Assessment and mitigation of the risk of transformation products in drinking water
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Toxicological risk assessment is an important tool to ensure the quality of our drinking water. Pesticides that are widely used in agriculture are especially of concern as they leach into surface- and groundwater which is used for the production of drinking water. An additional problem is the transformation of the active substances of pesticides during the water treatment process. This transformation may lead to exposures to newly formed transformation products that are not considered in conventional risk assessments. In this research, a literature study provides an overview of tiered risk assessments that give an insight on how to assess human and animal health risks of transformation products. In addition, methods to derive water quality guidelines for humans and livestock are investigated as these guidelines can help to reduce the exposure to toxic chemicals. The specific focus was on guidelines for livestock, because there are no official regulations for drinking water quality for livestock as there are for humans. As a result, five main methods have been identified that are used in tiered risk assessments for pesticide products, namely: toxicity testing, threshold of toxicological concern (TTC), quantitative structure-activity relationship (QSAR), hazard quotient (HQ) and species sensitivity distribution (SSD). For the derivation of water quality guidelines two main methods are identified. The tolerable daily intake (TDI) approach (for humans and livestock) and the TTC approach (only for humans). For the assessment of transformation products seemed the TTC approach and the use of QSARs most suitable as they are relatively simple methods that do not need toxicity data. When a chemical is identified as a risk, establishing drinking water quality guideline values can help to mitigate the risk for both humans and animals.