Flame retardants travel hand to mouth on dust.
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Stapleton, HM, SM Kelley, JG Allen, MD McClean and TF Webster. 2008. Measurement of polybrominated diphenyl ethers on hand wipes: Estimating exposure from hand-to-mouth contact. Environmental Science and Technology 42(9):3329-3334. |
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| nealz/Flickr |
| PBDE-laden dust may be especially dangerous for children, who spend more time on dusty floors and have more hand to mouth contact than adults. |
Context
Flame-retardant chemicals known as polybrominated diphenyl ethers (PBDEs) are a group of similar, individual compounds used in many commercial products to slow burning. Carpets, electronic equipment (cells phones, remotes, computers) and foam (in chairs, beds and other furniture) are some items that contain the chemicals
PBDEs are released from products over time and significant concentrations have been found in the environment and in indoor house dust. The amount and types of PBDEs found in house dust are related to the types and amounts of PBDE-containing products in the building.
Indoor air pollution may be more of a health risk than outdoor air pollution because chemical contaminants can accumulate at much higher levels in enclosed areas. If less time spend outside and more time indoors, the concentrated pollutants can be breathed.
PBDEs are long-lived (persistent). They contaminate the environment and accumulate in wildlife and humans. Only a few studies have investigated the levels of these compounds in adults and children. Those that have find increasing levels in animals and people during the past quarter century -- the time when PBDE use has also increased.
PBDEs are measured in human fat, blood and breast milk. US women have some of the highest breast milk levels in the world when compared to Europe, Canada and Japan (Schecter 2003). PBDEs tend to cling to fat and so congregate in breast milk. No one knows if, or how much, of these chemicals are transferred to nursing babies and what affect this type of exposure would have on growing children.
The main ways flame reducing chemicals enter people and the extent they remain in the body are not clear. Generally, chemical exposure is from a variety of sources, including diet, water and air. So, even though many persistent pollutants (e.g. DDT and PCBs) are no longer used in the US, they continue to contaminate soil and water.
Since PBDEs most likely contaminate the environment in much the same way as other persistent chemicals, it is probable that eating, drinking and breathing are the main exposure routes of PBDEs. Yet, which of these contributes the most to human body burdens is not known.
Recent studies suggest that PBDE concentrations in food are not high enough to explain levels found in humans, therefore, eating or breathing dust may be a significant source (Lorber 2008). And, correlations have been found between the levels of PBDEs in house dust and the levels found in human breast milk.
A dust exposure route for PBDEs may be very significant for babies and young children as their crawling and mouthing behaviors result in eating dust. Children accumulate lead from house dust; it may be a potential route for PBDEs, as well.
PBDEs have toxicological effects in an array of organisms. In laboratory studies (mainly rodents and fish) PBDEs adversely affect the endocrine system, especially thyroid hormone regulation. The chemicals also have effects on neurodevelopment. Some states and the European Union have banned several types of PBDEs because of health concerns.
An key step to reduce exposures and their related health effects is to understand the routes and patterns of PBDE exposure.
What did they do?
Researchers tested whether PBDEs attached to indoor dust particles could be a major source of human exposure to the chemicals.
The authors' calculated exposure levels from hand to mouth contact. They based their findings on the amount of dust found on the hands of 33 men (16) and women (17) and six children (1 girl and 5 boys).
Hands were wiped with sterile gauze pads soaked in isopropyl alcohol. The pads removed dust and surface oils from the skin. The pads were analyzed for several types (congeners) of common PBDEs. The total levels of PBDEs and the concentrations of the individual congeners that they found on each of the hand wipe samples were reported.
Three people also provided 1) four separate wipe samples during two months to see if levels varied over time or if the dust was a constant exposure and 2) wipes from the top and the bottom (palm) of their hands to look for differences in the surface contact areas.
The authors used a new method they devised to calculate exposures. They based their estimates on total PBDEs on hands, efficiency of the transfer and estimates of how many times hands were placed near mouths or food items were handled when eating.
What did they find?
PBDEs were found on all of the hand wipes. Total amounts of the 15 most-measured congeners ranged from 2.6 to 1,982 nanograms. Penta and deca varieties were found most often, and BDE 209, a widely used PBDE, was detected in 67 percent of the samples.
The types and patterns of individual BDE congeners found on the hand wipes were similar to those from house dust samples. The similar patterns suggest that house dust got on the hands; although, direct contact with PBDE-laden products could also be a source.
The three people who repeated wipes during the year had both similar (woman and child) and varied (a man) PBDE levels at each time-point. Hand washing, behavior, day of the week and time of day may account for the variability, although more samples are needed to fully understand time trends.
PBDE levels were greater on the bottom of the hands relative to the top of the hands.
The calculated potential human exposure from hand-to-mouth contact, considering behaviors such as smoking, nail biting and eating finger foods, was, on average 154 nanograms/day for adults. However, in children, estimated amounts were nearly 10-fold higher at 1,380 ng/day.
What does it mean?
The estimates calculated in this study show that a dust-hand-mouth route contributes more PBDEs in humans than does eating contaminated food. This suggests that hand-to-mouth contact may be a significant and key way that people take up and accumulate PBDEs.
The results are of particular importance for babies and young children who are in contact with the floor and repeatedly place their hands and other dust-laden products in their mouths.
In the limited studies that have looked at PBDE levels in human blood, concentrations are much higher in children compared with adults. The dust-hand-mouth exposure route may contribute to these higher levels. Past models that use median dust ingestion rates may be underestimating exposure from hand to mouth contact.
Household pets also may be at risk. Pets are constantly exposed to dust settling on floors and other surfaces. While grooming, cats and dogs lick dust off their fur. Therefore, this dust-PBDEs-ingestion route may result in significant doses of the chemicals.
This preliminary study used a very small sample size and more follow-up is needed to confirm if the estimates found here are applicable to a larger population. More information is needed to determine how the estimated ingested amounts compare to what is measured in people's blood and if these amounts relate to significant health effects, especially in growing children.
Ultimately clean hands may lower exposure to PBDEs and other chemicals that stick to hands with dust or from direct contact and transfer of chemicals. Washing hands prior to eating lowers the risk of bacterial infections, and now seemingly, may lower risk of exposure to chemical pollutants, too.
ResourcesHooper, K and TA McDonald. 2000. The PBDEs: An emerging environmental challenge and another reason for breast-milk monitoring programs. Environmental Health Perspectives 108:387-392. Lorber, M. 2008. Exposure of Americans to polybrominated diphenyl ethers. Journal of Exposure Science and Environmental Epidemiology. 18(1):2-19. PBDEs - Fire retardants in dust. Environmental Working Group. Persistent toxic chemicals. Washington Toxics Coalition. Polluted pets. Environmental Working Group. Schecter, A, M Pavuk, O Päpke, JJ Ryan, L Birnbaum and R Rosen. 2003. High levels of brominated flame retardants in breast milk. Environmental Health Perspectives 111:1723-1729. |
PBDEs
