Cancer Risk Assessment of Polycyclic Aromatic Hydrocarbon Contaminated Soils Determined Using Bioassay-Derived Levels of Benzo[a]pyrene Equivalents
- DOI
- Language of the publication
- English
- Date
- 2014-12-30
- Type
- Article
- Author(s)
- Lemieux, Christine L.
- Long, Alexandra S.
- Lambert, Iain B.
- Lundstedt, Staffan
- Tysklind, Mats
- White, Paul A.
- Publisher
- American Chemical Society
Abstract
Here we evaluate the excess lifetime cancer risk (ELCR) posed by 10 PAH-contaminated soils using (i) the currently advocated, targeted chemical-specific approach that assumes dose additivity for carcinogenic PAHs and (ii) a bioassay-based approach that employs the in vitro mutagenic activity of the soil fractions to determine levels of benzo[a]pyrene equivalents and, by extension, ELCR. Mutagenic activity results are presented in our companion paper.1 The results show that ELCR values for the PAH-containing fractions, determined using the chemical-specific approach, are generally (i.e., 8 out of 10) greater than those calculated using the bioassay-based approach; most are less than 5-fold greater. Only two chemical-specific ELCR estimates are less than their corresponding bioassay-derived values; differences are less than 10%. The bioassay-based approach, which permits estimation of ELCR without a priori knowledge of mixture composition, proved to be a useful tool to evaluate the chemical-specific approach. The results suggest that ELCR estimates for complex PAH mixtures determined using a targeted, chemical-specific approach are reasonable, albeit conservative. Calculated risk estimates still depend on contentious PEFs and cancer slope factors. Follow-up in vivo mutagenicity assessments will be required to validate the results and their relevance for human health risk assessment of PAH-contaminated soils.
Plain language summary
Under the Federal Contaminated Sites Action Plan, Health Canada is an Expert Support Department, which means that it provides expert advice, guidance, training and tools on best practices and innovative methods for human health risk assessment to other federal departments. Health Canada has previously shown that the total mutagenic activity of complex mixtures extracted from contaminated soils appears to be dominated by a small number of polycyclic aromatic hydrocarbons (PAHs) that have been prioritised and whose toxicity is well characterised. The purpose of this study was to extend those analyses and estimate the excess lifetime cancer risk (ELCR) posed by the PAH-contaminated soils investigated. Risk was calculated using (1) the additive, priority PAH approach currently advocated by several regulatory agencies, and (2) a novel approach that employs a mouse cell bioassay response to assess the mutagenic activity of the complex PAH-containing extracts. The former involves chemical analyses for prioritised PAHs, conversion of the values to equivalents of the noteworthy carcinogen benzo[a]pyrene (BaP), and determination of risk using the total BaP equivalents. The latter involves comparing the mutagenic activity of the complex PAH-containing extract to that of BaP alone to determine a bioassay-derived level of BaP equivalents. In both cases, actual risk estimates were determined using the reported carcinogenic potency of BaP. The results show that ELCR values determined using the targeted, chemical-specific approach are within an order of magnitude (i.e., 10-fold) of values calculated using the bioassay-derived level of BaP equivalents. However, the bioassay-based approach is advantageous since it does not require a priori knowledge about the composition of the complex mixture under consideration, or an assumption of additivity. However, both methods still require the use of a BaP carcinogenic potency value, and there is no universal agreement regarding the most appropriate value for regulatory decision-making. Overall comparisons of ELCR estimates calculated using the two aforementioned methods revealed that values determined using an approach based on a small number of targeted substances are surprisingly close to values determined using a bioassay response to the complex mixture, and moreover, that the final risk estimate can be heavily influenced by the choice of a BaP carcinogenic potency value. Follow-up work is employing animal exposures (i.e., in vivo assessments) to validate the results obtained here and their relevance for human health risk assessments of PAH-contaminated soils.
Subject
- Health,
- Health and safety