S1: In vitro and in vivo bioassays
In vitro and in vivo bioassays in environmental monitoring
Swiss Centre for Applied Ecotoxicology
Group Leader of the Aquatic Ecotoxicology Team
Current regulatory practises in monitoring of surface waters focus on setting environmental quality standards (EQS) for individual chemicals. These EQS signify concentrations of compounds that should not be exceeded in water or biota. At present, 45 compounds are regulated in this way at the level of the European Union (EU). In Switzerland, some 80 EQS have been developed by the Ecotox Centre and a large number of these EQS will soon be incorporated into Swiss legislation.
Monitoring water quality directly with organisms is an obvious and alternative monitoring strategy to EQS compliance checking – after all – EQS are mainly derived from toxicity data generated using single species. Such in vivo monitoring is implemented in a regulatory context in Germany for screening industrial effluents but not surface waters. Although in vivo water quality monitoring has high relevance it is also costly. Particularly with a shift of emphasis from acute to chronic toxicity, in vivo testing becomes more costly still. It is easier to detect acute toxicity in a 24 h fish test than to monitor reproductive injury in fish covering long time frames.
Ultimately, effects observed in organisms follow an adverse outcome pathway (AOP). For example, reproductive injury can be linked to a sequence of steps that started with a chemical triggering an initiating event. A well-known example for such an AOP are the receptor mediated effects of 17α-ethinylestradiol (EE2) that result in loss of reproductive output and intersex in fish. Knowledge on AOPs offers a way around in vivo testing, as e.g. receptor mediated effects can be easily verified using estrogen receptor transactivation assays. In vitro test results can then serve as a risk indicator of the final outcome, namely reproductive injury.
Implementing in vitro assays into monitoring offers several benefits – at the cost of losing some level of integration. In vitro tools require less sample and time and can be more easily standardised. They cover mixture effects and in some cases they are more sensitive than chemical analysis (e.g. EE2). These aspects support the implementation of in vitro tools in environmental monitoring. Depending on progress in the next few years, in vitro tools may be implemented for regulatory environmental monitoring purposes within the EU and Switzerland.