By Clif Cleaveland
Add pesticides to the list of suspected causes of attention-deficit/hyperactivity disorder in children.
ADHD affects up to 7 percent of school-age children, and boys are more frequently affected than girls. Symptoms of ADHD include restlessness, inattention, difficulty concentrating and impulsive behavior. Diagnosis can be complex because symptoms overlap with normal behavioral patterns in young children.
Genetic and environmental factors contribute to ADHD. Smoking, consuming alcohol and use of illicit drugs during pregnancy are recognized risk factors. Head injuries and exposure to lead during early childhood increase the risk of ADHD.
Research by Maryse Bouchard and colleagues reported in the May issue of Pediatrics links ADHD to exposure of children to common pesticides that contain organophosphates (OP). OP initially were developed as nerve gases such as sarin to be used in warfare. Since World War II, OP such as malathion and diazinon have commonly been used as pesticides especially in the spraying of crops and the control of household insects. Currently, 40 pesticides that contain OP are approved for use by the Environmental Protection Agency.
Organophosphates may be absorbed through the skin, lungs and digestive tract. Exposure may be measured by analysis of urine samples for breakdown products of OP. Children have higher concentrations of these substances in their urine than adults. The developing brains of children seem especially vulnerable to toxic effects of OP. Earlier studies have shown that exposure to OP during pregnancy impairs intellectual development of infants.
From a large, ongoing, nationwide study of children from diverse backgrounds, the researchers identified 148 children with ADHD. These scientists determined that children with higher levels of OP products in their urine were more likely to have ADHD compared to children with minimal or undetectable levels. The risk of ADHD rose with the concentration of these chemicals in urine samples.
In all animal species, insects as well as people, organophosphates inactivate an enzyme that is vital to the transmission of impulses in the nervous system and from nerves to muscle. Acute OP poisoning in people can be rapidly fatal, causing severe digestive symptoms, breathing difficulties, shock, seizures and coma. ADHD may be the consequence of chronic OP exposure to fetuses, infants and children. Longer-term studies with periodic monitoring of urine OP levels are needed to strengthen the proposed association.
The commonest source of organophosphates exposure for children is from pesticide residue in the food that they eat. The Environmental Working Group website (www.ewg.org ) offers a "shopper's guide to pesticides." Celery, peaches, strawberries, apples, blueberries and imported grapes have high pesticide residues. Those who eat fruits and vegetables from the "dirty dozen" list are exposed to 10 or more pesticides daily. Onions, avocado, sweet corn and cabbage are among the "cleaner" foods. Selecting foods from this list limits pesticide exposure to no more than two agents.
Careful washing of fresh fruits and vegetables removes some, but not all, pesticide residue. Fruits and vegetables that are grown organically are safer but more expensive and beyond the reach of people with limited incomes. Unfortunately, there is no way to determine pesticide contamination by inspection or by reading labels on fresh, frozen or canned fruits and vegetables.
The Food and Drug Administration, Department of Agriculture and Environmental Protection Agency all have a stake in setting standards for application of pesticides and the availability of safe food. Unfortunately, the websites of these agencies are complex and not user-friendly.
Parents also should avoid using household pesticides in the presence of children or around their toys, bedding or areas of play.
Assuring safe food and promoting safe household environments are necessary functions of state and national government.
E-mail Clif Cleaveland at firstname.lastname@example.org.