Prenatal Chemical Exposures Linked to ADHD in Boys

Beyond Pesticides

New research conducted in New Bedford, Massachusetts suggests that organochlorine chemicals, which were first linked to learning problems in children more than two decades ago, may play a role in attention-deficit hyperactivity disorder (ADHD), especially in boys. Previous research has reported associations between organochlorines and ADHD-related behaviors, but this research found sex-specific effects in children born to mothers who lived near the contaminated harbor and dumpsites in low-income communities. This study adds to a growing body of literature associating learning disorders with prenatal chemical exposures.

According to the study, Neuropsychological Measures of Attention and Impulse Control among 8-Year-Old Children Exposed Prenatally to Organochlorines, boys who were exposed to higher levels of the organochlorines -polychlorinated biphenyls (PCBs) and DDE (a metabolite of DDT)- in the womb scored lower on focus and concentration tests, which indicates they are more likely to have attention problems often related to ADHD.

In the study, umbilical cord blood was collected from 788 newborns born between 1993 and 1998 from four towns near New Bedford Harbor, Mass., to see what they were exposed to in the womb. Roughly eight years after they were born, almost 600 of these children underwent two tests. One measured their ability to focus on and react to a specific target—in this case, the image of a cat on a computer screen- and to inhibit their response to another animal’s image. The other exam included parts of an IQ test that measured their processing speed and distractability, which tests whether they can maintain attention over time. Boys exposed to the highest levels of PCBs during their mother’s pregnancy failed to press a button for the on-screen cat 12 percent more often than children exposed to the lowest levels. Those same boys also scored slightly lower in the other test. The same link was not found in girls. Animal data suggest that hormone-disrupting chemicals, including PCBs, affect each gender differently, but the connection in humans remains unclear.

All of the children studied were born to mothers who lived near the contaminated harbor and dumpsites in low-income communities, where twice as many people live below the poverty line than the Massachusetts average. Unfortunately, children from low-income families are typically exposed to higher levels of environmental chemicals—some currently used and some long banned—than U.S. children from other socioeconomic backgrounds. The exposures in this New Bedford study were fairly low (median: 0.19ng/n PCB; 0.31ng/g DDE), which is comparable to children’s levels throughout much of the U.S. This means that a connection between PCBs and attention problems in boys could exist in other communities as well. Boys are two to three times as likely as girls to develop ADHD, the most common learning disorder reported in children worldwide. In 2007, U.S. parents reported that nearly 10 percent of children between the ages of 4 and 17 had been diagnosed with ADHD, according to the Centers for Disease Control and Prevention.

Banned in the U.S. more than 30 years ago, PCBs belong to the same class of chemicals as other notorious persistent pollutants, including DDT and chlordane. These chemicals persist in the environment for extraordinarily long periods of time and even accumulate in food chains. Nearly every U.S. resident still has detectable levels of an organochlorine chemicals in his or her blood. PCBs and its chemical cousins have the ability to disrupt hormones, which can alter how the brain develops. One study found a link between organochlorines and non-Hodgkin’s Lymphoma.

Organochlorines have previously been linked to a number of adverse effects on human health, including birth defects and diabetes. This study illustrates how the health impacts of pesticides are often long-term and multigenerational, with pesticides no longer in use continuing to affect public health. This also reinforces the need for a more precautionary approach to regulating pesticides and industrial chemicals. Once released into the environment, many chemicals can affect health for generations, either through persistence in the environment or long-term changes to the genetic code of humans and other animals.

In response to the growing evidence linking pesticide exposures to numerous human health effects, Beyond Pesticides launched the Pesticide-Induced Diseases Database to capture the range of diseases linked to pesticides through epidemiologic studies. The database, which currently contains hundreds of entries of epidemiologic and laboratory exposure studies, is continually updated to track the emerging findings and trends.

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