Trends for Monitoring Micro- and Nanoplastics in Soil

In a recent study published in TrAC Trends in Analytical Chemistry, scientists from multiple universities and research institutes in Europe discussed testing protocols that are currently being used to monitor and control micro- and nanoplastics (MNPs) in soil (1).

Farmer holding soil in hands close-up. Male hands touching soil on the field. Farmer is checking soil quality before sowing wheat. Agriculture, gardening or ecology concept | Image Credit: © maxbelchenko - stock.adobe.com

Microplastics and nanoplastics (MNPs) are prominent soil contaminants, from sources like plastics and sewage sludge-based fertilizers, compost, runoff, and littering. Plastic contamination is estimated to be 23 times higher on land than in the ocean, according to an article from the UN Environment Programme. This has led to international bodies imposing regulations on MNP monitoring; for instance, in 2023, the European Commission created new chemical legislation to prevent the sale of microplastics and restrict microplastics intentionally added to products (2). This restriction covers synthetic polymer particles below five millimeters that are organic, insoluble, and resistant to degradation. Its purpose is to reduce emissions of intentional microplastics from as many products as possible.

Current knowledge on the effects of MNPs on soil ecosystems is fragmentary, which stems from a lack of guidelines, harmonization, and reference materials to conduct an ecological risk assessment. This is something that will become a future component in environmental protection regulations, the authors wrote. However, such proceedings will require strategies to reduce complexity of testing, representative exposure scenarios to address questions inherent to the risk of different material mixtures, and sensitive and representative endpoints and risk thresholds for direct and indirect effects (1).

Standardized single-species toxicity tests will likely be valuable for assessing MNPs in soils, the authors wrote. These tests are based on the framework of representative species to evaluate the risk of chemical contaminants. However, a critical issue in this regard is data reliability, relevance, and reporting in ecotoxicological studies and how considering this factor can prevent data reuse in hazard assessment. While there have been recommendations to advance the quality of MNP research in freshwater ecosystems, this has not yet been holistically approached regarding soils. In this paper, the scientists addressed the need to create more complete and environmentally relevant test strategies for assessing MNP environmental hazards in soils, especially using single-species and simplified community toxicity tests. Additionally, they hoped to provide recommendations for practically implementing measures to fulfill quality criteria in environmentally relevant ecotoxicology tests on MNP effects.

According to the team, these tests must focus on environmentally relevant experimental designs, guidelines for MNP test materials selection and characterization, analysis of MNPs and additives in soil and biota, and a proposal for relevant soil physicochemical properties to be assessed during ecotoxicity testing. It has been proposed that quality assessment/quality control (QA/QC) criteria should be created for ecotoxicity testing of nanoplastics. As for microplastics, QA/QC criteria have been developed for detection in biota, freshwater and drinking water, sediment, soil, and for ecotoxicity tests with aquatic organisms. However, there is no current criteria regarding soil hazard assessment. As such, these criteria should be further developed, with a further step including the design of minimum reporting standards, which can facilitate potential reuse of data generated in hazard assessment for secondary analysis, meta-analyses, or integration with other datasets. There is more work to be done, but ecological hazard assessment of MNPs in soil can help further our understanding of environmental safety protocols and what scientists can do to help further these efforts.

References

(1) Kokalj, A. J.; Kalčíková, G.; Selonen, S.; Bosker, T.; et al. Strategy Towards Producing Relevant and Reliable Data for the Hazard Assessment of Micro- and Nanoplastics in Agricultural Soils. TrAC Trends Analyt. Chem. 2024, 172, 117567. DOI: https://doi.org/10.1016/j.trac.2024.117567

(2) Protecting Environment and Health: Commission Adopts Measures to Restrict Intentionally Added Microplastics. European Commission 2023. https://ec.europa.eu/commission/presscorner/detail/en/ip_23_4581 (accessed 2024-4-3)