Development of tools for assessing genotoxicity: Science Report – SC030102/SR

Background In addition to the measurement of sets of single-substance standards, known as Environmental Quality Standards (EQSs), or Environmental Assessment Levels (EALs), the aqueous environment is protected by measurements of biological effect. Ecotoxicological tests and bioassays are also employed to determine the toxic hazard posed by chemicals and environmental samples. The Environment Agency currently uses such tests within its Direct Toxicity Assessment (DTA) programme to set toxicity targets for selected effluent discharges to surface waters. Aims and objectives A limitation of DTA tests and bioassays is that they usually measure acute toxicity and lethality and, as such, provide little information regarding sub-lethal biological effects, particularly at the genetic level. This report presents the results of a series of research and development studies, which aimed to coordinate laboratory and field exposure studies between the Environment Agency and the University of Plymouth. Conclusions and recommendations Investigations were carried out to assess the potential for biomarkers of genotoxicity to be applied in association with currently employed DTA methods in the same target species. The conclusions and recommendations from this report are as follows: • The chromosome aberration (CAb) assay was successfully developed and validated against reference mutagens in the embryo-larval stages of the Pacific oyster, Crassostrea gigas. • The CAb assay was successfully applied to test the genotoxic potential of whole effluents and sediment elutriates using the embryo-larval stages of C. gigas. • As a method for routine monitoring of environmental samples, the CAb assay is somewhat laborious compared with some DTA methods. In addition, fully trained and experienced staff are required to observe and analyse the chromosomes. This restricts the testing of numerous water samples for genotoxic potential. But compared with other methods (Ames and GreenScreen® assays), it appeared to be the most sensitive in terms of detecting genotoxicity. • The induction of metallothionein, inhibition of acetylcholine esterase activity, and ferric reducing antioxidant power may be useful measures of sub-lethal biological effects. Further optimisation and validation is required for these methods in Arenicola marina. Cause–effect relationships can only be extrapolated with additional inter-discipline data. • Initial results indicate that other methods for detecting genotoxic effects such at the Comet assay can be applied in species such as A. marina. Application of this method requires further optimisation and validation.