Appendix D Food Codes for NHANES - OEHHA

Scientific Review PanelSRP Draft Version 2 February,June 2012
Each reference half-life was derived from data on occupational exposures
(Flesch-Janys et al., 1996; van der Molen et al., 1996) or dietary intake of the
general population (Ogura, 2004). Note that mean half-lives vary by more than 2fold
among dioxin, 5-fold among furans and more than 100-fold among PCB
congeners.
In an initial review of the literature, Milbrath et al (2009) reviewed evidence about
factors that can affect elimination rates. Personal factors such as body fat,
smoking status and past lactation practices can affect body burden and
elimination rates. For example, smoking has been associated with a 30% to
100% increase in elimination rates of some dioxin congeners (Flesch-Janys et
al., 1996; Milbrath et al., 2009). As well, the onset of lactation sets a new
elimination pathway into effect and can substantially reduce the maternal body
burden of PCBs during 6 months of lactation (Niessen et al., 1984; Landrigan et
al., 2002).
Half-lives derived from children would be less than that from older adults due, in
part, to the effects of the growing body on estimates of blood concentrations.
Models based on rat data demonstrate a linear relationship between increasing
fat mass and half-life length at low body burdens, with the impact of adipose
tissue on half-life becoming less important at high body burdens (Emond et al
2006). At high body burdens, dioxins are known to up-regulate the enzymes
responsible for their own elimination. Human data suggest that the serum
concentration of TCDD where this transition occurs is 700 pg/g and 1,000 –
3,000 pg/g for PCDFs (Kerger et al 2006, Leung et al 2005). Therefore,
investigators selected a subset of data based on the following criteria:
• blood serum concentrations of PCDD/Fs were less than 700 pg /g
blood lipid total toxic equivalents (TEQs) at the time of sampling
• subjects were adults
• measurements were not reported as inaccurate in later studies
Milbrath et al selected the reference values to represent a 40- to 50-year-old
adult with blood dioxin concentrations in the range where fat drives the rate of
elimination (i.e. at lower body burdens). In addition, Milbrath rejected half-lives
longer than 25 years if the original study calculated half-lives assuming steadystate
conditions.
For the retained subset, the investigators calculated the mean and range of halflives
to establish a representative set of half-lives for each congener in a
moderately exposed adult (Milbrath et al., 2009). They also adjusted reference
half-lives for age, body fat, smoking habits and breast-feeding status as these
factors were all strong determinants of half-life in humans (Milbrath et al., 2009).
A generally accepted approach to estimating the concentration of a lipophilic
chemical in milk is outlined by Smith (1987). This approach is based on average
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