A contrasting alteration of sulfamethoxazole bioaccessibility in two different soils amended with polyethylene microplastic: In-situ measurement using diffusive gradients in thin films

Microplastics and veterinary antibiotics are both emerging environmental contaminants that could be co-occurrence in agricultural soils. However, it's still unclear how the microplastics affect the bioaccessibility of antibiotics in a real soil environment. An in-situ measurement using diffusive gradients in thin-films devices suitable for polar organic compounds (o-DGT) coupled with soil moisture sampling were used to reveal such effects. Sulfamethoxazole (SMX) that was selected as a representative antibiotic and polyethylene (PE) microplastic with an average diameter of 35 μm were amended to the paddy soil and saline soil for the study. The result indicated that SMX degradation in the paddy soil was higher than that in the saline soil, meanwhile, PE microplastic addition promoted SMX degradation in both soils. In the paddy soil, PE microplastic addition enhanced release of SMX from soil solid to soil solution but no effects on the bioaccessibile SMX. However, in the saline soil, the PE microplastic addition reduced both SMX in soil solution and bioaccessibile SMX significantly (p < 0.05). The potential resupply ability of the labile SMX from soil solid to soil solution which was expressed as R value enhanced significantly in saline soil, while such a change was negligible in the paddy soil. This implied that long-term release risk of SMX in the PE microplastic contaminated saline soil could not be neglected. Therefore, co-occurrence of PE microplastic and SMX in the soils might increase uptake of SMX by biotas and such effects depended on soil properties.