Pregnant women and children in the US are exposed to multiple toxic pollutants that impair a child's brain development.
It’s now known that many chemicals can cross the placenta, once believed to be a sacrosanct barrier. This is disquieting, because the vast majority of these chemicals have never been tested for human health effects. Furthermore, the medical community agrees that many diseases and conditions, including obesity, cancer, and autism, are modulated by both genes and fetal exposures.
The center’s early studies found significant associations between pollutants measured in the mothers and difficult birth outcomes, including low birth weight and small head circumference.
As many as one in six children nationwide has a neurodevelopmental disability, including autism, speech and language delays, and attention deficit hyperactivity disorder. The Centers for Disease Control and Prevention estimates that ADHD alone affects 14 percent of children... the National Research Council of the National Academy of Sciences estimated that 3 percent of brain disorders are caused outright by environmental toxicity and an additional 25 percent by environmental exposures interacting with genetic susceptibilities.
... scientists need to look at both the genome and—to use a term coined in 2005 by Christopher Wild, a cancer epidemiologist—the “exposome.”
“In the past, we took a reductionist approach,” Perera says, “a single exposure, a single effect. But now we think that pollution interacts with nutritional and social susceptibility factors. We’re making heroic attempts to measure these. We’re building the exposome.”
Grandjean and his co-author, Philip Landrigan, of Mount Sinai Hospital in New York City, identified 201 heavy metals, solvents, pesticides, and endocrine disruptors known to have toxic effects in the human brain (at least 1,000 other substances are neurotoxic in animals but haven’t been tested in humans). Of those 201, about half are “high production volume” chemicals, made in or imported to the United States in excess of one million pounds per year.
... showing evidence of developmental toxicity in the fetal brain, ... the count is now up to 10 and growing. All of these neurotoxicants are relatively common, routinely found in the blood of pregnant women. They include the usual suspects—lead, methylmercury, and PCBs—but also organochlorine pesticides like DDT (which was banned in the 1970s but still persists in soil and water), organophosphate chemicals like the roach-killer chlorpyrifos, PAH, PBDEs (this pervasive class of flame retardants is now being phased out), arsenic, ethanol, and the solvent toluene.
Different neurotoxicants affect children differently. At high levels, methylmercury appears to cause memory deficits, while lead primarily decreases attention span and pesticides tend to impair spatial perception. Black carbon apparently affects attention and processing speed.
Many of these substances disproportionately affect the poor, but not all. Poor kids are exposed to more lead and first- and secondhand tobacco smoke. More affluent populations accumulate more mercury from their diet. Urban kids may be exposed to more PAH and black carbon, farm kids to more pesticides and arsenic from well water.
... brominated flame retardants may be the most democratic. Although levels of PBDEs are now dropping in pregnant women, Americans still have the highest levels tested anywhere in the world.
What worries Landrigan is how easily many neurological effects can fly under the radar. These are not the kinds of acute poisonings that land kids in emergency rooms. Most doctors are not trained to look for prenatal or childhood environmental exposures. If parents ask them about it, he says, “they tend to offer bland reassurance.” But for the individuals and families involved, learning, psychological, and behavioral impairments can have dramatic, lifelong impacts on meaningful measures from happiness to income.
But do a few IQ points matter? Should society care if a boy behaves a few shades more or less aggressively? These are questions that currently interest epidemiologists more than family physicians. One of Landrigan’s associates at Mount Sinai, research scientist Megan Horton,..., told me that an average drop of five IQ points in the United States translates into 2.4 million gifted kids instead of 6 million, and 9.4 million mentally retarded children instead of 6 million, or a 57 percent increase. Leonardo Trasande, a pediatrician formerly at Mount Sinai and now at the New York University School of Medicine, has estimated that mercury exposures alone have led to losses of 0.59 to 3.2 IQ points in several hundred thousand children born every year in the United States, resulting in decreased lifetime economic productivity valued at $8.7 billion annually. [emphasis mine]