Levels of PCDDs, PCDFs, and dioxin-like PCBs in human milk among Hong Kong mothers

Dioxins are a family of persistent organic pollutants (POPs) listed under the Stockholm Convention, and include PCDDs, PCDFs, and dioxin-like PCBs. These toxic chemicals are carcinogenic, widely dispersed, and have long half-lives. They have contaminated the food web and, being fat-soluble, accumulate in adipose tissues and milk in the human body. To assess human exposure, we collected breast milk samples from 137 first-time mothers recruited from around Hong Kong. Samples were analysed by HRGC-HRMS in four pools, according to the subject's age and length of residency. Exposure was related to age, duration of stay, and possibly diet. Generally, older mothers, and mothers with a longer stay in Hong Kong, had higher levels of dioxins in their milk. This pattern was clearest for the PCBs, although deviations were observed for some of the PCDD/Fs. Mean concentrations, measured per gram of lipid weight in terms of WHO toxic equivalents (WHO-TEQs), were 7.48 pg/g for PCDD/Fs and 3.79 pg/g for PCBs, giving a total of 11.27 pg/g for PCDD/Fs and PCBs combined. Compared to an earlier Hong Kong study we conducted in 2002, the mean WHO-TEQ values in our latest findings were about 9% lower overall for PCDD/Fs and 19% lower for PCBs, with the mean total WHO-TEQ for PCDD/Fs and PCBs being around 13% lower in this study. This indicates a general declining trend in the levels of POPs in Hong Kong. However, our levels were still high when compared to those in some other Asian-Pacific countries. More stringent policies on reducing and eliminating POPs should help to lower these. Continued surveillance for POPs in human milk, as well as in common foodstuffs, will provide us with important information on human exposures that will be necessary for tracking our progress, and making future health risk assessments.

A sensitivity analysis using alternative toxic equivalency factors to estimate U.S. dietary exposures to dioxin-like compounds

EPA recommends sensitivity analyses when applying the toxic equivalency factor (TEF) method to evaluate exposures to dioxin-like compounds (DLCs). Applying the World Health Organization's (WHO) 2005 TEF values and estimating average U.S. daily dietary intakes of 25 DLCs from eight food categories, we estimate a toxic equivalency (TEQ) intake of 23 pg/day. Among DLCs, PCB 126 (26%) and 1,2,3,7,8-PeCDD (23%) dominate TEQ intakes. Among food categories, milk (14%), other dairy (28%), beef (25%), and seafood (18%) most influenced TEQ intakes. We develop two approaches to estimate alternative TEF values. Based on WHO's assumption regarding TEF uncertainty, Approach1 estimates upper and lower TEFs for each DLC by multiplying and dividing, respectively, its individual TEF by ± half a log. Based on compiled empirical ranges of relative potency estimates, Approach2 uses percentile values for individual TEFs. Total TEQ intake estimates using the lower and upper TEFs based on Approach1 were 8 and 68 pg TEQ/day, respectively. The 25th and 75th percentile TEFs from Approach2 yielded 12 and 28 pg TEQ/day, respectively. The influential DLCs and food categories remained consistent across alternative TEFs, except at the 90th percentile using Approach2. We highlight the need for developing underlying TEF probability distributions.