The effects of estrone and 17β-estradiol on microbial activity and bacterial diversity in an agricultural soil: Sulfamethoxazole as a co-pollutant

摘要

Estrogens and veterinary antibiotics (VAs) that are contained in animal excrements are spread into agricultural soil when using animal wastes on farmland. The impacts of VAs on soil health have already been well documented. However, there is limited knowledge regarding the influence of estrogens, particularly the combined effects of estrogens and VAs, on the soil microbial community. In this study, a short-term analysis (11 days) of the effect of the estrogens estrone and 17β-estradiol on soil microbial activity and on bacterial community structure was performed using a dehydrogenase activity (DHA) test and a PCR-denaturing gradient gel electrophoresis (DGGE) assay, respectively. Meanwhile, the potential influence of the VA sulfamethoxazole (SMX) as a co-pollutant on the effects of estrogens was examined. It was found that (1) estrone and 17β-estradiol biodegraded within hours in non-sterilized soil, even in the presence of up to 100 mg/kg SMX. (2) Estrone or 17β-estradiol alone markedly promoted soil DHA and stimulated the growth of partial bacteria strains, which were demonstrated as new or more intensive bands in DGGE profiles relative to the control treatment at the later incubation period. (3) The presence of SMX as a co-pollutant at concentrations of 10 and 100 mg/kg removed the stimulatory effects of estrogens on soil DHA and significantly reduced the DHA level to below the level of the untreated control. SMX also depressed the appearance of bacterial bands that were stimulated by estrone or 17β-estradiol alone. Moreover, the coexistence of SMX and estrogens induced additional bacterial bands, which may be tolerant strains. Overall, these results imply that the load of estrogens might serve as nutrient substances for soil microorganisms, whereas VAs as co-pollutants would cause a shift of these positive effects toward a significant threat to the natural soil microbial community. Therefore, the removal of VAs in animal waste is essential to ensure the safe use of animal waste in agricultural land.