US EPA

The United States Environmental Protection Agency’s (EPA) Reassessment of dioxins and related compounds (Reassessment), which began in 1991 and culminated in a draft report reviewed by the National Academies of Science beginning in 2004 and ending in 2006, included a characterization of background exposures to dioxin-like compounds. This characterization entailed an estimate of an average background intake dose and an average background body burden. The dose as well as the body burden were derived from data generated in the mid-1990s. The dose was estimated by combining average concentrations of dioxin found in food, air, soil, and water surveys, with average contact rates. The body burden data came from a set of regional non-statistical studies of dioxins in blood. Studies conducted in the 2000s were gathered in an attempt to update the estimates generated by the Reassessment. While these studies suggest declines in the average background dose and body burden, a precise quantification of this decline is difficult because of the treatment of non-detects in the generation of congener average concentrations. At background concentrations, dioxins are near trace levels for many of the congeners in exposure media and blood. The Reassessment generated congener averages by assuming non-detects were equal to one-half detection limit (ND = ½ DL) in the surveys, and this led to an intake dose of 61.0 pg Toxic Equivalents (TEQs)/day for background adult exposures (calculated, as are all estimates in this paper, using 2005 WHO toxic equivalency factors, TEFs, including dioxins, furans, and coplanar PCBs; originally calculated as 65.8 pg TEQ/day using WHO 1998 TEFs). This quantity was reexamined by deriving an intake estimate at ND = 0 from the same data sets, and it was found to be 43.7 pg TEQ/day. This exercise was duplicated with more recent data from the 2000s, and the estimates at ND = ½ DL and 0 were now 40.6 and 34.5 pg TEQ/day, respectively The average body burden at ND = ½ DL from the surveys in the mid-1990s was given in the Reassessment as 22.9 pg TEQ/g lipid weight (lwt), and it was 21.9 pg TEQ/g lwt at ND = 0. More recent blood concentration data, from the National Health and Nutritional Examination Survey (NHANES) 2001/2, suggest an adult average at 21.7 pg TEQ/g lwt at ND = DL/√2 and 17.2 pg TEQ/g lwt at ND = 0. So while declines in both intake dose and body burden are suggested, the ability to quantify that decline precisely, as well as even conclude that it is statistically significant, is not possible because of these two primary issues: the lack of direct comparability between data sets in the two time periods, and the issue of the high frequency of non-detects and treatments of non-detects in generation of averages and TEQs.

The purpose of this study was to update the general population exposure estimates from the Dioxin Reassessment. These estimates, including an estimate of daily intake and body burdens, were derived based on studies from the 1990s. Studies conducted in the 2000s were gathered and used in this update.

LORBER, M., D. Patterson, J. Huwe, AND H. KAHN. Evaluation of Background Exposures of Americans to Dioxin-Like Compounds in the 1900s and 2000s (Article). CHEMOSPHERE. Elsevier Science Ltd, New York, NY, 77(5):640-651, (2009).