Relative potencies of PAHs and PCBs based on the response of human cells

P450 reporter gene system (RGS) utilizes a human hepatoma cell line stably transfected with a plasmid containing firefly luciferase linked to human CYP1A1 promoter sequences. Luciferase expression in these cells is used to detect and quantify compounds that activate the Ah receptor (AhR) and induce CYP1A1. In this study, concentration-response curves were used to determine the relative potencies and calculate induction equivalency factors (IEFs) for non-ortho and mono-ortho coplanar PCBs and high-molecular weight PAHs. Relative potencies of PCBs were: 3,4,4',5-TetraCB (81)>3,3',4,4',5-PentaCB (126)>3,3',4,4'-TetraCB (77)≈2,3,4,4',5-PentaCB (114)>2,3',4,4',5-PentaCB (118)≈2',3,4,4',5-PentaCB (123)>3,3',4,4',5,5'-HexaCB (169). In addition, two other mono-ortho congeners, 2,3,3',4,4'-PentaCB (105) and 2,3,3',4,4',5-HexaCB (156), did not induce luciferase in these cells. Relative potencies of the PAHs were: benzo[k]fluoranthene>dibenz[a,h]anthracene>benzo[b]fluoranthene≈indeno[1,2,3-cd]pyrene>benzo[a]pyrene>chrysene≈benzo[a]anthracene>benzo[g,h,i]perylene. Relative potencies of PAHs are similar to those of PCBs.