Comments on "Children's Health, Susceptibility, and Regulatory Approaches to Reducing Risk from Chemical Carcinogens." (Correspondence)
Landrigan, Philip J., Mattison, Donald R., Boardman, Barbara, Bruckner, James V., Jackson, Richard J., Karol, Meryl H., Krewski, Daniel, Weil, William B., Environmental Health Perspectives
In their recent commentary, "Children's Health, Susceptibility, and Regulatory Approaches to Reducing Risk from Chemical Carcinogens," Charnley and Putzrath (1) noted the seminal importance of the National Academy of Sciences (NAS) report Pesticides in the Diets of Infants and Children (2) in having catalyzed current concern about risks to children's health from environmental chemicals. As members of the NAS committee who wrote that report, we thank Charnley and Putzrath (1) for their acknowledgement. We are concerned, however, that their suggestion that child-protective safety factors be subjected to cost--benefit analysis would undercut a major recommendation of the NAS committee as well as a central provision of the Food Quality Protection Act (FQPA) (3). Specifically, the FQPA, motivated in part by our committee's report, calls for the application in risk assessment of an additional margin of safety to protect children's health in two circumstances: a) in the absence of data demonstrating assurance of safety, and b) in the presence of data showing children to be at greater risk to a particular chemical than adults.
Child-protective safety factors would not be a necessary default in risk assessment if good data were available on children's exposure and sensitivity to each of the many chemicals that they encounter. That, however, is not the case. Quantitative data on the exposures of fetuses, infants, and children to most chemicals are limited, as are data on the toxicity of most chemicals. A recent analysis by the U.S. Environmental Protection Agency (4) indicates that even minimal toxicologic data exist for only 43% of the 15,000 chemicals produced each year in quantities of over 10,000 pounds; data on developmental toxicity, the sort of data that would permit direct comparison of child versus adult sensitivities, are available for only about 20% of these high-production volume chemicals.
To address these large gaps in data, the NAS Committee on Pesticides in the Diets of Infants and Children (2) recommended that "there should be a presumption of greater toxicity to infants and children." The committee suggested that
an uncertainty factor up to ten-fold ... be considered ... when data from toxicity testing relative to children are incomplete.
The committee coupled this recommendation with a call for expanded research that would enhance the "current limited database on relative sensitivity." It was the NAS committee's clear intent that the presumption of greater toxicity and the imposition of an additional safety factor would catalyze expansion of the database on developmental toxicology.
Charnley and Putzrath (1) questioned the wisdom of incorporating child-protective safety factors in risk assessment. They asked whether the cost is worth the benefit. The principal basis for their question lies in a comparison they presented of the relative sensitivities of children and adults to a series of carcinogenic chemicals. Drawing upon the work of our NAS committee, they found that adult animals are more susceptible to 53% of carcinogens, that young animals are more susceptible to 37%, and that there is no age-related difference in 10%.
We agree with those findings because they come mainly from our report (2). However, Charnley and Putzrath (1) presented their argument in a vacuum, and they manifested little apparent cognizance of the enormous voids in knowledge that surround it. The limitations in their analysis are threefold.
First, Charnley and Putzrath (1) mentioned only in passing the great differences in exposure that exist between adults and children. The NAS committee found, however, that differences in exposure are often orders of magnitude greater than differences in susceptibility. We noted in our report that children drink more water, eat more food, and breathe more air per pound of body weight than adults and thus are disproportionately exposed to any toxic chemicals contained in those media (2). …