Epsilon Open Archive

Abstract

Pharmaceutical residues are not efficiently removed by current sewage treatment plant (STP) technologies. This allows for the release of pharmaceutical residues into the aquatic environment. Pharmaceuticals and their metabolites are problematic because they are designed to affect biological processes in non-target aquatic species. It is therefore of interest to limit the release of pharmaceutical residues in order to protect the surface water environment. One potential method for the improvement of sewage effluent treatment is ozonation, a technology capable of eliminating pharmaceutical residues.

This licentiate thesis aimed to evaluate the biological effects in adult and embryonic zebrafish, Danio rerio, exposed to ozonated effluent at a Swedish municipal STP outfitted with a full scale effluent ozonation step. Reproduction-related endpoints (e.g. fecundity and gonad maturation), behaviour and hepatic gene expression (e.g. vitellogenin) were sampled in fish exposed for 21 days. Responses in fish exposed to ozonated STP effluent diverged from fish exposed to the normal, non-ozonated STP effluent and tap water control. Firstly, they produced twice the amount of fertilized eggs and had a higher degree of gonadal maturation. Secondly, male hepatic vitellogenin gene expression was induced, indicating estrogenicity due to ozonation. Thirdly, fish exposed to the ozonated effluent effluent exhibited a stress-like behaviour.

While ozonation has proven to be very efficient in reducing pharmaceutical parent compound concentrations in STP effluents (on average 77% at Knivsta STP), much remains unclear regarding potentially toxic ozonated by-product (OBP) formation. Therefore, the second part of the thesis explored how zebrafish embryotoxicity of three pharmaceuticals of environmental relevance would be modulated by ozonation in a bench-scale ozonation study. Carbamazepine embryotoxicity increased following ozonation, possibly explained by formation of the OBP carbamazepine-epoxide. Furthermore, ozonation of oxazepam seemingly potentiated its anxiolytic mode of action in exposed zebrafish larvae. Diclofenac embryotoxicity was however completely abolished by ozonation.

The results presented in this thesis highlight the importance of new chemical and toxicological knowledge regarding the formation of OBPs in post-ozonated effluents.