Chronic bioassays of chlorinated humic acids in B6C3F1 mice.

Abstract

Humic acids (Fluka), chlorinated to carbon:chlorine (C:Cl) ratios of 1:1 and 1:0.3, were administered to B6C3F1 mice, 50 males and 50 females per group, in the drinking water at a total organic carbon (TOC) level of 0.5 g/L. The mice were 6 to 8 weeks old at the beginning of the bioassays. The doses used were based on short-term (8 weeks) evaluations for toxicity, palatability, and weight gain. The chronic bioassays included the following control groups: unchlorinated humic acids (0.5 g/L), no-treatment (100 males and 100 females), dibromoethane (DBE, 2.0 mM in drinking water; positive control) and 0.44% sodium chloride in drinking water, i.e., at the same concentration as those receiving chlorinated humic acids. The chlorinated humic acids were prepared freshly and chemically assayed once per week. All chemicals were, with the exception of DBE, administered for 24 months; DBE was administered for 18 months. The volumes of solutions consumed were measured once weekly. All treatment groups showed normal weight gain except the DBE group. At the completion of exposure, the animals were sacrificed and necropsied, and tissue sections were taken for histopathology. No markedly significant increases in tumor incidences were evident in any of the organs and tissues examined in the chlorinated humic acid groups compared to unchlorinated humic acids and the no-treatment control groups. DBE caused the expected high incidence of squamous carcinomas of the forestomach. The chlorinated humic acids tested contained direct-acting alkylating agents, based on their reactivity with p-nitrobenzylpyridine (PNBP), and showed mutagenic activity in S. typhimurium.

Modulating effects of humic acids on genotoxicity induced by water disinfectants in Cyprinus carpio

“…The present results are also in agreement with those obtained from in situ plant genotoxicity tests, where clear clastogenic/aneugenic effects of NaClO-and ClO 2 -disinfected surface waters were reported in different monitoring seasons [22]. Mutagenic activity induced by chlorinated humic acid compounds was also shown in bacteria [52,1,2]. On the other hand, the Comet assay did not detect any significant increase or decrease in DNA migration.…”

“…In view of the possible relevance of the results in relation to drinking-water consumption, we tested the disinfectants at low concentrations: the highest concentration employed (0.2 ppm) corresponds to the maximum free disinfectant residue adopted in surface water disinfection experiments [18,22]. The humic acids concentration (0.1 ppm) was chosen to obtain a 1:0.32 molar-ratio C:Cl for the highest NaClO concentration and a 1:0.08 molar-ratio for the lowest concentration (0.05 ppm), so as to achieve almost complete reaction of chlorine with organic carbon, according to carcinogenicity/mutagenicity studies [4,52,53].…”

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 ].…”

“…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] ].…”

Vascular Effects of Chronic Arsenic Exposure: A Review

“…Since no control mice were used, no conclusion of causality can be drawn from this study. In a much larger series of 300 mice exposed to humic acids in their drinking water for 24 months, gangrenous changes were not reported (40).…”