PBS : Trade Secrets : Children at Risk

America’s children today are generally healthier and better nourished than at any time in history, but as research in humans and animals progresses, scientists are beginning to verify just how dangerous some synthetic chemicals are to human health – especially to children. While a great deal of uncertainty remains, a growing body of peer-reviewed scientific literature strongly suggests that the young are far more susceptible to toxic effects than adults.

Children get heftier proportional doses of pollutants because of their small sizes. "Children eat, drink, and breathe more for their body weights than adults do, so they get bigger proportional doses of whatever is out there," explains University of Pittsburgh School of Medicine psychiatrist Herbert Needleman, who pioneered studies linking lowered intelligence with early childhood exposures to lead.

Faster metabolisms in children speed up their absorption of contaminants. “Children absorb a greater proportion of many substances from the intestinal tract or lung,” says pediatrician Dr. Philip Landrigan, Chairman of Community and Preventive Medicine at the Mount Sinai School of Medicine in New York, and a former senior adviser to EPA on Children’s Health and the Environment. “For example, children take up approximately half of the lead that they swallow while adults absorb only about one-tenth.”

Children live closer to the ground, where the highest concentrations of many air pollutants settle. They play in the dirt and on carpets where they are exposed to contaminants that attach to dust particles. In a 1998 study to investigate a possible association between cancer risks and pesticides in house dust, the National Cancer Institute found residues of 31 chemicals in carpet dust samples from 15 Washington, DC area homes. The NCI found seven organochlorine pesticides, including DDT, Methoxychlor, heptachlor, and chlordane, three highly toxic carbamates, five types of PCBs and other potentially toxic chemicals.

Children spend a considerable amount of time putting things in their mouths. In 1998, scientists at Rutgers University discovered that pesticides sprayed in a home evaporate from floors and carpets, and then re-condense on plastic and foam objects such as pillows and plush toys. By observing how frequently a group of pre-schoolers put clean toys in their mouths, the researchers calculated that contaminated toys are likely to give young children much higher doses of poison than adults would get in the same environment.

Babies don't excrete contaminants or store them away in fat in the same ways that adults do, making the poisons more available to affect rapidly growing bodies. Furthermore, because a baby’s immune system is not fully functional, a baby’s body cannot counteract toxic effects as well as an adult can. In an adult, a blood-brain barrier insulates the brain from many of the potentially harmful chemicals circulating through the body. But in a human child, that barrier isn't fully developed until six months after birth.
Many contaminants such as dioxins and PCBs have an affinity for fatty tissue. During pregnancy, women mobilize their amassed stores of body fat to provide nourishment for their growing babies; the contaminants in the fat are then passed to their children. Nursing mothers also transfer a good portion of their lifetime accumulation of chemicals to their babies.
Children exposed in the womb are at greatest risk of all. Because cellular structures change so rapidly during embryonic and fetal growth, a toxic exposure at the wrong moment can permanently alter further development. According to Dr. Landrigan, the central nervous system is especially vulnerable. To function properly, the developing brain must lay down an intricate web of interconnecting neurons. Small doses of neurotoxins during critical periods of brain development can alter those crucial neural pathways – one mistake early on, and the brain may be forever changed in subtle or serious ways. Government and university scientists are currently investigating the possibility of a connection between fetal exposures to toxics and developmental disabilities such as attention deficit hyperactivity disorder (ADHD).
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