdown of plastic materials in the environment, as secondary MPs⁶. Severe MPs contamination in the air, sea, and soil was demonstrated over the past 10 years, primarily concentrated around major urban and industrial areas and it is estimated that close to 5 million tons of plastic debris are discharged yearly into marine environments alone^7,8,9. Widespread plastic use coupled with inadequate end-of-life disposal resulted in an estimated 22 million tons of plastic materials leaking into the environment in 2019, contributing to persistent and long-term plastic pollution¹⁰. Since the coronavirus pandemic in 2019, the global demand and extensive use of face masks and single-use plastic items exponentially increased, leading to further pressure on waste management and unprecedented levels of fiber pollution reported from untimely degradation of such single-use materials^11,12,13. Although strategies to collect and remediate MPs from wastewater streams have been developed^{14,15,16,17,18}, challenges related to meaningful quantification and occurrence assessment remain critical¹⁸.

Three major challenges associated with MPs pollution remain poorly understood and necessitate further investigations. First, besides being relatively chemically stable with expected half-lives spanning years to decades^6,19, MPs may fragment over time under the influence of sunlight, salinity, enzymatic reactions, and abrasion or shear stressors^3,4,5, therefore reducing the size distribution of MPs over time to the nano/micro scales¹⁹. In natural environments, MPs are more likely to be fragmented into particles smaller than 1 μm called nano-plastics, which are largely unaccounted for in current surveying studies due to the limitation of current characterization techniques and the challenges inherent in extracting these particles from complex matrices such as water or sedimental^20,21. Second, MPs may act as vectors for organic or inorganic toxicants, biological compounds, and micro-organisms across various biomes through surface adsorption^22,23. This may lead to highly localized concentrations of contaminants, posing significant ecological and health risks^24,25. Last, their natural buoyancy, broad size and increasingly minute sizes, coupled with their ability to carry surface contaminants, enable their widespread distribution across all aquatic and sedimental layers, from deep sediments to surface waters. Consequently, MPs can penetrate diverse biological systems, such as aquatic organisms, terrestrial organisms, atmosphere, and even human tissues, potentially impacting ecological system and human health significantly^{26,27,28,29,30,31,32}. Although the global footprint of MPs^33,34,35,36 and the load capacity of contaminants across their surface, including biological and non-biological remains poorly understood³⁷, the transportability and migration of MPs will follow natural air and water flows as well as human transport routes which are currently considered as major pathways for pollution diffusion³⁷. In addition, the occurrence of MPs at measurable levels in soils and ice cores in extremely remote locations disconnected from any human transport routes^38,39

These challenges raise a major question of the transportability of MPs and their ability to contaminate pristine environments with non-native or present contaminants. This transport risk is particularly important when dealing with biological and micro-organisms able to transfer and colonize new biomes way faster than naturally possible^40,41,42.

There is some research on the occurrence and transportation of MPs around the world in the aquatic^{43,44,45,46,47,48}, terrestrial^49,50 and air matrix^51,52,53,54. Most studies provide only an overall overview of the transmission mechanism^47,50 or conduct small-scale studies⁴⁸, including the migration in the human respiratory system⁵⁵. The limited reviews also mainly focused on the occurrence^43,56 at a global scale⁵⁷. However, the MENA region, with rich diversity in cultures, traditions, and natural landscapes, faces distinct environmental challenges, with plastic pollution emerging as a significant concern. In 2019, the MENA region had the second-highest share of mismanaged and uncollected litter globally, second only to India⁵⁸. This underscores the critical importance of reviewing the occurrence and transmission of MPs in the MENA region.

This review provides an in-depth analysis of the transport pathways of MPs to and from the MENA region. Initially, the discussion highlights the correlation between human population density, the presence of industrial and harbor hubs, and the occurrence of MPs. The methodology for the review included first a systematic analysis of reports of MP occurrences, which were correlated to both major urban and industrial centers in the MENA region and to both demonstrated atmospheric rivers and oceanic currents. The rigorous approach was aimed at establishing relationships to explain transport of MPs across various geographical domains and provide beside a review a thorough analysis of the challenges related to MPs pollution. Correlations to other geographical blocks, when data were not readily available, were also performed to sustain claims and potential explanations on transport pathways. This manuscript goes beyond the sole scope of a review by providing a unique analysis over the links between occurrence of MPs and both vertical and horizontal transport mechanisms, relevant to the various biomes within the MENA region. The impact of the manuscript is to present for the first time major relationships of MP transport that are critical to develop specific waste and contamination strategies and policies for the region. This may only be achieved through cross-borders and international collaborations and this review reflects on the need for such greater political engagement. The discussion will focus on current trends and solutions developed at the global level and assess their relevance to the specific challenges faced by the MENA region.

MPs occurrence and trends

MPs reported in natural habitats are primarily made of synthetic polymers such as poly(ethylene) (PE) and poly(propylene) (PP) in the form of fibers and micrometric to millimetric randomly shaped fragments. Since E. J. Carpenter and K. L. Smith alarmed the population of MPs on the surface of North Atlantic Ocean in 1972⁵⁹, the occurrence of MPs in seawater and soils/beaches around the world has been repeatedly documented. In this section, an overview of the global waste mismanagement status and of MPs occurrence will be first provided prior to focusing on the MENA region to evaluate MPs contamination and generate correlations between the MPs abundance and human activities. Geographical analysis of MPs occurrence will be organized by area, namely from the Caspian Gulf to the Arabian Gulf, from the Eastern to the Western Red Sea, and from the Eastern Mediterranean Sea to the shores of North Africa. Specifically, the MENA countries used for this study include Oman, Saudi Arabia, Djibouti, Iran, Yemen, Iraq, United Arab Emirates, Syria, Jordan, Qatar, Kuwait, Israel, Lebanon, Bahrain, Malta, Egypt, Turkey, Palestine, Cyprus, Sudan, Libya, Tunisia, Morocco, and Algeria.

Statistics on global waste management and worldwide MP occurrences

Over the past two decades, the ubiquity of MPs’ presence and persistence across various natural environments⁶⁰ such as in soils, seawater, fresh water streams, as well as atmosphere was demonstrated everywhere in the world, from high-density human activity areas to remote and desertic locations^61,62. MPs are primarily originating from two sources, 80% of MPs reported were attributed to land-based waste dumping, while the remaining 20% arose from fishing activities and illegal dumping of plastic debris into the ocean^63,64. Figure 1a, b summarize the global MPs occurrence and abundance as of 2020⁶⁵. To date, Portuguese, Southeast Brazil, Greek-Levantine and South Korean beaches showed the greatest number (larger than 100,000,000 items/km²) reported^66,67,68,69, followed by the northeastern Turkish coast as well as the Israelian Mediterranean and the Italian coast^70,71,72. These areas also exhibit large coastal urban centers with high population density, on the order of 100 (people/km²) (Fig. 1c)⁵⁸.

Perspectives on transport pathways of microplastics across the Middle East and North Africa (MENA) region — **Fig. 1: The density of microplastics is uneven globally and may not only be related to urban and industrial sites locations and to the intensity of their activities.**

Research on the occurrence of MPs within the MENA region is limited and predominantly centered on its more developed nations. Globally, the annual production of polymer and plastic items, as well as plastics waste generation has doubled over the past two decades, presenting significant environmental risks, particularly in regions with limited documentation⁷³. Since the contamination risks are closely associated to the waste management and disposal methods, and given the lack of infrastructures as well as pro-active recycling policies, about 22% of mismanaged and uncollected plastic litter around the world is expected to account for a very large proportion of the released MPs into the environment^74,75. In relatively sparsely populated areas, such as the MENA region, just 5% of waste plastics ever generated had been recycled, while 40% remained mismanaged and uncollected, and 54% was landfilled (Fig. 1d)⁷⁵. These statistics underscore the need for a critical evaluation of waste management policies and the establishment of robust public awareness campaigns.

MPs contamination in the MENA region

This section will map the distribution of MPs in sediments, seawater, and air around the MENA region. The analysis of the literature was performed to reveal potential hot spots and trends toward transport pathways. Occurrence in soils, air, water and macro-organisms will be discussed.

Occurrence in shore sediments and soils

Sediments and soils may be polluted by MPs arising from polymer synthesis and production industries, tourist activities and agricultural pollution⁷⁶. In order to understand the relationship between urban centers and MPs pollution densities, distribution maps shown in Fig. 2a illustrated the distribution of the population density (people/km²) distributed across the MENA region⁷⁷. The major cities with over 1 million inhabitants are primarily located along the sea shore of the Gulf and Red Sea regions as well as the northern and eastern part of the Mediterranean sea^78,79. Mismanaged large pieces of waste plastics released from such high population density cities may be degraded into MPs by microorganisms living in the sediments and soils, as well as from wear and tear through circulation in various water streams⁸⁰. The correlation between urban centers densities and industries, and MPs occurrences was however not found to be direct and systematically positive, despite sources of pollution being clearly identified. Accumulation was found to be primarily related to wind and atmospheric currents as well as oceanic currents, leading to accumulation in gyres or in sediments, based on buoyancy of the materials. The lack of large-scale surveying studies and of seasonal data however limited the scope to establish more direct relationships.

**Fig. 2: The major locations in the MENA region where microplastics were reported across different biomes show primarily a coastal focus.**

Table 1 has been organized to present observations of MPs in littoral sediments in the southern Caspian Sea to Arabian Gulf, from Red Sea to Eastern Mediterranean Sea and North Africa in the MENA region as depicted in Fig. 2b. The table contains a descriptive analysis of the sampling locations and concentration of MPs as well as the analyzed size range, polymer type, and shapes reported. The studies reported in the table were carried out from 1994–2023 in the MENA region. The detected MPs were categorized into fibers, fragments, film, sphere, filament, and percentages in terms of MPs shapes distributions within sediments on the basis of sampling location. Most items collected were PE and PP polymers accounting for 82%⁸¹, while the most predominant shapes of MPs were found to be fibers over fragments. In addition, 100% of the tested soil samples exhibited MPs presence in sediments.

Table 1 Overview of MPs occurrence and characterization in sediments studies performed in the MENA region

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Based on Fig. 2b, ubiquitous MPs contamination can be seen along the southern coast of Caspian Sea north of Iran (Table 1, Entry 1 and 2)^82,83. The first study reported uneven presence of MPs (25–330 items/kg) sized from 0.25–0.5 mm. Another analysis studied the spatial distribution of MPs across sandy beaches to inshore sediments and offshore sediments where the water depth ranges from 20–50 m⁸³. Results show a dilution from 196.67 ± 11.58 item/kg of MPs in sandy beaches to 103.15 ± 7.21 items/kg of MPs in the inshore-offshore sediments. The observed MPs are likely constituted from the inputs of local rivers, hydrodynamics as well as fishing, tourism, and industrial activities.

As mapped in Fig. 2b, along the northern coastline of Arabian Gulf, highly uneven MPs were reported^84,85,86,87. In December 2019, the documented mean MPs density was 190 ± 35.5 items/kg along the northern shores of the Arabian Gulf (Table 1, Entry 3)⁸⁴. Sampling stations were located in Khuzestan, Bushehr, and Hormozgan provinces where the fishing, tourist and residential areas coincide, including commercial ports. The northern cities Hendijan and Genave were found to have the lowest abundance, where Emam Hassan, Bushehr, Bandar Abbas, Lengeh, and Qeshm presented heavier contamination. The Khark Island, located in the Arabian Gulf, southwest of Iran, which geologically forms an asymmetrical anticline, was highly polluted by unevenly distributed MPs (295–1085 items/kg) (Table 1, Entry 4)⁸⁵. During the summer of 2015 in Bushehr city, the MPs abundance varied from 451 items/m² to 15,391 items/m² in the sediments along Bushehr (Table 1, Entry 5)⁸⁶. The different reported units (items/m², items/kg) and different sampling times from these two studies make it difficult to make a complete cross-comparison. In October and November of 2019, at the beaches of Bandar Lengeh and the sediments in the mangrove forests of the other four locations, present relatively low counts of MPs in the 19.5 ~ 34.5 items/kg range, (Table 1, Entry 6)⁸⁷. Along the western Arabian Gulf, three studies were carried out along the beaches of the United Arab Emirates (UAE) (Table 1, Entry 7, 8, and 9). In 1994, early research reported highly uneven MPs distributions (50 ~ 15,000 items/m²) along an approximately 200 km stretch of UAE beach attributed to the occurrence to industrial plastics contamination (Table 1, Entry 7)⁸⁸. Similar locations were probed in 2014 showing an extreme 40-fold increase per m² in terms of abundance of MPs, attributed to a leak of petrochemical products from a large industrial complex (the Saudi Basic Industries Corporation) in Jubail. The presence of light density polymers (less than 1 g/cm³) such as PE and poly(styrene) (PS) were observed on beaches and attributed to spills during shipping processes. The presence of MPs was reported along the northern shores of the UAE including areas around Sharjah, Ajman (Table 1, Entry 8)⁸⁹, and Dubai (Table 1, Entry 9)⁹⁰. In 2021, the occurrence of MPs in sediments and oysters collected from 5 sites along the northern coastline of the UAE was assessed and MPs were found to be present within sediments across all sites tested, with a mean concentration at 191.7 ± 95.5 items/kg of sediments. The majority of the particles were fibers and fragments made of low-density poly(ethylene) (LDPE) (Table 1, Entry 8)⁸⁹. Along the coast of Dubai, all sixteen sampling locations exhibited the presence of MPs with up to 165 items/m² PE (64%) and PP (33%) (Table 1, Entry 9)⁹⁰. In sandy beaches along the coastline of Qatar, varied concentration of MPs showed little significant differences among the 8 beaches examined (Table 1, Entry 10)⁹¹. The number of MPs found at Pearl Beach and Doha Bay, among the 8 sampling sites along a 700 km coastline, was the highest. This could be associated with variations in population density within the Doha municipality, which houses approximately 1 million people. Additionally, the significant presence of visible litter and marine debris on the beach in Al Ruwais, located in northern Qatar, is attributed to a lack of beach cleaning efforts, resulting in accumulation over time. In Saudi Arabia, there is limited available data on the occurrence of MPs on sandy beaches in the Gulf (Table 1, Entry 11) in 2022⁹². The presence of MPs was observed to be evident but relatively low in abundance. Across all beach samples from Salwa, Damma, Jubail, and Khafji, ranging from south to north of the Saudi coastline, the abundance varied from 5.5 ± 1.55 to 21.2 ± 0.68 items/km in the low tide zone and from 6.3 ± 4.05 to 16.5 ± 4.98 items/km in the high tide zone. Along the western coastline of the Arabian Gulf, there were relatively low counts of MPs in Kuwait Bay, particularly in the area stretching from Ras Al-Ard to Shuwaikh port. This may be attributed to regular beach cleaning efforts in this region (Table 1, Entry 12)⁹³.

MPs contamination was also documented along the Gulf of Oman, as seen in Fig. 2b. In 2020, PE, PP, and poly(amide) (PA) MPs were be reported in Oman with limited abundance and uniform distribution (138.3 ± 4.5 to 930.3 ± 49.1 items/kg, Table1, Entry 13)⁹⁴. However, when compared to the beaches of UAE (less than 15,000 items/m², Table 1, Entry 7), the eastern beaches of Oman showed a much lower accumulation of MPs (50–200 items/m², Table 1, Entry 14)⁸⁸.

In the eastern Red Sea region, the analysis of large-scale variability patterns primarily relied on samples collected during a single sampling period, with most studies focusing on Jeddah (Fig. 2b)⁹⁵. Around Jeddah, which hosts one of the highest population densities (bigger than 3 million people) in Saudi Arabia and features a metropolitan area with significant land-based industries and a growing tourism sector⁹⁶, MPs were observed at a density of approximately 119 items/km (Table 1, Entry 15)⁹⁵. Moving across the Red Sea to the western coastline in Egypt, studies on MPs were conducted along the Nile River, revealing higher densities of MPs (386–506 items/km) in sediments compared to river waters therefore confirming long term accumulations from upstream river pollution (Table 1, Entry 16)⁹⁷. This trend was attributed to the presence of large ports and higher population density compared to the northern coastline of the Red Sea. Specifically, at the Ras Gharib station, the highest concentration of MPs in sediments was recorded at 506 ± 40 items/km along the Red Sea, whereas the lowest concentration was found at the Ain Sukhna station (386 ± 30 items/km) (Table 1, Entry 16)⁹⁷.

Studies along the eastern coast and basin of the Mediterranean Sea have primarily been conducted in Israel, Egypt, Lebanon, and Türkiye, as depicted in Fig. 2b. In the eastern Mediterranean basin, MPs in the Nile River delta and estuaries were observed at levels ranging from 167 ± 137 to 1,630 ± 1,303 items/kg of dry sediments (Table 1, Entry 17)⁹⁸. Along the 23 km Damietta branch, densities of MPs (180–1310 items/km) were found, similar to results obtained at the Damietta and Port Said stations downstream the Nile River (766 ± 40 items/km)⁹⁷. Along the Rosetta branch, an uneven and notably high magnitude of MPs density (300–3045 items/km) was reported at the Burullus headland⁹⁸. Apart from the presence of MPs around the Nile River delta, sediment abundance within the Marsa Matruh and Alexandria stations was found to be relatively low in the area (480 ± 50 items/km, 546.6 ± 18 items/km respectively)⁹⁷. On the western coastline of Israel, 168 ± 16 items/km of MPs were detected (Table 1, Entry 18)⁹⁹, while further north along the Lebanese coast, particularly around the city of Tripoli, the highest concentration in this region was reported at 4680 items/km (Table 1, Entry 19)⁵⁶. The eastern Turkish coast of the Mediterranean Sea also exhibited higher and uneven distribution of MPs (118 ± 97–1688 ± 746 items/km), attributed to industrial complexes (Table 1, Entry 20)¹⁰⁰.

The presence of MPs along the coastline of the Mediterranean Sea in North Africa has been documented in only a few countries, primarily Tunisia and Algeria. In Tunisia, along the southern Mediterranean coast and northern Tunisia, including the Gulf of Tunis, Gulf of Hammamet, and Gulf of Gabes, variable levels of MPs ranging from 0.5–1 mm were detected (10–110 items/km). MPs occurrences were characterized by Raman Microscopy analysis (129–606 items/km) due to its higher resolution, capable of analyzing smaller MPs ranging from 0.5 mm to 1.2 µm (Table 1, Entry 21)¹⁰¹. One study also reported abundant MPs ranging from 141 to 461 items/km along the north coast of Tunisia (Menzel Bourguiba around the Bizerte Lake, north and south Lake of Tunis, Goulette, and Carthage adjacent to the Gulf of Tunis) (Table 1, Entry 22)¹⁰². The highest contamination levels were reported in a harbor in Southeast Tunisia, with up to 252–5332 items/km of sediments (Table 1, Entry 23)¹⁰³. The density of MPs in Tunisia was found to primarily depend on geographic factors; for example, the Sidi Mansour Harbor exhibited the highest abundance (5332 items/km), while the relatively low density (252 items/km) along the southern Mediterranean coast was attributed to high shear seawater-based currents capable of diverting and concentrating pollution in sediments further north. Along the coastline of the Gulf of Annaba in Algeria, adjacent to the northwest of Tunisia, very high occurrences of up to 649.33 items/km were also reported (182.66–649.33 items/km) (Table 1, Entry 24)¹⁰⁴.

Overall, the highest mean density of MPs (15,391 items/m²) was reported at Jofre in Bushehr city according to the items/m² unit⁸⁶. Then MPs abundance of 5 orders of magnification (15,000 items/m²) were observed at the Arabian Gulf of UAE in 1992 where there was a leakage from the nearby Industry⁸⁸. Based on the items/kg unit, the abundance of 4 orders of magnification’s MPs contamination at Khark Island in Iran⁸⁵, Nile Rive in Egypt⁹⁸, Levantine Basin along Lebanese coast⁵⁶, and along the Turkish coast of the Eastern Mediterranean Sea¹⁰⁰ as well as along Sidi Mansour Harbor of Southeast Tunisia¹⁰³ was documented. The highest MPs pollution reached up to 5332 items/kg was reported along Sidi Mansour Harbor, followed by the 4680 items/kg density observed Levantine Basin along Lebanese coast. Tens and hundreds items per kg of MPs were found in elsewhere like Southern coasts of the Caspian Sea in Iran^82,83 along with northern coast along the Arabian Gulf^84,87, northern shores of UAE^89,90, coastlines along the Arabian Gulf in Qatar, Kuwait^91,93, the eastern coastline of Saudi Arabia^92,95, the northern and eastern shores in Oman^94,88, the eastern coastline of Egypt along the Red Sea⁹⁷, the eastern Mediterranean coast in Isreal⁹⁹, the southern Mediterranean coast in Tunisia^101,102 and Algeria¹⁰⁴. The least contaminated places located in northern coast of the Arabian Gulf, near the Qeshm Island⁸⁷, the eastern coastline of Saudi Arabia⁹² and Kuwait coastal areas⁹³ with only tens items per kilogram.

Occurrence in coastal seawaters and river waters

This section will provide an overview of the occurrence of MPs in both surface seawater and freshwater. Reports on MPs contamination in rivers is scarce in the MENA region due to the limited surface water systems present in the region. As a note, although underground aquifers or groundwater may also represent a potential pathway for MP transport, no studies to date evaluated occurrences into such streams. As illustrated in Fig. 2c and detailed in Table 2, most of the reported data in the MENA region to date has focused on MPs with size fractions ranging from 0.1 to 5 mm. Regarding the two different reported units (items/km² and items/m³), the variations stem from the different sampling methods employed. When the distance covered during the sampling procedure is recorded using GPS coordinates at the start and end stations, and then multiplied by the width of the opening of the nets used in the test, the data is usually reported in items/km². Conversely, when the volume of water passing through nets during sampling is measured using a flow meter fitted to the mouth of the net, the unit is reported as items/m³. In this section, the sequence of MPs abundance in the water column will be discussed, starting from the Arabian Gulf^{84,91,105,106,107}, then moving to the Gulf of Oman^108,109, followed by the Red Sea^97,110, the eastern Mediterranean Sea^{56,68,71,98,100}, and finally addressing MPs occurrence in the southern Mediterranean Sea^111,112.

Table 2 Overview of MPs occurrence and characterization in seawater/freshwater systems studies performed in the MENA region

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In December 2019, the occurrence of MPs in surface seawater was assessed at the same sampling location as that reported for shore sediments along the eastern Arabian Gulf. The mean density recorded was 9.28 ± 2.1 items/km² (Table 2, Entry 1)⁸⁴, which was relatively lower than the average density found for the Arabian Gulf (18,000 ± 1100 items/km²) (Table 2, Entry 2)¹⁰⁵. Further investigation across the Arabian Gulf, specifically in the northeastern marine waters of Qatar, revealed an average MPs concentration of 0.71 items/m³ (Table 2, Entry 3)¹⁰⁶. Surface seawater samples collected from eight beaches along the Arabian Gulf indicated a wide range of MPs abundance, from 43,800 to 1,460,000 items/km² (Table 2, Entry 4)⁹¹. These findings underscored the higher prevalence of MPs in coastal marine environments of the Arabian Gulf and the western coast of Doha Bay. Alarmingly high levels of MPs pollution were also observed in the freshwater column of Al-Asfar and Al-Hubail Lakes, with concentrations ranging from 700 to 800 items/m³ and 1100 to 9000 items/m³, respectively (Table 2, Entry 5)¹⁰⁷. In these samples, small MPs ranging from 0.25 to 0.50 mm were predominant, with fibers comprising over 50% of the total MPs detected.

In the Gulf of Oman, specifically within Chabahar Bay in Iran, two studies conducted in 2019 and 2020 revealed significantly varied concentrations of MPs, with differences of up to five orders of magnitude, ranging from 0.49 ± 0.43 items/m³ to 218,000 ± 170,000 items/m³ (Table 2, Entry 6, 7)^108,109. The fluctuation in MPs density observed at these sampling stations was closely correlated with human activities and the geographic locations. The city of Chabahar, which hosts an international port and experiences high population density (approximately 300,000 people/km²), exhibited large contaminations of MPs attributed to tourism, fishing activities, and the density of industrial plants.

In the eastern Red Sea, a widespread distribution of MPs was observed in near-shore surface seawater. Despite the extensive Arabian coastline spanning 1500 kilometers, the abundance of floating plastic debris remained relatively low, with densities below 50,000 items/km² and an average density of 3546 ± 8154 items/km² (Table 2, Entry 8)¹¹⁰. The reasons behind this occurrence in a sparsely populated region could be attributed to specific mechanisms of surface plastic transport, such as seasonal ocean currents, or factors related to their uptake by organisms or filtration by the region’s extensive coral reefs and mangroves¹¹⁰. Although not studied to date, changes based on seasons, since both atmospheric and water currents may change particularly between winter and summer times, may also affect the transport pathways. In the western coastline of the Red Sea, a study conducted in Egypt revealed dense pollution levels in the Red Sea waters, with concentrations ranging from 506,600 to 660,000 items/m³ (Table 2, Entry 9)⁹⁷. The majority of these pollutants consisted of polyethylene (PE), polyethylene terephthalate (PET), and rayon polymeric fibers.

In the context of the Mediterranean Sea, the map depicting a uniform distribution of MPs is presented in Fig. 2c. Along the eastern Mediterranean Sea, surface seawater samples from the same study revealed relatively high densities of MPs, ranging from 466,600 to 693,000 items/m³ (Table 2, Entry 9)⁹⁷. In the freshwater systems of the Rosetta and Damietta branches of the Nile River, notably high densities and uneven distributions of MPs were reported, ranging from 761 ± 319 to 1718 ± 1008 items/m³ (Table 2, Entry 10), attributed primarily to land-based anthropogenic sources⁹⁸. Egypt, with its very high population density (higher than 100 people/km², as shown in Fig. 2a), especially in municipalities like Cairo, Giza, and Alexandria located along the Nile River delta, contributed significantly to the MPs source, with approximately 7.7 million, 3.8 million, and 2.4 million people respectively⁷⁷. Moving northward, surveys of Israeli Mediterranean coastal waters in 2017, comprising 108 samples from 17 locations, revealed mean concentrations reaching up to 7.68 ± 2.38 items/m³ (or 1,520,000 items/km²) (Table 2, Entry 11)⁷¹, representing a density 1 to 2 orders of magnitude higher than that found in other MENA regions. Notably, various plastic patches were observed, with one patch densely packed with MPs reaching up to 324 items/m³ (65,000,000 items/km²). Along the coast of Lebanon, PE polymeric MPs were found, with the highest mean abundance recorded at 6.7 items/m³ in surface water near Sidon, close to Betzet in the northern part of Israel (Table 2, Entry 12)⁵⁶. Mean density fluctuations were observed annually, with 1.46 ± 0.73 items/m³ in 2013, followed by 16.52 ± 19.55 items/m³ in 2014^56,71. Comparatively, the abundance in Iskenderun Bay (225,400 items/km², Table 2, Entry 13) was slightly lower than that in Mersin Bay (682,700 items/km², Table 2, Entry 13)⁶⁸. In surface seawater near the northern shoreline of the Mediterranean Sea, MPs occurrence was found to fluctuate from 0.18 ± 0.10 items/m³ to 2.21 ± 1.75 items/m³ (Table 2, Entry 14)¹⁰⁰, correlating with changes in population density and industrial activity. Particularly noteworthy was the disparity between the density in the Gulf of Antalya and other locations, suggesting a clear relationship between population density and MPs abundance.

Along the southern coastline of the Mediterranean Sea, as depicted in Fig. 2c, studies on littoral seawater surface in Tunisia have been limited. Concentrations of MPs around the Bizerte Lagoon in Tunisia, where the population density exceeds 75 people/km², revealed significant and varied concentrations of MPs ranging from 2340 ± 227.15 to 6920 ± 395.98 items/m³ (Table 2, Entry 15)¹¹¹. Similarly, in the Gulf of Gabes in southern Tunisia, concentrations of up to 63,739 items/m³ of polyethylene (PE) and polypropylene (PP) were discovered (Table 2, Entry 16)¹¹².

Occurrence in macro-organisms

Although numerous studies have examined the occurrence of MPs in aquatic organisms worldwide, research focusing on the MENA region (Fig. 2d) remains scarce. Studies discussing MPs occurrences have been conducted in Iran’s fish markets located in the south and southeast of the Caspian Sea^113,114, as well as in the Gharesu River¹¹⁵. In the Arabian Gulf^84,89,116, the Gulf of Oman¹¹⁷, the Red Sea^28,95,97, the eastern Mediterranean Sea^56,118, and the western Mediterranean Sea¹¹⁹, only a limited number of studies have investigated MPs uptake by macro-organisms. The morphology of MPs has been identified as a key factor facilitating their ingestion by aquatic organisms as a food source¹²⁰. Additionally, urbanization near watersheds exacerbates plastic pollution and influences the likelihood of MPs ingestion across the food chain. MPs can be ingested by organisms at various trophic levels, with predators potentially ingesting MPs through trophic transfer, leading to biomagnification and posing a threat to human life¹²¹.

In northern Iran, situated on the southern coast of the Caspian Sea, MPs were detected within fish, revealing widespread distribution across marine habitats. The prevalence of MPs varied from 2.29 to 11.4 items/fish, as observed at over 130 sampling points along the southern coastline (Table 3, Entry 1, 2)^113,114. Fish in the Kermanshah region, particularly in the Gharesu River, faced significant risk due to high quantities of ingested MPs, ranging from 4.20 ± 3.32 to 12 ± 11.31 items/fish (Table 3, Entry 3)¹¹⁵.

Table 3 Overview of MPs occurrence and characterization in macro-organisms within the MENA region

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In the Arabian Sea, as depicted in Fig. 2d, the assessment of MPs in macro-organisms primarily concentrated along the shoreline of the Arabian Gulf. Along the eastern MENA region, specifically the Iranian coastline of the Arabian Gulf, the average density of MPs in fish lay at approximately 0.33 ± 0.05 items/fish (Table 3, Entry 4)⁸⁴. This content of MPs within marine organisms and seafood may serve as an indicator of the potential occurrences within the ocean¹²², with reported concentrations ranging from 200 to 21,000 items/km of mollusk species in the northern part of the Arabian Gulf (Hormozgan province) (Table 3, Entry 5)¹¹⁶. The density was calculated to vary from 3.7 to 17.7 items/organism, notably higher in the Hara mangrove forest protected area in southern Iran, located near several urbanized and densely populated areas with populations exceeding 1 million, including Qeshm Island and the major city of Bandar Abbas. Furthermore, an investigation along the northern shores of the UAE, specifically the coast of Dubai, revealed a density of 101.2 ± 93.8 items/km of organism tissue (Table 3, Entry 6)⁸⁹. Moving beyond the Strait of Hormuz to the Omani sea, MPs occurrence was examined in the bay of Chabahar, with 3.1 to 4.14 items/fish (2700–6470 items/km) in marine fish (Table 3, Entry 7)¹¹⁷.

The abundance of MPs in fish within the Red Sea exhibited significant variability, with concentrations ranging from 0 to 30 items/fish (Table 3, Entry 8, 9)^28,95. Along the Egyptian coastline, marine fish in both the Red Sea and the Mediterranean Sea contained MPs in their bodies. The impact of MPs on marine biota manifested in concentrations ranging from 2.33 to 5.66 items/fish (equivalent to 10.84 to 24.61 items/km) in the Red Sea, and from 2 to 8.66 items/fish (equivalent to 3.45 to 29.79 items/km) in the Mediterranean Sea (Table 3, Entry 10)⁹⁷.

In the densely populated Nile River area of the eastern Mediterranean Sea, the presence of MPs in freshwater fish exhibited variability and appeared to be species-dependent. Nile tilapia, for instance, showed an average of 7.5 ± 4.9 items/fish, while Catfish presented an average of 4.7 ± 1.7 items/fish (Table 3, Entry 11)¹¹⁸. Along the Lebanese coast and the Levantine Basin, MPs were found in fish and oysters, with concentrations reaching up to 2.9 ± 1.9 items/fish and 8.3 ± 4.4 items/oyster, respectively (Table 3, Entry 12)⁵⁶. Additionally, in the southwestern Mediterranean Sea, MPs were detected in six commercially harvested mollusks from the Bizerte Lagoon in Tunisia, in 2019 (Table 3, Entry 13)¹¹⁹, with concentrations ranging from 704 ± 110 to 1483 ± 19 items/km of wet seafood product (mollusks).

Occurrence in air

Anthropogenic activities have been identified as significant contributors to the abundance of MPs in the atmosphere, particularly those composed of fibrous materials¹²³. Available occurrence data suggest that fibers, shed from clothing, serve as a major source of atmospheric MPs, along with particles from high-speed tires on roads^124,125. However, research on the contamination of atmospheric fallout by MPs is still limited and represents an emerging area of study. Typically, the abundance of MPs in air matrices is reported in units such as items/m³, items/m², or items/g of dust. Some studies investigating MPs in indoor air^126,127 or outdoor air^{128,129,130,131,132,133,134} have been conducted, particularly in Iran and Kuwait.

In the southwestern region of Iran, specifically in the central area of Fars province, MPs contamination was investigated in school classrooms located in the capital city of Shiraz (Table 4, Entry 1, 2)^126,127. Both studies revealed that the predominant types of MPs were polyethylene terephthalate (PET) and polypropylene (PP), with lengths typically ranging from 0.05 to 5 mm. Discrepancies in the airborne MPs abundances could be attributed to differences in sampling numbers and locations, and that sample analysis, treatment, and identification methods. Apart from the investigation of MPs pollution in indoor dust, the contamination of outdoor environments by MPs is also significant due to the greater mobility of particles in open spaces. A study estimated the presence of low-density polyethylene (LDPE) in wind-eroded sediments in the entire Fars province, with concentrations ranging from less than 4 to 6 orders of magnitude (0.067–1.133 items/g of dust) (Table 4, Entry 3)¹²⁸. Shiraz, a municipal city with a population density of 5200 inhabitants per square kilometer (approximately 1.25 million people in 2023⁷⁹), occupies an area of 240 square kilometers and is surrounded by Mount Derak, which rises 1300 meters above the Shiraz plain. The pollution level in Shiraz was found to be higher (average of 1900 items/m²) compared to Mount Derak (mean of 366 items/m²), likely due to its semi-arid and rainless climate (Table 4, Entry 4)¹²⁹. In arid and semi-arid regions where dust storms are common climate events, researchers studied MPs contamination during an intense storm in May 2018 in Shiraz. Samples collected from parked cars showed a density of the fine-sized MPs (averaging 0.02 mm) made of polyamide (PA), PP, and PET, ranging from 0.04 to 1.06 items/g of dust (Table 4, Entry 5)¹³⁰. Additionally, street dust deposited from atmospheric MPs was surveyed in northern Iran, in the Tehran province, with abundances ranging from 2.9 to 201 items/g of dust in urban deposits (Table 4, Entry 6)¹³¹.

Table 4 Overview of MPs occurrence and characterization in air within the MENA region

Full size table

Along the western coastline of Iran, near the northern part of the Arabian Gulf, researchers investigated ultrafine atmospheric MPs ranging in size from 1 to 25 µm¹³². In the urban area of Bushehr port, atmospheric MPs within PM2.5 showed significantly higher levels on dusty days (10.3 items/m³) compared to normal days (2.1 items/m³) (Table 4, Entry 7)¹³². The study indicated that during the winter, the high density of MPs in deposited dust suggested the influence of distal areas such as Iraq and Saudi Arabia, which mainly contribute petrogenic dust, on atmospheric MPs density in the study area. Another study highlighted a widespread contamination of MPs ranging from 21 to 165.8 items/g of dust in urban street dust of Bushehr (Table 4, Entry 8)¹³³. The study also found a positive relationship between MPs concentration and traffic conditions, with higher MPs density observed in the northern part of Bushehr city where traffic congestion is heavier compared to the southern part¹³³. Recently, a study investigated MPs concentrations in street dust and airborne dust collected from Asaluyeh country, revealing distinct size fractions. Street dust predominantly contained MPs sized from 0.10 to 1 mm, whereas airborne dust contained smaller MPs ranging from 2 µm to 0.1 mm (Table 4, Entry 9)¹³⁴. Moving to western side of the Arabian Sea, studies on airborne MPs were even scarcer, with only one documented study in Kuwait. The presence of ultrafine airborne MPs, some as small as 0.45 µm, was observed in indoor aerosols in Kuwait. Evaluation revealed an uneven distribution of MPs in indoor aerosol dust, ranging from 3.2 to 27.1 items/m³ (Table 4, Entry 10)¹³⁵.

Challenges related to sampling and sensitivity analysis requirements

One of the most significant challenges in sediment-based studies lies in the substantial disparities, compounded by variations in experimental and sampling conditions, as well as inconsistent analytical methods. Additionally, seasonal variations in sampling can lead to significant analytical differences⁶. The typical process for analyzing soil involves several steps: collection, extraction using liquids or dissolution methods, manual sorting, and eventual characterization of the MPs.

The sampling methods for MPs in sediments, water systems, biota, and the atmosphere differ somewhat. When collecting sediment samples, researchers typically gather them randomly from the top layers of the sediment down to a depth of either 5 cm^89,136 or 1 cm^90,137. However, assuming a homogeneous vertical distribution throughout the depths can affect the accuracy of estimating abundance in terms of items/m². The size of the sample quadrat also varies significantly, ranging from 0.3 by 0.3 meters⁹³ to 1 by 1 meter¹³⁸, which can influence the normalization of collected volumes and thus the statistical significance of the results. Surface water samples are typically filtered using various types of nets, such as phytoplankton nets⁹⁸ or manta trawl nets^56,100, with mesh sizes ranging from 52 to 333 µm. The volume of water filtered is calculated using a flowmeter, and similar chemical, color, and shape characterization methods are employed as in MP studies on sediments.

The mesh size of sieves used to separate MPs from sediments and waters varies significantly, ranging from as small as 20 µm⁹¹ to as large as 2 mm⁸⁹. This wide range of mesh sizes, coupled with the often absence of intermediate steps and sub-micrometer mesh, likely leads to significant discrepancies in the reported sizes of MPs. Additionally, the separation methods typically employed do not facilitate the collection of nanoparticles. Furthermore, the digestion steps in the analysis process may impact the presence of other contaminants, such as heavy metals and man-made chemicals originating from industries like petrochemicals, pharmaceuticals, and agriculture, which can be adsorbed onto MPs¹³⁹. It is important to systematically perform extraction while also assessing co-contaminants to ensure that there is no further degradation or fragmentation of the MPs during processing.

The identification process typically follows a consistent pattern across studies, beginning with visual quantification using optical microscopy, followed by confirmation of the chemistry and nature of the polymers through Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy. However, particles smaller than 10 µm are often overlooked during this analysis due to technological limitations and the absence of Infrared (IR) mapping technology⁹¹. As a result, standardizing the assessment process for MPs is crucial to ensure that laboratory analyses are both valuable and relevant to the broader scientific community¹⁴⁰.

When it comes to air sampling, the typical approach involves collecting air samples using a pump that draws air onto quartz fiber filters or vacuum cleaner bags¹⁴¹, or directly sampling from deposited dust. While employing a multi-stage cascade impactor to capture smaller MPs has proven to be effective in quantifying ultrafine MPs, this technique has not yet been systematically adopted.

Conclusions on occurrences of MPs within the MENA region

This section provides a comprehensive overview of the distribution of MPs across terrestrial, aquatic, biotic, and atmospheric compartments in the MENA region. The presence of MPs, as evidenced across the Mediterranean, Gulf, and Red Seas, is primarily concentrated along coastlines, particularly in mega cities, metropolitan areas, and estuaries formed by river networks. Interestingly, the occurrence of MPs is not always directly correlated with the largest urban and industrial centers, indicating that the pollution can be transported across the region from other sources, such as the Indian subcontinent and the European or Anatolian peninsulas.

Understanding the role of water and atmospheric currents is crucial for comprehending the transport and potential transfer of pollution to pristine areas. The next section will explore transport considerations and leverage the trends identified in this section to discuss potential pathways and routes for the diffusion of MPs.

Transport of MPs – mechanisms and routes within the MENA region

The MPs transport through natural processes like airborne dispersal, marine currents, and river flows, as well as human activities, presents a challenging area of study due to the complexities involved in accurately tracking their migration and quantifying their movements. Understanding how MPs traverse various ecosystems and biomes is crucial for assessing their potential to transport contaminants, including biological ones, to pristine environments.

This section will begin by critically examining the global-scale transportability of MPs, followed by an exploration of potential transport mechanisms within atmospheric and oceanic environments. Subsequently, using the MPs occurrence map as a guide, the specific transport dynamics of MPs within the MENA region and adjacent areas to elucidate spatial transfer patterns will be presented. However, discussions on soil transfers will be omitted due to the lack of sufficient data on mass transfer kinetics for these matrices.

Demonstrations of MPs transportability at global scale

MPs traverse the Earth’s ecosystems—encompassing the pedosphere, atmosphere, and hydrosphere—where they can be encountered by organisms through inhalation and ingestion. Their global dispersion is evident in the atmosphere, reaching polar regions^51,142 and high-altitude locales like the Himalayas and Alpine glaciers^143,144,145. Meteorological phenomena play a crucial role in this dispersion, acting as key drivers that transport MPs far from their original sources^146,147. Wind, rainfall, and snowfall facilitate their penetration into pristine soil and hydro-spheric environments^142,146,148. Studies suggest that approximately 1.2 tons of small-sized MPs are annually transported from terrestrial sources to the marine environment annually¹⁴⁹, with initial estimates indicating that 101 kilograms of MPs within the top 9.42 meters of sea air in November to December 2018 originated from nearby continents.

In the vast expanse of the open sea, a significant portion of MPs finds its way into the marine environment, often propelled by ocean surface dynamics towards large garbage patches or remote regions off the beaten track, and sometimes even washing ashore on coastal lines^{150,151,152,153}. As of 2019, close to one quarter of the global volume of household rubbish generated was mismanaged (Fig. 1d) and released into ecological surroundings⁷⁵. Annually, several million tons of plastic waste enter the world’s oceans, originating from coastlines and inland sources transported by rivers before being deposited on shores^7,8,154. Ocean currents play a pivotal role with respect to the transport of MPs^{43,155,156,157}, given MPs’ low buoyancy properties. The strong ocean currents within large bodies of seawater, augmented by wind forces, contribute to this movement¹⁵⁸. The Great Pacific Garbage Patch (GPGP) serves as a notorious example, spanning thousands of square kilometers in the North Pacific Ocean. MPs accumulate within the center of the gyre, where currents exhibit lower velocities, creating less turbulent areas^159,160. In 2018, it was estimated that at least 79,000 tons of garbage were inter-connected within the Eastern Garbage Patch, located in the subtropical waters between California and Hawaii¹⁶¹. Simulation studies indicated that particles experiencing greater atmospheric drag were more likely to escape the Eastern Garbage Patch and drift into other subtropical gyres, such as the North Pacific subtropical gyre if the plastics exit from the south of Eastern Garbage Patch, or the North Pacific subpolar gyre near Alaska when departing from the north of the Eastern Garbage Patch¹⁶¹. Additionally, besides the Eastern Garbage Patch between California and Hawaii, other patches have been reported in subtropical areas, such as the Western Garbage Patch of the GPGP and the trash vortex spanning hundreds of miles off the North America’s Atlantic coast from Cuba to Virginia (between 22 and 38 degrees north latitude)^162,163. Polar regions also serve as repositories for MPs, facilitated by thermohaline circulation, acting as strong sinks for discarded plastic items^{61,62,164,165}. The Arctic Ocean, particularly in the northernmost and easternmost areas of the Greenland and Barents seas, hosted hundreds of thousands of pieces of plastic per square kilometer. Reports of large patches in the distant North Atlantic were also attributed to thermohaline circulation¹⁶⁵.

In addition to being transported by native water currents, MPs exhibit vertical movement within water columns over time, driven by density discrepancies between the MPs and seawater. Surface fouling, scaling, microorganism biofouling, and weathering of MPs contribute to their displacement and vertical distribution in the water column. This process facilitates the movement of MPs beyond surface currents, deeper into the ocean, thereby extending their reach to new areas¹⁶⁶. Surface biofouling, a common occurrence in oceans where microorganisms colonize the surfaces of MPs, alters the density of the clusters, hastening their descent to greater depths^167,168,169.

Mechanisms of MPs transfers within airborne, water systems and terrestrial matrix

This section will delve into the mechanisms of MPs transfers within airborne, aquatic systems, and terrestrial matrices, respectively. To begin, as illustrated in Fig. 3, atmospheric fallouts are influenced by various meteorological variables, such as relative humidity, temperature, rainfall, wind speed, and direction, all of which impact the transport patterns and altitude attained by the materials. Moreover, the physicochemical properties of MPs, including their density, size, and shape, play a crucial role in determining their transport pathways^170,171.

**Fig. 3: The mechanism of the atmospheric transport of airborne MPs (pathways from ① to ⑤.**

The predominant forces shaping the fate of airborne MPs revolve around wind dynamics and precipitation. Driven by high winds, MPs smaller than 1 mm can ascend into the atmosphere (Fig. 3, pathway ①). Subsequently, MPs ranging from 0.05 to 1 mm in size precipitate along with wind drifts and street dusts (Fig. 3, pathway ②). Very fine MPs, even at the nano scale (smaller than 0.1 mm), are transported high in the air (Fig. 3, pathway ③), traversing considerable distances before gravitational and precipitation mechanisms lead to their deposition in remote regions (Fig. 3, pathways ④ and ⑤)¹⁴⁷. Due to scavenging effects, the majority of airborne MPs are swiftly removed from the atmosphere and deposited into water bodies.

In open seas, depicted in Fig. 3, the physical properties of MPs significantly influence their transport within global oceanic circulation. With over 65% of globally produced polymers having a lower density than water, these high-buoyancy materials tend to float or remain suspended in both fresh and saline waters¹⁷², facilitating their transport by winds and water currents (Fig. 3, pathways ⑥ to ⑪)^173,174. Floating MPs in the ocean can be lifted into the atmospheric system via pathway ⑥ (Fig. 3). One primary driver of large-scale ocean current circulation is the thermohaline exchange between inshore and offshore regions¹⁷⁵ (Fig. 3, pathway ⑦). Along ocean fronts, characterized as boundaries between distinct water masses or regions with rapid changes in physical properties^176,177, buoyant materials tend to accumulate, especially at convergence fronts where downwelling occurs, leading to the aggregation of plastic debris (Fig. 4a)^121,178. This aggregation, particularly along nutrient-rich ocean fronts, significantly heightens the risk of marine organisms interacting with MPs¹⁷⁹. The presence of landmasses, such as sandbanks, further influences the transport and distribution of MPs. Plastic waste entering marine waters undergoes displacement, with various mechanisms responsible for the buoyant plastics drifting on river or ocean surfaces and within their depths^180,181. Approximately 35% of produced polymers have a higher density than seawater, causing them to sink readily to riverbeds and beaches unless altered by aging or surface coatings affecting their wettability or buoyancy (Fig. 3, pathway ⑧). Additionally, land-based low-density MPs can be carried into sea water body by currents forces and undergo lateral transport on the water surface (Fig. 3, pathway ⑧, ⑨). In marine environments, the trajectory of plastic waste is often governed by a combination of wind patterns, wave action, and ocean currents, ultimately culminating in the formation of garbage patches at the center of ocean gyres, facilitating the transport and accumulation of MPs (Fig. 3, pathway ⑩). However, high-density polymer MPs have been observed to more likely reach landmasses under increased windage coefficients¹⁶¹, or sink to specific depths determined by density disparities between seawater and MPs, influenced by salinity levels. This results in their suspension within water columns or deposition along the deep-sea floor (Fig. 4b ①)¹⁸², facilitated by vertical transport (Fig. 3, pathway ⑫). Within this vertical transport pathway, biological processes also impact MP buoyancy through biofouling, wherein incorporation into biological matrices alters their buoyant properties (Fig. 4b ②)^{183,184,185,186}.

**Fig. 4: The mechanisms of microplastics transport vary based on the properties and composition of the carrying stream.**

Compared to previous modes of transport observed in terrestrial matrices, the potential for MPs to be transported from sediments or soils is likely constrained due to the relatively low mobility of items within soil structures⁴⁹. However, the biological activities of soil-dwelling organisms, such as earthworms and collembolans, have emerged as significant agents facilitating the transport and incorporation of MPs into soil matrices, thereby enhancing their fixation¹⁸⁷. This transfer process often involves the deposition of MPs through casts, which alter soil hydraulics during burrow formation, followed by their subsequent egestion and adherence to the worm’s skin^187,188. As these worms move within their surrounding biomes and interact with broader ecosystems, the exposure of other soil biota to MPs increases, leading to extended residence times for MPs at greater depths and potentially facilitating their transfer into groundwater^189,190. The mobility of MPs bears significant implications for soil ecology, including heightened exposure of soil biota to coexisting MPs, prolonged retention periods of MPs within deeper strata, and the eventual infiltration of MPs into groundwater reservoirs.

Direct airborne transfers of MPs in the MENA region

Atmospheric circulation plays a pivotal role in the global transport of MPs^{43,57,157,191}. Owing to their small size and lightweight nature, MPs are exceptionally susceptible to atmospheric circulation, enabling them to traverse vast distances, particularly during major storms and weather events^192,193. Similar to other pollutants such as soot and aerosols, which have been observed to travel thousands of kilometers within days¹⁹⁴, MPs can also exploit atmospheric pathways, facilitated by these carriers, thereby dispersing across expansive regions.

In the MENA region, characterized by the Köppen climate classification as a hot desertic and semi-arid climate area, the coastal areas generally experience low levels of precipitation. As illustrated in Fig. 5a, which depicts the annual precipitation depth (in mm per year) distribution by countries¹⁹⁵, Iran, located in the eastern part of the MENA region, receives a relatively moderate average precipitation level with 228 mm per year. However, countries situated on the Arabian Peninsula, such as Saudi Arabia, Qatar, and the UAE, receive substantially lower amounts of rainfall, averaging at 59 mm, 74 mm, and 78 mm per annum, respectively. The southern coast of Oman and the Arabian Sea receive a comparatively larger share of precipitation, totaling 125 mm annually. This region benefits from its position at the tail end of the Asian monsoon, which seasonally influences airborne currents over the southern Red Sea. Moving towards the Mediterranean Sea, eastern and northern countries exhibit relatively higher precipitation levels, with Lebanon, Israel, Greece, and Italy receiving 661 mm, 435 mm, 652 mm, and 661 mm, respectively. Conversely, precipitation in Egypt (18.1 mm), Libya (56 mm), and Algeria (89 mm) remains notably low, with Tunisia being an exception at 207 mm.

Fig. 5: Atmospheric transportation in the MENA region is dominated by strong continental winds from Europe and Africa in the North Africa region while more from oceanic winds from the Indian Ocean in the Arabic peninsula.

Figure 5b, c provide insights into the wind circulation patterns across the MENA region. In the vicinity of the Mediterranean Sea, the direction of winds remains relatively consistent throughout the seasons, while their speeds exhibit seasonal variability (Fig. 5b)¹⁹⁶. Notably, December, February, and March emerge as the windiest months, contrasting with the calmer conditions typically experienced in August, June, and September. Mean annual wind patterns predominantly originate from the north and northwest over the Mediterranean Sea for most of the year, with the Gulf of Lions and the Aegean Sea identified as the regions with the highest wind speeds. At an elevation of 10 meters above sea level, mean annual wind speeds in these regions can reach up to 27 km/h, mirroring the conditions observed across major straits within the basin¹⁹⁶. The Mediterranean Sea, characterized by its intricate morphology and sub-basins, exhibits diverse wind patterns. Along its westernmost perimeter, northeast (Levanter wind) and southwest (Vendaval wind) winds prevail (Fig. 5b). Over the northwestern Mediterranean Sea, the Mistral wind, predominantly blowing from the northwest, extends across the western and Tyrrhenian sub-basins, occasionally reaching African coastlines. Concurrently, converging with the northeasterly forward Libeccio wind, the Libeccio wind contributes to eastward winds over the Ionian-Meridional sub-basin, potentially facilitating the transport of oceanic and atmospheric MPs towards the eastern Mediterranean Sea. Furthermore, northerly winds, particularly the Etesian winds blowing from the north/northwest, significantly impact the movement of oceanic MPs within the Levantine-Aegean sub-basin, particularly during the summer months (Fig. 5b)¹⁹⁷.

In the vicinity of the Red Sea, prevailing southeastward winds emerge as the predominant patterns, influenced by the continental patterns of Africa, particularly over the northern Red Sea and the majority of the Arabian Gulf (Fig. 5c). In the southern region of the Red Sea, air circulation is characterized by seasonal variations¹⁹⁸. During winter, relatively robust southeast monsoon winds, with speeds reaching up to 32.4 km/h, play a crucial role in transporting dust from the desert to the Red Sea¹⁹⁸. Concurrently, reversal winds prevailing over the Arabian Gulf flow from the Asian continent towards the Gulf (Fig. 5c). The influence of the northeast monsoon winds is notable in directing airflow towards the Gulf of Aden and the southern Red Sea, owing to the presence of the Ethiopian highlands and the coastal mountain ranges of northern Somalia (Fig. 5c). Conversely, during the summer, the entire Red Sea experiences northwest monsoon winds, including the northern part maintains a northwest wind pattern throughout the year. Similarly, in the Arabian Gulf, winds predominantly flow in a southeast direction, mirroring the patterns observed in the northern part of the Red Sea. This northwest wind dominance persists throughout the year in the Arabian Sea (Fig. 5c).

In the MENA region, violent sandstorms driven by winds sweeping sands from inland deserts constitute significant factors contributing to the transport of particulate matter and MPs, as they lift MPs when the dust is stirred up. As depicted in Fig. 5d, during summer, southwestern sandstorms originating from Saudi Arabia and the UAE traverse the Arabian Gulf, reaching Iran¹⁹⁹. Evidence of this transport phenomenon is substantiated by the presence of MPs in street dust samples collected from Shiraz city in Iran, confirming the influx of MPs transported by sandstorms originating across the Arabian Gulf (Fig. 5d)¹³⁰. Moreover, in the Kavir and Lut deserts of Iran, the occurrence of MPs within both deserts may also be attributed to the transport facilitated by strong northerly and northwesterly winds, which carry sand southwards²⁰⁰.

Circulation of MPs driven by ocean currents within the MENA region

This section will begin by examining the primary water currents in these regions. Subsequently, the dynamics of seaborne plastics, which typically wash up and accumulate on beaches, will be discussed. These plastics may concentrate along the tide line or disperse across the back beach and wash-over flat, providing insights into potential pathways for MPs transport.

Surface current dynamics, MPs patterns and beaching behavior in the Arabian Gulf-Gulf of Oman complex, in the southern Arabian margin and non-MENA region

The Arabian Gulf, connected to the Gulf of Oman via the Strait of Hormuz, shares structural similarities with the Red Sea, functioning largely as an inverted estuary. Covering a length of approximately 1000 km and a width ranging from 58 to 338 km, with Iran dominating the northern coast and Saudi Arabia occupying most of the southern coast, it features relatively shallow depths, with a maximum of around 90 m and an average depth of approximately 50 m²⁰¹. The shallow nature of the Arabian Gulf renders southward wind stresses and thermohaline forces pivotal in shaping marine currents. As depicted in Fig. 6a, the region is not significantly impacted by monsoons, with occasional rainfall occurrences on the Gulf coast resulting from the sporadic influence of tropical storms. Notably, consistent southward wind stress, particularly evident in the northern half of the Gulf, plays a crucial role in delineating distinct coastal current patterns along the Saudi (downwelling) and Iranian (upwelling) coasts. In the northern regime, the coastal currents along the Saudi-Emirate coast are notably influenced by inflows from the Iraqi Shatt-al-Arab waterway²⁰². However, the freshwater input from the north creates relatively stagnant conditions along the Kuwait and Saudi coasts. In Kuwait Bay, a dense bottom water mass continually flows into the Arabian Gulf basin, inducing reverse estuarine circulation in the northern Arabian Gulf, ultimately reaching the central Gulf basin²⁰³. Moreover, a persistent thermal front traverses the Arabian Gulf, seemingly associated with thermohaline exchange through the Strait of Hormuz, roughly aligned with the latitude of Qatar.

**Fig. 6: Marine currents and gyroids dominate the transfer of microplastics in the MENA region leading to high density of microplastics occurrences far from urban and industrial centers.**

Similar to the complex dynamics of the Red Sea, the Arabian Gulf connects to the Arabian Sea and the Indian Ocean through the Gulf of Oman, a deep gulf exhibiting a bathymetric profile strikingly similar to that of the Gulf of Aden²⁰⁴. The narrow Strait of Hormuz, with a width ranging from 39 to 96 km (averaging 56 km), has a shallow depth of approximately 60 m (varying from 52 m to 102 m). Upon crossing this entrance strait, deep seawater with high salinity levels (38,000–42,000 ppm) flows out, forming a coastal plume along the northeastern side of Oman, transiting along the UAE and Oman coasts before reaching the major underwater promontory of Ras al Hadd²⁰¹. To maintain water flow equilibrium across the strait, surface inflow enters northwestward, generating an upwelling current along the Iranian coasts. As the deep outflow descends into the Gulf of Oman, currents are primarily influenced by sub-mesoscale eddies, continuing their trajectory towards the Arabian Sea. At Ras al Hadd, situated at the entrance to the Gulf of Oman, the outflow from the Arabian Gulf intermixes with seasonal currents along the southern Arabian Peninsula. During summer, this outflow encounters upwelling currents along the coast of Yemen and Oman, forming a front and dipole vortex before dispersing into the Arabian Sea. Notably, in the northern part of the Indian Ocean, subtropical gyres do not occur due to landmass obstruction. Instead, during monsoon events, temperature disparities between the northern landmass and the ocean dominate and dictate oceanic dynamics¹⁵³.

The Arabian Gulf, due to the constraining effect of the Strait of Hormuz, experiences minimal influence from currents potentially carrying MPs from the Indian Ocean (Fig. 6a)⁸. The occurrence of MPs in this region is predominantly linked to littering from inflows of the Iraqi Shatt-al-Arab waterway and other rivers in Iran, along with emissions from coastal urban centers⁸. Consequently, endogenous MPs within the Arabian Gulf are likely to circulate with ocean currents along the western shore of Iran, from southeast to northwest. As these MPs move with littoral currents, some may migrate towards the central area of the Arabian Gulf. In the northern Arabian Gulf, MPs tend to be transported southeastward, accumulating notably around Khark Island⁸⁵. Similarly, along the western coastline of the Arabian Gulf, MPs are conveyed by southeastward ocean currents and accumulate in the western shoreline of Qatar²⁰⁵. A study conducted in Fall 2019 outlined the transport pathway of plastics, indicating that plastic items were carried to the coast of Qatar by prevailing winds and currents from neighboring countries surrounding the Arabian Gulf, with some materials estimated to have been produced within the past two years. As depicted in Fig. 6a, anticyclonic eddies in the eastern section of the gulf facilitate the accumulation of the majority of MPs¹⁰⁶. This behavior is echoed in Doha Bay, where the high abundance of MPs is attributed to low-turbulence currents⁹¹. Geographical characterization, particularly in the southern Arabian Gulf, thus emerges as a critical determinant in the transport dynamics of MPs^89,90.

The transfer of MPs between the Arabian Gulf and the Gulf of Oman is likely restricted by the presence of the Strait of Hormuz⁸. In the northern region of the Gulf of Oman, areas such as Chabahar Bay, characterized by a 14 km wide entrance in the east-west direction and extending 17 km from south to north, along with the bay of Beheshti, which features mangroves, harbor stagnant waters with low turbulence levels. Moreover, both bays, situated in densely populated areas, are subject to anthropogenic pollutants primarily originating from industrial activities, tourism, and residential sources^94,108. During summer, southeastward ocean currents originating from the sub-Indian continent (Fig. 6e) are proposed to transport MPs from the Gulf of Oman to coastal areas of India, Sri Lanka, and the Bay of Bengal¹⁵³.

Surface current dynamics, MPs patterns and beaching behavior in the Red Sea-Gulf of Aden complex, in the southern Arabian margin and non-MENA region

The Red Sea spans approximately 2000 km in length and is relatively narrow, measuring only 350 km in width. It links to the Gulf of Aden through the Bab al-Mandab strait, which is relatively narrow at 25 km wide and shallow with a depth of 310 m, extending into the Indian Ocean²⁰⁶. Functioning as an inverted estuary, the surface currents in the Red Sea are primarily influenced by seasonal wind forces and thermohaline processes^207,208,209. During winter, southeast winds drive the mean current flow northward across the Red Sea, with consistent velocities observed over most of its width (Fig. 6b). Additionally, southward geostrophic flows develop along the eastern and western coasts, giving rise to energetic anticyclonic and cyclonic eddies, respectively²⁰¹. In contrast, summer brings dominant northwest winds, resulting in south-oriented geostrophic currents over the Red Sea, which diminish the inflow of water from the Indian Ocean along the eastern coastline (Fig. 6c)²⁰¹. The Bab al-Mandab strait experiences highly seasonal exchange currents, governing transfers between the Red Sea and the Gulf of Aden. In winter, upwelling intermediate intrusion leads to surface narrow inflows into the Red Sea, accompanied by deep outflow spilling into the Gulf of Aden and extending into the Indian Ocean, with maximum intensity occurring²⁰¹. However, during the summer period three-layers exchange dominates the seasonal flow through the Bab al-Mandab strait. In addition to an inflowing layer from Gulf of Aden and a weak outflowing deep layer, the exchange is characterized by a thin surface outflow from the Red Sea propelled by the southeastward winds²⁰¹. Along the southern Arabian Peninsula, driven by seasonal winds, the main oceanic dynamic along the coasts of Yemen, Oman, and Somalia exhibits southwestward flow in winter and northeastward flow in summer (Fig. 6d, e). The northeastward flowing Oman coastal current extends up to 200 km offshore into the Indian Ocean, with velocities reaching up to 0.4 m/s, contributing to the strong southwestern winds prevalent in summer²¹⁰. The transition to northeastern winds in winter results in a complete reversal of the Oman coastal current direction to a southwestern flow.

Seasonal ocean current dynamics exert noteworthy influence along the Red Sea coastline, potentially facilitating the seasonal transfer of MPs from deep waters to the shore, resulting in beach sedimentation. While establishing direct relationships between currents and the occurrence of MPs remains challenging, particularly along the Saudi Arabian and Egyptian coastlines, transfers are highly probable given the circulation patterns of the currents. The presence of MPs in seawater surface samples, marine macro-organisms, and associated products within the Red Sea has been documented on numerous occasions, even in locations distant from major urban centers (Fig. 2c, d, and Tables 2, 3). However, the density of MPs in the Red Sea remains relatively low and exhibits fluctuations over time and no study evaluated specifically the impact of seasonality over multiple years on the variations in occurrences of MPs.

The Red Sea, while semi-enclosed like the Mediterranean Sea and the Arabian Sea²¹¹, exhibits relatively low MPs abundance. This phenomenon has been attributed to sparse population density and the efficient removal of MPs from surface waters by coral reefs, seagrass, and mangroves^110,212. Along the eastern shore of the Red Sea, northwestward currents (Fig. 6b) transport MPs from the Indian Ocean into the Red Sea’s surface waters during winter¹¹⁰. In this season, MPs within eddies along the eastern Red Sea may be transported to coastlines at relatively high transfer velocities. However, during winter, the export capacity of floating MPs is constrained by the hydrodynamic pattern, characterized by the exchange of surface inflow of low-salinity water over a deeper outflowing high-salinity water layer at the strait²¹³. Additionally, strong south winds in winter drive MPs towards the western shore of the Red Sea, where they accumulate on sandy beaches. This is corroborated by reports of sediment analysis along the Red Sea coastlines, with higher MP densities observed on the eastern coastline of Egypt compared to the eastern Red Sea coastline (Table 1, Entry 15, 16)^95,97.

In the southern Arabian margin and non-MENA region, influenced by seasonal currents (Fig. 6d, e), MPs are predominantly transported southwestward into the Gulf of Aden and along the southeastern coastline of Africa during winter, and northeastward during summer. According to a buoyancy model, a significant portion of MPs found along the Omani and Yemeni coastlines likely originates from countries such as India and Sri Lanka¹⁵³. However, for countries like Somalia, situated farther from the main sources of MPs in India and Sri Lanka and lacking significant plastic waste input from neighboring rivers, instances of MPs washing ashore along their coastlines have been observed¹⁵³. During summer, MPs carried by northeastward oceanic currents should therefore converge with southeastward currents along the Omani coast before being transported towards the Arabian Sea and further south into the Indian Ocean.

Confirming these trends would require tracking studies, which are currently lacking. However, based on previous reports from other regions regarding the transportability and impact of both winds and oceanic currents, it is reasonable to assume that the depicted trends offer a realistic representation. It is important to highlight that, unlike the South Mediterranean region, this area lacks major river systems such as the Nile. Consequently, the likelihood of river inputs is extremely limited in this context.

Surface current dynamics MPs patterns and beaching behavior in the Mediterranean Sea

In the Mediterranean Sea, the currents primarily consist of intense mesoscale circulation patterns, with limited exchange with the Atlantic Oceanic basins (Fig. 6f)¹⁹⁹. Anticlockwise currents along the extensive coastline serve as the main conduits for transporting MPs from the densely populated northern regions, including the European and Anatolian peninsulas, towards the southern and eastern coastlines. As illustrated in Fig. 1b, MPs are consistently abundant in the northern Mediterranean Sea throughout the year. Along the coastlines of southern European countries like Italy, reports indicate MPs occurrence exceeding one million items/km² ^70,71,72. Similarly, elevated pollution levels have been documented along the northeastern Levantine coastlines of Türkiye, Lebanon, and Israel within the Mediterranean Sea^70,71,72.

Several currents along the southern coastline, driven by seasonal winds and bringing deep-sea waters to the coast, may contribute to the deposition of MPs onto North African beaches and sedimentation near-coast seafloors, as evidenced by previous occurrence studies, particularly in Tunisia^101,102. However, the density of MPs along the southern Mediterranean Sea was found to be lower than that along the eastern Mediterranean Sea, with the Tyrrhenian sub-basin identified as a potential retention area for MPs¹¹². As depicted in Fig. 6f, west currents along the southern Mediterranean Sea towards the eastern Mediterranean Sea exhibit higher shear, potentially contributing to the observed density differences and diverting MPs pollution further northward.

Moreover, the Nile River serves as a significant source of plastic pollution in the eastern Mediterranean basin, with an estimated 85,000 tons per year of MPs being transported by it¹⁵⁴. The flux of MPs from the Nile estuaries into the Mediterranean Sea is estimated to range from 80 to 1000 billion MPs per year⁹⁸. The densely populated areas along the banks of the Nile River, spanning from South Sudan to Egypt, are likely responsible for a sizable portion of the MPs entering the southeastern Mediterranean Sea. The occurrence of MPs around the Nile River delta (Fig. 2b–d) and their abundance highlight the Nile River as a key determinant of high concentrations of MPs in the Mediterranean Sea. These MPs are then transported by northeastward currents (Fig. 6f) towards the eastern coastline of the Mediterranean Sea, establishing the eastern basin of the Mediterranean as one of the primary areas for local plastic accumulation.

Conclusions on MPs transportability and consequences to ecosystems

The analysis of MPs delivery pathways within ecological systems has been conducted comprehensively and systematically. The atmospheric environment plays a crucial role in the transport of MPs, capable of dispersing them to sparsely populated areas and even across gulfs and seas via high winds and intense sandstorms. While circulation across atmospheric rivers may be limited, freshwater rivers and ocean currents emerge as the primary means of MP transport. Inland riverine MPs pollution is primarily conveyed by river networks, with MPs being transported and accumulating at riverbeds, estuaries, and shorelines before eventually discharging into seawater systems. MPs in seawater can also originate from sea-based activities such as petroleum extraction, shipping, and fishing. However, transport is predominantly governed by major oceanic currents, particularly energetic anticyclonic and cyclonic eddies.

Conclusions and perspectives

A comprehensive understanding of potential MPs transport pathways across the MENA region has been developed. Sewage discharge in densely populated and industrial areas was found to be positively correlated with the abundance of MPs occurrence. Once waste is discharged into the environment, it undergoes investigation and degradation by macro-organisms and micro-organisms. Degraded MPs can then be carried by winds or sandstorms to remote, sparsely populated areas such as deserts, where they may precipitate onto land with rain or snow. Geographical specificities also play a significant role in the delivery of MPs within the MENA region. In areas with low turbulence and high population density, MPs are often trapped in bays. Additionally, ocean currents can transport MPs seasonally to remote, sparsely populated areas like polar regions. As MPs move with wave forces, they gradually deposit on beaches, seabed, or riverbeds.

Further research is imperative to fully comprehend the extent and consequences of MPs pollution and dispersion within the region. In regard to the status of MPs contamination, the challenge facing by the researchers firstly is to establish standard research protocol for the MPs’ detection, such as sampling method, MPs’ collection method and characterizations for virous environmental matrix. To publish consistent research results is critical for analyzing and comparing MPs pollution abundance within the MENA region. Then the challenge is the studying of nano scale plastics that are more hazardous to environments and human health. The technology limitation usually led to inaccurate research result, missing the nano scale sizing plastics publication exerting in the environments. By improving the precision of mesh to nano scale or developing novel sorting methods can significantly increase the observation of nano-plastic beads. Tracking the migration of MPs is a challenging task, whether in water columns or air columns. This is a long-term effort due to the seasonal patterns of natural forces. The impact of seasonality is of particular importance since both atmospheric and oceanic currents may shift or reverse between winter and summer. Air mass backward trajectory analysis proves to be a valuable qualitative tool for identifying potential sources and transport mechanisms of atmospheric pollutants. Similarly, leveraging state-of-the-art technologies, such as modeling based on satellite-tracked buoy data, is advocated for exploring MPs migration in open seas and accurately tracing MPs pathways. Considering the importance of ocean to diverse marine biota, in addition to the surface delivery studies, the vertical transportation of MPs as well as localized research are worth studying. Further understanding these transport routes will aid in identifying prevalent pathways of movement and facilitate appropriate collection and removal strategies from environmental settings. This systematic assessment of the MPs cycle provides insights for subsequent pollution control measures based on transport characteristics. Strengthening policy coherence and fostering collaboration throughout the MENA region will streamline the monitoring of long-range plastic pollution transport, contributing to more effective environmental protection and management strategies. The first and most important step is to raise public awareness of how to minimize the generation and wasting of MPs. Appealing the population to use biodegradable packaging alternatives and promoting recycling has the potential to alleviate the MPs’ pollution. There already are many activities launched by different countries to support this. Morocco is reviving to produce eco-friendly productions. In the UAE, there are “the Recyclable Material Collection Centers” and several initiatives encouraging community participation in recycling efforts. The countries in the MENA region should unite to improve eco-education to foster a sense of environmental responsibility. The introduction of enhanced waste treatment technologies to developing countries, along with the establishment of regulations and laws can yield significant benefits. Overall, the comprehensive review emphasizes the urgent need for further research on the occurrence, migration tracking and responsive strategies for MPs pollution in the MENA region.

Introduction

MPs occurrence and trends

Statistics on global waste management and worldwide MP occurrences

MPs contamination in the MENA region

Occurrence in shore sediments and soils

Occurrence in coastal seawaters and river waters

Occurrence in macro-organisms

Occurrence in air

Challenges related to sampling and sensitivity analysis requirements

Conclusions on occurrences of MPs within the MENA region

Transport of MPs – mechanisms and routes within the MENA region

Demonstrations of MPs transportability at global scale

Mechanisms of MPs transfers within airborne, water systems and terrestrial matrix

Direct airborne transfers of MPs in the MENA region

Circulation of MPs driven by ocean currents within the MENA region

Surface current dynamics, MPs patterns and beaching behavior in the Arabian Gulf-Gulf of Oman complex, in the southern Arabian margin and non-MENA region

Surface current dynamics, MPs patterns and beaching behavior in the Red Sea-Gulf of Aden complex, in the southern Arabian margin and non-MENA region

Surface current dynamics MPs patterns and beaching behavior in the Mediterranean Sea

Conclusions on MPs transportability and consequences to ecosystems

Conclusions and perspectives

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