Canaries in the mine
Evidence of chemical effects on kids mounts
Courier Press - Gleaner
Dec. 21, 2003
By Joan Lowy, Scripps Howard News Service
Across the nation, evidence of a growing number of children diagnosed with attention, learning, behavioral and emotional disorders have perplexed doctors and researchers and worried teachers and parents.
The disturbing conclusion some experts are reaching is that a significant share of these conditions may be caused by environmental toxins that interfere with brain development in children beginning in the womb and which may be lowering the intelligence of the population at large.
There is no shortage of toxic suspects including lead, PCBs, mercury, pesticides, dioxins, flame-retardants and alcohol. Most children are exposed to some level of all these chemicals, raising the possibility of combined effects -- a question that scientists are only now beginning to research.
"You can almost think of the children who have been diagnosed with these clinical syndromes as the tip of the iceberg," said Deborah Rice, a toxicologist with the Maine Department of Environmental Protection.
"These are the kids that stand out, the ones that can actually go into a doctor's office and the doctor can say, 'Yes, this child has autism,' " Rice said. "But for every one of those children there may be many more children that don't reach the clinical criteria, but nonetheless may have been affected by the chemicals and other environmental milieu of a child's life."
Autism researcher George Lambert describes children as society's "canaries in the coal mine" because they are so much more sensitive than adults to poisons in the environment. They eat more food, breathe more air and drink more fluid per pound of body weight than adults -- and their brains and nervous systems are still developing. The most sensitive of all is the developing fetus.
In California, state health authorities have documented a 273 percent increase between 1987 and 1998 in diagnosed cases of autism, a neurodevelopmental disorder that usually appears before age 3 and can affect a child's ability to communicate, form relationships and respond to the world around them.
Reported autism cases in California doubled again over the last four years and the rate of increase appears to be accelerating, according to a follow-up study released earlier this year. In November, the U.S. Department of Health and Human Services held a two-day "autism summit" in Washington in response to demands from parents of autistic children for greater federal action to counter what they call a national "epidemic" of autism.
In North Port, Fla., kindergarten teacher Susan Owens said she has seen a dramatic increase in attention and learning disorders in children of all levels of intelligence and family income over the last 30 years.
Retarded students she taught in the late 1960s were better able to retain basic knowledge and skills such as the days of the week or simple addition and subtraction than many of today's kindergarteners of average intelligence, said Owens, 60.
"I can go over the days of the week with my children now the entire year, but if I say to them, 'Today is Friday. What will tomorrow be?' 50 percent of them will still not be able to tell me that tomorrow is Saturday," Owens said.
Epidemiologists caution that personal observations or even documented trends in diagnosis are not proof that any of these disorders is increasing in children. Only a national study that investigates and tracks tens of thousands of children -- something that has never been done in the United States -- would be able to determine the true prevalence of these problems and whether they are actually increasing.
"One can say there has been an increase in conduct disorders -- in violent and aggressive behaviors -- over the last 50 years in children, but the problem with saying the same thing about ADHD (attention deficit/hyperactivity disorder) or autism is that we simply don't have good enough data to draw conclusions," said Jane Costello, a psychiatric epidemiologist at Duke University Medical Center.
What is clear is that scientific understanding of the potential effects that toxins can have on the human brain has expanded markedly. Scientists now know that the timing of the exposure is just as critical as the amount -- or dose -- of the toxin. Very small amounts of chemicals at critical windows in fetal development or early childhood can have far more devastating effects than greater exposure later in life.
Scientists also know more about the relationship between genes and environment in the creation of disease. Even as researchers are linking individual genes to specific diseases, they are also discovering that particular substances in the environment can "turn off" or "turn on" these genes. The description often used by scientists is that "genetics loads the gun, but environment pulls the trigger."
Studies of identical twins show that 68 percent of the time when one twin has autism, the other twin will too, indicating that the disease probably has a genetic link. But 32 percent of the time one twin will not have autism. Since twins have identical genetic makeup, that means some environmental influence is involved in autism as well, Lambert said.
Scientists also are exploring the relationship between ADHD and toxins known to interfere with brain development. Rice found that monkeys exposed in early life to lead and PCBs in amounts similar to what children often encounter develop learning and behavioral problems that look remarkably like attention deficit disorder.
PCBs (polychlorinated biphenyls) were widely used to insulate electrical equipment until it was discovered that they were accumulating in the bodies of people and animals virtually everywhere in the world. Although PCBs were banned in 1972, children born three decades later still have small amounts of the chemical in their bodies.
"This is not to suggest that ADHD is caused exclusively by neurotoxic agents in the environment," Rice wrote in an article published in Environmental Health Perspectives. "However, it seems reasonable to postulate that environmental neurotoxicants contribute to the prevalence of ADHD currently being identified in children."
An Environmental Protection Agency report earlier this year identified ADHD as one of two "emerging issues" in children's environmental health. Children with ADHD are characterized by having chronic inattention, impulsive hyperactivity or both to an extent that daily functioning is impeded.
The second emerging issue identified by the EPA is mercury, a metal long known to be extremely toxic to the human nervous system. The term "mad hatter" described the severe effects of mercury used by 19th century hat makers in Danbury, Conn., to soften felt.
Most Americans have small amounts of mercury in their bodies, primarily from eating fish. Fish consumption in the United States has risen sharply since the 1980s, when doctors began urging patients to reduce beef in their diet to help prevent heart disease.
Tests by the Centers for Disease Control and Prevention show 8 percent of women of child bearing age have mercury levels in their blood that exceed the government's safety standard. That means about 320,000 children are born each year at risk for neurological damage from mercury.
Over the years, scientists have repeatedly lowered their estimates of how much mercury people can tolerate. The same is true for lead, which has been known for over a century to cause brain damage.
Two recent studies have concluded that there is no safe level for lead exposure. Although lead levels in children have dropped dramatically, government data show that about 90 percent of the nation's children have between 1 and 10 micrograms of lead in their blood, which means they are at risk for lowered intelligence.
While the dangers of lead, mercury and PCBs are established, scientists are also discovering that chemicals with less well understood effects are widespread in the environment and in people's bodies.
In 1999, researchers reported finding traces of a widely used group of flame-retardants known as PBDEs in the breast milk of Swedish women. In California, state toxicologists saw the Swedish study and decided to do their own studies. Not only did they find PBDEs in every woman tested, but the levels were significantly higher than those found in European women and they were increasing rapidly over time.
Laboratory studies show some PBDEs can alter brain development in mice during the important brain growth spurt. In humans, the growth spurt occurs from the last trimester of pregnancy to age 2. The concern is that PBDEs could have the same effect in children exposed through their mother's blood during pregnancy and through breast milk after birth.
Alarmed, the California General Assembly passed a law earlier this year phasing out the two PBDEs that showed the highest accumulation in women. Last month, Great Lakes Chemical Corp. of West Lafayette, Ind., agreed to cease production of the two chemicals by the end of 2004.
Industry officials contend children are not at risk from the flame-retardants because levels found in women are too low to pose harm. They also note that PBDEs are very effective flame-retardants, saving hundreds of lives every year.
Some scientists see PBDEs as a cautionary tale.
"We came across PBDEs really by chance because we looked for it, found a strange blip on screen and then it snowballed," said Tom McDonal, a toxicologist with the California Department of Environmental Protection.
"There are thousands of chemicals used in commerce and hundreds of new chemicals introduced each year, many of which we have very little information on their human toxicity and even less information on exposures."