Kids at Risk
Chemicals in the environment come under scrutiny as the number of childhood learning problems soars
Potentially hazardous chemicals should be judged "guilty until proven innocent," says EPA adviser and Yale University Prof. John Wargo. But the EPA doesn't work that way. The agency requires chemical manufacturers to prove that their products do not cause cancer or birth defects, but it does not require them to provide data on neurological effects--even though the technology for such testing now exists. The EPA is caught in a bind: It can't require a company to submit data without proof that a product is harmful. But it can't prove harm without the data. "We're in the dark," says Ward Penberthy, an EPA deputy director.
Children are particularly vulnerable to toxic chemicals. Normal brain development begins in the uterus and continues through adolescence. It requires a series of complex processes to occur in a carefully timed sequence: Cells proliferate and move to the correct spot, synapses form, neural circuits are refined, and neurotransmitters and their receptors grow. Neurotoxicants may slow, accelerate, or otherwise modify any of these processes. Says Philip Landrigan of New York's Mt. Sinai School of Medicine: "You end up with gaps in the wiring."
The idea that substances in the environment can harm the human brain is not new. In ancient Rome, miners were felled by what the medical literature of the time called "lead colic." The Mad Hatter in Lewis Carroll's Alice's Adventures in Wonderland comes from the 19th-century expression "mad as a hatter," a reference to mercury's effects on felt-hat makers. Over the past 70 years, adults and children around the world have been poisoned--and, in some cases, killed--by mercury in fish, PCBs in rice oil, a fungicide in seed grain, and a rat-killing agent in tortillas. After hearings in 1985, the House Committee on Science and Technology reported that there were 850 known neurotoxicants, any of which "may result in devastating neurological or psychiatric disorders that impair the quality of life, cripple and potentially reduce the highest intellect to a vegetative state." The report prompted virtually no action.
Today, however, the federal government is under increasing pressure from pediatricians, academics, and its own scientists, all clamoring for more testing of neurotoxicants. Agency officials are focusing on the following areas:
Pesticides. Organophosphate pesticides are domesticated versions of wartime nerve agents. The best known, Dursban and Diazinon, have been on the market since 1965 and 1956, respectively. The active ingredient of Dursban, chlorpyrifos, is found in some popular Raid sprays and Black Flag roach and ant killer. After re-examining the toxicity of chlorpyrifos, however, the EPA announced last week that it will ban nearly all household uses of it and restrict its use on tomatoes, apples, and grapes. The EPA found that Dursban could damage the brain. It also determined that children could receive up to 100 times the safe dose in some cases.
Diazinon, one of 37 other organophosphates under review, could be next. A preliminary EPA analysis recently found that a child could inhale up to 250 times the safe amount after a basic "crack and crevice" treatment by an exterminator. Linda Meyer, a toxicologist with Novartis, which makes Diazinon, says that the EPA extrapolated from a worst-case Novartis study--in which rats were placed in a chamber pumped full of the pesticide in aerosol form. As a result, Meyer says, "the risk for children is grossly overestimated." Novartis also notes that the EPA, in its draft analysis, states that animal studies of Diazinon have revealed "no evidence of abnormalities in the development of the nervous system."
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