Introduction
The maritime environment is said to be the sink for the improperly handled garbage. A prominent illustration of this occurred during the floods in several regions of India, as land-based plastic waste that had been transported to marine waters by runoff found its way back onto the beaches [
1]. To put it another way, according to a study by Belioka et al., 2024 [
2], by the end of 2060, all plastic waste produced worldwide will either be recycled, disposed of in landfills, burned, or, in the worst case, completely mismanaged. To reduce the consequences of pollution in the future, plastic trash must be properly addressed [
2]. Plastics should be recycled wherever possible, and if that isn’t practicable, they should either be burned with energy recovery or landfilled in an environmentally friendly manner. This lessens the quantity of inappropriately handled garbage and leaves only hard-to-treat leakage sources, including microplastics (MPs) and uncollected litter. As a result, rates of incorrect trash disposal will decrease and rates of recycling will rise globally [
3].
Microplastics are a type of pollution that is becoming more and more of a worry since the plastic waste that is dumped in the marine environment breaks down into tiny fragments for a variety of reasons [
4,
5]. All additional microplastics—aside from the basic microplastics—are created by breakdown from bigger plastics. In the marine environment, the conversion of macroplastics into microplastics is contingent upon their duration of residence in the ecosystem; a longer residence period leads to a greater degree of degradation [
5]. While MPs in aquatic systems have been researched in great detail, little is known about their existence and ultimate fate in agricultural systems. Weather conditions are one of the factors that direct MPs to agricultural soils. The use of compost and biosolids, irrigation with wastewater, mulching film, polymer-based fertilizers and pesticides, and atmospheric deposition are the main contributors to MPs contamination in agricultural soils. The properties of the soil, agricultural techniques, and soil biota variety are the primary factors influencing the fate and dispersal of MPs in the soil environment. Despite the fact that MP contamination in the soil environment is on the rise, there are currently no established methods for detection and measurement. Because of this, emphasis is placed on understanding the causes that drive microplastic transport from aquatic environments and steaming to farmland and agricultural soils [
6].
Agricultural soil systems are the primary sources of microplastics; they are exposed to them in a variety of ways, and a range of environmental and weathering conditions may have an impact on how the microplastics behave. The primary sources include air deposition, agricultural operations, and input from irrigation and fertilizer. Microplastics are broken down and broken down in agricultural soils by mechanical abrasion and photo-oxidation, with UV irradiation playing a major role in the early phases of the microplastic degradation process. Additionally, depending on the features of the soil environment, agricultural practices, and the qualities of the microplastics themselves, microplastics may move through soil systems in both physical and biological ways. By directly ingesting or accumulating in organisms, microplastics have a variety of effects on agricultural soils. They can also indirectly change the microbial population or soil’s qualities [
7]. Extreme weather is being impacted globally by Earth’s changing climate. There is an increasing frequency and intensity of extreme weather events like as heat waves that shatter records both on land and in the water, torrential rains, major floods, prolonged droughts, intense wildfires, and extensive flooding during storms. It is anticipated that some extreme weather event types may become more frequent, intense, and damaging due to climate change [
8].
Dry and wet atmospheric fallouts are the means by which airborne microplastics reach the aquatic and terrestrial habitats. Concerns about airborne microplastics have grown, as has the number of places investigated since proof of their existence in atmospheric fallouts was discovered [
9]. Research is concentrating on various environmental kinds. Only a portion of the destiny of microplastics in the atmosphere is known [
10]. Microplastics were discovered in the dry and wet atmosphere in alpine regions, metropolitan areas, and maritime habitats. They showed patterns in relation to the quantity of precipitation, whether it be in the form of rain or snow, as well as the direction and intensity of the wind [
11,
12].
In higher altitude ecosystems, precipitation—snow and rain—is thought to be the main factor causing MP deposition. Due of their low density, MPs are carried by wind into the upper atmosphere where they settle as a result of precipitation or snowfall. This presents serious environmental problems [
13]. Airborne MPs settle at various altitudes thanks to the transport, dispersion, and deposition processes in the atmosphere brought on by downward air movement, local turbulence, and wind flow. Additionally, it has been observed that smaller MPs and smaller relative densities have been detected at greater elevations than larger MPs. Hence, MPs’ abundance and dispersion at faraway locations may be facilitated by air movement [
14].
It is well accepted that microplastics can act as carriers to encourage microbial colonization and biofilm development, and eventually turn into a pelagic habitat for microorganisms because of their extended half-life and hydrophobic surface [
15]. Microplastics also increase the possibility of potentially harmful bacteria spreading over long distances, which has an ecological impact on the original environment. According to some research, tropical cyclones—also known as tropical storms and typhoons—and other catastrophic storm occurrences can have a major impact on coastal ecosystems [
16].
Recent studies have highlighted surface runoff as a major source of microplastic contamination, suggesting that it contributes more to the problem than point sources do. Furthermore, a few recent researches have looked at the temporal dynamics of microplastics’ abundances and properties. Significant fluxes in microplastic abundances in freshwater and marine ecosystems have been documented following rainfall events, storms, floods, and typhoons, with regards to the impacts of runoff on the receiving water bodies [
17]. Most of the studies calculated that the wet or monsoon season contributed more to the yearly emissions of microplastics than did the dry season. Furthermore, relationships based on regression analysis have been shown between microplastic abundances and rainfall features [
18]. A characteristic example is the waste from masks during COVID-19 period and how weathering conditions contributed to their transportation. After the soil weathered, a significant amount of fibers on the mask’s surface were released into the surrounding area and were entangled on the broad soil surface. The combination of soil microorganisms and hydraulic erosion during wet weather also contributed to the release of microplastics. Significant amounts of microfiber were released by microplastics from mask waste; the sequence of release ability, from greatest to smallest, is soil > ocean > river > air > new mask [
19].
Information on the potential origins and routes of microplastics in the marine environment may be gleaned from the distribution of microplastics in relation to the geographic characteristics of the region. Furthermore, it is anticipated that the temporal variations in the distribution of microplastics will shed light on how natural events like floods and oceanographic characteristics like wave height affect the microplastic contamination of the maritime environment. Microplastics are predicted to be transported in large quantities from the terrestrial to the marine environments during floods. However, there isn’t much information in the academic literature about how flooding affects microplastic pollution [
1]. The majority of research done to date has been carried out in industrialized nations with temperate climates, where precipitation may occur year-round, and where plastic waste management is generally effective. Developing nations with high GDP are known for their poor handling of plastic trash, which causes significant environmental plastic pollution and it can have serious consequences after a natural disaster for example [
11,
20].
Here, our goal is to create a mini-review that investigates how the distribution of MPs in farmlands and agricultural soils is affected by changes in seasonality and harsh weather. This brief overview offers information on three key topics related to microplastic distribution: (1) seasonality and its consequences; (2) the effects of typhoons, rainstorms of varying intensities, and other meteorological phenomena; and (3) a link with inappropriate plastic waste management. Additionally, a statistical study has been conducted to categorize the impact of the most severe natural disasters. We note that increased microplastic abundances are detected during (1) the wet season with higher precipitation and during (2) extreme weather events with heavy precipitation, strong wind, and storm surge. These findings are supported by earlier research on the impacts of seasonality.
Research Methodology
This mini-review compiles findings from researches about natural phenomena and natural disasters together with weathering conditions that affect the transport and accumulation of Microplastics in agricultural soils and farmlands. The number of publications on such topics is limited and the number of relevant articles is small. The reason is that research studies focus mainly in aquatic environments, oceans, rivers, lakes and coastal areas instead of agricultural soils and farmlands. Therefore our review has a small data base with a total of 80 papers.
The terms “microplastics” and “transport” were combined with the following keywords to extract literature from the databases of Google Scholar, Scopus, and Web of Science: “natural disaster,” “natural phenomena,” “weather,” “weathering conditions,” “climate,” “climate change,” “farmlands,” and “agricultural soils.” The studies that were retrieved were categorized according to the monitoring technology they covered. Every article that was found was released between 2004 and 2024. Moreover, research conducted in aquatic environments—such as lakes, rivers, and oceans—was also included because they describe the mechanisms of MPs transportation.
After conducting the necessary searches in the relevant databases, we came to an end when we discovered many pages of results lacking any relevant publications from Scopus, Google Scholar, or Web of Science. Conference papers, postgraduate and doctoral theses, and articles written in languages other than English were all disregarded since the search was limited to locating publications that included literature reviews. As a consequence, relevant publications were added to our collection after published papers were sifted using the previously mentioned criteria (title, keywords, and abstract). Each article’s content was examined, with particular attention paid to the abstract and conclusion sections. This review paper’s research methodology followed the optimal reference criteria for systematic reviews and meta-analyses established by Moher et al. approach as you can see from
Figure 1 [
21].
Results and Discussion
The ecology is seriously threatened by microplastic contamination, which can be impacted by a variety of meteorological conditions. Evaluating the impact of weather on coastal microplastic contamination is critical, as extreme weather events have become more frequent in recent years [
22].
One of the biggest problems nowadays is the pollution of freshwaters, seas, and soils by microplastics (MP). Large amounts of MP are carried from the land to the sea via river systems, where they end up in floodplains and river sediments that damage agricultural soils and farmlands. Floodplains and the soils inside them are recognized for their ability to act as sinks for pollutants, nutrients, and sediments as a component of the river system [
23]. Still unanswered are the following: How much of this deposition happens in soils in floodplains? Which is the geographical distribution of MP accumulations that may be caused by various environmental drivers? The attempt is made here to compile information and carefully look at each of the variables (natural phenomena and disasters) that influence the buildup of MPs in farmlands and agricultural soils.
Microplastics (MP) enter wastewater treatment facilities through three different channels: stormwater, household wastewater, and industrial wastewater.
The pace at which MP enters wastewater treatment plants can be changed by extreme weather circumstances, such as increased temperatures and excessive rains brought on by climate change. The distribution and destiny of MPs can be impacted by natural catastrophes or events, as demonstrated by seasonal changes and a thorough investigation of MP dispersion in various phases of wastewater treatment plants [
24]. Additionally, a significant positive association was discovered between the MP concentration and the quantity of precipitation. A large amount of MPs from our daily lives end up in wastewater and are used in agriculture as sewage sludge. Thus, a closed loop is produced. Enhancing my writing skills requires a deeper comprehension of the movement and final destination of microplastics in wastewater treatment facilities [
25].
Microplastics are mostly stored in soil [
26]. Large amounts of microplastic fibers or debris have been discovered in compost fertilizers and sewage sludge by several research [
27,
28]. These sludges are frequently utilized in agricultural activities [
29,
30]. Researchers have found various microplastics in soil ecosystems, which may have originated from applying organic fertilizers or sewage sludge to farmlands, from atmospheric deposition, from flooding or polluted waters, from littering, from the weathering and disintegration of plastic films on farmlands, from the fragmentation of plastic waste and items in landfills, and from littering [
31,
32]. Furthermore, some industrial, agricultural, marine, urban, suburban, and even floodplain soils have been shown to contain microplastics [
33]. Below there is a classification of the different weathering conditions, natural phenomena that affect the transport of MPs in soils and farmlands.
Figure 2 shows the classification of the most often natural phenomena that contribute to the MPs transport in agricultural soils and farmlands after a comprehensive statistical analysis of the studies presented in this mini-review. The most dominant phenomena are floods and storms together with winds and tidal having together a percentage very close to 50%, almost the half. Typhoons and monsoons occupied together the second position with a perecentage close to 36%, which means that together with the first category the 86% of the accumulation of MPs is due to natural and meteorological phenomena. The rest belongs to phenomena of minor importance such as snow and precipitation, meteorological parameters at high altitude areas and drought together with dust storms. It is important to highlight that there is almost a 2% contribution to MPs transportation due to the salinity of the water.
Figure 3 shows the literature review’s results that refer to the frequency of case studies produced in each country on this topic and it is worth noting that the first two places are occupied by China and India, followed by Japan and Australia, then a few European countries, even fewer African and South American countries and no North American countries.
Floods and Storms
The ecology is seriously threatened by microplastic contamination, which can be impacted by a variety of meteorological conditions. Evaluating the impact of weather on coastal microplastic contamination is critical, as extreme weather events have become more frequent in recent years. Cheung et al. (2023) carried out follow-up studies following typhoon and rainy events in addition to a year-long baseline survey on surface seawater and beach sediment in Hong Kong. According to our research, the quantity of microplastics was five times more in the rainy season than in the dry season. However, the seasonal fluctuation was negligible when the baseline condition was taken into account, indicating that extreme weather events are the primary cause of the seasonal variation in the distribution of microplastics. Larger amounts of microplastic in beach sand and a higher percentage of hard pieces after severe weather point to a greater mobility of heavier plastic debris from a wider source. Positive correlations were found between plastic levels and various weather variables, such as rainfall, wind, and tide [
22]. These findings raise the possibility of microplastics entering the Earth through surface runoff and wind transport, as well as the possibility of microplastics being redistributed from deep sediment to surface sediment by wave agitation. Additionally, they found a highly positive correlation between the abundance of macro- and microplastics in beach sediment, indicating the possibility of plastic fragmentation under high wave abrasion. This could exacerbate the pollution of farmlands nearby by coastal microplastics [
22].
Cheung et al. (2019) investigated the relationship between the dynamics of microplastics in rivers and the degrees of pollution they cause, by measuring the quantity and characteristics of microplastics at the surface of an urban river during a rainy event in Hong Kong. Following a three-day rainstorm event, plastic samples were gathered at the river’s surface, and the microplastic abundance was almost twice as high as that of the coastal sea surface in the same region. The discovery of a ten-fold reduction in microplastic abundances in a span of two hours indicates a very dynamic temporal distribution of river microplastics following rainfall [
34].
Water contamination is mostly shaped by urban surface runoff (USR) and drainage system overflows during rainy weather (WWF). In particular, it is uncertain how much contamination from microplastics affects metropolitan water bodies. In six primary urban drainage systems along Suzhou Creek in the Chinese megacity of Shanghai, Sun et al. carried out an in-field analysis. They determined the effects of land use and storm conditions on the real-time dynamic changes in microplastic abundance and features in USR and WWF. In both USR and WWF, they discovered statistical evidence of the broad relationships between microplastic abundance and storm variables (accumulated storm depth and WWF flow). Both USR and WWF have the first flush phenomena of microplastic dynamics. The properties of microplastics also varied dynamically with storm duration. Polypropylene and small-sized (<1 mm) microplastics in USR occurrences rose and then declined with significant storm components [
35].
In order to evaluate the quantity and make-up of microplastic pellets (MPPs) along the Chennai coast prior to and following the 2015 flood, Veerasingam et al. (2016) examined the effects of the flood on the distribution of MPPs on Chennai beaches, along with potential sources and controlling factors, and identified the types of polymers present in the soils [
36].
A significant amount of new MPs swept down the Cooum and Adyar rivers from land during the storm, as evidenced by the three-fold increase in MP abundance in November 2015 compared to March 2015. The movement and deposition of MPs from the sea to beaches in November was mostly driven by winds and surface currents [
36].
Due to its unusual geographic location, Kerala, which borders the western coast of peninsular India and lies to the west of the Western Ghats mountain ranges, receives abundant monsoon rains. A study made by Kumar et al., (2021) demonstrated that the 2018 and 2019 Southwest monsoon was terrible since it brought about river flooding. The extremely heavy rainfall raised the water load in nearly every reservoir’s catchment region, pushing the water levels above critical limits. The need to quickly activate reservoir flood gates contributed to the intensity of the floods. Waste from the land, such as plastic, construction, and biological debris, may be carried by floods caused by overflowing canals, rivers, and dams. Surprisingly, the quantity of microplastics in the samples gathered during the flood continued to be high. In both of the flood period samples, there was a significant concentration of microplastics in soils. Furthermore, more industrial pellets were found during the flood months than at any other time throughout the test period. One potential cause might be the flood overflow from the surrounding plastic manufacturing sector [
1].
Wind and rainfall have been shown to have an impact on the fluxes of microplastic deposition in air fallouts from temperate regions, as well as from both urban and distant locations. Surface runoff, urban drainage (stormwater drainage), and interflow (from the near-surface unsaturated zone) are some of the mechanisms that provide direct runoff, which is the quick delivery of water to the stream.
Farmlands are expected to have a large amount of direct runoff contributing to the overall MP load of the water and soil. According to Moses et al.‘s 2023 assessment, every headwater source is located in the lower mountain range, near to agricultural soils and farmlands [
37]. Balthazar Silva et al. verified and emphasized that local-scale variability is dependent on tides, beach hydrodynamics, and distance from source, whereas regional scale variation is driven by rainfall and source distance [
38].
In another study carried out in 2024 by Imbulana et al., microplastics mobility may also be influenced by rainfall intensity and event length. The research has indicated that microplastic mobilization happens when rainfall intensity surpasses 2.5 mm/h for a period more than two hours. Despite the fact that microplastic discharge characteristics can vary greatly between catchments and rainfall events, our data from the lowest rainfall event suggested that two hours at an intensity of 1.5 mm/h would be enough to introduce over two billion MPs into the river. Furthermore, the findings demonstrate that, in order to fully capture the range of variability in MP emissions, consideration should be given to the effective time during which a rainfall event may impact river flow, rather than the duration of the rainfall.
The primary routes via which land-sourced microplastics enter the world’s seas are urban waterways. While the concentrations of MPs were correlated with the number of preceding dry days, the inter-event total loads of MPs correlated strongly with the total rainfall. At lesser rainfall intensities, MPs above 2000 μm are released immediately after the peak rainfall intensity, whereas smaller MPs (10–40 μm) are mobilized quickly. Furthermore, <70 μm MPs show a surge that occurs after periods of intense rainfall because of turbulent flow conditions that put the deposited MPs back into suspension [
18].
Xia et al., 2020 also looked at the connection between surface water microplastic content and rainfall. During the summer, the experiment was carried out at China’s largest urban lake, Lake Donghu. The findings showed a substantial relationship between microplastic content and rainfall. Therefore, in order to effectively assess microplastic contamination and its effects, high frequency sampling and rainfall data are required [
39].
Hitchcock (2020) investigated the changes in microplastic concentrations during a storm event in an urban estuary. Rain and storm events are accountable for the mobilization and transport of various contaminants in aquatic systems. High-frequency sampling was carried out before to, during, and following a storm event that resulted in flooding in Australia’s Cooks River estuary. The quantity of microplastics rose from 400 particles per cubic meter prior to the storm event to as high as 17,383 particles per cubic meter following two days of intense rain. The five-day average antecedent rainfall was positively correlated with variations in microplastic abundance. The findings emphasize how crucial rain and storm-related events are for the pollution of aquatic systems with microplastics. The findings have implications for estimating the maximum amount of microplastics to which aquatic life may be exposed and for managing stormwater to reduce the amount of microplastics entering aquatic environments [
17].
Since deposition plays a significant role in microplastic migration and transport in the atmosphere and urban areas are the most severely affected by microplastic pollution, Jia et al. (2022) looked into the characteristics of atmospheric microplastic deposition in megacities in order to shed light on the contributions of anthropogenic and meteorological factors as well as to identify the sources of atmospheric microplastics. Microplastic characteristics were correlated and variance-analyzed with meteorological and anthropogenic factors (land-use, atmospheric pollutants, and urban indicators). The results indicated that wind and precipitation had an impact on deposition flux, size, and shape, and that these effects were more pronounced at small scales (individual cities), while the population was the primary microplastic influence at large scales. Shanghai’s atmospheric microplastics may be mostly produced by external sources due to a combination of the microplastics’ properties, wind, and backward trajectories. The destiny of urban air microplastics was also disclosed by this study, and it has consequences for the contaminating of agricultural areas and farmlands [
40].
One important route for the transfer of microplastics to land from aquatic habitats is thought to be stormwater runoff. Rainfall-splashed particles and MPs block soil pores, sealing off the soil’s surface and preventing adequate water penetration. Rainwater will gather and flow downslope in sheet or rill erosion rather than seeping into the soil.
Microplastics found in stormwater runoff from residential and industrial regions were examined by Cho et al. in 2023. When there were more antecedent dry days (ADDs), the concentration of microplastics in stormwater was greater. During a rainfall event, the concentration of microplastics often peaked in the early stages of runoff and fluctuated depending on the severity of the rainfall. The overall rainfall depth had a significant impact on the microplastic load and contamination level. The majority of microplastics were carried by early runoff to agricultural soils, while the percentage of bigger, heavier particles increased throughout the runoff’s final stages. It is likely that stormwater runoff is the primary means of introducing microplastics into aquatic habitats since the amount of microplastics released by stormwater runoff was much larger than the amount released through wastewater treatment plant effluent in the same location [
41].
Pollutant levels in marine habitats are significantly increased by floods brought on by heavy rain. Gündogdu et al. (2018) assessed the impact of many floods that took place in Turkey’s northeastern Mediterranean area between December 2016 and January 2017 on the amount of microplastic pollution in Mersin Bay in another research. The current structure and the spatial and temporal distributions of microplastics were hinted at by sampling from four different stations both before and after the flood period, along with a hydrodynamic modeling study. The results showed that severe rains and floods can significantly raise the levels of microplastics in various environments, such as the sea or the mainland [
42].
Due to the paucity of research on the quantity and distribution of microplastic in rivers, as well as how they are distributed in farmlands and agricultural soils, Wong et al. (2020) looked at the contamination of the Tamsui River and its tributaries in northern Taiwan with microplastics. Each sample had varied levels of microplastics, which suggests that the Tamsui River and its tributaries are heavily polluted. Precipitation and the quantity of microplastic particles detected in the rivers have been determined to positively correlate, according to the data. Furthermore, a significant geographical and temporal fluctuation in the quantity of microplastic in the left, center, and right parts of each river was noted [
43].
Yadav et al. (2022) also highlighted that microplastics (MPs) exist in water bodies, and in certain places, runoff, floods, and irrigation bring these aquatic MPs onto the agricultural fields and farmlands [
44]. Crop fields that are close to water resources are more likely to experience this, and soil contamination also results from irrigation from rivers, lakes, and groundwater that already contain microplastics. Another significant factor is flooding, which has the power to carry enormous volumes of trash and waste from water bodies and even landfills onto agricultural land [
45].
Another study confirms that precipitation and atmospheric deposition might potentially be sources of MP contamination in agricultural soils. Due to intense rains, the Luo Yongming study group discovered MP levels in China’s coastal towns’ air environments for the first time. These MPs that have been deposited in the sky have the potential to directly contaminate agricultural nonpoint sources with MPs by penetrating the topsoil of suburban agriculture [
46]. Furthermore, there exists a linear negative correlation between the average particle size of microplastics and soil depth. Smaller particle size microplastics are more easily migrated via soil pores when water is applied following intense rainfall and fertilizer application [
47].
In their 2020 study, Gorman et al. attempted to provide an explanation and understanding of the ways in which fluvial processes—the materials that rivers and streams carry into coastal waters—cause microplastic particles to travel and concentrate in estuarine coastal waters and agricultural soils near rivers. According to model results, the debris field is most likely to be in the near- and offshore locations (between 34 and 40 km
2), intermediate at the river mouth (mean 34 km2), and modest within the estuary (between 3.6 and 8.1 km
2). The study found that the spatiotemporal dynamics of microplastic debris movement and accumulation within dynamic coastal habitats are significantly influenced by the fluvial forcing (rainfall and estuary flushing) [
48].
Osinski et al. (2020), selected Baltic sea in their case study to examine how natural phenomena and disasters affect the transport of microplastics. The selection of a storm event was made because severe wave heights lead to significant sediment erosion to generally unaffected depths; hence, these occurrences are essential for identifying the accumulation zones. The determination of metocean characteristics in such harsh weather events demonstrates that storm events dictate the movement of settled MP, and it has been discovered that atmospheric circumstances significantly influence the amount of material that is deposited and degraded [
49].
Rainfall increases surface water runoffs, which transfer microplastics from land-based soils into the aquatic ecosystem [
50]. The concentration of microplastic in the river surface water was double that of the coastal saltwater in Hong Kong after a three-day rainstorm event [
34]. According to Xia et al., surface water microplastic content rose four times during a period of intense rainfall [
39]. Because they become trapped in the raindrops, atmospheric microplastics can be carried into the aquatic environment via precipitation [
51]. Furthermore, rainfall may have an inverse link between suspended microplastics and sediment by altering the hydrodynamics of water flow and resuspending the microplastics in the sediments [
52]. Acid rain has the potential to bleach coral reefs and enhance the discharge of microplastics that have been stored, which will cause a redistribution of microplastics [
53,
54].
A baseline study conducted by Cheung et al. (2023), on Hong Kong’s beaches and surface waters for a full year, with follow-up studies conducted following typhoons and rainstorms. The research shows that the quantity of microplastics was five times more in the rainy season than in the dry season. However, the seasonal fluctuation was negligible when the baseline condition was taken into account, indicating that extreme weather events are the primary cause of the seasonal variation in the distribution of microplastics. Rainstorms and typhoons increased the amount of microplastics in sediments by 11.7 and 36.4 times, respectively. Larger amounts of microplastic in beach sand and a higher percentage of hard pieces after severe weather point to a greater mobility of heavier plastic debris from a wider source [
22,
34]. The results of this study showed that there are positive correlations between plastic levels and a number of meteorological variables, such as rainfall, wind, and tide. These findings raise the possibility that microplastics may be transported from deep sediment to the surface by waves, or that they may be introduced onto land through surface runoff and wind transport. Additionally, a highly positive association was found between the concentration of macro- and microplastics in beach sand, indicating the possibility of plastic fragmentation under high wave abrasion, which might exacerbate the microplastic pollution along the coast [
22].
Salinity in Combination to Weathering Conditions
Because of the stratification and mixing that occur at the interface between salty saltwater intrusion and fresh riverine flows, salinity should be taken into consideration while tracking the geographic distribution of MPs in river estuaries. The aforementioned interaction causes the salinity in the estuary and may thus affect the buoyancy of MPs, despite the fact that several studies showed no relationship between MP abundance and salinity. Estuaries are divided into three categories based on their salinity structure: thoroughly mixed, somewhat mixed, and salt wedge estuaries.
Restricted tidal fluctuation is a characteristic of salt wedge estuaries. The contact between a surface freshwater outflow and a bottom seawater input is where the salt wedge forms. Salinity is often lower at the estuary’s head than it is at the mouth. Furthermore, the lack of high winds that would exacerbate turbulence in the estuary is necessary for the creation of a salt wedge. It works better to blend fresh and salt water in estuaries with a large tidal range. An estuary that is partially or well mixed depends on the degree of mixing. The salinity front in salt wedge estuaries creates a barrier that prevents MPs from moving from upstream to downstream and vice versa. Because of the salt wedge’s poor circulation, MPs and other particles sediment at high rates. The movement of buoyant microplastics (MPs) in freshwater flow into the ocean and the sedimentation of negatively buoyant MPs are facilitated by the circulation in a salt wedge estuary. Nevertheless, MPs acquire a negative charge that encourages settling when they come into touch with the salt water at the incursion.
The saline front’s limit, which is determined by tidal and climatic factors, is known as the estuarine turbidity maximum (ETM). The center of the estuary is where salt intrusion originates during the dry season, having the lowest concentration there. Salinity drops during the rainy season, and salt wedge estuaries serve as makeshift sources and sinks during the wet season [
67]. By monitoring the shift in the chemicals’ partition coefficient with salinity, one may assess the effect of salt on the adsorption of compounds by MPs. The adsorption caused by hydrophobic contact may not be impacted by salt, while salinity does alter the adsorption caused by electrostatic interaction [
68]. In their 2014 study, Bakir et al. examined the movement of POPs (persistent organic pollutants) by MPs in estuaries and discovered that while salinity had no influence on POP adsorption and desorption rates by PE and PVC, for example, it did cause a drop in overall adsorption as salinity increased [
69].
Abrasion and photo-oxidation are the most practical microplastic weathering processes. The weathering process modifies the adsorption behavior and performance of MPs. Even though most synthetic polymers are made to be robust, they can break down through photo-oxidative reactions that are triggered by solar UV radiation. This can result in the creation of secondary microplastics and the release of chain scission products into the nearby aquatic environment [
70]. According to certain viewpoints, physical factors including UV irradiation, mechanical abrasion, and temperature variations may cause microplastics in soil to physically decompose and be transfered [
71].
Wind and Tidal
Wind speed enhances the transportation of microplastics from terrestrial zones to their eventual sinks, as well as to urban regions in the western United States and along European shorelines. The atmosphere provides a channel for the microplastic to travel over tens of kilometers to distant places. Typhoons in China, for instance, raised the amount of microplastics in the aquatic environment nearby [
78]. Microplastics were thought to be an airborne pollution that traveled to far-off places up to the Antarctic snow top. The wind carried the microplastics to the Antarctic ice sink [
79]. Microplastics in the air are known to cause localized warming or cooling of the atmosphere and to have direct radiative effects. Their ability to absorb light allows the local air temperature to rise even higher [
80]. Airborne microplastics in the polar areas would cause the cryosphere to melt, releasing the microplastics contained in the ice. According to Dong et al.‘s estimation, microplastics may have traveled by air to the isolated lake basin in the Tibetan Plateau (an ecosystem of alpine lakes) [
81]. The movement of microplastics, their concentration in surface water, and wind speed are all positively correlated [
10]. After reaching isolated areas, storms and precipitation would carry atmospheric microplastics into surrounding rivers and snow beds, or they would migrate to other cities [
54].
Seasonal variations in the wind and currents can cause microplastic abundance in different places. When items are floating on the sea surface, wind can be a useful propellant. Given that a flood tidal current may carry microplastics, the direction in which the tidal current flows may also be a driving factor in the spread of marine debris [
82].
Depending on the characteristics of the microplastic and the surrounding circumstances, the aquatic habitat may act as the main sink in the environmental matrix, where microplastics can float in the water column, sink to the bedrock, and collect in sediments. Global warming would increase wind and rainfall, which would improve water circulation and make it easier for microplastics to get to far-off aquatic zones. Microplastics are carried by the atmosphere to glacier environments at higher wind speeds. The melting of ice caps results in the release of accumulated microplastics when temperatures rise. The destiny of terrestrial soil microplastics is determined by floods and droughts. Flooding causes the microplastics to migrate between the terrestrial soils and the marine ecosystem, while dryness causes them to stay stuck in the soil [
54].
Paris is in a very different climate and is around 150 kilometers from the coast. There are no typhoons or monsoonal lows in Paris. It does, however, mostly receive onshore winds from the Atlantic Ocean and North Sea, which are particularly powerful during the winter [
83]. Dris et al. (2016) found that there was often higher deposition throughout the winter. Wintertime reduces the possibility of dust or plastic becoming atmospherically entrained since the ground is moist or covered with snow. The bulk of the recorded fallout is likely to have originated from local or regional land, and the unique urban radiative microclimate makes comparison difficult at this early stage of research, impacting the region’s farmlands and agricultural soils [
84].
The primary factors influencing the movement of microplastics in the marine environment are water currents, wind, and tides [
85]. These factors cause the microparticles to sink slowly and migrate along the seashore (Bagaev et al., 2017). Denser polymers, like PVC, may still be carried by underlying currents, but buoyant polymer particles, like PE and PP, are often carried on the sea surface. According to Bagaev et al. (2017), microfibers are either resuspended by bottom currents or trapped by increased turbulence in the benthic boundary layer for a specific amount of time once they reach the bottom [
86].
Conclusions
In this review the natural and weathering phenomena that contribute to MPs transportation in different systems and especially in farmlands and agricultural soils have been studied. All review articles have been classified in categories according to the natural phenomena that are presented in them.
From a statistical classification of the physical factors associated with microplastic transport and presented in
Figure 2, it appears that typhoons, monsoons, winds together with tidal and floods together with storms are the most dominant and predominant factors that contribute the most to microplastic transport and concentration among the physical phenomena that have been presented and discussed above at length.
This might be due to a variety of factors, including particle redistribution to the surface sediment by wave agitation, fragmentation under severe abrasion pressures, and terrestrial inputs via surface runoff and wind transport. Severe weather conditions have the potential to transfer heavier and more varied kinds of microplastics from the land to the ocean. The results of the review papers show that the seasonal fluctuation may have been caused by extreme weather events that mostly happened during wet seasons, contrary to earlier research that primarily linked seasonal variability in microplastic level to higher rainfall in rainy seasons.
It is critical to continue evaluating the effects of various extreme weather conditions on the dispersal of plastic debris since climate change has led to an increase in the number of extreme weather events worldwide as well as their intensification. A characteristic gap in the resulting research is that there are not enough case studies related to natural disasters and phenomena from developed countries. As shown in
Figure 3, the US is missing from the countries with relevant publications, while Europe, Asia and Africa together account for less than half of the total. Dominant countries in this are Asian as China, India and Japan due to the natural phenomena they face have more studies related to this.
Farmland may become more contaminated by plastic as a result of the growing use of plastics in agriculture. Global MP pollution is getting worse, and agricultural soil dangers require care.
All the experimental findings, extracted from MPs measurements, from the reviewed papers indicate a changing environmental issue. The climate crisis brings to the surface a new serious factor in the transport and dispersion of microplastics, that of natural disasters and extreme weather events.
Further study on MPs is necessary in light of scientific knowledge, particularly to develop a standard procedure for isolating, quantifying, and characterizing MPs from the soil environment
There is connection between mechanisms causing MP buildup in various ecosystems and poorly managed plastic waste. Despite the recent growth in study on MPs found in rivers, lakes, and oceans, more has to be discovered about the outside forces affecting MP transit and dispersion in farmlands and agricultural soils. The distribution and quantity of microplastics (MPs) in different environmental systems are expected to increase dramatically in the upcoming decades due to the rising amount of plastic entering the environment. Incorrect waste management together with extreme weathering phenomena due to climate change would result in an increase in plastic garbage, severely harming agricultural soils and farmlands unless immediate worldwide action is taken.