Development of TEFs for PCB congeners by using an alternative biomarker - Thyroid hormone levels

Polychlorinated biphenyls (PCBs) are ubiquitous toxic contaminants Health risk assessment for this class of chemicals is complex the current toxic equivalency factor (TEF) method covers dioxin-like (DL-) PCBs, dibenzofurans. and dioxins. but excludes non-DL-PCBs To address this deficiency, we evaluated published data for several PCB congeners to determine common biomarkers of effect We found that the most sensitive biomarkers for DL-non-ortho-PCB 77 and PCB 126 are liver enzyme (e g., ethoxyresorufin-O-deethylase. EROD) induction. circulating thyroxine (T4) decrease. and brain dopamine (DA) elevation For DL-ortho-PCB 118 and non-DL-ortho-PCB 28 and PCB 153, the most sensitive biomarkers are brain DA decrease and circulating T4 decrease. The only consistent biomarker for both DL- and non-DL-PCBs is circulating T4 decrease The Calculated TEF-(TH), based on the effective dose to decrease T4 by 30% (ED30) With reference to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). is identical to both TEF-(WHO98) and TEF-(WHO05) for TCDD and DL-PCBs (correlation coefficients are r = 100, P < 0.001, and r = 0 99, P < 0.001, respectively) We conclude that T4 decrease is a prospective biomarker for generating a new TEF scheme which Includes some non-DL-congeners. The new TEF-(TH) parallels the TEF-(WHO) for DL-PCBs and, most Importantly. IS useful for non-DL-PCBs in risk assessment to address thyroid endocrine disruption and potentially the neurotoxic effects of PCBs Published by Elsevier Inc