Combined effects of microplastics and agrochemicals on soil microbial communities
Agricultural soils are major reservoirs of microplastic (MP) pollution, with European farmland receiving up to 430,000 tons annually. Besides their direct ecological impacts on soil ecosystems, MPs were shown to readily adsorb and concentrate organic pollutants present in adjacent soil onto their surfaces, potentially creating local hotspots of chemical exposure and increasing risks to sensitive soil microbial communities. Here, we tested the single and combined effects of four MP types (LDPE, PBAT, starch-based plastic, and a Mix) and two common agrochemicals (pyraclostrobin and albendazole) on bacterial, fungal, and protist communities in three contrasting European soils (French, Greek, Dutch) over a 90-day microcosm experiment. Microbial community shifts were assessed by high-throughput sequencing of bacterial 16S rRNA, fungal ITS, and protistan 18S rRNA regions. MPs alone significantly altered microbial diversity, with responses depending on soil properties and polymer type. Biodegradable MPs notably increased fungal and protist diversity in the low-diversity Greek soil, whereas effects in richer soils were weaker or delayed. Our selected organic pollutants ALB and PYR alone had limited impact, but their combination with MPs produced stronger, non-additive shifts, particularly in the Greek soil, where sensitive taxa declined and disturbance-tolerant groups increased. Bacteria showed transient responses, fungi exhibited polymer- and soil-specific restructuring, and protists were the most sensitive, with persistent declines under co-exposure. These results demonstrate that MP effects on soil microbiota are highly context-dependent and can amplify the ecological risks of agrochemicals. Our findings highlight the need for risk assessments and management strategies that consider polymer-specific effects, the sensitivities of different microbial groups, and the frequent co-occurrence of MPs with organic pollutants. Such approaches are essential for effectively protecting soil biodiversity and function in agricultural landscapes.