Use of biological assay systems to assess the relative carcinogenic hazards of disinfection by-products.

Abstract

Other workers have clearly shown that most, if not all, drinking water in the U.S. contains chemicals that possess mutagenic and/or carcinogenic activity by using bacterial and in vitro methods. In the present work, increased numbers of tumors were observed with samples of organic material isolated from 5 U.S. cities administered as tumor initiators in mouse skin initiation/promotion studies. Only in one case was the result significantly different from control. In studies designed to test whether disinfection practice contributes significantly to the tumor initiating activity found in drinking water mixed results have been obtained. In one experiment, water disinfected by chlorination, ozonation or combined chlorine resulted in a significantly greater number of papillomas when compared to nondisinfected water. In two subsequent experiments, where water was obtained from the Ohio River at different times of the year, no evidence of increased initiating activity was observed with any disinfectant. Analysis of water obtained at the comparable times of the year for total organic halogen, and trihalomethane formation revealed a substantial variation in the formation of these products. Considering the problems such variability poses for estimating risks associated with disinfection by-products, a model system which makes use of commercially obtained humic acid as a substrate for chlorination was investigated using the Ames test. Humic and fulvic acids obtained from two surface waters as well as the commercially obtained humic acid were without activity in TA 1535, TA 1537, TA 1538, TA 98 or TA 100 strains of S. typhimurium. Following treatment with a 0.8 molar ratio of chlorine (based on carbon) significant mutagenic activity was observed with all humic and fulvic acid samples. Comparisons of the specific mutagenic activity of the chlorinated products suggests that the commercial material might provide a useful model for studying health hazards associated with disinfection reactions by-products.

A toxicological evaluation of a fulvic and humic acids preparation

“…The results of our bacterial reverse mutation test are consistent with those of the majority of previous bacterial reverse mutation experiments on humic test items that had not been subjected to chemical disinfection [ 20 , [23] , [24] , [25] , [26] , [27] , [28] ]; however, Ueno et al explored the effects of ozonation on three different HA samples (one from peat, one from wastewater, and one from soil) in a bacterial reverse mutation test and observed differences in the mutagenic potential of each [ 22 ].…”

“…Due to the heterogeneous nature of humic substances, toxicological evaluation of a single specific substance has been considered inadequate for extrapolation to the group as a whole although efforts have been made to identify a suitable model substance [ [20] , [21] , [22] ]. As such, a number of toxicological investigations of humic substances of various origins have been published although, due to the natural occurrence of low levels of humic matter in surface waters, many of these were conducted in order to investigate the mutagenic potential of byproducts formed during disinfection of water supplies.…”

“…Indeed, chlorination, under conditions of decreasing pH and adequate HA and chlorine concentrations, of organic non-volatile substances contained in HA and FA is known to result in formation of compounds (such as mucochloric acid and 2,3,3-trichloropropenal) that are mutagenic in bacterial reverse mutation tests. However, in general, these studies have been negative with respect to humic substances that have not undergone disinfection, which were often included as control substances or investigated for other reasons [ 20 , [23] , [24] , [25] , [26] , [27] , [28] ].…”

A Multiple-Purpose Design Approach to the Evaluation of Risks From Mixtures of Disinfection by-Products*

“…Toxic eects from exposure to low-concentration environmental mixtures have not been found in animal studies 6,7 . Epidemiologic studies, on the other hand, of chlorinated drinking water exposures in humans suggest weak associations with bladder, rectal and colon cancer 8,9,10,11,12 and limited evidence of reproductive and developmental eects 13, 14, 15, 16 . There are a few studies available on de®ned mixtures of DBPs that show evidence of dose-additivity for hepatotoxicity in mice exposed to mixtures of THMs 17 and of synergistic activity by mixtures of HAAs for promotion of cancer 18 .…”

Molecular size distribution of dissolved organic matter in water of the Pearl River and trihalomethane formation characteristics with chlorine and chlorine dioxide treatments

“…The US Environmental Protection Agency (US EPA) has imposed more stringent regulations for DBPs in drinking water due to their suspected health impacts (e.g., toxic, carcinogenic, and mutagenic) to humans when ingested over an extended period of time [28][29][30]. Understanding the role of DOM characteristics in DBPs formation may provide insight to development of more effective solutions for their control during drinking water treatment and operations.…”