Effects Of Antibiotics On Degradation Of Estrone And Its3-Sulfate Salt In Animal Manure And Natural Water

Steroid estrogens are typical endocrine-disrupting compounds (EDCs) in the environment, and can adversely affect the endocrine system of fish and other wildlife at low concerntrations. Steroid estrogens are excreted from the human and animals mainly in urine as conjugates, including sulfate and glucuronate salts. The urine is usually mixed with manure in animal feeding operation, therefore large amounts of estrogen conjugates are present in the animal manure. Atibiotics are extensively used for treatment of anamial diseases and as animal growth promoter. Only a minority of the antibiotics fed to animals remains in the animal body, and the majority is excreted in the form of parent antibiotics or their metabolites. When the manure is used as fertilizer, the estrogens and antibiotics will enter soil and probably natural water. Due to the incomplete remowal in sewage treatment plants, estrogen conjugates and antibiotics occur always in the effluent, which will also contaminate the receving water. Therefore it is important to study the fate of estrogen conjutates in the manure and natural water.However, because of the complexity of environmental matrixes, time-consuming pre-treatments of samples are usually required to reduce the interference of the matrixes. The limitation of detection methods also leads to higher pollutant concentrations used in the laboratory experiments than that in the real environment, therefore, it is difficult to reflect the real environmental fate of estrogen conjugates.14C-labelled radioisotope technology can not only locate estrogen conjugates and their degradation products in complex environment samples, but also reduce the concentration used in the experiments, and is therefore essential in studies on the environmental fate of estrogen conjugates. I synthesized three14C-labelled estrogen conjugates, i.e.,14C-estrone-3-sulfate potassium salt (14C-E1-3S),14C-17β-estradiol-17-sulfate potassium salt (14C-E2-17S), and14C-17β-estradiol-3,17-sulfate potassium salt (14C-E2-3,17S), using14C-estrone and14C-17β-estradiol as precursors. The radiochemical purity of the radioactive products were all>98%. The14C-labelled estrogen conjugates provide possibilities for studying their fate in the environment.I studied the effects of antibiotics on the degradation of14C-E1-3S in the pig manure. The results showed that14C-E1-3S was degraded without mineralization.14C-E1was found as a primary metabolite, and another compound14C-X as a secondary metabolite which was more polar than14C-E1. Due to the complete degradation of14C-E1-3S before first sampling, the effects of antibiotics on the degradation of14C-E1-3S wre not able to be observed. I also studied the degradation of the primary metabolite C-E1in the manure. The results showed the presence of the polar metabolite14C-X. Erythromycin, sulfamethoxazole and oxytetracycline were able to inhibit the degradation at concentrations of both10ppm and100ppm. Streptomycin sulfate exhibited the inhibition at the concentration of10ppm, but it had almost no effect on the degradation when the concentration was increased to100ppm. The reason for this needs further studies.I also studied the fate of E1-3S and E1in natural waters, i.e., Xuanwu Lake and Qinhuai River water. The results showed degradation of E1-3S and E1, and the degradation rate was related to the water quality. E1-3S had almost no degradation in Xuanwu Lake water except for the treatment with0.5ppm streptomycin sulfate and degraded completely in the Qinhuai River water within5.5days. Oxytetracycline at1ppm could strongly inhibit the degradation of E1-3S in Qinhuai River water whereas1ppm streptomycin sulfate had only weak effect. E1degraded in both waters, but more rapid in the Qinhuai River water. Oxytetracycline and streptomycin sulfate could inhibit the degradation of El in Xuanwu Lake at20ppm, but they would facilitate the degradation at the later stage of experiment at concentrations of0.5ppm and5ppm. The degradation of El in Qinhuai River water was less affected by oxytetracycline and streptomycin sulfate at the concentration of1ppm.Future work should focus on the degradation mechanisms of estrogens and their conjugates, and the effect of different factors on the degradation process. Besides, the isolation and identification of microorganisms responsible for the degradation is also a research area in the future.