摘要:

The concept of toxic equivalency factors (TEFs) has been developed to facilitate risk assessment and regulatory control of exposure to complex PCDD, PCDF and PCB mixtures. Recently the European Centre for Environment and Health of the World Health Organization (WHO-ECEH) and the International Programme on Chemical Safety (IPCS) jointly reevaluated the TEFs of PCDDs, PCDFs and dioxin-like PCBs for mammals and derived consensus TEFs for birds and fish (Stockholm, 1997). From a mechanistic point of view it can be concluded that, although the quantitative response will vary depending on the congener involved, the occurrence of a common mechanism (binding to the Ah receptor) legitimates the use of the TEF concept across species. But there also is criticism regarding the TEF concept. Pharmacokinetic differences between species can significantly influence the TEF value, and uncertainties due to additive or nonadditive interactions, to differences in species responsiveness and to differences in the shape of the dose response curve might hamper the derivation of consensus TEF values. In this context it should be noted, however, that using TCDD alone, as the only measure of exposure to dioxin-like PCDDs, PCDFs and PCBs, would severely underestimate the risk from exposure to these compounds. Therefore, it can be concluded that, for pragmatic reasons, the TEF concept remains the most feasible approach for risk assessment purposes, in spite of the uncertainties associated with its use.

ISSN:0265-203X    

DOI:10.1080/026520300283414

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs) exist as complex mixtures in environmental and biological samples. There is sufficient evidence that the toxic congeners share a common mode of action, involving binding to the Ah-receptor. Toxic equivalency factors (TEFs) and chemical residue data are used to calculate toxic equivalent (TEQ) concentrations in environmental samples, foods, animal and human tissues. Two different approaches have been used in the risk assessments of PCDDs, PCDFs and dioxin-like PCBs. WHO and most countries outside the USA have derived Tolerable Daily (or weekly) Intakes (TDI) in the order of 1–10 pg per kg of body weight for TCDD or TEQs based on data from rodent carcinogenicity studies. These countries have assumed the existence of a threshold dose for the carcinogenicity of dioxins, while US EPA and USFDA have used probabilistic estimates of cancer potency, treating cancer as a non-threshold effect and using a descriptor that addresses upper bound risk, the Risk Specific Dose (RsD). In the USA and other countries there is a growing concern over the noncancer effects of dioxin-like compounds. In general, the various risk assessments have identified groups of the population that are at particular high risks and all have stressed the urgent need to reduce the sources of the environmental contamination with these compounds to the lowest possible.

ISSN:0265-203X    

DOI:10.1080/026520300283423

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor