Removal Rule, Ecological Risk, and Full-Scale Assessment of Antibiotics in Three Organic Fertilizer Production Methods

The occurrence of antibiotic residues present in organic fertilizers produced by diverse techniques is largely unknown. Large-scale evaluation and standardization are imperative to identify the concentration and risks of residual antibiotics during different treatment techniques of livestock manure (i.e., compost, carbonization, and anaerobic treatment). In this study, we assessed the concentration and ecological risks of 30 antibiotics in three types of commercial organic fertilizers by the risk quotient (RQ) method. The highest levels of residual antibiotics in the organic fertilizers produced by composting, carbonization, and anaerobic treatment were 142.58 μg/kg (dry weight) oxytetracycline, 2.53 μg/kg (dry weight) oxytetracycline, and 341.86 mg/L chlortetracycline. We observed that the compost and carbon-based organic fertilizers had an RQ of less than 0.1, indicating a low risk. In contrast, liquid organic fertilizer had an RQ of 0.93, indicating a medium risk. After a comprehensive comparison and evaluation, the “carbonization + anaerobic treatment” mode was found to be more appropriate for most cases. Moreover, the preparation method of organic fertilizers needs further optimization to minimize the concentration of residual antibiotics within the range of low ecotoxicity.