Children as “Indicator Species”?
Apparently I was caught up in an odd fit of presentiment when I wrote that post three weeks ago about pets as indicator species for the domestic environment. This week, as reported widely on the web, the results of a study published by the Environmental Working Group revealed that young children have three times the blood levels of fire-retardant chemicals as their mothers. Linda Birnbaum, PhD, a senior toxicologist with the EPA was quoted in an article on WebMD as saying:
The gap between mothers and their children was a surprise finding. Because of typically similar diet and exposures in the same household, “we would have expected similar levels,” says Anila Jacob, MD, MPH, a senior scientist at EWG. “What we found was, kids on average had three times the levels of toxic retardants polluting their blood compared to their moms.”
The chemicals are hormone-disrupting and potentially hazardous, especially to young brain development, Jacob and her colleagues say. But a spokesman for the flame retardant industry countered that the levels of chemicals, known as PBDEs or polybrominated diphenyl ethers, found in the study are quite low, in the parts per billion range.
I can not help but question Dr. Jacob’s understanding of the word “exposure.” According to the EPA, an exposure assessment is defined as: “Identifying the pathways by which toxicants may reach individuals, estimating how much of a chemical an individual is likely to be exposed to, and estimating the number likely to be exposed.” In most human adult populations exposure pathways like direct ingestion of dusts, particles and coatings are negligible. But in toddler and pet populations – creatures who spend much of the day crawling around on all fours and putting things into their mouths – these represent major exposure pathways.
It is even more ironic that EWG missed this parallel to pets’ and childrens’ potential exposure pathways when one considers that the levels of PBDEs found in children who participated in the study were comparable to those “found harmful in laboratory animals:”
There is no established standard for safe blood levels, according to Jacob and Sonya Lunder, MPH, a senior analyst at EWG and a co-author of the report. “These findings raise concern about the effect of PBDEs on children’s brain development,” Lunder says. “These levels are uncomfortably close to doses found harmful in laboratory animals.”
Although there are no human studies, Jacob and Lunder point to studies conducted by the Environmental Protection Agency (EPA) and others finding that PBDEs can be especially toxic to the developing brains of animals, with even a single dose of PBDEs causing ill effects.
What levels of PBDEs in blood or tissues DO cause “ill effects” – no one knows. According to WebMD:
The EPA has set a “reference dose” for Deca, she says, which states that a daily oral dose of 7 micrograms per kilogram of body weight is believed to be without appreciable effects. But translating that to “safe” blood levels is not easy, she says, because the oral dose is different than what is stored in the body.
So now you ask, just exactly what are PBDEs? Well – generally speaking – PBDEs are a class of relatively large, artificially created molecules consisting of 209 possible congeners that contain 1-10 bromine atoms each. There are three common commercial mixtures of PBDE: Pentabromodiphenyl Ether (PeBDE or penta), Octabromodiphenyl Ether (OBDE or octa) and Decabromodiphenyl Ether (DBDE or deca).
Why the heck do we use them? Well, PBDEs are used as flame retardant additives in many common polymers, foams, plastics, upholstery, adhesives, sealants and coatings. They are added to the materials treated, not chemically bonded with them. This makes them more susceptible being separated and lost from the materials they were added to. According to a report published in June 2006 by Environment Canada:
It has been estimated that approximately 90% or more of PeBDE produced globally is used in polyurethane foams in office and residential furniture, automotive upholstery, sound insulation and wood imitation products. OBDE produced globally is added to polymers (mainly acrylonitrile butadiene styrene), which are then used to produce computers and business cabinets, pipes and fittings, automotive parts and appliances (WHO 1994; European Communities 2003). DBDE is used as a flame retardant, to a large extent in high-impact polystyrene and other polymers, with broad use in computer and television cabinets and casings, general electrical/electronic components, cables and textile back coatings
Penta BDE and Octa BDE, were banned in Europe and their use has largely been discontinued in the U.S. because of their persistence, toxicity, and tendency to bioaccumulate. As a group, PBDEs have a low vapor pressure, low water solubility and a high octanol / water partition coefficient. In common English this means that they have a tendency to remain as solid particles in the environment where they will preferentially bond to organic constituents.
Deca PBDE is still used and produced in the US today. Penta and Octa PBDEs, though no longer involved in most manufacture, are still present in older materials in nearly all modern homes. A further concern is the creation of potentially toxic breakdown products as these materials decay. Because they are rare and are not created in a controlled manner, little is known about these breakdown products. According to a July 22, 2008 web release from the American Chemical Society:
An EU ban on Deca BDE’s use began on July 1, and it has also been banned in some U.S. states. If the BDE-209 molecules that make up the majority of the Deca BDE formulation are conclusively shown to debrominate in the environment to produce the lighter-weight PBDE compounds, or congeners, associated with these discontinued formulations, the finding would increase pressure to end Deca BDE’s use in North America. Toxicology research has linked PBDEs to liver and thyroid toxicity and to learning, behavior, and memory problems.
La Guardia … notes that both he and Stapleton have detected in environmental samples what he calls “oddball congeners,” such as BDE-179, BDE-184, and BDE-202, which contain seven or eight bromine atoms; these congeners are not found in any commercial mixture. In fact, Stapleton says that many studies now demonstrate significant formation of the so-called oddball congeners under environmentally relevant conditions.
How common are PBDEs (and their breakdown products) in the environment? A report published in June 2006 by Environment Canada reports that:
PBDE concentrations have increased exponentially in arctic biota over the past two decades and have been measured in Arctic air. This suggests efficient long-range atmospheric transport of PBDEs.
PBDEs have been detected in all environmental media as well as sewage sludge, and there is evidence that their levels in the North American environment are increasing.
Measured data indicate that tetra-, penta- and hexaBDE are highly bioaccumulative and satisfy the criteria for bioaccumulation in the CEPA 1999 regulations. Concentrations of PBDEs in herring gull eggs have increased exponentially between 1981 and 2000 at Lake Ontario, Huron and Michigan sampling sites. Concentrations of PBDEs (predominantly tetra- and penta BDE congeners) have also increased exponentially between 1981 and 2000 in Arctic male ringed seals.
I can’t help but wonder what kind of PDBE concentrations we’d find if we tested house pets. I suspect that since they appear to be subject to exposure pathways that are similar to our young children, that we’d see levels that were similar – if not higher – in their blood and tissues.
I hope that the increasing incidence of cancer seen in our pets isn’t a harbinger of what we can expect for our children. Given that many dog breeds suffer from significantly higher incidences of certain types of cancers than others; inbreeding, founder effects and related genetic problems are likely a factor; but our pets’ much higher exposure to the thousands (millions?) of trace additives found in modern household products may also be an important factor.
How important a factor? Well – until further research is done the answer, once again, is “We don’t know.”