Chicken Embryo Hepatocyte Bioassay for Measuring Cytochrome P4501A-Based 2,3,7,8-Tetrachlorodibenzo- p-dioxin Equivalent Concentrations in Environmental Samples

A bioassay that uses chicken embryo hepatocyte (CEH) primary cultures for measuring 2,3,7,8-tetrachlorodibenzo- p -dioxin equivalent (TCDD-EQ) concentrations in extracts prepared from wild bird eggs contaminated with complex mixtures of polychlorinated biphenyls (PCBs), dibenzo- p -dioxins (PCDDs), dibenzofurans (PCDFs), and other halogenated aromatic hydrocarbons is described. The CEH bioassay uses an efficient method for measuring ethoxyresorufin- O -deethylase (EROD) in hepatocytes cultured in 48-well plates to obtain bioassay-derived TCDD-EQ concentrations (TCDD-EQ bio ). Induction equivalency factors (IEFs) were determined for 39 PCB congeners, 2,3,7,8-TCDD, 1,2,3,7,8-PCDD, and 2,3,7,8-TCDF. TCDD-EQ bio concentrations in eggs from herring gulls, Larus argentatus, and great blue herons, Ardea herodias, were highly correlated with TCDD-EQ concentrations calculated (TCDD-EQ calc ) from chemical residue data and IEFs ( r 2 = 0.977, slope = 0.99). Unlike other in vitro bioassays, 2,2‘,3,4,4‘,5‘-hexachlorobiphenyl (PCB 138) made a significant contribution to TCDD-EQ calc in CEH cultures. TCDD-EQ bio concentrations were also highly correlated to TCDD-EQ calc obtained using toxic equivalency factors (TEFs) derived from various in vivo and in vitro toxic and biochemical end points. The CEH bioassay is a cost-effective method for measuring TCDD-EQ bio concentrations in environmental samples.