Reproductive risks from contaminants in drinking water.

Reproductive toxicity is a complex subject which, besides birth defects or sterility, includes adverse effects which may be less readily observed but more relevant to chronic low-level exposures (e.g., impaired functional development of target organs or systems, secretion of toxic chemicals in maternal milk). Sodium chlorite, when present at high concentration, may be related to impaired reproduction; among water chlorination by-products, further research is required on the developmental toxicity of chloroacetic acid and dichloro- and trichloro acetonitrile. Among the water pollutants which may pose significant developmental hazards, risk assessments have been performed for nitrates/nitrites, fluorides and lead. Molinate (a herbicide), dibromochloropropane (a nematocide) and the halogenated contaminants ethylene dibromide and epichlorohydrin show an almost selective male reproductive toxicity, although they are likely to pose a risk mainly at occupational exposure conditions. Ethylene thiourea, an environmental metabolite of some fungicides is markedly teratogenic in the rat: however, other toxic effects are induced at levels of exposure significantly lower than the teratogenic ones. Such poorly water-soluble compounds as TCDD or hexachlorobenzene also need to be considered, because of their remarkable potentials for reproductive toxicity. Finally, it should be noted that the data on reproductive toxicity for a number of chemicals do not allow a risk assessment at present: this holds true also for some substances which might pose concerns on the basis of their levels in drinking water (e.g. tetrachloroethylene, nickel). Another area which deserves more attention is the investigation of the possible interactions of several contaminants present together at low levels.