Toxicity Characterization of Complex Mixtures Using Biological and Chemical Analysis in Preparation for Assessment of Mixture Similarity

Abstract

In the United States, several proposed approaches for using bioassays for the risk assessment of complex hazardous mixtures require that selected mixtures be "sufficiently similar" to each other. The goal of this research was to evaluate the utility of a protocol using in vitro bioassays and chemical analysis as a basis for assessing mixture similarity. Two wood preserving wastes (WPWs) containing polycyclic aromatic hydrocarbons and pentachlorophenol were extracted and fractionated to generate potentially similar mixtures. Chemical analysis was conducted using gas chromatography/mass spectrometry. Genotoxicity was evaluated using the Salmonella/microsome and Escherichia coli prophage induction assays. The crude extract of one WPW was also tested in the chick embryotoxicity screening test (CHEST) assay. The CHEST assay provided the most sensitive measurement of toxicity. Overall, the biological potency of the samples was not well correlated with predicted potency based on chemical analysis. Although several mixtures appeared similar based on chemical analysis, the magnitude of the response in bioassays was often dissimilar. Fractionation was required to detect the genotoxicity of mixture components in vitro. The results confirm the need for an integrated protocol, combining chemical analysis, fractionation, and biological testing to characterize the risk associated with complex mixtures.

Long-term exposure to low-concentrations of Cr(VI) induce DNA damage and disrupt the transcriptional response to benzo[a]pyrene

“…Assessing the effects of combined exposures to non-metabolizable halogenated aromatic hydrocarbons has been proposed based on the relative potency of the individual compounds (Birnbaum and DeVito 1995) and to PAHs based on their relative carcinogenic potency (Collins et al 1998). These approaches, while valuable, are limited to mixtures of similar compounds (Cizmas et al 2004) and are of little use when dealing with complex mixtures of multiple components, because combined exposures generate substance-specific changes in gene expression that cannot be attributed to a single mechanism.…”

Long-term exposure to hexavalent chromium inhibits expression of tumor suppressor genes in cultured cells and in mice

“…Assessing the effects of combined exposures to non-metabolizable halogenated aromatic hydrocarbons has been proposed based on the relative potency of the individual compounds [2] and to PAHs based on their relative carcinogenic potency [3]. These approaches, while valuable, are limited to mixtures of similar compounds [4] and are of little use when dealing with complex mixtures of multiple components, because combined exposures generate substance-specific changes in gene expression that cannot be attributed to a single mechanism.…”

Genotoxicity of polar fractions from a herbicide‐contaminated soil does not correspond to parent contaminants

“…Such approaches cannot assess the impact of different contaminants in the soil, and some toxins can be masked [5]. Therefore, the fractionation to assess the impact of different pollutants was suggested [5]. However, limitations exist in different fractionation approaches.…”

“…However, neither approach differentiates which species are major contributors to soil toxicity. Therefore, combining fractionation with biological and chemical analysis has been proposed to characterize the risk associated with complex samples [5]. Ecotoxicity of soils frequently is assessed using mutagenicity/genotoxicity assays such as the SOS Chromotest.…”