Toxicity measurements in concentrated water samples - Rivm

major factor for deviation of the desired ecological quality. This does not imply that a good ecological
status will be reached with reducing toxicity. Ecological quality can be influenced by many stressors,
like pH, eutrophication or hydromorphology (Heugens et al., 2001). The eco-epidemiological approach
is a promising technique to discriminate the role of toxicants from other potential stressors (De Zwart,
2005).
Although bioassays can be useful additionally to surveillance monitoring, it is expected that it won’t be
used that way within short notice within the WFD. For the first period until 2015, monitoring programs
have already been made and additional research will only increase monitoring costs. Within operational
monitoring, bioassays can be useful to monitor the biological effectiveness of measures. Operational
monitoring is used for locations where problematic substances are known, which have to be monitored
chemically. Bioassays can only be used additional to the chemical monitoring, so in that case the
surplus value will be small.
8.4.3 WEA application
Whole Effluent Assessment is an effect-based method to judge the environmental effect of effluents.
As presented in section 7.3, this method can be used to identify the sources for toxic effects. It can also
be used to investigate to what extend an effluent causes toxic effects within a water system. Which
bioassays should be used and how the sample should be concentrated depends on the type of substances
expected. More specific concentrations techniques and bioassays can be used for specific substance
groups, and can be interpreted with simpler techniques. The presented bioassays in this report do not
cover all toxic modes of action. The concentration technique presented in this report works rather well
for narcotic substances, but can have restrictions for other type of substances. Especially for upcoming
substances, new techniques are necessary and are studied at the moment (e.g. antibiotics).
8.5 Conclusions
- The presented method can partially provide information on effects of substances on organisms;
- For specific purposes, a simple setup with a limited set of bioassays and a simple interpretation
method gives sufficient information on problems and their causes in water systems;
- For an ecologically relevant approach, the method should be extended with other representative
test organisms and more sensitive methods.
The presented method is useful for monitoring goals and setting priorities in water quality
management, although it should be taken into account that the presented method is not suitable for all
type of substances possibly present in the ecosystem. Investments in new extraction methods are useful,
especially for more polar and new substances, because these types of substances are increasingly
relevant for the environment.
Demonstrating relevant ecological risks will especially be useful for WFD purposes. Water managers
will be able to demonstrate whether the presence of toxic substances influences the Good Ecological
Status and to what extend toxic substances will harm the ecosystem.
In addition, the presented method is suitable for diagnosis and is a solid ground for considering
measures.
RIVM Report 607013010 97