Effects of plasticizer on removal of antibiotics and antibiotic resistance genes from agricultural soils via soil microbial fuel cells

Abstract

Soil microbial fuel cells (MFCs), a novel ecosystem technology, have recently been intensively studied for antibiotic-polluted soils. However, actual agricultural soils are always contaminated by mixed pollutants, especially plasticizers from extensively used agricultural plastic films. The aim of this study was to investigate the effects of di-2-ethylhexyl phthalate (DEHP), a representative plasticizer in soil, on the removal of sulfadiazine (SDZ), a frequently detected antibiotic in natural environments, and antibiotic resistance genes (ARGs) and microbial community in soil MFCs. Soil MFCs maintained a good antibiotic removal ability even under the influence of residual DEHP and achieved a higher removal performance at higher DEHP concentrations due to enhanced power generation. Specifically, a higher DEHP concentration had a favorable effect on antibiotic removal in soil MFCs, with the SDZ concentration decreased in both the upper and lower layers (from 4.867 ± 0.221 to 0.268 ± 0.021 and 0.293 ± 0.047 mg kg^-1, respectively) of polluted soils. Moreover, a high DEHP concentration significantly promoted the abundance of bacteria associated with electricity generation compared with a lower DEHP concentration, resulting in the promotion of extracellular electron transfer and enhancing SDZ degradation. The increased ARG abundance may be caused by the enrichment of ARG potential hosts brought about by high DEHP concentration, likely due to the increased conjugative transfer frequencies of plasmid RP4 by decreasing cell membrane permeability and increasing reactive oxygen species content. The results revealed the ecological risk of residual DEHP in soil that promotes ARG transmission in soil MFCs, although it has the potential to reduce SDZ toxicity through horizontal gene transfer. We also highlight concerns regarding the management of antibiotics and plasticizers in soil. The negative effects of plasticizers on antibiotic removal should be carefully evaluated when using soil MFCs for the in-situ remediation of antibiotic-contaminated soil.