BTO rapport - BTO 2017.008

Effect-based monitoring with bioassays-a roadmap


There is growing support for the implementation of in vitro bioassays, parallel to chemical analyses, in the context of (drinking) water quality monitoring. Clear advantages to include in vitro bioassays is the provided insight in the risks associated with exposure to complex low-level mixtures of pollutants in water. This report describes the state-of-the-art for different crucial steps in the selection, implementation and interpretation of in vitro bioassays for chemical water quality monitoring in the context of human health related risks and drinking water production, and proposes clear procedures and protocols. These steps are illustrated by a case study concerning application of the ToxTracker assay.
A plethora of in vitro bioassays is available that can be used to test effects on different biological processes and in different types of models. The most relevant toxicological endpoints considered in this perspective are carcinogenesis, adverse effects on reproduction and development, effects on xenobiotic metabolism, modulation of hormone systems, reactivity and adaptive stress responses. Only few in vitro bioassays to study mechanisms related to effects on reproduction and development are available. A scoring matrix has been designed to evaluate (candidate) bioassays for their applicability and performance, including the coverage of different toxic mechanisms, cost-effectiveness, performance (sensitivity with regard to realistic environmental mixtures of chemicals in low concentrations, reproducibility), possibilities for high-throughput and ease of implementation with regard to laboratory requirements or specialist knowledge. Data for a list of reference chemicals could be shared in a database to allow comparisons between in vitro bioassay methods. Further miniaturization and automation may allow a more efficient collection and connection of analytical chemistry and bioassay information. Also, the impact of different SPE approaches on the presence of different (types of) chemicals in the concentrate needs to be more firmly established as it is known that different types of chemicals behave differently in SPE extraction.
Due to the high sensitivity of in vitro bioassays, responses can be expected (far) below exposure concentrations that are relevant for human health. Effect-based trigger values are therefore needed for bioassay interpretation. Different approaches are currently being followed including trigger values based on relative ecotoxicity potency, health-based threshold values for chronic exposure in humans and kinetics of reference chemicals, and
read-across from guidelines. It is important that trigger values are sufficiently but not too
conservative, to serve as indicators of potential health effects. Mechanistic manners of interpreting in vitro bioassay data based on the link between cellular and molecular effects in vitro and potentially associated adverse outcomes in the intact organism are expected to become feasible in the (near) future. It is expected that a common understanding of crucial steps in the selection, implementation and interpretation of in vitro bioassays including clear procedures and protocols, will facilitate legal embedding in the context of water quality monitoring for drinking water production. To support a statutory basis for the legal implementation of in vitro bioassays, it is recommended that an overview of effect- monitoring data is collected in a national database.

Een stappenplan beschrijft de selectie en evaluatie van in vitro bioassays voor de chemische waterkwaliteit, dat verder ontwikkeld kan worden tot een standaardprotocol om de prestaties en toepasbaarheid van nieuwe kandidaat in vitro bioassays empirisch te testen. Daarmee kan de toegevoegde waarde van nieuwe bioassays gestructureerd worden vergeleken met analysemethoden die al in gebruik zijn. In vitro bioassays vormen een waardevolle aanvulling op de analytische chemie bij het beoordelen van de chemische waterkwaliteit omdat ze op een efficiƫnte manier inzicht geven in het gezamenlijke effect van mengsels microverontreinigingen. Omdat er veel verschillende in vitro bioassays beschikbaar zijn, is gestructureerde selectie van groot belang. Voor dit onderzoek is een verkennende studie met de ToxTracker assay voor genotoxiciteit uitgevoerd.

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