Degradation of streptomycin in aquatic environment: kinetics, pathway, and antibacterial activity analysis

Streptomycin used in human and veterinary medicine is released into the environment mainly through excretions. As such, its elimination in water should be investigated to control pollution. In this study, the degradation of streptomycin in water was studied, and the influence of variables, including light exposure, solution pH, temperature, ionic strength, dissolved organic matter (DOM), and coexisting surfactants, on degradation was investigated. Streptomycin degradation was consistent with the first-order model in aquatic environments. Its degradation rate under light exposure was 2.6-fold faster than that in the dark. Streptomycin was stable under neutral conditions, but it was easily decomposed in acidic and basic environments. Streptomycin degradation was enhanced by high temperature, and its half-life decreased from 103.4 days at 15 °C to 30.9 days at 40 °C. This process was also accelerated by the presence of Ca²⁺ and slightly improved by the addition of HA. Streptomycin degradation was suppressed by high levels of the cationic surfactant cetyltri- methylammonium bromide (CTAB), but was promoted by the anionic surfactant sodium dodecyl benzene sulfonate (SDBS). The main degradation intermediates/products were identified through liquid chromatography-mass spectrometry, and the possible degradation pathway was proposed. The antibacterial activity of streptomycin solution was also determined during degradation. Results showed that STR degradation generated intermediates/products with weaker antibacterial activity than the parent compound.