Evaluating Human Risk from Exposure to Alkylated PAHs in an Aquatic System

ABSTRACT

Polycyclic aromatic hydrocarbons (PAHs) are a large class of organic chemicals typically found as mixtures in the aquatic environment from natural, petrogenic, and pyrogenic sources. People can be exposed to PAHs through ingestion or dermal contact with contaminated sediments or through ingestion of finfish and shellfish exposed to contaminated sediments. Although more than 100 PAHs have been identified, human exposure and risk are commonly evaluated for 18 individual PAHs. Other PAHs, such as alkylated PAHs, likely contribute to biological activity of environmental PAH mixtures; however, insufficient toxicity data are available to quantify their potential risk. This article presents an initial evaluation of the potential for human health risk from exposure to alkylated PAHs in sediment and fish. Individual alkylated PAHs have been observed to have potentially mutagenic, tumor-promoting, or carcinogenic activity. However, except for 1-and 2-methylnaphthalene, insufficient toxicity data are available to quantify toxicity or cancer risk from exposure to individual alkylated PAHs or mixtures of alkylated PAHs. This article describes a proposed strategy to better understand the potential human health risk from exposure to alkylated PAHs. Implementation of this strategy will contribute to evaluations of human exposure to complex PAH mixtures in the environment.

Keywords:

• polycyclic aromatic hydrocarbons
• human health risk assessment
• alkylated PAHs
• relative potency factor
• complex mixtures

ACKNOWLEDGMENTS

The authors gratefully acknowledge thoughtful technical comments from Dr. Harlee Strauss on a previous version of this manuscript. This work was supported by funding from the US Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS (DACW42-03-C-0022) and Menzie-Cura & Associates, Inc.

Notes

¹Although PAH mixtures can contain other toxicologically active alkylated PAHs such as polynuclear sulfur heterocycles (thiopehenes) (McFall et al. 1984; Hellou et al. 1994a, b; Gabos et al. 2001; Brandt et al. 2002), this article focuses on alkylated PAHs containing hydrogen and carbon in aquatic environments.

¹ Selected alklyated PAHs and their unsubstituted parent PAH evaluated for GJIC, mutagenicity, or tumorogenicity.

² Bay region present in parent PAH; baylike region created by methylation of parent PAH; “bay region methyl group” and “bay with opposing methyl group” refer to locations of methylation as identified by authors if reference is listed and otherwise determined from review of structures on ChemID (National Library of Medicine).

³Evidence of inhibition of GJIC as reported by authors. Across studies, different durations of exposure were studied and different criteria were used to evaluate inhibition.

⁴ Evidence of mutagenicity in the presence of metabolizing enzymes (rat liver microsomes S-9).

⁵ Tumorogenicity includes tumors resulting from any of these exposure protocols: chronic animal bioassay, subcutaneous injection, skin tests with and without promoters.

²The bay region is formed by the fused aromatic rings.

³Baylike regions are similar to the classic “bay region” associated with BaP but, as illustrated in Figure 1, the baylike regions are formed by the addition of a methyl group to the PAH ring structure.

⁴USEPA has recommended the application of the age dependent adjustment factors for BAP and PAHs evaluated using relative potency factors (Science Policy Council Cancer Guidelines Implementation Workgroup Communication II: Performing risk assessments that include carcinogens described in the Supplemental Guidance as having a mutagenic mode of action. June 14, 2006. http://epa.gov/osa/spc/pdfs/CGIWGCommunication_II.pdf).