Does Sorption to Mulch Film Increase Bioavailability of Two Model Pesticides for Earthworms and Bacteria in Soil?

Abstract

Microplastic pollution and resulting environmental impacts have been a research topic for decades, with degraded mulch films as important source for agricultural soil. The interaction of mulch film microplastic and pesticides, with the parameters of bioavailability and toxicity, still needs to be understood.We investigated the interaction of pesticides with mulch films by choosing the neonicotinoid Thiacloprid and the fungicide Tebuconazole in their commercial formulations as plant protection products, serving as representative hydrophobic and hydrophilic substances.First, the impact of PE microplastic (150 mg/kg) on the extractability and earthworm mortality of both pesticides was determined. The hypothesis was that the bioavailability of pesticides in the soil decreases with microplastic presence, and hence, reduced earthworm toxicity might be observed. Chemical analysis and acute toxicity testing confirmed this. Reduced bulk soil pesticide concentrations might explain the reduced toxicity.Secondly, the impact of pesticides on the microbial degradation of mulch films was assessed. Consequently, these studies were conducted with biodegradable PBAT-PLA mulch film particles and reported reduced degradation in pesticide presence.Our research shows that microplastic at application-relevant concentrations can retain pesticides and reduce pesticide toxicity, while pesticides reduce microbial biodegradation. These findings might impact pesticide efficiency in soils that accumulate microplastic, potentially requiring the adaptation of agricultural practices. Also, complete plastic mineralization might be hindered or at least prolonged, accumulating plastic particles. This study underscores the need for further research and mitigation strategies as our understanding of the interactions between pesticides and microplastics in soil evolves.

Keywords: Microplastic, Soil, pesticide, biodegradable plastics, microbes, earthworm toxicity