MPs are widely distributed in water, atmosphere, soil and other environments, so it is necessary to use different samplers to collect MPs samples in various environmental media（Figure 1）. Direct sampling method and large volume sampling method are usually used in water environment. The sampling tools of direct sampling method include stainless steel screen, trawl and plankton net to directly collect plastic particles. However, the direct sampling method is easy to cause mesh blockage, and it is unable to collect plastic particles smaller than the mesh size, resulting in deviation in the estimation of MPS abundance^[16]Large volume sampling method refers to that all samples are retained without plastic separation on site, and metal barrels and other tools can be used for sampling, but the sampling volume is limited and time-consuming. The acquisition methods of atmospheric MPs can be divided into passive sampling and active sampling according to the different research objects and purposes^[17]Passive sampling is collected through stainless steel or glass funnel, which is suitable for settlement collection in long-term and remote areas. The active sampling method uses the pump sampler to collect the samples in the atmosphere onto the filter membrane. The suction flow of the pump can be adjusted to meet the requirements of different studies. According to the characteristics of the sampling area, simple random sampling, systematic grid sampling, systematic random sampling and other methods can be used to collect MPs in soil^[18]Sampling tools include spade, metal spoon, etc. At present, more and more evidences prove that MPs in water, atmosphere and soil can enter organisms. To understand the accumulation of MPs in biota, it is very important to select appropriate sampling methods. For the sampling of aquatic organisms from small phytoplankton to large fish, trawls of different sizes are usually used; Bivalve shellfish can be collected by manual capture; Benthic species can be captured by bottom trawl and sediment grab. However, it is difficult to directly sample MPs from biota at present, and MPs usually need to be extracted from collected organisms through anatomy or digestion^[19]。

The separation methods of MPs in samples mainly include density flotation, screening filtration, electrostatic separation and magnetic extraction^[20]The density separation method is the most common and extensive method for extracting MPs because of its low cost, easy operation and good separation effect. Sodium chloride (NaCl) and calcium chloride (CaCl) are generally selected₂）, zinc chloride (ZnCl₂）, sodium iodide (NAI) and other high-density solvents. In addition, the organic matter in the sample will interfere with the determination of MPs, so it needs to be removed by digestion solution^[21]The common digestion methods include oxidation digestion, enzyme digestion and alkali digestion. Common oxidative digesters include H₂O₂Fenton reagent, enzyme digestion including protease K, lipase and protease, alkali digestion including Koh NaOH。 The separation of MPs in the sample can remove other particulate matter (sand, soil, organic matter, etc.) in the sample, so as to improve the accuracy and reliability of subsequent identification results. However, the separation process may destroy the properties of MPs. Therefore, the best separation method should be selected according to different samples in the experiment, so as to ensure the recovery of MPS while removing impurities and not damaging the properties of MPs.

The identification and analysis of MPS need to consider its qualitative characteristics such as size, composition, morphology, aging degree and quantitative characteristics such as content and abundance. At present, there are three common methods for identifying MPs: visual inspection, spectroscopy and mass spectrometry（Figure 1）. Among them, the visual inspection method is the most commonly used detection method, which has the advantages of simple operation, low cost and no chemical hazards by identifying the shape, color and particle size of MPs. MPs can be identified by conventional optical microscope, field emission scanning electron microscope (SEM), laser confocal microscope (CLSM), transmission electron microscope (TEM), etc^[22]The spectral method analyzes and identifies MPs based on the characteristic spectral lines of energy induced molecular vibration, which has the advantages of fast detection speed and high accuracy. The commonly used spectral detection instruments mainly include Raman spectroscopy (Raman), Fourier transform infrared spectroscopy (FTIR), laser infrared imaging system (ldir) and terahertz spectroscopy (THz). FTIR and Raman are the two most commonly used technologies, especially for MPS particles with small particle size (<100 μ m)^[23-24]In addition, various chromatography-mass spectrometry technologies, such as liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS), pyrolysis gas chromatography-mass spectrometry (py GC/MS), thermogravimetric analysis mass spectrometry (tga-ms), thermal extraction desorption gas chromatography mass spectrometry (ted-gc/MS), have been used for the qualitative and quantitative analysis of MPs^[25]These mass spectrometry based technologies can provide important information such as the structure, molecular weight, degree of polymerization, elemental composition, main functional groups and terminal structure of MPS and its additives, which are usually not limited by the size of MPs, and can provide information about the mass concentration of MPs for accurate quantification of MPs in samples. However, the structure and composition of MPs are relatively complex, and there are still limitations in the detection of different methods, and the lack of a unified identification method hinders the comparison of results between different studies. Therefore, it is necessary to establish a more rapid and accurate detection method to reflect the characteristics of MPs in the environment.

MPs pollution has spread all over the global marine ecosystem. River outflows, ocean currents, drift, wind, ocean depth, and other factors will carry MPs particles farther away^[26]MPs exist from the offshore to the ocean, from the equator to the polar, from the surface of the ocean to the depths of the ocean^[27]MPs are distributed in the whole marine environment, and their types, shapes, colors and sizes are different^[28]The abundance of MPs in the ocean is not only affected by the intensity of human activities, but also by the ocean current velocity, ocean depth, wind direction, distance from the coastline and the density of plastic itself^[29]Under the influence of these factors, the MPS density in the adjacent sea areas may have an order of magnitude difference. The MPS abundance in China Sea area is 0.00013~0.545 items/L, which is at a medium level. Fiber is the main shape. Polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET) are the main types of MPs. Most MPs are white and transparent, and the size range is 0.5~1.0 mm^[30]However, MPs pollution is more serious in the coastal areas seriously disturbed by human activities. In Qingdao coastal bathing beach, the concentration range of MPS detected by fluorescence microscope was 5.05~12.50 items/L, and the average concentration was 7.61 items/L^[31]MPs concentrations of 0.21-1.17 items/L were detected in Tianjin coastal waters. Pet was detected by micro infrared Raman spectroscopy, Most types of PP and PE^[32]Researchers have also conducted a large number of MPS surveys in other sea areas around the world, desforge et al^[33]MPs were detected in the groundwater of the northeast Pacific Ocean, with the abundance ranging from 0.008 to 9.180 items/L, and most of them were fibers. Blue, red, black and purple MPs were the most common, and the sizes were the most abundant in the range of 0.1 to 0.5 mm. The concentration of MPS detected in the Atlantic Ocean is 0.013~0.501 items/L, the size range of plastic particles is 0.007~0.407 mm, and fibers account for 40% of all identified MPs. Raman microspectroscopy analysis shows that about half (48%) of MPs are PE and PP^[34]In 2020, kanhai et al^[35]MPS was found in the sea water under the ice floes in the Arctic Ocean, with a concentration of 0-0.018 items/L. the main types of polymers were PE, pet and PA, and the size was less than 2 mm, mainly blue (58%) and red (18%). Giuseppe et al^[36]916 seawater samples were collected from 617 locations in six marine basins covering the Mediterranean, Indian Ocean and Atlantic Ocean for MPS detection. The results showed that fiber was the most important form of MPs, and the concentration range was 0.020~2.58 items/L. Globally, fiber is the most common MPs shape in the marine environment^[37]， PP, PE and PVC are the most common types of MPS^[38]As a big country in plastic production and use, MPs pollution along the coast of China is more serious than that in other regions. In addition, the ocean, as an important part of the global circulation system, is also a serious disaster area of the global pollution problem. As an important sink, the destruction of marine ecological environment caused by MPs has become the focus of current research. More and more studies have found high concentrations of floating plastic debris in remote marine areas, which has increased people's concern about the accumulation of plastic waste on the ocean surface. However, the current identification methods of MPs in the ocean still have some limitations, especially for small size MPs, which are difficult to effectively separate and identify. Therefore, one of the main trends of marine MPs research in the future is to develop rapid and automated analysis technology, improve the efficiency of MPS analysis and monitoring, and scientifically explore the impact on marine ecology. In addition, at this stage, the detection methods of marine MPs are uneven, so it is necessary to build a unified MPs pollution risk assessment standard system, and ensure the accuracy of the assessment through the implementation of standardized and standardized detection procedures, so as to provide scientific support for the maintenance of marine environment and ecological security.

Compared with the marine environment, the research on the occurrence status of MPs in fresh water is still limited. Existing studies have found that there are varying degrees of MPS pollution in inland waters, estuaries and even in polar regions with little human activity^[39]It indicates that MPs has been widely existed in freshwater environment. MPs pollution of different degrees has been found in inland waters and estuaries of China. Our previous study showed that the concentration of MPs in Chishui River, a tributary of the Yangtze River in China, ranged from 1.77 to 14.33 items/L^[40]It mainly exists in the form of fiber. The study of Poyang Lake and other lakes also detected the presence of MPs in the concentration range of 5-34 items/L, mainly in the form of fragments and fibers^[41-42]Studies have shown that MPs are widely distributed in aquatic environment worldwide. MPs concentration in Humber River, Birmingham, UK is 165 items/l^[43]The concentration of MPs in the Rhine and main rivers in Germany ranges from 228 to 3763 items/L^[44]The concentration of MPS detected in different sections of the antua River in Portugal is 0.058~1.265 items/L. PP and PE are the main components and exist in the form of foam and fiber^[45]The concentration range of MPS detected in the Snake River and lower Columbia River in the United States is 0~5.405 items/L, and the polymer types identified by micro Raman spectroscopy are PP, PE and pet^[46]MPs with a concentration level of 0.293~4.76 items/L and a size of 0.05~0.15 mm were detected in the surface water of Nakdong River in South Korea, mainly in the form of fibers^[47]The abundance of MPS detected in Ontario, Canada is 0.8~15.4 items/L, which exists as fragments and fibers, and the main components are PE, PS, PP and pet^[5]There are significant differences in MPS pollution levels in different freshwater environments worldwide, but the main components are PP, PE, pet, PS and other widely used plastics, and most of them exist in the form of white, black, transparent fibers, films, fragments and so on. Although the research methods and measurement data of various countries and regions are slightly different, the overall trend shows that the pollution level of MPs in China's freshwater environment is relatively high. This may be related to China's huge population base, rapid industrialization and agricultural production. The sewage treatment plant is the most important source of MPs in the freshwater environment. The abundance of MPS detected in the effluent from the violinmaking sewage treatment plant in Finland is 3.5 items/L^[48]The average abundance of MPS detected in the effluent of 7 wastewater treatment plants in the Netherlands is 52 items/L^[49]It is estimated that the average discharge of microplastics from municipal wastewater treatment plants in the United States is 1.3 × 10¹⁰ items/L^[50]Therefore, it is of great significance to improve the removal process of MPs in sewage treatment plants to reduce MPs pollution in the water environment. The research on freshwater MPs is increasing year by year, but the concentration units of some research results are different, and the pretreatment methods and detection limits are also different, which makes it difficult to compare the MPS pollution in different regions. In order to effectively obtain the global pollution of freshwater MPs, it is necessary to establish and adopt standardized sampling and analysis methods in order to understand the distribution and impact of MPs in water. In addition, MPs in freshwater environment is also easy to become the carrier of other pollutants (pesticides, polycyclic aromatic hydrocarbons, heavy metals, etc.), which poses a greater threat to organisms^[51]Therefore, it is of great value to explore the environmental behavior of MPS under the coexistence of MPS and other pollutants for the scientific assessment of the ecological risk of MPs.

More and more evidences show that soil is the largest MPs repository on earth^[52]It is estimated that the discharge of plastic waste to land is 4-23 times that of the sea^[53]. from rillig^[54]Since the first report of MPs in soil, MPs pollution in soil has received extensive attention. Ren et al^[55]The concentration and distribution of MPs in farmland of 28 provinces in China were analyzed based on the data collected from 40 articles. The results showed that the concentration range of MPS was 1.6~6.2 × 10⁵items/kg， The average concentration is 4536.6 items/kg, and the main components are PE PP、 Polyethersulfone (PES), PS and polyamide (PA). Our previous research found that the pollution of soil microplastics in Northwest China was severe, and the concentration of microplastics in Typical Farmland Soils in Shaanxi Province was 1430-3410 items/kg^[56]The concentration of microplastics in Mu Us sandy land is 1360-4960 items/kg, and the average concentration is 2696.5 items/kg^[57]MPs is also widely detected in soil environment of other countries. Harms et al^[58]The study of farmland soil in northern Germany found that the concentration of MPS ranged from 0 to 217.8 items/kg, and the average concentration was (3.7 ± 11.9) items/kg. The color was mainly black (63%) and white (18%), and the shape was mainly foil (61%) and debris (28%), and the main component was PE. Palazot et al^[59]The analysis of 33 soil samples in France showed that the overall plastic concentration in France was 6.7~80 items/kg, and the main components were PE (56%) and PP (30%). The concentration of MPs in Arizona soil is 122-1399 items/kg^[60]Katsumi et al^[61]The results showed that the concentration of MPs in Japanese paddy soil was 16745 items/kg, and the main components were PE (27%), ethylene vinyl acetate (16%), polyurethane (15%) and PP (12%). In South Korea, researchers also found high concentrations of soil MPs. The average concentration obtained by stereo microscope was 700 items/kg. The main components were synthetic rubber (43%), PP (22%) and PE (20%). The colors were mostly black (65.5%) and white (12.3%), and the shapes were mainly debris (66.1%) and film (19.2%). It can be seen that the concentrations of MPs in soils of different countries and regions are significantly different, which may be related to local environment, application of agricultural plastics, local climate and other factors^[62]At present, most of the global reports on MPS in soil come from China^[63]As a large grain producing country, the mass production and use of agricultural plastics make soil MPs pollution more common and severe in China, and the overall level is higher than that of other countries and regions. Although more and more studies have reported MPs pollution in soil, the data show that the number of studies on terrestrial ecosystem only accounts for about 5% of MPS related data^[64]And most studies only focus on the distribution characteristics of MPS (abundance, type, color, etc.), but lack the ecological risk assessment related to MPs. In the future, more studies on the source, distribution and impact of soil MPs on soil ecosystem need to be carried out to provide background data and valuable reference for the ecological risk assessment and prevention and control of soil MPs pollution.

The atmosphere is an important way for many pollutants to spread around the world, and MPs also widely exists in the atmospheric environment. In recent years, studies have detected MPs in the atmosphere of many places around the world, even over the sea and in remote areas, which shows that atmospheric transport is an important link in the global transmission and circulation of MPs. Zhu et al^[65]A survey of atmospheric MPs in five large cities in China (Beijing, Tianjin, Nanjing, Shanghai and Hangzhou) found that the average abundance of MPS was 282 ± 127 items/m³The concentration of atmospheric MPs in North China is higher than that in South China, which is related to population density and economic development level. DRIs et al^[66]It is detected that the atmospheric MPs concentration level in Paris, France is 1-6 items/m³And fiber is the main shape. Gaston et al^[67]The indoor and outdoor air in California was detected, and the MPS level in the outdoor air (0.620 items/m) was found³）Lower than indoor air MPs level (1.590 items/m³）Fibers and debris are the main existing shapes, which may be that the indoor air is in a more closed state than outdoor, so MPs in indoor air may be more difficult to spread to reduce its concentration level. In addition, microplastics were also detected in the air above the ocean. Researchers detected microplastics concentrations of 0-1.37 items/m over the Western Pacific³Fiber is the main component^[68]In general, although the data of different regions and countries are different, they mainly exist in the form of fibers and fragments. The high level of atmospheric MPs pollution in China may be related to regional economic development and population density^[69]In order to comprehensively understand and effectively manage MPs pollution in the atmosphere, it is necessary to promote standardized sampling and analysis methods around the world, study the propagation path and life cycle of micro plastics in the atmosphere, and understand its global diffusion mode, so as to establish a more perfect pollution database and assessment system.

After entering the environment, MPs will undergo continuous aging under the action of various environmental factors, resulting in changes in surface morphology, particle size, microstructure and surface functional groups. After long-term aging, the functional groups of MPs will change, and the oxygen-containing groups generated will increase the polarity, hydrophilicity and charge of MPS surface^[70]Therefore, the microstructure, specific surface area and surface functional groups of MPS after aging can be characterized and analyzed to determine the aging degree of MPs. In the natural environment, MPs aging occurs mainly through abiotic and biological effects. MPs will be worn and aged by waves, tides, sand, stones, etc. after entering the environment, resulting in surface cracks or even smaller particles^[38,71]MPs in the environment will also be aged through photooxidation, thermal degradation and Fenton reaction. MPs in the environment absorbs the solar ultraviolet radiation and thus has oxidative aging reaction with oxygen in the environment. The essence of MPS photoaging is a free radical chemical reaction induced by sunlight, which can be divided into three steps: initiation, propagation and termination^[72]First, photons need to be absorbed by chemical bonds, leading to chain breaks and free radicals^[73]For example, the weak C-H bond in MPS is easy to crack and form stable free radicals to continue photooxidation. During propagation, oxygen is rapidly reacted to form peroxy radicals (e.g. o₂^•-）Peroxy radicals in turn obtain hydrogen from adjacent chains to form hydroperoxide groups and new radicals (such as · oh and¹O₂）^[74]The reaction was terminated after the free radicals combined with MPS and formed inactive/stable groups^[75]The release and accumulation of heat caused by the increase of temperature can also cause the aging of MPs, and will accelerate the effect of UV to promote the photoaging of MPs. The mechanism of thermal aging of MPS is that high temperature is conducive to reaching the dissociation energy of MPs, random breaking of molecular chains and falling off of branched chains, generating alkyl radicals, and then entering the autoxidation cycle^[76]Fenton and persulfate treatment can also lead to the aging of MPs. The · Oh in Fenton reaction and the · oh/so produced by persulfate treatment₄^•-Their high redox potential may enhance the oxidation of MPS^[77-78]In addition, some other chemical reactions in the environment will also lead to the direct aging of MPs, such as the nucleophilic substitution/addition reaction between sulfide and c=c bond in polymer, the reaction between ozone and MPs, etc^[79]The type and concentration of inorganic anions in water will also have a significant impact on the conversion of MPs. For example, the presence of halogen ions will halogenate MPs particles and accelerate their aging^[80]Organic matter in the environment, including dissolved organic matter and particulate organic matter, can produce free radicals and³DOM * promotes MPs aging^[81-82]In addition, microorganisms are ubiquitous and have the inherent ability to adapt to different environments and use different substances, usually accelerating the weathering of MPS through biodegradation^[83]Microorganisms can colonize MPs and promote biodegradation and biotransformation by adhering to the surface of MPS and forming biofilms. For example, in terms of degradation of polyurethanes (PU), Cladosporium spp., Penicillium chrysogenum and powdery mildew all showed the ability to promote Pu degradation, but wood saprophytic fungi and ectomycorrhizal fungi will not degrade Pu, which may depend on whether they have a variety of enzymes^[84]The microorganisms colonizing on the surface of MPS tend to use MPs as a nutrient source, which will promote the aging of MPs. For example, bacillus and Rhodococcus can use PP as a carbon source to promote its aging. In high-temperature compostingDeinococcus-thermusAging degradation of PS promoted by biological oxidation characteristics^[85-86]In addition to microorganisms, MPs can also be transformed after being ingested by organisms. During animal feeding, MPs will be broken due to the physical stress caused by animal chewing behavior, and then swallowed into the intestines and stomach; MPs also breaks, shortens and oxidizes under the action of specific biological enzymes in animals^[87-88]These aging processes will lead to cracks in MPS, which will lead to the fragmentation of MPs, and even the change of properties, including size, surface morphology, crystallinity and functional groups, which will also cause the leaching of additives.

There are many factors that affect the aging process of MPs. Temperature has a great influence on the abiotic and biological aging process of MPs. For abiotic processes, temperature can affect the kinetic energy of polymer molecular chains, thus controlling the dynamics of various physical processes and chemical reactions. High temperature will promote the pyrolysis and dissociation of newly formed peroxides, produce free radicals, and eventually lead to the chain fracture of MPs. Low temperature makes MP more brittle and easier to fracture, which is conducive to the formation of hydrogen peroxide in the process of photooxidation and promotes the degradation of plastics^[89-90]For biological processes, temperature will also change the microbial community structure and metabolic activities, thus affecting the biodegradation rate^[91-92]The ions widely existing in the environment such as halogen ions and inorganic anions will also have a significant impact on the conversion of MPs. The presence of halogen ions will halogenate MPs particles and accelerate their aging, such as br^-It can react with · Oh to form active bromine free radicals, which can promote the aging of MPS^[80]. inorganic anions, such as no₃⁻It can produce more reactive substances under light excitation, and then accelerate the photoaging of MPs; HCO₃⁻It can be converted into carbonate radical in water, and carbonate radical can only oxidize electron rich compounds, such as nitrogen-containing or sulfur-containing compounds, and generally does not participate in MPS aging. Therefore, HCO₃⁻Photoaging of MPS is usually inhibited^{[80,93 -94]}In addition, organic matter in the environment, including dissolved organic matter and particulate organic matter, can also generate free radicals and³DOM * promotes MPs aging^[81-82]The increase of salinity in the environment will lead to the high refractive index of water, and may form attached salt crystals on the surface of MPs, thus inhibiting the photoaging of MPS by reducing the absorption efficiency of light^[95-96]There are still some deficiencies in the study of MPS aging. Firstly, the artificial accelerated aging method can not well simulate the natural aging process. The aging of MPs in the real environment is often affected by a variety of factors. Therefore, efforts should be made to narrow the gap between the laboratory simulation method and the environmental natural aging process through in-situ experiments or multi factor simulation coupling experiments; Secondly, the aging effect of MPs in artificial systems, such as landfills, sewage treatment plants, composting plants, etc., should also be considered; Finally, the aging degree of MPS cannot be qualitatively/quantitatively unified in one or several ways. Therefore, it is necessary to develop qualitative/quantitative means to unify the steps and degree of MPS aging mechanism research in the follow-up study.

The migration of MPs in the environment is an important part of its environmental geochemical behavior. The migration of MPS into the environment is mainly divided into horizontal migration and vertical migration. Atmospheric transport of MPS is considered to be an important carrier, which may lead to the deposition of MPS into soil or aquatic environment. This migration strongly affects the source and sink dynamics of plastic pollution in different ecosystems^[97]MPs in the atmospheric environment migrates horizontally mainly through the action of wind. MPs particles are lifted by wind and become atmospheric suspended particles for long-distance propagation. Research shows that MPs can travel hundreds of kilometers through the atmosphere, even across continents and oceans. In the water body, MPs migrate in the surface water body through wind, wave, tide and ocean current, especially the ocean current and tidal movement will further promote the long-distance horizontal migration and transportation of MPs in the ocean. MPs not only migrates in the horizontal plane, but also settles from the water body to the sediment, and resuspends into the water body under the action of water flow and biological activities^[98]Biological transport is also an important way for MPs to migrate horizontally in water. Marine organisms (such as fish, seabirds and plankton) spread MPs to new environments through migration or predation after ingesting MPS^[98-99]In addition, the migration of MPs at the water and soil interface is affected by rainfall and agricultural irrigation, which scours the MPs in the soil to the surface water, and then flows into rivers, lakes and marine environment through runoff^[100]The vertical migration of MPs in soil is mainly through infiltration and biological activities. Surface runoff and groundwater flow are the main ways of vertical migration of microplastics. Rainfall and irrigation activities can accelerate the infiltration of microplastics in the soil, and MPs particles will penetrate into the deep soil with water^[101]In addition, biological activities such as the absorption of plant roots and the excavation of soil animals can promote the vertical distribution of microplastics in soil^[102]In specific environments, such as arid and windy sand areas, wind can carry micro plastic particles and affect their distribution in the soil surface^[103]The vertical migration of microplastics in the environment may affect the activity of soil microorganisms, change the physical and chemical properties of soil, and then affect the growth of plants, and even pass to higher trophic organisms through the food chain, posing a potential threat to human health.

The migration process of MPS is affected by many factors, including environmental conditions (such as temperature, humidity, wind speed and water velocity) and MPs' own characteristics (such as density, shape, size and surface properties). The strength and direction of water flow are the key factors affecting the horizontal migration of microplastics. In rivers, lakes and oceans, micro plastics will move with the current, but under the action of tides and waves, they can be carried farther away. The size and shape of microplastics affect their suspension ability and deposition rate in water. Smaller particles are easier to suspend in water, while larger particles may deposit faster^[104]The density of microplastics determines their floating and sinking state in water. The chemical properties of microplastics, such as surface charge and hydrophilicity, will affect their interaction with water molecules, and then affect their migration in the environment^[105]Wind waves and biological activities (such as feeding and excretion of plankton) can make MPs enter the middle and deep water bodies from the surface. In addition, the size, structure and composition of soil particles will affect the penetration depth and rate of MPs. Fine grained soil (such as clay) has low permeability, and the vertical migration of MPs in it is slow, while sandy soil is the opposite^[106]And MPs with small particle size has stronger migration^[107]However, some researchers have found that the soil dry wet cycle can not only increase the downward migration depth of MPs, but also promote the upward migration of MPS through buoyancy^[108]The atmosphere is considered to be the "highway" of MPs, but at present, the occurrence and migration of MPs in the atmosphere are not fully studied. It is necessary to further study the application of other technologies, such as epitope tracing and deep learning, in order to establish a reliable dynamic circulation model of MPs in air, land and aquatic systems and predict the migration of MPs in the natural environment.

As the primary producer and decomposer of organic matter in the ecosystem, microorganisms will participate in the transformation and circulation of pollutants, which is essential to maintain the stability of the ecosystem. However, due to the widespread presence of MPs, the structure and function of microorganisms and microbial communities in the environment will inevitably be directly or indirectly affected（Table 5）. MPs will change the diversity of microbial community structure and may further affect the biogeochemical cycle of coexisting substances. Seeley et al^[110]It was found that the presence of 0.5% (w/W) MPs changed the composition of microbial communities and nitrogen cycle in sediments, and this effect varied with different types of MPs. MPs may also affect the metabolic and ecological functions of microorganisms. Yu et al^[117]The results showed that 1% (w/W) MPs treatment changed soil microbial diversity and metabolic function, and significantly increased the abundance of nitrogen cycle related genes such as nifk, NIRS and AOB. In addition, MPs may also affect the diversity of environmental microorganisms by affecting the physical and chemical properties of environmental media. MPs can change soil aggregate size, porosity, water cycle and oxygen flux, which may affect the activity of anaerobic and aerobic microorganisms^[118]MPs will release various additives and dissolved organic matter (DOM) during aging, which will change the chemical properties of the surrounding environment, thus affecting the growth and activity of microorganisms^[119]. Qiu et al^[120]It was observed that after adding PE and polylactic acid (PLA) to the soil, the molecular diversity of soil DOM decreased due to the release of mp-dom, and microorganisms participated in the metabolism of mp-dom, resulting in changes in the composition of microbial community.

MPs entering the environment can provide new ecological habitats for microorganisms, and the microbial community growing on MPS is called "plastic circle"^[121]There are significant differences in composition and function between the microbial community and the surrounding environment. Huang et al^[122]It was found that the diversity, structure and metabolic pathway of microbial community on PE were significantly different from those in the control group and PE added soil, and PE was enriched with potential plastic degradation bacteria and pathogenic bacteria. In addition, MPs in the environment has the ability to adsorb various organic pollutants and heavy metals, and the formation of "plastic ring" will enhance its adsorption ability^[123]This may affect the activity of microorganisms on the "plastic ring".

To sum up, although there have been many studies on the impact of MPs on environmental microorganisms, and it has been found that the presence of MPs will affect environmental microorganisms, change the diversity of microbial communities, and may affect the health and stability of the ecosystem, most of them are for non degradable plastics, and there are relatively few studies on the impact of biodegradable plastics on microorganisms in the process of biodegradation. Therefore, it is suggested that future research should pay more attention to the impact of biodegradable MPs on environmental microorganisms and the underlying mechanism. At the same time, the research on microbial community construction and interaction should be strengthened, and the reduction of MPS through biodegradation technology should be considered.

As an important part of the ecosystem, the growth of plants is inevitably affected directly or indirectly by soil MPs. Especially in the agricultural ecosystem, MPs may affect the yield, quality and biological safety of crops^[124]At present, studies on the growth of a variety of plants have been carried out through soil culture, hydroponics and field experiments, including wheat^[125], rice^[126], corn^[127], lettuce^[128], onion^[129]Etc（Table 6）. The changes of physical and chemical properties such as particle size, shape, species, concentration and aging degree of MPs will have a certain impact on plants. Compared with MPs with high molecular weight or large size, MPs with smaller particle size is more easily absorbed by plants. Jiang et al^[130]Studies have shown that 100 nm PS can accumulate in Vicia faba root and block cell junctions or cell wall pores to transport nutrients, so it has higher genotoxicity and damage ability than 5 mm PS. Lozano et al^[131]Studies on arid soil showed that the addition of fibrous MPs could promote the formation of soil aggregates, indirectly improve soil water retention, alleviate drought, and increase root diameter and root tissue density. Lower concentrations of MPs may increase the length, surface area, volume and diameter of plant roots. However, at higher concentrations, MPs may induce oxidative stress in plants to produce more reactive oxygen species, aggravate oxidative damage in tissues and cells, and inhibit the development of plant roots^[132]In addition, MPs entering the environment will undergo physical, chemical, biological and other aging effects, which will change the physical properties such as particle size and crystallinity, and increase the surface oxygen-containing functional groups. With the continuous aging, the additives contained in the MPs will gradually release into the soil and inhibit the growth of plants^[133]。

Limited by the detection and characterization methods, the research on the effect of MPs on plants and its potential mechanism is still in its infancy, and the mechanism of plant absorption, enrichment and transport of MPS is still unclear. The possible mechanisms proposed by existing studies involve changing soil structure, affecting water and nutrient transport pathways^[134]Due to the limitation of the pore size of plant cells, plants have high selectivity for MPS internalization, and the size is usually sub micron. In addition, due to the incomplete structure of the primary root tip of plants, there is no complete Kjeldahl zone in the meristematic zone to prevent the entry of external substances. Nano sized plastics can destroy the membrane structure of root tip cells, enter the root cells through passive transportation, and then enter the central column of the root system through the apoplast pathway^[135]Micron/submicron MPs can enter the root system at the germination site of lateral roots, and then enter the root column under the action of transpiration force, and then transport to the aboveground part^[68]On the other hand, due to the uneven surface of plant leaves, some small particle size MPs will be captured by the leaves in the process of gravity, wind, dry and wet deposition, which may enter the mesophyll cells through stomata, cuticle and other channels^[136-137]MPs entering plants may affect the expression of genes related to the synthesis and metabolism of substances with stress resistance function, such as plant pathogen interaction and MAPK signaling pathway^[138]In addition, it may affect the energy metabolism and amino acid metabolism pathway of crop leaves, and reduce the efficiency of glycogen accumulation of plants^[139]In conclusion, plants can adsorb and internalize MPs, but the qualitative and quantitative analysis of MPs in plants is still immature. Indirect characterization methods such as fluorescent group modification and noble metal doping show that the interaction between them is very limited, and it is difficult to further explain the potential mechanism of their cross barrier and migration and transportation. Therefore, it is urgent to propose a widely applicable, accurate and effective method for qualitative and quantitative visualization analysis of plant MPs.

The accumulation of MPs in the aquatic environment can easily lead to complex ecological problems, and have various negative effects on aquatic animals, including reproductive and developmental damage, bioaccumulation and biomagnification, chemical toxicity and exposure, behavior and physiological interruption, etc. Many aquatic animals, such as fish, molluscs and zooplankton, make MPs enter the body through filtration and ingestion, resulting in a series of toxic effects such as metabolic obstruction and decline of life activity（Table 7）. Lu et al^[143]It was found that the accumulation of MPS was observed in the gills, liver and intestines of zebrafish exposed to MPs for 7 days, which caused oxidative stress and neurotoxicity in zebrafish. In addition, MPs with smaller particle size (50-200 nm) can also break through the biological barrier and accumulate in gonads, reducing the fertility of female fish^[144]In addition, zooplankton also ingest MPs, resulting in changes in feeding behavior and reduced energy reserves^[145]. Martins et al^[146]Large fleas continuously exposed to higher concentrations of MPS (0.1 mg/L) were found（Daphniamagna Straus）The population will be extinct within 2 generations, and the developmental and reproductive toxic effects caused by 21 day exposure need at least three generations of reproduction to recover. Although there have been studies on the toxic effects of MPs on aquatic animals, they mainly focus on the harm to individual species such as zooplankton, fish and molluscs, and pay less attention to the harm of MPs to the whole food chain. In the future, more attention should be paid to the impact of MPs on the food chain in the aquatic system.

Compared with aquatic animals, the toxicological effects of MPs on terrestrial animals are very limited. Soil animals are important consumers and decomposers in ecosystem. At present, the toxicological studies of MPs on Soil animals are mainly focused on invertebrates, such as earthworms, nematodes, mites and snails（Table 6）. When earthworms or nematodes are exposed to MPs, they will produce various toxic effects, including reproductive toxicity, neurotoxicity and intestinal injury, which are mainly related to the concentration, type and morphology of MPs in soil. Moreover, MPs aged by ultraviolet radiation may cause more serious toxic effects on nematodes^[147-148]In addition, the intestinal microbiota composition and life history characteristics of Collembola after 28 days of exposure to PS MPs contaminated artificial soil (such as reproduction and avoidance behavior) will change^[149]For land snails exposed to pet, the average food intake of snails decreased, and the gastrointestinal wall of snails was significantly damaged^[150]Studies on mice as mammalian models also showed that the toxic effects of MPs on mice were intestinal barrier dysfunction, flora imbalance and metabolic disorder, leading to neurotoxicity, reproductive toxicity and inflammation^{[151⇓⇓-154]}The current research generally focuses on the single species toxicity effect analysis after exposure to MPs, and lacks deeper research (for example, at the population, community and ecosystem levels). In the future, more attention should be paid to the impact of MPs on multiple species and ecosystems in terrestrial systems.