The combination of levonorgestrel and quinestrol (EP-1) has been shown to have anti-fertility effects on several wild rodents.Our previous report indicated that quinestrol (E) alone has a significant anti-fertility effect on male Brandts voles.In recent years,quinestrol has been used for fertility control of the plateau pika populations on the Qinghai–Tibet Plateau.However,the environmental safety and fate of this compound are not well known.We have assessed the environmental safety of quinestrol in farmland,steppe soil and freshwater in Qinghai province.Our results showed that the degradation of quinestrol follows first-order kinetics in soil and freshwater,with a dissipation half-life of approximately 16.0 days in local soil.Microbial activity in soil heavily influenced the rate of biodegradation of quinestrol.The half-life of quinestrol in neutral water (pH 7.4) was 0.75 h when exposed to UV light (l=365 nm) whereas it was 2.63 h when exposed to visible light (l>400 nm) .Our results indicate that quinestrol is fully degraded (i.e.its estrogenic activity is lost) ,in a relatively short time in the natural environment.However,more detailed examination of the ecological and environmental safety of this compound is required.