The genotoxic hazards of domestic wastes in surface waters

Despite the noteworthy genotoxic potency of many industrial wastewaters, the genotoxic hazard posed to the downstream ecosystem and its associated biota will be determined by genotoxic loading. Municipal wastewaters, although ranking low in potency, can achieve loading values that are several orders of magnitude greater than those of most industries. Although these wastewaters are generally mixtures of wastes from several different sources, the volumetric proportion of the daily discharge that is of industrial origin rarely exceeds 30%. Genotoxicity calculations for the Montreal Urban Community (MUC) municipal wastewater treatment facility indicate that over 90% of the genotoxic loading (31.1 kg benzo(a)pyrene equivalents per day) is nonindustrial in origin. Moreover, a mass balance of surface water genotoxicity for St. Lawrence river at Montreal indicates that over 85% of the total contributions from the Montreal region are nonindustrial in origin. Additional calculations for the Great Lakes, and other rivers throughout the world, provide further support of a strong relationship between surface water genotoxicity and population. Despite some information about physical/chemical properties, the identity of the putative genotoxins in municipal wastewaters and surface waters remains a mystery. Likely candidates include potent genotoxins, such as N-nitroso compounds and aromatic amines, known to be present in human sanitary wastes, as well as genotoxic PAHs known to be present in many municipal wastewaters. Calculations based on literature data indicate that human sanitary wastes may be able to account for a substantial fraction (4-70%) of the nonindustrial loading from municipal wastewaters. Similar calculations suggest that pyrogenic PAHs that enter municipal wastewaters via surface runoff can only account for a small fraction (<5%) of the genotoxic loading values discussed.