Contribution of PAHs, PCBs, and PCDD/PCDFs to the Total Induction Equivalents (Sigma IEs) in mollusks

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 Progr am were analyzed for polycyclic aromatic hydrocarbons (PAHs) and persistent organochlorinated contaminants such as polychlorinated biphenyls (PCBs), p olychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Total Induction Equivalents (Sigma IEs) were calculated assuming a n additive mode of action. A set of seven PAHs (benz(a)anthracene, dibenz ( a,h) anthracene, benzo(b) fluoranthene, benzo(k)fluoranthene, chrysene, ben zo(a)pyrene, and indeno(1,2,3-c,d)pyrene), five PCB congeners (PCB105, PCB1 18, 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 calc ulations of the Sigma IEs. Concentrations of total PAHs, PCBs, and PCDD/PCD Fs on a dry-weight basis ranged from 21.5 to 19391 ng/g, 9.3 to 539 ng/g, a nd non-detected (ND) to 315.5 pg/g, respectively. The calculated Sigma 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 Sigma IEs with an averag e 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 estimat ed Sigma IEs. Contribution from the PCB congeners averaged 11% with ranges between 0 and 68% with PCB 126 as the major contributor to the calculated S igma IEs. In comparison, the contribution from PCDD/PCDFs to the calculated Sigma IEs was low and rarely exceeded 10%. These results clearly indicate the relative importance of PAHs when the evaluation of the impact of comple x mixtures is assessed based on the induction of cytochrome P4501A-dependen t 7-ethoxyresorufin-O-deethylase (EROD) enzyme activity by extracts from ca lculated environmental samples. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.