Effects of ozonated sewage effluent on reproduction and behavioral endpoints in zebrafish (Danio rerio)

Pharmaceutical residues and other micro-contaminants may enter aquatic environments through effluent from sewage treatment plants (STPs) and could cause adverse effects in wild fish. One strategy to alleviate this situation is to improve wastewater treatment by ozonation. To test the effectiveness of full-scale wastewater effluent ozonation at a Swedish municipal STP, the added removal efficiency was measured for 105 pharmaceuticals. In addition, gene expression, reproductive and behavioral endpoints were analyzed in zebrafish (Danio rerio) exposed on-site over 21 days to ozonated or non-ozonated effluents as well as to tap water. Ozone treatment (7 g O3/m3) removed pharmaceuticals by an average efficiency of 77% in addition to the conventional treatment, leaving 11 screened pharmaceuticals above detection limits. Differences in biological responses of the exposure treatments were recorded in gene expression, reproduction and behavior. Hepatic vitellogenin gene expression was higher in male zebrafish exposed to the ozonated effluent compared to the non-ozonated effluent and tap water treatments. The reproductive success was higher in fish exposed to ozonated effluent compared to non-ozonated effluent and to tap water. The behavioral measurements showed that fish exposed to the ozonated STP effluent were less active in swimming the first minute after placed in a novel vessel. Ozonation is a capable method for removing pharmaceuticals in effluents. However, its implementation should be thoroughly evaluated for any potential biological impact. Future research is needed for uncovering the factors which produced the in vivo responses in fish.