The relevance of non-relevant metabolites from plant protection products (PPPs) for drinking water: The German view

Non-relevant metabolites are those degradation products of plant protection products (PPPs), which are devoid of the targeted toxicities of the PPP and devoid of genotoxicity. Most often, non-relevant metabolites have a high affinity to the aquatic environment, are very mobile within this environment, and, usually, are also persistent. Therefore, from the point of drinking water hygiene. they must be characterized as relevant for drinking water like many other hydrophilic/polar environmental contaminants of different origins. Non-relevant metabolites may therefore penetrate to water sources used for abstraction of drinking water and may thus ultimately be present in drinking water. The presence of non-relevant metabolites and similar trace compounds in the water cycle may endanger drinking water quality on a long-term scale. During oxidative drinking water treatment, non-relevant metabolites may also serve as the starting material for toxicologically relevant transformation products similar to processes observed by drinking water disinfection with chlorine. This hypothesis was recently confirmed by the detection of the formation of N-nitroso-dimethylamine from ozone and dimethylsulfamide, a non-relevant metabolite of the fungicide tolylfluanide. In order to keep drinking water preferably free of non-relevant metabolites, the German drinking water advisory board of the Federal Ministry of Health supports limiting their penetration into raw and drinking water to the functionally (agriculturally) unavoidable extent. On this background, the German Federal Environment Agency (UBA) recently has recommended two health related indication values (HRIV) to assess non-relevant metabolites from the view of drinking water hygiene. Considering the sometimes incomplete toxicological data base for some non-relevant metabolites, HRIV also have the role of health related Precautionary Values. Depending on the completeness and quality of the toxicological evaluation of a non-relevant metabolite, its HRIV is either set as 1.0 mu g/l (HRIV(a)) or as 3.0 mu g/l (HRIV(b)) for lifelong exposure. In case a HRIV Would be exceeded, UBA recommends to keep on a Precautionary action Value (PAV) of 10 mu g/l for each non-relevant metabolite. The HRIV(b) is similar to the maximal Value derived by application of the TTC-concept for Cramer Class III (4.5 mu g/l). The HRIV(a) and the PAV are similar to values in the EU-guidance document for assessing non-relevant metabolites in ground water, with the important difference that the drinking water PAV is not intended to be tolerated for permanent exposure. Drinking water containing non-relevant metabolites below the respective HRIVs can also be considered as being sufficiently protective against toxicologically relevant oxidative transformation products which may be formed from non-relevant metabolites during drinking water treatment with ozone. However, even drinking water where one or several non-relevant metabolites are detected above substance-specific HRIVs is suited for human consumption without health risks. Only in special cases (relatively high non-relevant metabolite - concentrations), it could be indicated to examine the finished water for transformation products after treatment with ozone if there are no further treatment steps to eliminate or degrade polar compounds. UBA's non-relevant metabolite-Recommendation from April 2008 was positively picked LIP in 2009 by four important stakeholders in the domain of drinking water management as part of a voluntary cooperation agreement. The aim of such cooperation is to limit the transport of non-relevant metabolites into the drinking water to the functionally (and agriculturally) unavoidable extent and insofar to meet special precautionary demands. (C) 2009 Elsevier Inc. All rights reserved.