Toxicity measurements in concentrated water samples : evaluation and water samples

The National Institute for Public Health and the Environment, together with the Centre of Water Management, developed a method to measure the effects of toxic substances in surface water. This method can be used to find out if, when ecological targets following from the European Water Framework Directive are not met, this is caused by toxic substances. The method can also be used to identify sources of toxic substances. Traditionally, mainly chemical techniques are applied for these purposes, but the disadvantage is that they do not cover the large amounts of chemicals potentially present in surface waters. The method uses bioassays. For this purpose, the response of five species in the water under investigation is studied. If a response is found, the substances causing this can be identified (if desired). The method enables to investigate the combined effects of substances (synergistic or antagonistic). Another advantage can be achieved by sample pre-treatment with a resin, allowing to concentrate the toxic substances. This way acute tests can be used instead of chronic test (which are more expensive) even if no acute effects can be found in the original (not concentrated) sample. In addition, natural factors that influence the toxicity of surface water do not disturb the method after this pre-treatment. Unfortunately, the toxicity of metals can not be investigated with this method.