Dioxin for the 21st Century

Just about the time we’ve studied dioxin to death, as well as started seeing reductions in exposure, something else comes along to take its place. Environmental Health News provided this link to a forthcoming study in Environmental Health Perspectives that evaluates the dietary exposure to polybrominated diphenyl ethers (PBDEs). PBDEs have some similarities to dioxins in that meat, fish and dairy products are the largest sources of dietary exposure. However, the authors speculate that diet isn’t the only important source, and suggest that sources such as house dust (?) are also significant. That’s a topic needing further study in my mind, but it might be the impetus to vacuum your carpet more thoroughly. What was the more interesting conclusion from the exposure study was the result that PBDE intake from food was estimated at 307 ng/kg-day for nursing infants, and varied from 2 ng/kg-day at age 2-5 for both males and females to 0.9 ng/kgday in adult women. The occurrence of PBDEs in breast milk helps explain the elevated infant exposures.

We’re a bit behind the eight-ball with regard to PBDEs. The health impact isn’t well understood and the adverse effects of concern (neurobehavioral deficits), if truly significant, don’t bode well for future generations. A quick check of EPA’s IRIS database shows that the Reference Dose values for different PBDE isomers are all old, and not based on the critical adverse effects – essentially, we don’t really understand yet what the no adverse effect levels are in humans for the neurobehavioral effects. More recent studies in laboratory animals (here and here) lead me to wonder if there is much of a margin of safety between exposure levels in infant and the no adverse effect levels. Let’s hope it doesn’t take over a decade to figure this stuff out, as it has for dioxins.