Assessment of microplastics as a source and carriers of pesticides to earthworms (Eisenia fetida)

International audienceStudies addressing the contamination of soils with microplastics (MP) are few and the impacts on soil biota are poorly known. Less than 10% of peer-reviewed publications covering the period between 1972 and 2019 addressed studies related to microplastics and terrestrial environments. Some questions can arise related with this significant environmental issue, and its impacts on soils and terrestrialecosystems, mainly whether MPs could transport contaminants (e.g. agrochemicals) on the soil matrix and if they could be carriers of pesticides to soil organisms through ingestion. In order to contribute to the understanding of these issues, earthworms (Eisenia fetida) were exposed for 14 days to OECD soils containing MPs with two different sizes [large MPs (5 mm) and small microplastics (0.250 -1 mm)], previously sprayed or not with chlorpyrifos following the dose recommended by the supplier (4 L ha-1). This agrochemical is a broad-spectrum organophosphorothionate pesticide with several agricultural applications to a variety of food and feed crops, and it is used worldwide. Acetylcholinesterase activity and thiobarbituric acid reactive substances (TBARs) were measured to track the exposure of earthworms to the MPs alone or combined with chlorpyriphos. The behaviour of earthworms in the test containers was also assessed, as well as the movement of MPs on the soil. The concentration of chlorpyrifos in soil after 14 days differed between treatments with MPs of different sizes [17.9 ng g-1 and 2442 ng g-1 for large (5mm) and small MPs (1 mm), respectively]. Despite the ability of the MPs to release chlorpyrifos to the soil, the earthworms have firmly avoided the 1mm MPs treatment. At the lowest concentration of chlorpyrifos provided by large MPs, earthworms avoided it, but the contact time with contaminated soil was higher, as shown by the enhanced level of TBARs and acetylcholinesterase inhibition