Methodology for Evaluating the Genotoxicity of Hazardous Environmental Samples

Combining Different In Vitro Bioassays to Evaluate Genotoxicity of Water-Accommodated Fractions from Petroleum Products

Genotoxicity assessment is of high relevance for crude and refined petroleum products, since oil compounds are known to cause DNA damage with severe consequences for aquatic biota as demonstrated in long-term monitoring studies. This study aimed at the optimization and evaluation of small-scale higher-throughput assays (Ames fluctuation, micronucleus, Nrf2-CALUX^®) covering different mechanistic endpoints as first screening tools for genotoxicity assessment of oils. Cells were exposed to native and chemically dispersed water-accommodated fractions (WAFs) of three oil types varying in their processing degree. Independent of an exogenous metabolic activation system, WAF compounds induced neither base exchange nor frame shift mutations in bacterial strains. However, significantly increased chromosomal aberrations in zebrafish liver (ZF-L) cells were observed. Oxidative stress was indicated for some treatments and was not correlated with observed DNA damage. Application of a chemical dispersant increased the genotoxic potential rather by the increased bioavailability of dissolved and particulate oil compounds. Nonetheless, the dispersant induced a clear oxidative stress response, indicating a relevance for general toxic stress. Results showed that the combination of different in vitro assays is important for a reliable genotoxicity assessment. Especially, the ZF-L capable of active metabolism and DNA repair seems to be a promising model for WAF testing.

Toxicological evaluation of complex industrial wastes: implications for exposure assessment

We evaluated a variety of short-term bioassays to construct a battery of tests that could be used for assessing the biological effects of potentially hazardous complex industrial wastes. Ten samples were studied for hepatotoxicity; these samples and an additional 5 were studied for mutagenicity. Although the data are limited to these samples, the results suggest that the Salmonella assay (strain TA98) or a prophage-induction assay (both in the presence of S9) in combination with determination of relative liver weight and levels of a set of serum enzymes in rats may provide a battery of tests suitable to characterize complex industrial wastes for mutagenic and hepatotoxic potential. The biological activities exhibited by the wastes were not readily predicted by the chemical profiles of the wastes, emphasizing the importance of characterizing potentially hazardous complex industrial wastes by both chemical and biological means. DNA from liver, lung and bladder of rats exposed to some of the wastes was analyzed by the 32P-postlabeling technique for the presence of DNA adducts. A waste that produced mutagenic urine produced a DNA adduct in bladder DNA. The implications of this approach for assessment of exposure to complex hazardous waste mixtures are discussed.

Toxicity of complex waste mixtures: a comparison of observed and predicted lethality

The ability to predict the biological effect of complex waste mixtures from chemical characterization data was examined by comparing observed mortality to that predicted by a mathematical additivity model with literature LD50 values for the chemicals identified in the mixtures. Male F344 rats were exposed by gavage to 1 of 10 samples of complex industrial waste. Seven of the 10 waste samples caused death within 24 h of administration at dosages ranging from 1 to 5 ml/kg body weight. Two of the 7 lethal waste samples produced 100% mortality at a dosage of 2.5 ml/kg; another 2 waste samples produced 100% mortality at 5 ml/kg. The partial chemical analysis, although providing more extensive information on chemical composition than might normally be available for most complex waste mixtures, was not sufficient to distinguish lethal from nonlethal waste samples or to indicate lethal potency. Possible explanations for the apparent inability to predict readily lethality from the chemical characterization data include the possible inappropriateness of an additivity model due to the presence of interactions, such as synergism or antagonism; the kinetics of chemical absorption, distribution, and elimination, which may be affected by administration of the chemical in a complex matrix; and the presence of unidentified chemicals in the mixture that may have contributed to the observed toxicity.

Mutagenicity in salmonella of hazardous wastes and urine from rats fed these wastes

15 hazardous industrial waste samples were evaluated for mutagenicity in the Salmonella plate-incorporation assay using strains TA98 and TA100 in the presence and absence of Aroclor 1254-induced rat liver S9. Dichloromethane/methanol extracts of the crude wastes were also evaluated. 7 of the crude wastes were mutagenic, but only 2 of the extracts of these 7 wastes were mutagenic; extracts of 2 additional wastes also were mutagenic. In addition, 10 of the crude wastes were administered by gavage to F-344 rats, and 24-h urine samples were collected. Of the 10 raw urines evaluated, 3 were mutagenic in strain TA98 in the presence of S9 and beta-glucuronidase. The 3 crude wastes that produced these 3 mutagenic urines were, themselves, mutagenic. Adequate volumes of 6 of the 10 raw urines were available for extraction/concentration. These 6 urines were incubated with beta-glucuronidase and eluted through Sep-Pak C18 columns; the methanol eluates of 3 of the urines were mutagenic, and these were the same 3 whose raw urines also were mutagenic. In general, the C18/methanol extraction procedure reduced the cytotoxicity and increased the mutagenic potency of the urines. To our knowledge, this is the first report of the mutagenicity of urine from rodents exposed to hazardous wastes. Based on the present results, the use of only strain TA98 in the presence of S9 might be adequate for general screening of hazardous wastes or waste extracts for genotoxicity. The urinary mutagenesis assay does not appear to be a useful adjunct to the Salmonella assay for screening hazardous wastes. The problems associated with chemically fractionating diverse types of hazardous wastes for bioassay are also discussed.

Use of limited protocols to evaluate the genotoxicity of hazardous wastes in mammalian cell assays: comparison to Salmonella

Dichloromethane extracts of four diverse hazardous wastes (coke plant, herbicide manufacturing, pulp and paper, and oil refining) were evaluated for mutagenicity in strains TA98 and TA100 of Salmonella. These extracts also were tested for biological activity in short-term mammalian cell assays, including mutagenicity in L5178Y/TK +/- mouse lymphoma cells, chromosomal aberrations and sister chromatid exchanges in Chinese hamster ovary (CHO) cells, morphological transformation in BALB/c-3T3 cells, and teratogenic potential in mouse limb bud cells. The mammalian cell assays were performed using limited protocols that consisted of a preliminary testing of the extracts for cytotoxicity in CHO cells in order to estimate the appropriate dose range for the other assays. These assays were then performed once with only a few doses of extract; all but the mouse limb bud assay were performed in the presence of metabolic activation. Although all four of the wastes were presumptively positive for either mutation or cytogenetic effects, none of the wastes transformed BALB/c-3T3 cells. Further studies are needed to establish which mammalian cell assays, if any, might be useful complements to the Salmonella assay for the purpose of screening hazardous wastes.

Mutagenicity of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in the granuloma pouch assay

The rat granuloma pouch assay was used to assess the in vivo mutagenic potential of 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ), a heterocyclic aromatic amine which is formed during the frying of meat and broiling of fish. The assay was performed with and without pre-induction by Aroclor. In the initial experiment IQ was injected directly into the pouch of non-induced rats. A 10-fold increase in mutation frequencies was obtained with the 2.0 mg/pouch dose of IQ with uninduced cell populations. In a second study IQ was injected intraperitoneally and into the pouch of rats that had been pre-induced with Aroclor. The dose of IQ administered varied from 0.1 to 2.0 mg/pouch. A 10-fold increase in mutation frequencies was obtained with the 2.0 mg/pouch dose of IQ with uninduced cell populations. Aroclor treatment produced no significant increase in mutation frequencies over uninduced animals. Its mutagenic effect is about 10-fold weaker than that of benzo[a]pyrene or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG).