An application of a decision tree for assessing effects from exposures to multiple substances to the assessment of human and ecological effects from combined exposures to chemicals observed in surface waters and waste water effluents

The decision tree was used to evaluate human health and ecological effects from the combined exposure to 559 mixtures of substances measured in surface waters and effluents. The samples contained detectable levels of 2 to 49 substances. The key findings were, 1) the need for assessments of the combined exposures varied for ecological and human health effects and with the source of the monitoring data, 2) the majority of the toxicity came from one chemical in 44% of the exposures (human health) and 60% of exposures (ecological effects), 3) most cases, where risk from combined exposures was a concern, would have been identified using chemical-by-chemical assessments. Finally, the tree identified chemicals where data on the mode of action would be most useful in refining an assessment.The decision tree provided useful information on the need for combined risk assessments and guidance on the questions that should be addressed in future research.Humans and ecological receptors are continuously exposed to multiple chemicals; however, regulatory programmes have traditionally focused on regulating chemicals on a chemical-by-chemical basis. As a result, there is a concern that instances may occur where individual chemicals do not cause adverse effects but the combined effects of the exposures could pose a risk to human health and the environment. Such risks would not be detected in a chemical-by-chemical approach. In response to this concern, a number of organizations have investigated the issue of combined exposures to multiple chemicals [1-5].The Mixtures Industry Ad-hoc Team (MIAT) was created by the European Chemical Industry Council (Conseil Européen des Fédérations de l'Industrie Chimique, CEFIC) to address the issues associated with combined exposures to multiple chemicals. In 2010 the MIAT began the development of a decision tree for combined exposures to chemicals (hereafter referred to as the “decision tree”). The decision tree was based on concepts taken from a nu