Comparing root concentration factors of antibiotics for lettuce (Lactuca sativa) measured in rhizosphere and bulk soils

Plant uptake of antibiotics raises serious food safety concerns. Measurements and predictions of antibiotic uptake by plants are often based on root concentration factors (RCF) determined using antibiotic concentrations in bulk soil (RCEbs) rather than in rhizosphere soil (RCFbs) where root uptake actually occurs. This study investigated the fate and transport of nine antibiotics in the continuum of bulk soil, rhizosphere soil, roots and shoots of lettuce (Lactuca sativa) under soil-surface irrigation. Antibiotic concentrations in the lettuce shoots remained unchanged during 25-35 days after seedling transplantation. Compared with the RCFbs values, the RCEbs values were significantly greater for ciprofloxacin, lincomycin, oxytetracycline, sulfamethoxazole, and tetracycline (p < 0.05), similar for trimethoprim and tylosin, but significantly lower for monensin (p < 0.05). Ciprofloxacin, trimethoprim, and tylosin had the lowest translocation factors (TF) ranging between 0.03 and 0.05, suggesting their limited upward transport to the lettuce shoots. Oxytetracycline, monensin, and sulfamethoxazole had intermediate TF values of 0.36-0.64, whereas lincomycin had the highest TF value of 1.46. This study showed significant differences between RCEbs and RCFrs values, suggesting the need to reassess the utility of RCFbs in predicting the antibiotic root uptake in diverse soil-plant systems. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This study revealed significant differences in the uptake and transport of different antibiotics in plants under soil-surface irrigation, highlighting the need for further investigation in diverse soil-plant systems.