Pesticides May Harm Brain, Study Says
Pesticides May Harm Brain, Study Says: Health: Fetuses and young children in farm areas are at highest risk, research suggests, with intelligence, motor skills and personalities affected. By MARLA CONE, Times Environmental Writer.
Children exposed to pesticides in the womb or at an early age may suffer permanent brain defects that could change their lives by altering their behavior and their ability to do everything from drawing a picture to catching a ball, according to new scientific research.
Widely used pest-killing chemicals, in amounts routinely found in the environment in farm areas, seem to be capable of skewing thyroid hormones, which control how the brain of a fetus or young child develops, according to a study published today.
Scientists say the study and other recent research support an emerging theory that pesticides may exact a toll on the intelligence, motor skills and personalities of infants, toddlers and preschoolers.
"Data suggest that we may be raising a generation of children with learning disabilities and hyper-aggression," said Wayne Porter, a University of Wisconsin professor of zoology and environmental toxicology.
Porter's study, published today in the journal Toxicology and Industrial Health, shows that a common mix of insecticide, herbicide and fertilizer found in drinking water altered the thyroid hormones of young mice. It also changed their aggressiveness--measured by attacks on other mice--and suppressed their immune systems.
Although a study of mice alone is not overly compelling, the theory is bolstered by recent research on human beings.
In tests in the state of Sonora, Mexico, scientists found striking differences in hand-eye coordination and other mental and physical skills when comparing Yaqui Indian preschoolers in an agrarian region with those in adjacent foothills where no pesticides are used.
Four- and 5-year-olds living in the farm valley had trouble performing a variety of simple motor skills--drawing stick figures, catching a 12-inch ball from almost four yards away and a tennis ball from more than a yard away, and dropping raisins into a bottle cap from a distance of six inches.
They also had poorer memory skills and stamina, were more prone to physical aggression and angry outbursts, and were less sociable and creative while playing. Farm and household pest-killers are widely used there, and high levels of multiple pesticides have been found in the cord blood of newborns and the breast milk of mothers in the area.
Another study, in rural western Minnesota, found increased birth defects in children conceived during the spring growing season.
Most of the new research detects problems in agricultural communities--places found not just in rural regions but also in more urbanized areas, including Southern California. No one knows yet what it might mean for people who consume small traces of the chemicals in their food. Earlier this month, Consumers Union reported that many fruits and vegetables contain concentrations of pesticides that may be unhealthful for children.
The new hormone studies add to a growing body of research from around the world suggesting that dozens of commonly used pesticides and other chemicals mimic the hormones that control sexual and neurological development.
Called endocrine disruption, this is arguably the most controversial environmental issue of the past decade.
From alligators in Florida to polar bears in the Arctic, wild animals in pollution hot spots have been feminized by hormone-disrupting chemicals that imitate estrogen or block testosterone, scientists say.
But the impact on human beings--who generally are exposed to much lower levels of pollution--is more controversial and uncertain.
In addition to the possible neurological effects, some researchers theorize that the hormone disrupters could be reducing men's sperm counts or increasing diseases of the reproductive system.
Pesticide company representatives--and some toxicologists and other scientists--remain skeptical that commonly found levels of pesticides can alter human thyroid and sex hormones.
"I'm kind of dubious that low-level exposures to chemicals are raising all kinds of havoc with the endocrine system," said John McCarthy, vice president of a group representing pesticide manufacturers, the American Crop Protection Assn. "The human system has so many protective mechanisms, and our bodies are bombarded with all kinds of things."
Still, he said, the industry is highly concerned about the findings suggesting neurological damage, and would like to see a comprehensive review to evaluate all existing studies and figure out what they collectively show.
"We ought to be taking a very hard look at it," McCarthy said. "There's almost a study a week of one type or another, and it's hard to see how it all fits together. We have to take some time to say, 'OK, what does this all mean? Is this something that should require some abrupt change [in pesticides] or fine-tuning or more research?' "
No one knows how many pesticides out of 77,000 used in the United States might alter sex or thyroid hormones.
The U.S. Environmental Protection Agency requires tests that screen pesticides for cancer and birth defects--but not for hormone effects. A committee last year devised new testing requirements -- supported by the pesticide industry--that are expected to take effect in 2001.
It has long been suspected that various environmental pollutants can damage brain development. Industrial compounds called PCBs have been linked to learning disabilities in children of women who ate contaminated Great Lakes fish.
The link to pesticides is far from definitive, however, and big gaps in knowledge remain. Questions abound: How do the contaminants disrupt thyroid levels? What does that physically do to the brain? What dose of exposure does it take? Does the human body have some defense mechanism to fend off low levels of hormones? What do mixes of various man-made and natural hormones do to people?
Some scientists suspect that the damage is passed from a mother to her unborn child early in the first trimester, before most women even know they are pregnant.
Thyroid hormones guide the nerve cells that dictate how the brain of a fetus develops and the number of brain cells created. One theory is that if a mother receives a dose of pesticides during this critical phase, it can interfere with her thyroid levels--sometimes raising them, sometimes lowering them--irreversibly altering the child's nervous system.
How the child's brain circuitry develops determines his or her hand-eye coordination, motor skills and learning ability.
Thyroid hormones also can change behavior--an excess can make people quick to anger, while a low count could have the opposite effect. The hormones also can alter steroids that control aggression and immune systems.
"Thyroid hormones are important to brain development, and that's been known for a long time," said Dr. Harley Kornblum, a pediatric neurologist at the UCLA Medical Center. But, he and other neurologists say, it's debatable how important the mother's thyroid level is to the fetus, and it's even more uncertain what role environmental contaminants may play.
Porter said children up to age 8 who have developing brains and immune systems are "especially vulnerable" to changes in thyroid hormones.
Some symptoms of children exposed to pesticides are similar to attention deficit hyperactivity disorders, which have been increasingly diagnosed in American children. Some medical research supports a link between thyroid hormones and those disorders, but the connection, especially with pesticides, remains unclear.
The implication for adults, and whether pesticides might cause thyroid disorders, also is unknown.
In the study of 50 Mexican children, the scientists, led by anthropologist Elizabeth Guillette of the University of Arizona, said genetic and social factors--including income, education and health services--are so similar between the farm valley and the foothills that they cannot explain the differences in the youngsters' cognitive ability.
"These children share similar genetic background, diets, water mineral contents, cultural patterns and social behaviors. The major difference was their exposure to pesticides," Guillette and Mexican researchers said in a report published in June in the journal Environmental Health Perspectives.
Most of the stick-figure drawings by the 4- and 5-year-olds in the farm valley were unrecognizable as human beings--they look like the scribbles of a 2-year-old. In contrast, drawings by the foothill children had heads, eyes, torsos, arms and legs.
Experts say that the inability to draw a person indicates a breakdown between the brain's ability to process visual information and its ability to control fine muscles.
"Some valley mothers stressed their own frustration in trying to teach their child how to draw. In addition, two valley children drew pictures composed of boxes, arches and lines, claiming these pictures were people," the researchers reported.
Other tests pointed to recollection and stamina problems. One foothill child could jump for 336 seconds--over three times longer than the best-performing valley child.
Some scientists remain dubious of the results because the tests on the children were unusual, and are intrinsically subjective and difficult to interpret.
Dr. Richard Jackson, director of the National Center for Environmental Health at the federal Centers for Disease Control and Prevention, said his staff was "unimpressed by the scientific rigor" of the work in the report.
McCarthy said that although the differences between the two populations of children seem striking, other hidden factors, rather than pesticide exposure, cannot be ruled out.
Other studies, meanwhile, show that pesticide exposure during the first trimester of pregnancy increases birth defects.
The University of Minnesota and the federal EPA in a 1996 study found a high rate of birth defects in the children of Minnesotans who work as pesticide appliers as well as the general population of western Minnesota, a major farm region with heavy pesticide use.
The defect rate was the highest among babies born nine months after the spring season, indicating that the risk rises for children conceived during the time when pesticide use increases.
In Porter's 5-year study of mice, the animals drank water containing a mixture of two pesticides--aldicarb and atrazine--and nitrates from fertilizer.
The concentrations ingested by the mice were similar to those found in ground water in many agricultural areas, Porter said. Aldicarb, atrazine and nitrates are the three most abundant agricultural contaminants in the United States, although they do not rank high in use in California.
While the mix of the three chemicals altered the mice hormones, each one alone did not. That points out a gaping hole in the federal effort to protect consumers--the EPA only tests for effects of pesticides individually, not cumulatively.
The EPA tests, Porter said, "generate a great deal of false confidence in the safety" of pesticides.
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Drawing an Unsettling Picture
Scientists say children may suffer permanent brain defects from pesticide exposure. In Sonora, Mexico, a study found that Yaqui Indian preschoolers in a farming region exhibited poor motor skills compared with their counterparts in adjacent foothills where no pesticides are used. When asked to draw a person, the farm valley's 4-and 5-year-olds mostly drew meaningless circles and lines. See Results
Source: Environmental Health Perspectives, June 1998.
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