Chemical and biological characterization of hazardous industrial waste. I. Prokaryotic bioassays and chemical analysis of a wood-preserving bottom-sediment waste

The mutagenic hazards of aquatic sediments: a review

Sediments are the sink for particle-sorbed contaminants in aquatic systems and can serve as a reservoir of toxic contaminants that continually threaten the health and viability of aquatic biota. This work is a comprehensive review of published studies that investigated the genotoxicity of sediments in rivers, lakes and marine habitats. The Salmonella mutagenicity test is the most frequently used assay and accounts for 41.1% of the available data. The Salmonella data revealed mutagenic potency values for sediment extracts (in revertants per gram dry weight) that spans over seven orders of magnitude from not detectable to highly potent (10(5) rev/g). Analyses of the Salmonella data (n=510) showed significant differences between rural, urban/industrial, and heavily contaminated (e.g., dump) sites assessed using TA98 and TA100 with S9 activation. Additional analyses showed a significant positive correlation between Salmonella mutagenic potency (TA98 and TA100 with S9) and PAH contamination (r2=0.19-0.68). The second and third most commonly used assays for the analysis of sediments and sediment extracts are the SOS Chromotest (9.2%) and the Mutatox assays (7.8%), respectively. These assays are frequently used for rapid initial screening of collected samples. A variety of other in vitro endpoints employing cultured fish and mammalian cells have been used to investigate sediment genotoxic activity. Endpoints investigated include sister chromatid exchange frequency, micronucleus frequency, chromosome aberration frequency, gene mutation at tk and hprt loci, unscheduled DNA synthesis, DNA adduct frequency, and DNA strand break frequency. More complex in vivo assays have documented a wide range of effects including neoplasms and preneoplastic lesions in fish and invertebrate exposed ex situ. Although costly and time consuming, these assays have provided definitive evidence linking sediment contamination and a variety of genotoxic and carcinogenic effects observed in situ.

Toxicity assessment of complex mixtures remains a goal

One of the initial steps in remediating contaminated environments is to assess the human and ecological health risk associated with exposure to contaminants in a specific medium. Presented here are the results of a five-year study investigating the toxicity of simple and complex mixtures. A series of model compounds and simple mixtures including polycyclic aromatic hydrocarbons (PAHs), pentachlorophenol (PCP), and halogenated aliphatic hydrocarbons (HAHs) were analyzed. Mixture toxicity was studied using microbial genotoxicity assays and cytotoxicity assays with renal and neural cells. The majority of binary mixtures described here induced additive responses. A limited number of samples were identified where binary mixtures induced inhibitory effects. For example, benzo(a)pyrene (BAP) alone induced 30% renal cell death, whereas an equimolar dose of chrysene and BAP only produced 1.6% cellular death. In none of the mixtures tested did the mixture toxicity results deviate from the predicted results by an order of magnitude. The results from testing binary mixtures in this study indicate that the results did not deviate significantly from additivity. Complex mixture results were more difficult to interpret. The toxicity of complex mixtures could not be accurately predicted based on chemical analysis. This could be due to chemical interactions or due to the presence of unidentified chemicals, such as alkyl PAHs or high molecular weight PAHs that are not included in the standard risk assessment procedure. Even though the results from these in vitro studies indicate that additive assumptions will generally be appropriate for binary mixtures similar to the ones tested here, the risk associated with complex mixtures remains a challenge to predict. Before the results of toxicity testing can be used to adjust risk assessment calculations, it is important to fully appreciate the chemical composition and to understand the mechanism of observed chemical interactions in animals chronically exposed to low doses of chemical mixtures. This research was supported by ATSDR Grant no. ATU684505 and NIEHS SBRP Grant no. P42 ES04917.

Mutagens in contaminated soil: a review

The intentional and accidental discharges of toxic pollutants into the lithosphere results in soil contamination. In some cases (e.g., wood preserving wastes, coal-tar, airborne combustion by-products), the contaminated soil constitutes a genotoxic hazard. This work is a comprehensive review of published information on soil mutagenicity. In total, 1312 assessments of genotoxic activity from 118 works were examined. The majority of the assessments (37.6%) employed the Salmonella mutagenicity test with strains TA98 and/or TA100. An additional 37.6% of the assessments employed a variety of plant species (e.g., Tradescantia clone 4430, Vicia faba, Zea mays, Allium cepa) to assess mutagenic activity. The compiled data on Salmonella mutagenicity indicates significant differences (p<0.0001) in mean potency (revertents per gram dry weight) between industrial, urban, and rural/agricultural sites. Additional analyses showed significant empirical relationships between S9-activated TA98 mutagenicity and soil polycyclic aromatic hydrocarbon (PAH) concentration (r2=0.19 to 0.25, p<0.0001), and between direct-acting TA98 mutagenicity and soil dinitropyrene (DNP) concentration (r2=0.87, p<0.0001). The plant assay data revealed excellent response ranges and significant differences between heavily contaminated, industrial, rural/agricultural, and reference sites, for the anaphase aberration in Allium cepa (direct soil contact) and the waxy locus mutation assay in Zea mays (direct soil contact). The Tradescantia assays appeared to be less responsive, particularly for exposures to aqueous soil leachates. Additional data analyses showed empirical relationships between anaphase aberrations in Allium, or mutations in Arabidopsis, and the 137Cs contamination of soils. Induction of micronuclei in Tradescantia is significantly related to the soil concentration of several metals (e.g., Sb, Cu, Cr, As, Pb, Cd, Ni, Zn). Review of published remediation exercises showed effective removal of genotoxic petrochemical wastes within one year. Remediation of more refractory genotoxic material (e.g., explosives, creosote) frequently showed increases in mutagenic hazard that remained for extended periods. Despite substantial contamination and mutagenic hazards, the risk of adverse effect (e.g., mutation, cancer) in humans or terrestrial biota is difficult to quantify.

Neurotoxicity of polycyclic aromatic hydrocarbons and simple chemical mixtures

Polycyclic aromatic hydrocarbons (PAHs) are a major class of environmental pollutants. These chemicals are the products of incomplete combustion and are present in every compartment of the environment. While the carcinogenic potential of these chemicals has been investigated in numerous studies, very little is known about the potential of these chemicals to produce damage to neural cells. The objective of this study was to investigate the toxicity of several model PAHs and binary mixtures of these chemicals in neural cells. Chemicals tested included benzo[a]pyrene (BaP), chrysene, anthracene, and pentachlorophenol (PCP). Four end points, including amino acid incorporation, total protein, total cell count, and viable cells (trypan dye exclusion), were measured in SY5Y human neuroblastoma cells and C6 rat glioma cells. The most sensitive measure of PAH toxicity in neural cells was amino acid incorporation into proteins. BaP was the most toxic of all PAHs tested, and anthracene failed to produce a toxic response at any concentration tested. Without metabolic activation, BaP induced a significant cytotoxic response at a concentration of 30 microM. With activation (0.25% S9), BaP induced a response at concentration levels of 3 microM and 30 microM. Minimal toxicity was observed with chrysene at the highest concentration tested, and anthracene failed to produce a toxic response at any concentration tested. With mixtures of PAHs the majority of samples induced additive responses. The minimum concentration required to induce a significant response was reduced for the mixture of chrysene and BaP when compared to BaP alone. In addition, PCP appeared to increase the inhibition of acetylcholinesterase by mipafox. The data suggest that PAHs are capable of producing damage to neural cells only at concentrations that are near their solubility limits.

Multi-bioassay approach for assessing the potency of complex mixtures of polycyclic aromatic hydrocarbons

The chick embryotoxicity screening test (CHEST) and the Salmonella/microsome bioassay were used to evaluate embryotoxic and mutagenic endpoints from crude coal tar (CT) and its fractionated polycyclic aromatic hydrocarbon (PAH) mixtures (designated as A, B, C, D and E). In the CHEST assay, CT and PAH mixtures were injected into the egg yolk. A dose-dependent increase in embryo mortality was observed for all fractions. The E fraction resulted in 47% embryo mortality at a dose of 0.125 mg/kg and was more toxic than CT. At a dose of 1 mg/kg, 85-100% embryonic deaths occurred in fractions C and D and these two fractions were more potent than fractions A and B. The main visual toxic manifestations were liver lesions, discoloration of the liver, and edema. Both CT and fractionated PAH mixtures were also tested in the Salmonella/microsome plate incorporation assay with Salmonella typhimurium strain TA98 and were evaluated with and without metabolic activation at five dose levels. In the presence of S9, the CT and fractions C, D and E induced a dose-dependent positive response. Results from the Salmonella/microsome assay were in good agreement with findings from the CHEST assay suggesting that these two bioassays in combination may facilitate the rapid detection and ranking of complex PAH mixtures.

Sorption of organic genotoxins to particulate matter in industrial effluents

In an earlier work [White PA et al. (1996): Environ Mol Mutagen 27:116-139] we examined the genotoxicity of dichloromethane extracts from a variety of industrial effluent samples. in this companion work, we used the SOS Chromotest to investigate the sorption of the extracted genotoxins to effluent suspended particulate matter. The affinity of the genotoxins for particulate matter is expressed as a genotoxicity sorption partition coefficient (Kd-genotox). The results indicate that industries known for their emission of combustion by-products, such as polycyclic aromatic hydrocarbons, often have high Kd-genotox values (>/= 10(6). These include metal refining and founding industries as well metal surface treatment facilities. In contrast, Kd-genotox values for pulp and paper mills and sewage treatment facilities are several orders of magnitude lower (</= 10(4)). In several cases the calculated Kd-genotox values are in agreement with the Kow values of genotoxic substances isolated from genotoxic industrial waste samples studied by other researchers. The sorption partition coefficient, in conjunction with concentration of available particulate matter, was used to determine the percent of organic genotoxins adsorbed to effluent suspended particulate matter. Values range from 2.3% to 99.8%. High values (>70%) were obtained for metal surface treatment and inorganic and organic chemical production facilities. Low values (>30%) were obtained for sewage treatment facilities and pulp and paper mills. The results also demonstrate the effect of variations in the concentration of available particulate matter on the genotoxicity of both aqueous and particulate extracts. The results suggest that the sorptive properties of the particulate matter itself are reduced when the concentration of particulate matter is very high (>1,000 mg per 1). The use of sorption partition information in inferring the physical-chemical nature of the putative genotoxins and the implications of the results for assessing the hazard posed to aquatic biota by industrial genotoxins are discussed.

DNA damage induced by wood preserving waste extracts in vitro without metabolic activation, as assayed by 32P-postlabeling

Aqueous wood preserving waste (WPW) extracts were tested for their ability to damage DNA in vitro without metabolic activation. Two extracts were prepared from a surface tar and a surface clay soil sample of a WPW site. As assayed by 32P-post-labelling incubation of DNA with these extracts gave rise to highly complex, extract-specific profiles of DNA adducts whose formation depended on the concentration of WPW material. Most of the adducts appeared to be derived from polycyclic aromatic hydrocarbons (PAHs). Three mg organic WPW residue gave rise to total adduct levels of 13.8 (extract 1) and 66.2 (extract 2) DNA modifications in 10(7) DNA nucleotides, corresponding to 13.9 and 26.9 modifications, respectively, per 10 mg of soil. Thus, extract 2 was more active, although the parent residue had a 1.4-times lower PAH content as determined by gas chromatography/mass spectrometry (GC/MS). DNA adduct formation presumably was a consequence of (i) free radical reactions, possibly involving semiquinones and oxygen free radicals, and (ii) reaction of direct-acting electrophiles, derived from metabolism of WPW toxicants by soil microorganisms. These reactions appeared to be more active in sample 2. The results suggest that ground water at WPW sites contains DNA-reactive compounds posing a cancer hazard to humans. The in vitro DNA adduct assay represents a novel tool to readily assess this type of hazard and the possible effects of remediation measures.

The genotoxicity of industrial wastes and effluents

A review of the literature published on the genotoxicity of industrial wastes and effluents using short-term genetic bioassays is presented in this document. The importance of this task arises from the ubiquity of genotoxic compounds in the environment and the need to identify the sources of contamination so that efforts aimed at control and minimization can be implemented. Of even greater significance is the immediate concern for the welfare of human health and the environment. Subheadings of this document include a description of the genetic bioassays that have been used to test industrial wastes, a compendium of methods commonly used to prepare crude waste samples for bioassay, and a review of the genetic toxicity of wastes and effluents. Wastes and effluents have been grouped according to industrial source. Major categories include chemical and allied products, pulp and paper manufacturing, defense and munitions, petroleum refining, primary metal industries, and miscellaneous industrial manufacturers. Within each industrial category, a synopsis of individual genetic toxicity studies is presented, followed by an interpretation of results on a comprehensive, industry-wide basis. In this evaluation, a discussion of the types and extent of genotoxic damage caused by a particular set of wastes is presented, and potential sources of genotoxic activity are identified. Concluding the document is a commentary, which discloses potential shortcomings in the way in which current legislation protects human heath and the environment from the release of genotoxic substances via industrial wastes and effluents. It also provides an assessment of the genotoxic burden that industrial wastes place on the environment.

Pentachlorophenol

Pentachlorophenol (PCP) is a substance whose widespread use, mainly in wood protection and pulp and paper mills, has led to a substantial environmental contamination. This in turn accounts for a significant exposure of the general human population, with rather high exposure levels being attained in occupational settings. Investigations on the genotoxic activity of PCP have given rise to divergent results which would seem to make an evaluation difficult. By grouping them into 3 categories a somewhat clearer picture, allowing finally an (admittedly tentative) assessment, can be obtained. PCP does seem to be at most a weak inducer of DNA damage: it produces neither DNA-strand breaks nor clear differential toxicity to bacteria in rec-assays in the absence of metabolic activation. Also in SCE induction no increase can be observed in vivo, while PCP is found marginally active in a single in vitro experiment. Metabolic activation, however, leads to prophage induction and to DNA strand breaks in human lymphocytes, presumably through the formation of oxygen radicals. A possible further exception in this area might be the positive results in the yeast recombination tests, although their inadequate reporting makes a full evaluation difficult. PCP does not seem to induce gene (point) mutations, as most bacterial assays, the Drosophila sex-linked recessive lethal test and in vitro assays with mammalian cells did not demonstrate any effects. Marginally positive results were obtained in the mammalian spot test in vivo and in one bacterial test; the positive result in the yeast assay for cycloheximide resistance is fraught somewhat with its questionable genetic basis. PCP does, however, induce chromosomal aberrations in mammalian cells in vitro and in lymphocytes of exposed persons in vivo. Those in vivo results that were unable to provide evidence of chromosomal damage are hampered either by methodological inadequacies or by too low exposure levels. The (rodent) metabolite tetrachlorohydroquinone might be a real genotoxic agent, capable of binding to DNA and producing DNA strand breaks; this activity is probably due to semiquinone radical formation and partly mediated through active oxygen species. Since this compound has not been tested in the common bacterial and mammalian mutagenicity assays, the few ancillary results on this substance cannot be used in a meaningful human risk assessment of PCP. Furthermore, this metabolite has only been produced by human liver microsomes in vitro, but has not been detected in exposed humans in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)

Chemical and biological characterization of hazardous industrial waste. II. Eukaryotic bioassay of a wood-preserving bottom sediment

The eukaryotic haploid and diploid forms of Aspergillus nidulans were used to detect gene mutations and various types of chromosome damage, respectively, in the acid, base and neutral fractions of a wood-preserving bottom sediment. The corresponding response to prokaryotic mutagenicity assays and major chemical constituents of the 3 waste fractions were described by Donnelly et al. (1987). The haploid methionine system detected genotoxic compounds in all 3 primary waste fractions without metabolic activation. With metabolic activation, the maximum response observed in the gene mutation assay was induced by the base fraction. In the diploid assay without metabolic activation, the acid fraction induced the maximum number of major chromosome abnormalities, while the base fraction induced the maximum number of minor deletions or insertions. These results appear to reflect the different composition of the waste fractions since each fraction induced a different type of genetic damage in the two bioassays employed. Alternately, because exposure in the diploid assay was during a growth stage, the results may reflect a varying response at different points of the cell division cycle. The results obtained using eukaryotic bioassays indicate that the wood preserving waste contains compound(s) capable of inducing point mutations, chromosome damage, recombination, and compound(s) acting as spindle poisons.