E/The Environmental Magazine : July-August 1999
By Jennifer Bogo and Tracey C. Rembert
The 101st Congress declared the 1990s the "Decade of the Brain" to focus attention on the most vulnerable of human organs. But after 10 years of intensive research focusing on chemical threats to mental development, have we learned anything?
Yes. Although average IQ scores have continued to increase about three points a decade, certain populations are at high risk of impaired mental development through exposure to potentially dangerous neurotoxins, a phenomenon Dr. Christopher Williams, of the University of London's Institute of Education, calls Environmentally-Mediated Intellectual Decline (EMID).
Scientists say relatively low levels of pollutants that seem to have no immediate impact on adults may have devastating effects on children or fetuses, often disrupting the thyroid--a key organ in mental development. "A baby's intelligence depends as much on the levels of thyroid hormone reaching the brain during critical periods of development as on inheriting smart genes," write the authors of Our Stolen Future, a groundbreaking book that made the connection between pollution and reproductive abnormalities. Unfortunately, only 10 percent of the 70,000 chemicals used commercially have been tested for their neurological effects.
According to Dr. Theo Colborn, an endocrine disruptor specialist with the World Wildlife Fund and a coauthor of Our Stolen Future, five percent of American babies have had toxic exposure to polychlorinated biphenyls (PCBs) in breast milk high enough to affect intelligence. A 1996 study by Sandra and Joseph Jacobson of Wayne State University found that children exposed to low levels of PCBs in the womb grew up with a lowered Intelligence Quotient (IQ), poor reading comprehension, short- and long-term memory problems and difficulty paying attention.
PCBs, commercialized by Monsanto in 1929, have been found in nearly every human on Earth. The Jacobsons discovered that women eating just two to three meals per month of Great Lakes fish had children suffering from measurable mental decline. Their follow-up study, testing children at age 11, found that those with the highest prenatal PCB exposure had the lowest overall IQ and verbal scores; 11 percent measured an IQ drop of 6.2 points.
Domestic PCB use was prohibited in the 1970s, but production continued in many other parts of the world until recently, says Walter Rogan, an epidemiologist with the National Institute of Environmental Health Sciences (NIEHS). But Rogan says halting production doesn't stop the threat, as PCBs resist the natural processes that break down chemicals, and can last "for decades." He adds that the primary source of exposure is through diet--particularly fish and meat. ...
Considered one of the most toxic chemicals ever created, dioxin is an unwanted byproduct of many industrial processes, including waste incineration, paper bleaching and pesticide manufacturing. The good news is that dioxin levels have dropped in the environment by 50 percent in the last decade. Unfortunately, the dioxin that still persists is detrimental to IQ.
The authors of a Dutch study analyzing pregnant women near a Rotterdam hazardous waste incinerator found that even low levels--background levels deemed as normal exposure--resulted in abnormal mental development in offspring because of thyroid disruption. According to the EPA, exposure shortly before or after birth is more likely to impair intellectual development. ...
Although pesticides have long been identified as potent carcinogens,
they are part of an upcoming wave of research examining impaired mental function.
One recent study led by Elizabeth Guillette, a
researcher at the University of Arizona, found that pesticide-exposed
Yaqui children demonstrated striking differences from unexposed children
in memory, eye-hand coordination and drawing
skills. And adult Nicaraguan workers overexposed to organophosphate
pesticides have been found to have persistent problems with memory, attention
span and concentration, notes a
Dr. Gina Solomon of the Natural Resources Defense Council thinks people are finally waking up to the full toxic potential of pesticides. "But the chemicals are already out there, they're in widespread use, and they haven't been tested for these subtle functional effects."
Additional threats to IQ include nutrient deficiencies (mainly of iodine,
calcium and iron) which heighten chemical exposures; volatile organic compounds
(VOCs); furans; cadmium; zinc; aluminum; and antimony.