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Asian Journal of Environment & Ecology

13(1): 1-9, 2020; Article no.AJEE.57484 ISSN: 2456-690X

Effects of on Agriculture: A Mini-review

Kuok Ho Daniel Tang1*

1Health, Safety and Environment Program, Curtin University, CDT250, 98009 Miri, Sarawak, Malaysia.

Author’s contribution

The sole author designed, analysed, interpreted and prepared the manuscript.

Article Information

DOI: 10.9734/AJEE/2020/v13i130170 Editor(s): (1) Egbuonu, Anthony Chinedum Cemaluk, Michael Okpara University of Agriculture, Nigeria. Reviewers: (1) Mona Nassar, National Research Centre, Egypt. (2) Apurba Ratan Ghosh, The University of Burdwan, India. Complete Peer review History: http://www.sdiarticle4.com/review-history/57484

Received 24 March 2020 Mini-review Article Accepted 29 May 2020 Published 08 June 2020

ABSTRACT

Microplastics have permeated most, if not all, ecosystems including the terrestrial ones. The presence of microplastics in poses concerns on and agriculture. Microplastics alter soil biophysical properties including bulk density, water holding capacity and soil microbial interactions with water stable aggregates. The effects of microplastics on soil and plants frequently depend on the types and sizes of microplastics. This mini review presents a concise illustration of the impacts of microplastics on plants and crops. From the review, microplastics alter soil biophysical and chemical characteristics either positively or negatively depending on their types, concentrations, sizes and shapes. It reveals the ability of microplastics to affect enzymatic activities of plants which could to genotoxicity and oxidative damage. It unveils endocytosis of microplastics by specific cells as well as the uptake of microplastics via and their accumulation and in plants facilitated by transpiration. This review also shows microplastics reduce root growth and seed germination at least transiently while do not seem to alter content. Microplastics were found to not interfere with of metals by the common reeds. This review highlights the need of more studies to confirm the effects of microplastics on crops and plants as the existing studies in this area are limited.

Keywords: Microplastics; agriculture; soil; plants; crops. ______

*Corresponding author: E-mail: [email protected];

Tang; AJEE, 13(1): 1-9, 2020; Article no.AJEE.57484

1. INTRODUCTION through discharge of effluents and sludge containing microplastics. They concentrate Microplastics present a persistent environmental microplastics already present in natural problem due to their presence in the terrestrial waterbodies through treatment processes and and aquatic ecosystems, and the difficulty in eventually return the microplastics into the detecting them [1]. Microplastics have been environment [1]. Application of sludge for detected in atmospheric fallout indicating their agriculture to localized microplastics dispersion into and transportation via the air [2]. contamination which subsequently spreads The increasing uses of plastics as packaging, through transportation by runoffs, air and soil raw materials and in various consumers’ biota [8]. There are very few studies that products result in increasing microplastics in the examine how the elevated levels of microplastics environment. Microplastics can be primary, in agricultural soil affect the growths of crops and coming directly from the use of materials or threaten food supply. This mini review, therefore, products with microplastics as constituents, or aims to put together a concise review of the secondary, formed during the breakdown and implications of micro plastics in soil on crops and degradation of larger plastics [1]. agriculture.

Permeation of microplastics into multiple 2. IMPACTS OF MICROPLASTICS ON ecosystems raises concerns of their potential toxicity. Studies have shown that microplastics affect aquatic fauna physically, causing blockage Soil health is frequently associated with soil of digestive tracts and gills, as well as biophysical and chemical properties that behaviourally and physiologically through determine plant health. The physical properties disruption of hormones and enzymes [3]. of soil encompass its texture and surface area, Ecotoxicity of microplastics is complicated by the structure, bulk density, porosity, infiltration rate, ability of microplastics to adsorb an array of available water capacity and depth whereas the chemicals such as polyaromatic hydrocarbons, biological properties concern the soil organic antibiotics and antimicrobials, thus, concentrating carbon, microbial biomass as well as soil harmful chemicals in aquatic ecosystems [3]. enzymes and biota. Chemical properties of soil Microplastics also contain various additives and comprise pH, electrical conductivity, cation leaching of these chemicals into the aquatic exchange capacity, reserves, heavy environment could lead to toxicity [3]. In addition, metals, elemental balance and carbonates [9]. numerous studies on the effects of microplastics Soil health affects agricultural production. on terrestrial ecosystems demonstrated the Bacterial diversity as an indicator of soil health presence of microplastics in livestock [4] and was linked to net primary productivity of plants. birds [5], and the ingested microplastics could Trivedi et al. reported positive correlation release additives which are potential endocrine between bacterial diversity and net primary disrupters [6]. Similar to those in the aquatic productivity in the arid regions of Australia [10]. environment, terrestrial microplastics can be In the Australian continental and temperate transferred and biomagnified along the food zones, relative abundance of bacterial phyla was chains. Large amount of microplastics in soil is found to positively correlate with net primary known to adversely affect soil biophysical productivity and soil properties [10]. properties, including soil biota such as earthworms whose growth and reproduction In addition to agricultural intensification which declined as their guts’ microbiomes were strains soil health hence long-term agricultural disrupted by ingested microplastics [2]. productivity, microplastics have been reported to alter soil biophysical properties encompassing While many studies focus on the impacts of bulk density, water holding capacity and soil microplastics on fauna, few actually probed their microbial interactions with water stable impacts on plants and agriculture. It was found aggregates. The effects of microplastics on soil that farmlands contain substantial microplastics are dependent on types and concentrations of because sludge from wastewater and microplastics (6). Polyester fibers were observed treatment plants is often used as soil additives to increase water holding capacity of soil to a for agriculture [7]. In fact, wastewater and greater extent than polyethylene fibers with sewage treatment plants are significant increasing concentrations. Polyester fibers at contributors of environmental microplastics increasing concentrations also led to larger

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decline in soil bulk density compared to health and the directions of the effects remain polyacrylic and polyethylene microparticles [6]. inconclusive as either positive or negative effects However, the extents of changes in soil have been reported. In addition, the effects are properties are often not proportional where larger dependents of several factors such as the types, effects were elicited at low microplastics concentrations, sizes and shapes of micro- concentrations and the increase of effects did not plastics. In the following section, the direct appear to correspond uniformly with the increase impacts of microplastics on plants and crops are of microplastics concentrations [6]. This indicates further probed. that microplastics could exert substantial alterations in soil biophysical properties even at 3. IMPACTS OF MICROPLASTICS ON low concentrations and the interactions of CROPS AND PLANTS microplastic participles with soil matters are complex. It has been explained in the previous section that sewage and wastewater treatment sludge Microplastics were observed to change microbial captures microplastics. It was reported that activities and the change correlated to the approximately 50% of sewage sludge in Europe concentrations of microplastics instead of the and North America was eventually applied to types [11]. Another study reported the shape of farmlands as economic fertilizers, resulting in as microplastics could play a role in microbial much as 870 tons of microplastics per million activities with linear microplastics such as inhabitants to enter the European agricultural polyacrylic and polyester fibers causing lower . The amount could be higher in countries microbial activities compared to nonlinear with higher usage of plastics [8]. The use of microplastics [6]. As the soil microbial agricultural plastic films for mulching also communities affect and are affected by soil introduces microplastics into soil as the films aggregation, and microplastics could affect degrade [16]. There are currently very few microbial activities which reflect the metabolic studies on how microplastics affect crops. A rates of the communities, the presence of study showed fluorescent polystyrene microplastics may modify soil microbial nanobeads (< 100 nm) made their ways into communities, hence soil aggregation and health tobacco cells via endocytosis [17]. Li et al. [12,13]. demonstrated crops’ tissue cultures to uptake and accumulate polystyrene microplastics (0.2 Microplastics were also observed to change the µm) and implied potential transfer of the nutrient profile of soil. Addition of 28% of microplastics to human through food chain [18]. microplastics by weight to soil was shown to Moving beyond cellular level, Qi et al. reported significantly raise the nutrient contents in soil potential interference of biodegradable and solution through decomposition of dissolved polyethylene microplastics on wheat’s growth organic matter [11]. Even at a lower and biodegradable microplastics seemed to exert concentration of microplastics (7% w/w), nutrient larger negative effects [16]. The study also contents in soil solution were reported to be showed biodegradable microplastics reduced higher than control after 14 days. The nutrient fruit biomass and the presence of earthworm release was linked to the increased enzymatic partly negated the negative effects [16]. This activity of phenol oxidase which decomposed study highlighted a new concern for high-molecular weight compounds into low- biodegradable plastics which have been molecular-weight compounds. Microplastics also advocated as a substitute for conventional enhanced the activity of diacetate hydrolase, plastics to reduce environmental microplastics. indicating higher microbial hydrolysis of [11]. Microplastics addition was Having known that microplastics alter soil thought to increase microbial activity, thus biophysical properties, Rillig et al. added that improving bioavailability of soil C, N and P [14]. microplastics could improve penetration of plant This was in contrary to the decline in soil into soil, soil aeration and root growth via microbial carbon, nitrogen, as well as activities of lowering soil bulk density [19]. On the other fluorescein diacetate and soil dehydrogenase hand, fragments of plastic films added reported earlier [15]. experimentally to soil gave rise to channels which facilitated water movement and Different studies have demonstrated different evaporation, hence water loss from soil which effects of microplastics on soil properties, hence might affect plant health [20]. Plant health is also

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Tang; AJEE, 13(1): 1-9, 2020; Article no.AJEE.57484

influenced by alteration in soil microbial control after a 7-day treatment, indicating an communities induced by the presence of insignificant effect. Similarly, the increasing microplastics, and the influence is likely to be microbeads concentrations did not alter the negative if root symbionts such as levels of a and b significantly [24]. and nitrogen fixers were affected. Slow Contrarily, Mateos-Cárdenas et al. revealed degradation of microplastics has been linked to adding a concentration of 50,000 polyethylene microbial immobilization though there is currently microplastics/mL of water increased root length a lack of empirical evidence for the of duckweed (Lemma minor) between 24 hours immobilization [19]. Besides, microplastics may and 168 hours after addition though the increase serve as media which introduce phytotoxic was insignificant compared to control [25]. While substances into soil, thus adversely affecting the effects on root growth are inconclusive at this plant roots and health [21]. juncture, microplastics do not seem to significantly affect photosynthetic capacity of Generally, by altering soil structure and microbial duckweed [24,25]. diversity, microplastics could alter plant diversity and community composition [22,23]. In a study by Manjate et al., microplastics Nonetheless, while postulates were made by were reported to not interfere with relating changes in soil biophysical properties to phytoremediation of metals (the use of plant to the impacts of microplastics on plants, there are remove metal contaminants in soil) by common few studies to prove the postulates. Boots et al. reeds, scientifically known as found addition of synthetic fiber and australis, which hyperaccumulated at least 70 biodegradable polylactic acid reduced the shoot times more metals in their root tissues with height of perennial ryegrass (Lolium perenne) concentrations up to 1 mg/g of Cu and 70 but increased its chlorophylls a and b levels (7). µg/g of Cd in contaminated media [26,27]. Synthetic fiber and biodegradable polyacetic acid Addition of polyethylene microplastics also retarded seed germination though the did not affect the metal concentrations in the roof former was linked to an increase in root biomass. tissues of Phragmites australis [26]. Kalcikova et al. studied the effects of increasing Bosker et al. found significant reduction in the concentrations of polyethylene microbeads on germination rate of Cress (Lepidium sativum) duckweed (Lemna minor) and revealed the root seeds 8 hours after being exposed to plastic lengths to have decreased as concentrations particles of 50, 500 and 4800 nm, and the increased [24]. The leaves demonstrated 10% reduction positively correlated to plastic sizes growth inhibition compared to less than 8% in [28].

Fig. 1. Sources and impacts of microplastics on soil and plants

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Tang; AJEE, 13(1): 1-9, 2020; Article no.AJEE.57484

Table 1. Summary of the effects of microplastics on plants

Plant/ Crop Types of microplastics Treatment Findings References Zea mays (maize) Polyethylene and Maize grown in soil mixed with Biomass and leaf chlorophyll content of maize [29] polylactic acid 0.1%, 1% and 10% (w/w) decreased after exposure to 10% polylactic microplastics and spiked with 5 acid but phytotoxicity of polyethylene was mg Cd/kg soil. insignificant. Polyethylene and interacted significantly with root biomass. Lepidium sativum Green fluorescent 72-hour bioassay of cress seeds Significantly lower germination rate was [28] (garden cress) plastic particles exposed to 50 nm, 500 nm and observed after exposure to all three plastic 4800 nm plastic particles at particle sizes for 8 hours and increasing plastic concentrations between 103 and sizes caused more decline in the rate. 107 particles. After 24-hour exposure, the germination rate did not differ significantly. Root growth varied after 24-hour exposure but the variation was negligible after 48-hour or 72- hour exposure. faba (broad Polystyrene fluorescent Exposure of root tips of Vicia 5 µm plastics reduced root biomass and [30] beans) microplastics faba to 10, 50 and 100 mg/L of catalase activity but increased superoxide microplastics of 5 µm and 100 dismutase and peroxidase activities. nm. 100 nm plastics reduced root biomass only at 100 mg/L but caused greater genotoxicity and oxidative damage than 5 µm plastics Plant generally Type Hypothesis of effects on plants Changes on plant growth [19] Beads and fragments, based on how different types of Minor Large (+) Fibers, microplastics affect soil Intermediate (-) Films, biophysical properties, e.g. Intermediate (-) Biodegradable beads and fragments only Minimal to intermediate (-) Nanoplastics produce minor textural changes in soil, fibers cause alteration of soil structure and bulk density, while biodegradable microplastics temporarily immobilize nutrient in soil.

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Plant/ Crop Types of microplastics Treatment Findings References Lettuce Polystyrene microbeads Tracking of uptake and Roots of lettuce trapped, absorbed and [18] sized 0.2 and 1.0 µm distribution of polystyrene transported polystyrene microbeads to stems microbeads in lettuce. and leaves via transpiration. This indicates that microplastics can be taken up, accumulated and transferred in crops such as lettuce. Lolium perenne Biodegradable polylactic Exposure of perennial ryegrass Seeds of perennial ryegrass showed lower [7] (perennial ryegrass) acid and high-density to 1 g/kg dry soil of polylactic germination after exposure to polylactic acid polyethylene acid and high-density microplastics. Root biomass of perennial polyethylene with mean ryegrass was lower when exposed to polylactic diameters of 65.6 µm and 102.6 acid, compared to polyethylene microplastics. µm respectively. No significant variation in chlorophyll content was observed. Lemna minor Polyethylene Bioassay of duckweed exposed Duckweed adsorbed a maximum 7 [25] (Duckweed) microspheres to about 50,000 microplastics/mL microplastics per mm2 7-day after exposure to of bioassay suspension with the microplastics. Photosynthetic efficiency and diameter of 10-45 µm. growth of duckweed were not significantly affected Lemna minor Polyethylene Exposure of duckweed leaves to The microbeads did not significantly affect leaf [24] (Duckweed) microbeads microbeads from two commercial growth as well as chlorophyll content in the exfoliators. leaves but retarded root growth through mechanical blocking. Tobacco BY-2 cells Fluorescent polystyrene Exposure of BY-2 cells and Endocytosis of 20 nm-diameter beads by BY-2 [17] nano beads of 20 nm protoplasts to nano beads cells was observed while larger beads (100 nm) diameter followed by examination with were not internalized. Protoplasts internalized confocal microscope. beads as large as 1000 nm diameter.

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Tang; AJEE, 13(1): 1-9, 2020; Article no.AJEE.57484

However, differences in germination rates were for more studies on how microplastics affect not observed after 24 hours and this implies different plants to bridge the gaps of knowledge. transient negative effect of micro-/ nano- plastics As this review also highlights potential uptake on seed germination attributed probably to and internalization of microplastics by plants, it blocking of pores on seed capsules by plastic recommends more studies to examine the risks particles [28]. of human exposure to microplastics due to ingestion of agricultural produces. In addition, Wang et al. studied the interactions of agricultural impacts of microplastics can be microplastics with cadmium in soil and how the complicated by their ability to adsorb other interactions affected plant performance [29]. chemicals, and the events of climate change due They found polyethylene did not elicit significant to anthropogenic factors, which future studies phytotoxicity while 10% polylactic acid caused could aim to investigate [31]. decline in the biomass and leaf chlorophyll level of maize grown in soil contaminated with COMPETING INTERESTS cadmium. Both microplastics did not yield significance differences in the amount of Cd Author has declared that no competing interests accumulated in plant tissues [29]. In terms of exist. ecotoxicity, Jiang et al. reported decreased root biomass and root catalase enzyme activity of REFERENCES (broad beans) upon exposure to 5 µm polystyrene fluorescent microplastics at 1. Wong JKH, Lee KK, Tang KHD, Yap P-S. concentrations ranging from 10 to 100 mg/L for Microplastics in the freshwater and 48 hours while increase in the activities of terrestrial environments: Prevalence, fates, superoxide dismutase and peroxidase was impacts and sustainable solutions. Sci observed [30]. The study also revealed that 100 Total Environ. 2020;719:137512. nm polystyrene fluorescent microplastics caused 2. Zhu F, Zhu C, Wang C, Gu C. Occurrence a decline in root growth only at a higher and ecological impacts of microplastics in concentration of 100 mg/L but posed greater soil systems: A review. Bull Environ genotoxicity and oxidative damage on Vicia faba Contam Toxicol. 2019;102(6):741–9. [30]. Fig. 1 shows the sources and impacts of 3. Tang KHD. Ecotoxicological impacts of microplastics on soil and plants. A summary of Micro and nanoplastics on Marine Fauna. the effects of microplastics on plants and crops is Examines Mar Biol Oceanogr. 2020;3(2): presented in Table 1. 1–5. 4. CONCLUSION 4. Omidi A, Naeemipoor H, Hosseini M. plastic debris in the digestive tract of Microplastics have been shown to affect crops sheep and goats: An increasing and plants in various ways. At cellular level, environmental contamination in Birjand, microplastics alter enzyme activities and have Iran. Bull Environ Contam Toxicol. 2012; the potential to cause genotoxicity and oxidative 88(5):691–4. damage. Microplastics can also be internalized 5. Zhao S, Zhu L, Li D. Microscopic by certain plant cells and protoplasts. anthropogenic in terrestrial birds from Physiologically, microplastics demonstrate Shanghai, China: Not only plastics but also adverse effects on root growth and seed natural fibers. Sci Total Environ. 2016; germination but the duration of the effects is 550:1110–5. inconclusive and the extent of the effects depends on the types and sizes of microplastics. 6. de Souza Machado AA, Lau CW, Till J, It is possible for microplastics to enter plants via Kloas W, Lehmann A, Becker R, et al. roots, accumulate and move to various parts of Impacts of microplastics on the Soil the plants due to physiologically processes such biophysical environment. Environ Sci as transpiration. Microplastics have also been Technol. 2018;52(17):9656–65. hypothesized to affect plants by changing 7. Boots B, Russell CW, Green DS. Effects of biophysical properties of soil. However, the Microplastics in soil ecosystems: Above knowledge of the impacts of microplastics on and below ground. Environ Sci Technol. plants and crops, and agriculture as a whole, is 2019;53(19):11496–506. constrained by the relatively low number of 8. Nizzetto L, Futter M, Langaas S. Are studies in this area. This review therefore calls Agricultural soils dumps for microplastics

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Tang; AJEE, 13(1): 1-9, 2020; Article no.AJEE.57484

of urban origin? Environ Sci Technol. 20. Wan Y, Wu C, Xue Q, Hui X. Effects of 2016;50(20):10777–9. plastic contamination on water evaporation 9. Lal R. Soil health and carbon and desiccation cracking in soil. Sci Total management. Food Energy Secur. 2016; Environ. 2019;654:576–82. 5(4):212–22. 21. Galloway TS, Cole M, Lewis C. 10. Trivedi P, Delgado-Baquerizo M, Anderson Interactions of microplastic debris IC, Singh BK. Response of soil properties throughout the marine ecosystem. Nat and microbial communities to agriculture: Ecol Evol. 2017;1(5):116. Implications for primary productivity and 22. Pérès G, Cluzeau D, Menasseri S, soil health indicators, Frontiers in Plant Soussana JF, Bessler H, Engels C, et al. Science. 2016;7:990. Mechanisms linking plant community 11. Liu H, Yang X, Liu G, Liang C, Xue S, properties to soil aggregate stability in an Chen H, et al. Response of soil dissolved experimental grassland plant diversity organic matter to microplastic addition in gradient. Plant Soil. 2013;373(1):285– Chinese loess soil. Chemosphere. 2017; 99. 185:907–17. 23. van der Heijden MGA, Bruin S de, 12. Green VS, Stott DE, Diack M. Assay for Luckerhoff L, van Logtestijn RSP, fluorescein diacetate hydrolytic activity: Schlaeppi K. A widespread plant-fungal- Optimization for soil samples. Soil Biol bacterial symbiosis promotes plant Biochem. 2006;38(4):693–701. biodiversity, and seedling 13. Lehmann A, Zheng W, Rillig MC. Soil biota recruitment. ISME J. 2016;10(2):389–99. contributions to soil aggregation. Nat Ecol 24. Kalčíková G, Žgajnar Gotvajn A, Kladnik A, Evol. 2017;1(12):1828–35. Jemec A. Impact of polyethylene 14. Murugan R, Beggi F, Kumar S. microbeads on the floating freshwater Belowground carbon allocation by trees, plant duckweed Lemna minor. Environ understory vegetation and soil type alter Pollut. 2017;230:1108–15. microbial community composition and 25. Mateos-Cárdenas A, Scott DT, nutrient cycling in tropical Eucalyptus Seitmaganbetova G, Frank NAM, van P, plantations. Soil Biol Biochem. 2014;76: John O, Marcel AKJ. Polyethylene 257–67. microplastics adhere to Lemna 15. Wang J, Lv S, Zhang M, Chen G, Zhu T, minor (L.), yet have no effects on plant Zhang S, et al. Effects of plastic film growth or feeding by Gammarus duebeni residues on occurrence of phthalates and (Lillj.). Sci Total Environ. 2019;689:413– microbial activity in soils. Chemosphere. 21. 2016;151:171–7. 26. Manjate E, Ramos S, Almeida CMR. 16. Qi Y, Yang X, Pelaez AM, Huerta Lwanga Potential interferences of microplastics in E, Beriot N, Gertsen H, et al. Macro- and the phytoremediation of Cd and Cu by the micro-plastics in soil-plant system: Effects salt marsh plant Phragmites australis. J of plastic mulch film residues on wheat Environ Chem Eng. 2020;8(2):103658. (Triticum aestivum) growth. Sci Total 27. Tang KHD. Phytoremediation of soil Environ. 2018;645:1048–56. contaminated with petroleum 17. Bandmann V, Müller JD, Köhler T, hydrocarbons: A review of recent Homann U. Uptake of fluorescent nano literature. Glob J Civ Environ Eng. beads into BY2-cells involves clathrin- 2019;33–42. dependent and clathrin-independent 28. Bosker T, Bouwman LJ, Brun NR, Behrens endocytosis. FEBS Lett. 2012;586(20): P, Vijver MG. Microplastics accumulate on 3626–32. pores in seed capsule and delay 18. Li L, Zhou Q, Yin N, Tu C, Luo Y. Uptake germination and root growth of the and accumulation of microplastics in an terrestrial vascular plant Lepidium sativum. edible plant. Chinese Sci Bull. 2019;64(9): Chemosphere. 2019;226:774–81. 928–34. 29. Wang F, Zhang X, Zhang S, Zhang S, Sun 19. Rillig MC, Lehmann A, de Souza Machado Y. Interactions of microplastics and AA, Yang G. Microplastic effects on plants. cadmium on plant growth and arbuscular New Phytol. 2019;223(3):1066–70. mycorrhizal fungal communities in an

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Tang; AJEE, 13(1): 1-9, 2020; Article no.AJEE.57484

agricultural soil. Chemosphere. 2020; Vicia faba. Environ Pollut. 2019;250:831– 254:126791. 8. 30. Jiang X, Chen H, Liao Y, Ye Z, Li M, 31. Tang KHD. Implications of climate change Klobučar G. Ecotoxicity and genotoxicity of on marine biodiversity. Glob J Agric Soil polystyrene microplastics on higher plant Sci. 2020;1(1):1–6. ______© 2020 Tang; This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Peer-review history: The peer review history for this paper can be accessed here: http://www.sdiarticle4.com/review-history/57484

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