Bioaccumulation and adverse effects of three antibiotics in lettuce under environmentally-relevant levels

Despite growing concerns over antibiotic pollution, studies on the effects of low-level antibiotic exposure on plant growth remain limited. This study investigated the bioaccumulation and adverse effects of three typical antibiotics, enrofloxacin (ENR), sulfamethazine (SM2) and oxytetracycline (OTC), on lettuce (Lactuca sativa L.) at environmentally relevant concentrations (1, 10 and 100 µg/L). The results indicate that antibiotics were minimally accumulated in lettuce tissue (roots and leaves), with their bioconcentration factors (BCFs), root concentration factors (RCFs) and transfer factors (TFs) ranging from 0.05 to 10.35 L/kg, 1.14 to 236 L/kg, and 0.004 to 0.207, respectively. For each antibiotic, the BCF, RCF, and TF values generally decreased with increasing exposure concentrations (except for TF following OTC exposure). All three antibiotic treatments disrupted photosynthesis, reduced photosynthetic rates, triggered oxidative stress, and resulted in growth inhibition. Moreover, soluble protein and sugar contents declined, while antioxidant enzyme activities and lipid peroxidation products increased. In addition, microscopic observations revealed cellular structural damage, and elevated reactive oxygen species indicated intensified stress responses. Furthermore, transcriptomic analysis combined with functional enrichment showed that genes involved in photosynthetic processes and antioxidant defense were significantly downregulated with rising antibiotic concentrations, with KEGG pathway analysis highlighting the inhibition of key pathways related to energy metabolism and stress response.