Dioxin-like chemicals

Toxic equivalency factors (TEFs) are estimated relative to 2,3,7,8-TCDD, which is assigned a value of 1. They are measures of the toxicity of individual compounds relative to that of 2,3,7,8-TCDD. A variety of toxic indices, measured in vivo or in vitro, have been used to estimate TEFs, including reproductive effects (e.g., embryo toxicity in birds), immunotoxicity, and effects on organ weights. The degree of induction of P450 lAl is another measure from which estimations of TEF values have been made. The usual approach is to compare a dose-response curve for a test compound with that of the reference compound, 2,3,7,8-TCDD, and thereby establish the concentrations (or doses) that are required to elicit a standard response. The ratio of concentration of 2,3,7,8-TCDD to concentration of test chemical when both compounds produce the same degree of response is the TEF. Once determined, a TEF can be used to convert a concentration of a dioxin-like chemical found in an environmental sample to a toxic equivalent (TEQ). 

Thus, [C] X TEE = TEQ i , i , where [C] = environmental concentration of planar polychlorinated compound. The TEQ is an estimate of the concentration of TCDD that would produce the same effect as the given concentration of the dioxin-like chemical. 

Garrison, P.M., Tullis, K., and Aarts J.M.M.J.G. et al. (1996). Species specific recombinant cell lines as bioassay systems for the detection of dioxin-like chemicals. Fundamental and Applied Toxicology 30, 194-203. 

Whyte, J.J. Schmitt, C.J. Tillitt, D.E. 2004, The H4IIE cell bioassay as an indicator of dioxin-like chemicals in wildlife and the environment. Crit. Rev. Toxicol. 34 1-83. 

Intra- and interlaboratory calibration of the DR CALUX bioassay for the analysis of dioxins and dioxin-like chemicals in sediments... 

Denison, M.S., Rogers, W.J., Fair, M., Ziccardi, M., Clark, G., Murk, A.J., Brouwer, A. (1996). Application of the CALUX bioassay system for the detection of dioxin-like chemicals (Ah receptor ligands) in whole serum samples and in extracts fiom commercial and consumer products. Organohalogen Compounds 27 280-284. 

DeVito MJ, Bimbaum LS, Farland WH, et al. 1995. Comparisons of estimated human body burdens of dioxin-like chemicals and TCDD body burdens in experimentally exposed animals. Environ Health Perspect 103 820-831. 

Schecter A, McGee H, Stanley JS, et al. 1996b. Dioxins and dioxin like chemicals in blood and semen of American Vietnam veterans from the state of Michigan. Amer J Ind Med 30 647-654. 

The toxicity equivalent (TEQ) of TCDD is calculated by multiplying the exposure level of a particular dioxin-like compound by its toxicity equivalency factor(TEF). TEFs are based on congener-specific data and the assumption that Ah receptor-mediated toxicity of dioxin-like chemicals is additive. The TEF scheme compares the relative toxicity of individual dioxin-like compounds to that of TCDD. 

Action level for dioxin and dioxin-like compounds in soil. Action levels are concentrations of chemicals at which consideration of action to interdict exposure occurs 1 ppb TCDD in residential soil was identified by Kimbrough et al. (1984) as a "level of concern" and recommended as "a reasonable level to begin consideration of action to limit exposure." The conclusions of Kimbrough et al. (1984) were derived in part from an evaluation of the carcinogenic potential of TCDD, based on a 2-year oral chronic toxicity and oncogenicity study in rats (Kociba et al. 1978). With the advancement of knowledge about dioxin-like chemicals and their assumed common mechanism of toxicity, the TEQs were introduced into the risk assessment process. Since then, 1 ppb of total dioxins (expressed as TEQs) in soil has been used as an action level by ATSDR. 

Rogan WJ, Gladen BC, Guo Y-LL, et al. 1999. Sex ratio after exposure to dioxin-like chemicals in Taiwan. Lancet 353 206-207. 

The wide dispersal of the dioxin-like chemicals throughout the environment is primarily the result of atmospheric transport and deposition. Eventually the dioxin-Uke chemicals become adsorbed to dust particles and surfaces and are deposited in sediments. The two primary pathways for dioxin-like chemicals to enter the food chain are from the air-to-plant-to-animal and from water-and sediment-to-fish. A third route for dioxin-Uke chemicals to enter the food chain is through the accidental contamination incidents resulting from inappropriate handling and processing of feed and food substances. It has been estimated that more than 90% of human exposure to dioxin and dioxin-like chemicals is through the ingestion of contaminated food substances. ... 

Van Overmeire, L, Clark, G. C., Brown, D. J., Chu, M. D., Cooke, W. M., Denison, M. S., Baeyens, W., Srebmik, S., and Goeyens, L., Trace contamination with dioxin-like chemicals evaluation of bioassay-based TEQ determination for hazard assessment and regulatory responses. Environ. Set Policy, 4, 345-357, 2001. 

Dioxin-like Chemicals (PCBs, PCDDs and PCDFs)... 

A large variety of sources of dioxin have been identified and others may exist. Because dioxin-like chemicals are persistent and accumulate in biological tissues, particularly in animals, the major route of human exposure is through ingestion of foods containing minute quantities of dioxinlike compounds. This results in widespread, low-level exposure of the general population to dioxinlike compounds. 

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