Contribution of PAHs, PCBs, and PCDD/PCDFs to the Total Induction Equivalents (Sigma IEs) in mollusks
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abstract
Bivalve mollusks collected along the East, West, and Gulf of Mexico coasts of the United States as part of the NOAA's National Status and Trends Program were analyzed for polycyclic aromatic hydrocarbons (PAHs) and persistent organochlorinated contaminants such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Total Induction Equivalents (IEs) were calculated assuming an additive mode of action. A set of seven PAHs (benz(a)anthracene, dibenz(a,h)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene, benzo(a)pyrene, and indeno(1,2,3-c,d)pyrene), five PCB congeners (PCB105, PCB118, PCB77, PCB126, and PCB169), and four PCDD/PCDF congeners (2,3,7,8-TCDD, 2,3,7,8-TCDF, 1,2,3,7,8,PeCDD, and 1,2,3,7,8-PeCDF) were used for the calculations of the IEs. Concentrations of total PAHs, PCBs, and PCDD/PCDFs on a dry-weight basis ranged from 21.5 to 19391 ng/g, 9.3 to 539 ng/g, and non-detected (ND to 315.5 pg/g, respectively. The calculated IEs ranged from 2.6 pg/g (Long Reef, Aransas Bay, TX) to 5981 pg/g (Emeryville, San Francisco Bay, CA). For the vast majority of the samples analyzed, the contribution of the PAHs dominated the calculated IEs with an average of 87% of the total and a range between 19 and 100%. Benzo(k)fluoranthene (BkF) and benzo(b)fluoranthene (BbF) accounted for over 80% of the estimated IEs. Contribution from the PCB congeners averaged 11% with ranges between 0 and 68% with PCB 126 as the major contributor to the calculated IEs. In comparison, the contribution from PCDD/PCDFs to the calculated IEs was low and rarely exceeded 10%. These results clearly indicate the relative importance of PAHs when the evaluation of the impact of complex mixtures is assessed based on the induction of cytochrome P4501A-dependent 7-ethoxyresorufin-O-deethylase (EROD) enzyme activity by extracts from environmental samples.
