Exposure science can move us toward a more protective chemicals management policy by preventing human and ecological risks that may occur when existing “bad actors” are replaced with alternative chemicals that may not be as well studied.
Advances in analytical chemistry have allowed us to detect chemicals in the environment and in people at increasingly low concentrations, enabling us to better explore multiple pathways of exposure by assessing concentrations in air, water, and soil, as well as dust, furniture, and household products. Large-scale biomonitoring studies of chemicals in blood and urine, such as those by the Centers for Disease Control and Prevention, have provided snapshots of human exposure to a wide array of chemicals. This has “personalized” exposure science and increased awareness in the general population about chemical exposures. Research demonstrating that a chemical is unexpectedly bioaccumulating—e.g., polybrominated diphenyl ethers (PBDEs)—or appearing in humans—e.g., perfluorooctane sulfonate (PFOS)—often produces an intense response by the public, the media, manufacturers, and regulators. The responses range from voluntary phaseouts of the chemical to calls for restrictions on use to outright bans. However, actions taken to reduce exposures to those chemicals often result in increased use of existing alternative chemicals or new chemicals developed to fill the void. In some cases, we know less about the exposure potential and/or toxicity of the alternative/new chemicals. In other cases, we find that chemicals once banned for a specific use find their way back into the marketplace as replacement chemicals with new uses. The story of a class of flame retardants—PBDEs—illustrates the importance of holistic thinking in chemical use and the role of exposure science in facilitating this type of thinking.
Flame retardants have been employed to reduce fire incidence and fire-related death and property destruction. The use of two brominated flame retardants was restricted in the 1970s because of exposure and toxicity concerns: polybrominated biphenyls were inadvertently mixed with animal feed, resulting in livestock death and high human exposures, and tris(2,3-dibromopropyl)phosphate (tris-BP), used in clothing, including children’s pajamas, was reported to be mutagenic and a kidney toxicant. It was also discovered that children were exposed to tris-BP through skin contact with their pajamas. The use of tris-BP and tris-(1,3-dichloro-2-propyl)phosphate (chlorinated tris) in children’s clothing was banned in the late 1970s, but they are still used in textiles and polyurethane foam. Similarly, PBDEs and other flame retardants that were replacement chemicals in the late 1970s are still used in some textiles and hard plastics (Birnbaum and Staskal, 2004).
IMPACT AND IMPLICATIONS FOR EXPOSURE SCIENCE
In the late 1990s, a report on PBDEs in breast milk in Sweden showed that levels had increased exponentially since the early 1970s (see figure). Follow-up studies in the United States found that PBDE concentrations in breast milk were much higher than those in Sweden. Equally alarming were reports of widespread exposures to PBDEs in humans and ecosystems. Although people are exposed to PBDEs in food, household dust can be an even more important route of exposure. This exposure information, in combination with toxicity research, led to a series of voluntary phaseouts, restrictions, and outright bans from 2004 to 2009 on the production of two PBDE formulations (penta and octa), followed by restrictions on the third formulation (deca) beginning in 2009. It took about 5 years from the time of release of the Swedish study to the time of widespread restrictions on these compounds.
However, to maintain fire safety standards, existing alternative flame retardants are being used in greater volume and new replacement chemicals are being brought to market. These include brominated phthalates, chlorinated tris, and other chemicals (CIREEH, 2009). These chemicals have now been measured in household dust. Ironically, although chlorinated tris was banned in children’s pajamas more than 30 years ago, it is now one of the highest-volume flame retardants in use today. Current use of chlorinated tris results in human exposure from dust inhalation and ingestion.
Unfortunately, the story of brominated flame retardants is not an isolated one, nor is it one consigned to the history books. There are too many examples of chemicals taken off the market only to be replaced with chemicals that, in time, come to be considered “of concern.” We may be at such a juncture with replacement chemicals for bisphenol A (BPA) and PFOS. BPA, used mainly in the production of polycarbonates, has been measured in >90% of the general US population, prompting calls for bans, which have been enacted for certain uses in some parts of the United States and proposed in other countries. This has in turn resulted in a demand for alternatives to polycarbonate bottles, including glass and metal bottles and those made from a copolyester (C&EN News, 2009), which is marketed to both adults and children. Our literature search on some of the replacement copolyester chemicals revealed no exposure information. Years from now, will we be seeing exposure studies describing certain BPA alternatives as emerging chemicals of concern?
A similar issue has arisen with the replacement of PFOS—a compound used as, among other things, stain repellants and coatings for food packaging—with other perfluorinated compounds (PFCs). Once considered stable and nontoxic, PFOS is now known to bioaccumulate and has been measured in people, wildlife, and the environment around the world. As was the case with PDBEs, this type of exposure information led to a move away from its use (through voluntary phaseouts and restrictions) and toward other PFCs. Recently published levels of PFCs in household dust suggest the possibility of widespread exposure to some of these replacement PFCs (e.g., Kato et al., 2009).
By using exposure tools in a more holistic fashion, we may be able to avoid déjà vu all over again. Our experience with PBDEs clearly shows the high-priority need for a proactive exposure science approach toward evaluating emerging chemical constituents. We must break the cycle of introducing (or re-introducing) chemicals with potential for widespread human and ecosystem exposures without first understanding potential pathways and magnitude of exposure. Exposure scientists, including those conducting biomonitoring research, can influence this process by thoughtfully considering both existing and potential replacements and using state-of-the-science tools to help us evaluate the likelihood that future exposures to these chemicals will become widespread and/or increasing in concentration. This will enable us to make more informed decisions about the public and environmental health acceptability of replacement/new chemicals.
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Fire Technology (2015)