Understand the Science: What do we know?

Literature Reviews: Microplastics in Soil

Source, migration and toxicology of microplastics in soil. Guo, J.J., Huang, X.P., Xiang, L., Wang, Y.Z., Li, Y.W., Li, H., Cai, Q.Y., Mo, C.H. and Wong, M.H. 2020. Environment International 137: 105263.

• This article serves as a review of existing literature on the source, migration, trophic transfer, and implications of microplastics in soil in order to address the associated risks, identify gaps in research, and suggest direction for future research.

Focus topics on microplastics in soil: analytical methods, occurrence, transport, and ecological risks. Li, J., Song, Y. and Cai, Y. 2020. Environmental Pollution 257: 113570.

• This article reviews existing literature on microplastics in soils, particularly the analytical methods used to study them. These researchers conclude that the lack of a universal analytical method to study MPs is one of the biggest issues faced by this type of research, and that MP research contains considerable gaps as it is still in its infancy.

Environmental fate and impacts of microplastics in soil ecosystems: Progress and perspective. Wang, W., Ge, J., Yu, X. and Li, H. 2020. Science of The Total Environment 708: 134841.

• This article is a review of existing literature about microplastic occurrence in soils and a discussion of their sources, as well as a summary/comparison of extraction methodologies and an assessment of the toxicological implications of microplastic contamination of soil ecosystems.

Microplastics in the soil environment: occurrence, risks, interactions and fate–a review. Xu, B., Liu, F., Cryder, Z., Huang, D., Lu, Z., He, Y., Wang, H., Lu, Z., Brookes, P.C., Tang, C. and Gan, J., 2020. Critical Reviews in Environmental Science and Technology 50(21): 2175-2222.

• This article is a review and summary of existing literature on the effects of microplastic contamination of soil ecosystems, noting the broad range of implications that MP pollution has on soils such as soil chemical properties, microbial activities, and plant growth.

Microplastics in soils: A review of methods, occurrence, fate, transport, ecological and environmental risks. Zhou, Y., Wang, J., Zou, M., Jia, Z. and Zhou, S. 2020. Science of The Total Environment, 141368.

• This article is a review of existing literature on the impacts and sources of MPs with a stated intention that this review will help provide a “roadmap and inspiration” for future soil MP research and development of mitigation and remediation strategies.

Microplastics as contaminants in the soil environment: A mini-review. Wang, J., Liu, X., Li, Y., Powell, T., Wang, X., Wang, G. and Zhang, P. 2019. Science of the Total Environment 691: 848-857.

• This review was written with the intention of summarizing the prevalence, sources, and properties of microplastics in soil, analyze the cumulative effects of MPs, and discuss the potential risks that MPs pose to soil health, food safety, and human health.

Occurrence and ecological impacts of microplastics in soil systems: a review. Zhu, F., Zhu, C., Wang, C. and Gu, C. 2019. Bulletin of Environmental Contamination and Toxicology 102(6): 741-749.

• This review of existing literature on microplastics in soils summarizes the source and occurrence of MPs in soils, describes the observed effects on soil microbes and other organisms, and identifies gaps in existing knowledge that can be filled by future research.

Micro-and nano-plastics in edible fruit and vegetables. The first diet risks assessment for the general population. Conti, G.O., Ferrante, M., Banni, M., Favara, C., Nicolosi, I., Cristaldi, A., Fiore, M. and Zuccarello, P. 2020. Environmental Research 187: 109677.

• The human toxicity of microplastics is not yet fully understood and there is a lack of reliable data on microplastic presence in fruits and vegetables.  This study evaluated the number and size of microplastics in the most commonly-consumed fruits and vegetables, finding that apples were the most contaminated and lettuces the least.

Field evidence for transfer of plastic debris along a terrestrial food chain. Huerta Lwanga, E., Mendoza Vega, J., Ku Quej, V. et al. 2017. Scientific Reports 7:1407.

• The results of this study demonstrated that micro- and macroplastic contaminants have the potential to enter terrestrial food webs if not properly managed.

Microplastics & Soils

Microplastics & Soil Health/Soil Function

Effects of microplastics and drought on soil ecosystem functions and multifunctionality. Lozano, Y.M., Aguilar-Trigueros, C.A., Onandia, G., Maaß, S., Zhao, T. and Rillig, M.C. 2021. Journal of Applied Ecology

• This study found that single ecosystem functions can be positively or negatively affected by microplastics fibres depending on soil water status. However, our results suggest that microplastic fibres may cause negative effects on ecosystem soil multifunctionality of a similar magnitude as drought. Thus, strategies to counteract this new global change factor are necessary.

Wetland soil microplastics are negatively related to vegetation cover and stem density. Helcoski, R., Yonkos, L.T., Sanchez, A. and Baldwin, A.H. 2020. Environmental Pollution 256: 113391.

• The study explored the accumulation of soil microplastics in areas with varying density of vegetation, finding that vegetated wetlands are “important locations for microplastic distribution,” and that the vegetation and hydrodynamics impact the distribution between habitats.

Behavior of microplastics and plastic film residues in the soil environment: A critical review. Qi, R., Jones, D.L., Li, Z., Liu, Q. and Yan, C. 2020. Science of the Total Environment 703: 134722.

• This review summarizes key aspects of microplastic presence in soils based on previous literature, such as ecological effects, distribution and migration, and mitigation strategies, concluding with the identification of the most pressing challenges for future MP research.

Decrease in bioavailability of soil heavy metals caused by the presence of microplastics varies across aggregate levels. Yu, H., Hou, J., Dang, Q., Cui, D., Xi, B. and Tan, W. 2020. Journal of Hazardous Materials 395: 122690.

• Herein, long-term soil culture experiments and soil fractionation are combined to investigate the effects of microplastics on chemical speciation of Cu, Cr, and Ni with different particle-size soil aggregates. Results show that microplastics in soil decrease the exchangeable, carbonate-bound, and Fe-Mn oxide-bound fractions of metals but increase their organic-bound fractions via direct adsorption and indirect effects on the soil microenvironment conditions. The findings suggest that microplastics can promote the transformation of heavy metal speciation from bioavailable to organic bound. 

Effects of microplastics in soil ecosystems: above and below ground. Boots, B., Russell, C.W. and Green, D.S. 2019. Environmental Science & Technology 53(19): 11496-11506.

• This was a “mesocosm” experiment to assess the larger soil ecosystem in which microplastics were introduced to soils that contained the rosy-tipped earthworm and were planted with perennial ryegrass.  The researchers found that various microplastic exposures impacted seed germination, shoot height, biomass, and soil pH.

Microplastics can change soil properties and affect plant performance. de Souza Machado, A.A., Lau, C.W., Kloas, W., Bergmann, J., Bachelier, J.B., Faltin, E., Becker, R., Görlich, A.S. and Rillig, M.C. 2019. Environmental Science & Technology 53(10): 6044-6052.

• Researchers in this study found that microplastic exposure to spring onion plants was associated with changes to plan biomass, tissue composition, root traits, and soil microbial activity; the researchers also note that their findings suggest the potential for microplastic contamination to more broadly affect agroecosystems and terrestrial biodiversity.

Towards an ecology of soil microplastics. Helmberger, M.S., Tiemann, L.K. and Grieshop, M.J. 2020. Functional Ecology 34(3): 550-560

• The authors of this review argue that the issue of soil microplastics needs to be framed in terms of ecology in addition to discussing the potential interactions microplastics may have with soil communities, which provide crucial insights into their effects on terrestrial ecosystems.

Microplastic incorporation into soil in agroecosystems. Rillig, M.C., Ingraffia, R. and de Souza Machado, A.A. 2017. Frontiers in Plant Science 8, 1805.

• This review outlines the current knowledge on the movement of microplastic particles in soils and which organisms and factors influence that movement; the authors also identify potential direction for future research on the topic of microplastic particle movement.

Impacts of microplastics on the soil biophysical environment. de Souza Machado, A.A., Lau, C.W., Till, J., Kloas, W., Lehmann, A., Becker, R. and Rillig, M.C. 2018. Environmental Science & Technology 52(17): 9656-9665.

• This study aimed to uncover the potential role of microplastics in the disruption of the relationship between soil and water.  The results suggest that microplastics affected the water holding capacity, the bulk density, and the functional relationship between microbes and water stable aggregates; the authors note that these processes suggest that microplastics are “relevant long-term anthropogenic stressors and drivers of global change in terrestrial ecosystems.”

Microplastics as an emerging threat to terrestrial ecosystems. de Souza Machado, A.A., Kloas, W., Zarfl, C., Hempel, S. and Rillig, M.C. 2018. Global Change Biology 24(4): 1405-1416.

• This article introduces the pervasive microplastic contamination as a potential agent of global change in terrestrial systems, highlights the physical and chemical nature of the respective observed effects, and discusses the broad toxicity of nanoplastics derived from plastic breakdown.

Microplastics in soils: analytical methods, pollution characteristics and ecological risks. He, D., Luo, Y., Lu, S., Liu, M., Song, Y. and Lei, L. 2018. TrAC Trends in Analytical Chemistry 109: 163-172.

• This article identifies main sources of microplastics and assesses the nature of the relationship between those microplastics and soil physio-chemistry and biota, in addition to noting that microplastics can affect soil biota at different trophic levels and threaten human health via food chains.

Microplastic disguising as soil carbon storage. Rillig, M. C. 2018 Environmental Science & Technology 52: 6079-6080

• However, one question that is specific to soils has not been asked: is microplastic already making a hidden contribution to soil carbon storage? Microplastic particles, either already produced as such for industrial purposes, or fragmented from larger plastic following exposure in the environment, are extremely slow to decompose and thus likely accumulate in our soils as relatively persistent pollutant

Microplastic in Terrestrial Ecosystems and the Soil? Rillig, M. C. 2012. Environ. Sci. Technol. 46 (12):6453-6454

A probabilistic risk assessment of microplastics in soil ecosystems. Jacques, O. and Prosser, R.S. 2021. Science of The Total Environment 757: 143987.

• This study finds that certain microplastics have the potential to negatively impact soil biota, and these particular concentrations of microplastics in soil are likely to only increase over time due to the large quantity of plastics in the environment.

The effects of three different microplastics on enzyme activities and microbial communities in soil. Yi, M., Zhou, S., Zhang, L. and Ding, S. 2021. Water Environment Research 93(1):24-32. doi: 10.1002/wer.1327.

• In an experiment that studied the effects of three different microplastics on loamy and sandy soil, researchers found that microplastics “significantly altered the microbial community structure,” with fibrous polypropylene having a more persistent effect on microbial activity.

Microplastic fiber and drought effects on plants and soil are only slightly modified by arbuscular mycorrhizal fungi. Lehmann, A., Leifheit, E.F., Feng, L. et al. 2020.

Response of soil enzyme activities and bacterial communities to the accumulation of microplastics in an acid cropped soil. Fei, Y., Huang, S., Zhang, H., Tong, Y., Wen, D., Xia, X., Wang, H., Luo, Y. and Barceló, D. 2020. Science of The Total Environment 707: 135634.

• This study found that, when introducing two different types of microplastics (polyethylene and polyvinyl chloride) into an acid soil, they both had impacts on enzymatic activity with polyethylene-treated soils showing more severe effects.

Effects of microplastics on greenhouse gas emissions and the microbial community in fertilized soil. Ren, X., Tang, J., Liu, X. and Liu, Q. 2020. Environmental Pollution 256: 113347.

• In this study, researchers observed the influence of two different particle sizes of microplastics on certain subjects such as on dissolved organic carbon and bacterial and fungal communities in fertilized soil, concluding that MPs have an impact on microbes and demonstrate the potential to have a “serious impact on terrestrial biogeochemical cycles.”

Microplastics effects on reproduction and body length of the soil-dwelling nematode Caenorhabditis elegans. Schöpfer, L., Menzel, R., Schnepf, U., Ruess, L., Marhan, S., Brümmer, F., Pagel, H. and Kandeler, E. 2020. Frontiers in Environmental Science 8: 41.

• This experiment sought to examine the effects of microplastic exposure on the reproduction and body length of a soil-dwelling nematode species, finding that MP exposure was associated with fewer nematode offspring which may ultimately have a negative impact on key soil functions because of the nematodes’ importance in the soil food web.

LDPE microplastics significantly alter the temporal turnover of soil microbial communities. Wang, J., Huang, M., Wang, Q., Sun, Y., Zhao, Y. and Huang, Y. 2020. Science of The Total Environment 726: 138682.

• To estimate the response of soil bacterial community succession and temporal turnover to microplastic amendment, a soil microcosm experiment was carried out with polyethylene microplastics. Our results propose that the presence of microbial in soil ecosystem may lead to a faster succession rate of soil bacterial community, which provides new insights into the evolutionary

Microplastics in the agroecosystem: Are they an emerging threat to the plant-soil system? Zang, H., Zhou, J., Marshall, M.R., Chadwick, D.R., Wen, Y. and Jones, D.L. 2020. Soil Biology and Biochemistry, 148: 107926.

• This study assessed the relationship between the type and amount of microplastics on plant growth, soil microorganisms, and photoassimilate carbon allocation, finding that MPs can have a significant impact on soil cycles; the researchers conclude that steps should be taken to minimize MP presence in soil ecosystems.

Effects of polyethylene microplastics on the gut microbial community, reproduction and avoidance behaviors of the soil springtail, Folsomia candida. Ju, H., Zhu, D. and Qiao, M. 2019. Environmental Pollution 247:890-897.

• This study exposed springtails to soils contaminated with polyethylene microplastics, finding that the MPs had toxic effects on them and can impact their gut microbial community–this study can provide insight into the effects of MPs in terrestrial ecosystems.

Soil microplastics inhibit the movement of springtail species. Kim, S.W. and An, Y.J. 2019. Environment International 126: 699-706.

• This study found that microplastics are able to move into bio-pores “within seconds,” which disrupts the movement of springtails–that disruption indicated that MPs can have broader implications for soil management.

Evolutionary implications of microplastics for soil biota. Rillig, M.C., de Souza Machado, A.A., Lehmann, A. and Klümper, U. 2019. Environmental Chemistry 16(1): 3-7.

• This article identifies approaches for studying evolutionary responses to microplastic contamination of soils and assesses the evolutionary consequences of MPs in soils, which the authors argue “can yield new insights” into the effects of MPs and help understand the future responses of soil microbes.

Low-density polyethylene microplastics as a source and carriers of agrochemicals to soil and earthworms. Rodríguez-Seijo, A., Santos, B., da Silva, E.F., Cachada, A. and Pereira, R. 2019. Environmental Chemistry 16(1): 8-17.

• This study exposed earthworms to soils containing two different-sized microplastics, one of which had been sprayed with chlorpyrifos; researchers observed that earthworms avoided the contaminated microplastics at the highest contamination level.

Uptake and adverse effects of polyethylene terephthalate microplastics fibers on terrestrial snails (Achatina fulica) after soil exposure. Song, Y., Cao, C., Qiu, R., Hu, J., Liu, M., Lu, S., Shi, H., Raley-Susman, K.M. and He, D.,2019. Environmental Pollution 250: 447-455.

• This study sought to determine whether microplastic fibers are harmful for soil biota–the researchers evaluated the toxic effects of microplastic fibers on terrestrial snails and found that the fibers have adverse effects on soil organisms, which demonstrates the potential for ecological risks of MP pollution.

Microplastics from mulching film is a distinct habitat for bacteria in farmland soil. Zhang, M., Zhao, Y., Qin, X., Jia, W., Chai, L., Huang, M. and Huang, Y. 2019. Science of the Total Environment 688: 470-478.

• This study found that microplastics collected from cotton fields in Xinjiang, China had acted as a “distinct habitat” for bacteria in agricultural soils.

Exposure of soil collembolans to microplastics perturbs their gut microbiota and alters their isotopic composition. Zhu, D., Chen, Q.L., An, X.L., Yang, X.R., Christie, P., Ke, X., Wu, L.H. and Zhu, Y.G. 2018. Soil Biology and Biochemistry 116: 302-310.

• This study exposed Folsomia candida (springtails) to microplastic-contaminated soil and found that the exposure may impact the species’ microbiota which may lead to altered isotopic and elemental incorporation as well as growth and reproduction.

Transport of microplastics by two collembolan species. Maaß, S., Daphi, D., Lehmann, A. and Rillig, M.C. 2017. Environmental Pollution 225:456-459.

• This study found that soil microarthropods can potentially contribute to the accumulation of microplastics in the soil food web by the movement and distribution of microplastic particles by these organisms.

Microplastic transport in soil by earthworms. Rillig, M.C., Ziersch, L. and Hempel, S. 2017. Scientific Reports 7(1): 1-6.

• In testing whether earthworms can move microplastic particles down the soil profile, the results of this study found that earthworms can be “significant transport agents” of MPs through soils