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In order to secure a safe drinking water supply, the setting of tolerable/acceptable ceilings of drinking water hygiene is required with regard to xenobiotics resulting from several anthropogenic impacts. This is done in practice by using drinking water guidelines or standards as quantitative objectives. The list of the new EU Directive or the German drinking-water standards is limited to those parameters that have the highest relevance for drinking water quality; nitro compounds (NCs) are not regulated. Because other substances contained in water can also represent a hazard for human health, the German Drinking Water Ordinance clarifies that specific actions must be implemented if compounds other than those regulated appear at concentrations that may be a cause for concern regarding human health. NCs serve as intermediates for dyes, pharmaceuticals, and synthetic materials; they themselves are used as solvents, explosives, and pesticides. During their commercial production or from their use, they may be released to the environment and lead to a contamination of aquatic systems and thus also of drinking water resources. In practice, therefore, a need for assessment is frequently given for relevant NCs. For 19 nitro-, amino-, and aminonitroaromatics, nitramines, and nitrate esters health-based drinking water guide values have been derived. For toxicological evaluation and derivation of guideline values for the NCs of interest, the tolerable daily intake approach was used for chemicals exhibiting a threshold for toxic effects. This was done by using established tolerable body doses for humans based on an identified no-observed-adverse-effect level/low-observed-effect-level for the most sensitive indicator for toxicity. In the case of nonthreshold chemical substances, suitable estimates of excess lifetime cancer risk have been applied.

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Inorganic arsenic, which is extensively metabolised in humans into even more toxic methylated arsenicals, is a potent carcinogen, causing tumours of the skin, lung, urinary bladder, and other organs. It also induces a number of non-cancer effects. Consumption of drinking water highly contaminated by arsenic causes serious health problems in some countries in southeastern Asia, and arsenic poses problems for drinking-water safety world-wide. Existing risk assessments are based on epidemiological studies from regions with high exposure concentrations (in the mg/L range). It is a matter of debate whether these findings are useful at predicting arsenic-induced effects at low concentrations. In recent years numerous epidemiological studies on cancer and non-cancer effects of inorganic arsenic have been published. This work aims at reviewing recent toxicological and epidemiological data on inorganic arsenic with emphasis on effects at low exposure concentrations. Information obtained from epidemiological studies is supplemented with mechanistic data from in vitro and in vivo studies. Various modes of action for arsenic carcinogenicity are discussed. The information gathered was used to evaluate the reliability of existing cancer-risk assessments and to improve current assessments of non-cancer health effects. A tolerable daily dose, based on epidemiological studies on arsenic-induced skin disorders, is presented.