Toxicology and Risk Assessment of POPs

Abstract

Polyhalogenated industrial compounds and combustion by-products including the polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) have been identified in almost every component of the global ecosystem including fish, wildlife and humans. Many of these compounds such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induce a common pattern of biochemical and toxic responses that are mediated through initial binding to the aryl hydrocarbon receptor (AhR). These compounds primarily differ in their potencies, and risk/hazard assessment for these AhR-active contaminants can be determined using a toxic equivalency factor (TEF) approach where TCDD equivalents (TEQ) of a mixture is equal to the sum of the concentrations of individual components times their potency (TEF) relative to TCDD. A number of studies also demonstrate that AhR-inactive POPs including ortho-substituted PCBs and hydroxy-PCBs also induce multiple toxic and biochemical responses; however, methods for risk assessment of these chemicals have not yet been developed.