The fate of erythromycin in soils and its effect on soil microbial community structure.

Erythromycin is one of the most commonly used macrolide antibiotics. However, little is known currently about the environmental behavior and fate of erythromycin in soils. Here erythromycin was C-labeled to investigate its degradation, mineralization and bound residues (BRs) in three typical agricultural soils. Results indicated the fate of C-erythromycin in soils varied greatly with soils types. Erythromycin was rapidly mineralized in black soil (BS) and fluvo-aquic soil (FS), whereas it rapidly formed large amounts of BRs in red soil (RS) with slow mineralization. At 120 d, about 90% of the introduced C-erythromycin was mineralized as CO in BS and FS, but only 30% in RS. There was still a certain proportion of BRs in all soils, especially in RS, up to 50%. Erythromycin residues (ERs) may be underestimated if its residues are only assessed by extractable residues. We recommend to include a practical silylation procedure to quantify Type I BRs in regular erythromycin residue monitoring, which can be used as signal of the need to initiate further laboratory BRs experiments. The degradation of erythromycin was mainly attributed to soil microorganisms, which promote erythromycin mineralization and lead to the re-release of BRs. Microbial analysis showed that erythromycin persisted longer in soils with lower microbial diversity and richness. Erythromycin at 2.5 mg kg showed no significant impact on soil microbial diversity in all treatments, but caused changes in soil community composition. This study provides a reference for scientific evaluation and pollution remediation of erythromycin in soils.