Elimination rates of dioxin congeners in former chlorophenol workers from Midland, Michigan.
BACKGROUND
Exposure reconstructions and risk assessments for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other dioxins rely on estimates of elimination rates. Limited data are available on elimination rates for congeners other than TCDD.


OBJECTIVE
We estimated apparent elimination rates using a simple first-order one-compartment model for selected dioxin congeners based on repeated blood sampling in a previously studied population.


METHODS
Blood samples collected from 56 former chlorophenol workers in 2004-2005 and again in 2010 were analyzed for dioxin congeners. We calculated the apparent elimination half-life in each individual for each dioxin congener and examined factors potentially influencing elimination rates and the impact of estimated ongoing background exposures on rate estimates.


RESULTS
Mean concentrations of all dioxin congeners in the sampled participants declined between sampling times. Median apparent half-lives of elimination based on changes in estimated mass in the body were generally consistent with previous estimates and ranged from 6.8 years (1,2,3,7,8,9-hexachlorodibenzo-p-dioxin) to 11.6 years (pentachlorodibenzo-p-dioxin), with a composite half-life of 9.3 years for TCDD toxic equivalents. None of the factors examined, including age, smoking status, body mass index or change in body mass index, initial measured concentration, or chloracne diagnosis, was consistently associated with the estimated elimination rates in this population. Inclusion of plausible estimates of ongoing background exposures decreased apparent half-lives by approximately 10%. Available concentration-dependent toxicokinetic models for TCDD underpredicted observed elimination rates for concentrations < 100 ppt.


CONCLUSIONS
The estimated elimination rates from this relatively large serial sampling study can inform occupational and environmental exposure and serum evaluations for dioxin compounds.
Summit Toxicology, LLP, Falls Church, Virginia, USA; 2The Dow Chemical Company, Midland, Michigan, USA. laylward@summittoxicology.com
Lesa L
LL
Aylward
James J
JJ
Collins
Kenneth M
KM
Bodner
Michael
M
Wilken
Catherine M
CM
Bodnar
D002733:Chlorophenols / Q000633:toxicity*; D004147:Dioxins / Q000633:toxicity*; D004781:Environmental Exposure / Q000517:prevention & control*; D008824:Michigan; D016273:Occupational Exposure / Q000517:prevention & control*
D002733:Chlorophenols; D004147:Dioxins