Soil bacterial community and vanadium fate shaped by co-exposure to polyethylene microplastics and native vanadium pollution

Abstract

The co-occurrence of microplastics (MPs) and heavy metals in agricultural soils poses a complex ecological risk, yet the combined effects of polyethylene microplastics (PE-MPs) and vanadium (V) under different pollution legacies remain poorly understood. This study investigated the interactive effects of PE-MPs at two concentrations (0.1% and 1% (w/w)) and two particle sizes (100-mesh and 1000-mesh) and V on soil properties, microbial community structure, enzyme activities, V fractions, and plant uptake in two soils with distinct native pollution backgrounds. Results revealed that PE-MPs altered soil properties and V fate in a strongly background-dependent manner. Despite increasing soil pH by up to 0.45 units in the LV1 treatment, PE-MPs suppressed both microbial diversity (e.g., Shannon index decreased by 8.9%) and soil sucrase activity. Conversely, in MV2, PE-MPs decreased pH and enhanced enzyme activities (e.g., urease increased 1.7-fold). PE-MPs differentially modulated V bioavailability: the acid-soluble fraction decreased in LV1 but increased in MV2. Consequently, V accumulation in maize organs varied: in MV2, 1% PE-MPs increased V in leaves by >80%, whereas in LV1, the promoting effect was minimal or even suppressive. These findings underscore that the ecological impact of MPs in co-contaminated systems is not intrinsic but is decisively shaped by the soil's pollution history. This highlights the necessity of incorporating native contamination levels into ecological risk assessments to develop targeted and effective management strategies for agricultural soils under complex pollution scenarios.