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What comes after the Sun? On the integration of soil biogeochemical pre-weathering into microplastic experiments

Büks, Frederick; Kaupenjohann, Martin

FG Bodenkunde

Recent studies have been engaged in estimating the adverse effects of microplastic (MP) on soil quality parameters. Mass concentrations of MP, as found in highly contaminated soils, have been shown to weaken the soil structure, and parts of the edaphon are adversely affected mainly by the <100 µm MP size fraction. However, the vast majority of these studies used pristine particles, which have surface characteristics different from those of environmental MP. Exposed to UV radiation, plastic undergoes photochemical weathering with embrittlement and the formation of surface charge, leading to an alteration of physiochemical behavior. When plastic particles then enter the soil environment, further aging factors appear with yet unknown efficacy. This little explored soil biogeochemical phase includes biofilm cover, decay with enzymes (as shown in laboratory experiments with both conventional and biodegradable plastics), contact with biotic and abiotic acids, oxidants, and uptake by the soil fauna that causes physical fragmentation. Such transformation of the surfaces is assumed to affect soil aggregation processes, soil faunal health, and the transport of plastic colloids and adsorbed solubles. This perspective article encourages us to consider the weathering history of MP in soil experiments and highlights the need for reproducing the surface characteristics of soil MP to conduct laboratory experiments with closer-to-nature results.