Impact of WHO 2005 revised toxic equivalency factors for dioxins on the TEQs in serum, household dust and soil


In 2005, the World Health Organization (WHO) – International Programme on Chemical Safety reevaluated the toxic equivalency factors (TEFs) for dioxin-like compounds and made changes that affect the calculation of the total toxic equivalent (TEQ). The impact of these changes on the TEQs for human blood and abiotic matrices such as soil and household dust has not been widely assessed or reported.

Methods and results

Using a major exposure study which examined blood, household dust, and soil levels of dioxin-like compounds in several regions of Michigan, we found the mean total TEQ was significantly reduced by 26%, 12% and 14% for serum, household dust, and soil, respectively, when the TEQ was based on the 2005 TEFs compared to the 1998 TEFs. The decrease in the serum total TEQ was largely due to the down-weighting of the TEFs for the majority of mono-ortho PCBs. In contrast, the decrease in the soil total TEQ was mostly due to the down-weighting of the TEF for 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) (1998 TEF = 0.5, 2005 TEF = 0.3). For household dust, the decrease in total TEQ was not due to any single TEF but was due to small changes in a number of compounds. There was a dramatic decrease (−88%) in the mean and 95th percentile for mono-ortho PCB TEQ due to the 2005 TEFs.


These findings suggest that comparisons between studies based on the TEQ-WHO98 and TEQ-WHO05 may need to consider an appropriate conversion factor to assure comparability. Furthermore, the changes in TEFs may have impact in locations where regulations of soil contamination are triggered by specific TEQ levels.