Data just released from the Centers for Disease Control and Prevention (CDC) show that rates of attention-deficit/hyperactivity disorder (ADHD) continue to rise, jumping from 6.7 percent of U.S. children in 2000 to 9 percent of U.S. children in 2009. As doctors and scientists try to uncover the causes of ADHD, attention is turning to all the chemicals children and pregnant moms encounter in their daily lives. "Certainly there's a genetic component to the disorder," says Brooks Gump, Ph.D., M.P.H., associate professor in the department of public health, food studies, and nutrition at Syracuse University, noting that roughly 50 percent of cases are genetic. "But there are environmental factors involved, as well." The disorder has already been linked to pesticides found in chemically grown food, and now Gump has shown in a new study that one of the chemical causes of ADHD might be perfluorinated chemicals (PFCs), a class of highly toxic chemicals used to make stain- and water-repellent fabrics and nonstick cookware that linger in the environment for very long periods of time, building up in the blood of animals that enter the food chain and, ultimately, in people.
There have been a few observational studies finding associations between a diagnosis of ADHD and high PFC levels in blood. But Gump's new study, published recently in the journal Environmental Science & Technology, shows real-world situations in which children with high PFC levels exhibited characteristics of the disorder, mainly impulsive behavior.
THE DETAILS: Eighty-three children between the ages of 9 and 11 took part in the study. Blood samples were taken and measured for the presence of 11 different PFCs, including PFOA, used to manufacture Teflon and other nonstick finishes, and PFBS, a chemical made by 3M to replace the toxic PFOS, which was found to cause liver damage and increase chances of infant mortality before 3M phased it out 10 years ago. Then the children took a 20-minute computer test designed to detect something called impaired response inhibition, or impulsive behavior, a primary characteristic of children with ADHD. "What it translates into are risky behaviors that ultimately may translate into things like drug use," says Gump. Children who are too impulsive have also been found to have lower IQs, he adds, and can have difficulty stopping certain behaviors when asked. "For whatever reason, impulsivity is a cognitive process that's particularly sensitive to toxicants."
During the computer game, the children were told they could win 25 cents if they could wait 20 seconds before hitting the space bar, with the potential to win $15 upon completion of the game; responses made sooner than 20 seconds indicated a child with high impulsivity. The authors found that the higher a child's PFC blood level, the shorter his or her response time was, and those children's response times got shorter and shorter as the 20-minute game wore on. The strongest association between the chemicals and impulsive behavior was seen in children with high levels of PFHxS, a PFC that was also made by 3M (and also phased out 10 years ago) that was widely used in carpet treatments and in some forms of food packaging. It was detected at some level in all the children participating in the study, as were PFOA and PFOS.