"We know it can be harmful, but what the EPA is trying to determine is, how much is too much, and at what level are people affected?" said Zoeller.
Concern centers around the potential effects on the thyroid gland from exposure to perchlorate in the environment, specifically in drinking water. Perchlorate is both a naturally occurring and manufactured chemical, and is used as a propellant for airbags as well as in rocket fuel, Zoeller says. Wastes from the manufacture and disposal of perchlorate-containing chemicals are increasingly being discovered in soil and water, according to the EPA. Although pockets of perchlorate have been found in 20 states – including in Massachusetts, on Cape Cod – the preponderance of contamination has been found in the western United States, in areas of Nevada and California.
And, because water is believed to be the primary source of the contaminant, it's extremely difficult to determine how much is safe within a given water supply. "There are so many variables," explained Zoeller. "How much tap water do you drink? Do you cook your food in this water? Is the danger level for a grown man the same as for an infant who is nursing and who weighs 15 pounds?" Perchlorate doesn't build up within the human body, Zoeller notes, although it may in plants – including vegetables that are irrigated with contaminated water. He notes that scientists do not believe that perchlorates are overtly toxic; that is, "it's not going to give you cancer or a liver problem."
Zoeller's research over the last eight years has focused on how contaminants in the environment disrupt the endocrine system. In recent years, his research has focused particularly on thyroid hormone, and its role in fetal brain development. "We know that thyroid hormone from the mother is essential for proper development of the fetal brain," Zoeller said. "We don't know when during gestation it comes into play, what it does, or how it works. But we do know that if a fetus can't make thyroid hormone, anything that happens to the mother's thyroid will affect the baby's brain."
Perchlorate blocks the thyroid gland's ability to concentrate iodine from the diet, and humans need iodine in order for their thyroid glands to work properly, explained Zoeller. In adults, the thyroid helps to regulate metabolism. In children, the thyroid plays a major role in growth and development, in addition to metabolism. Impairment of thyroid function in mothers may affect fetuses and nursing newborns, resulting in behavioral and learning disorders, such as lower IQ and attention deficit disorder.
"Even when we control for the improved tools we have to diagnose specific learning disabilities such as attention deficit disorder, there is nevertheless a much higher incidence of them now compared to 20 or 30 years ago," said Zoeller. "This appears to be a real problem, and there's a great deal of concern that the problem is related to environmental contaminants."
In order to determine a safe level for perchlorate exposure, the EPA has asked 17 scientists, including Zoeller, to evaluate some 500 pages of information on the chemical. Scientists in disciplines ranging from immunology to genetics submitted their comments to the EPA in May; the agency is expected to publish a proposed safe level – called a draft reference dose – late this summer. Zoeller notes that the draft reference dose is an early step in a lengthy process to determine whether the agency should set a federal drinking-water standard for this contaminant.
Zoeller's efforts with the EPA will reach into the classroom next fall, when he teaches endocrinology to undergraduates. The laboratory component will require students to design and perform an experiment using modern molecular techniques that address specific issues not addressed in the studies evaluated by the EPA. "This is an excellent educational opportunity for students to work on an issue of national significance, and perhaps even to have their findings published in the scientific press," said Zoeller. "And working on the thyroid hormone system will teach them a great deal about how the endocrine system works in general."
Note: Thomas Zoeller can be reached at 413/545-2088 or tzoeller@bio.umass.edu