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 is to investigate the effect of di-2-ethylhexyl phthalate (DEHP, a representative plasticizer in soil) on the removal of sulfadiazine (SDZ, a frequently detected antibiotic in natural environments), antibiotic resistance genes (ARGs), and the microbial community in soil MFCs. Our results confirmed that 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 because the biodegradation efficiency was improved in both the upper (i.e., to 0.268 ± 0.021 mg kg−1 from 4.867 ± 0.221 mg kg−1) and lower layers (i.e., to 0.293 ± 0.047 mg kg−1 from 4.867 ± 0.221 mg kg−1) 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 have been caused by the enrichment of ARG potential hosts brought about by high DEHP concentrations, likely due to the increased conjugative transfer rates of the RP4 plasmid due to decreased membrane permeability and an increased 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.