Pesticides in drinking water--a case study.

Pesticides occupy a unique position among chemicals found in drinking water, since they are deliberately used to control pests in agriculture and public health. They comprise a variety of compounds of various chemical properties (many of which being persistent in the environment), toxic potential, and mechanism of action. Safety assessment for drinking water is conducted by allocating health-based guidelines for exposure through this environmental medium. The tolerable daily intake (TDI) approach is used by WHO in the case of pesticides with assumed thresholds of effect, while low-dose extrapolation is used in the case of non-threshold carcinogens. Risk management, however, can also be based on the precautionary principle. Risk assessment evaluates the risk emanating from a given exposure on the basis of all available data.