based on an article originally published in National Wildlife Magazine, by Vicki Monks

In 1993, the National Academy of Sciences concluded that infants and children are not sufficiently protected by pesticide regulations--in part because in many cases the risks have been calculated for adults. Medical scientists are concerned about kids' exposure to persistent traces of banned chemicals as well as to chemicals that continue to be released into the environment.

Not long ago, scientists considered cancer to be the main threat from exposure to toxics. Now there is new understanding that poisons also can affect the young's immune systems, brains and reproductive organs.

Scientists rely on animal research to give us clues about the ways in which toxic substances may harm humans. In many cases, our own biological systems function in much the same way as they do in animals. Whenever medical scientists have documented toxic damage in humans, the effects were almost always observed earlier in laboratory animals or wildlife. "It's important for us to realize that if we're seeing abnormalities in wildlife, similar kinds of mechanisms may exist in humans," says University of Florida zoologist Louis Guillette. "We are just another species in the ecosystem; if other species are harmed, we may be too." Adds University of Missouri reproductive biologist Frederick vom Saal, "If these chemicals are causing animals to develop abnormally--getting into wildlife and causing changes in their brains, their behavior and their reproductive organs--we have to operate on the assumption that humans could respond in similar ways."

DEFORMED NEWBORNS: In the early 1950s, before anyone understood that the world's first modern industrial pollution disaster was underway in Minamata, Japan, fishermen there noticed that seabirds were dying and feral cats that scavenged fish from the docks seemed stiff legged. Then, cerebral palsy and mental retardation started turning up in children, and adults were showing signs of illness. At first, people thought the symptoms were of a new disease. By the late 1960s, it was clear that mercury discharges from a chemical plant had poisoned the seafood--as well as those who ate it.

The problem has not been limited to Japan. In the 1970s in this country, scientists discovered widespread mercury contamination--though at far lower levels than the Minamata case--throughout the Upper Midwest and in fishing grounds along the Texas Gulf Coast. The extent of possible harm from mercury to people in this country is unclear, but one thing is certain: Children, especially those exposed to mercury before birth, are likely to suffer far greater damage than adults. "These poisons creep up on you," says toxicologist Bernard Weiss of the University of Rochester, who has studied the Minamata tragedy. "You see a few cases of animals dying or people getting sick. You catch a few clues. The evidence begins to mount."

At the time of the Minamata poisonings, science held that the womb was a protected environment capable of screening out harmful substances. But in Japan, many women who ate contaminated fish without becoming obviously ill themselves, gave birth to children with severe mental retardation and physical deformities. That led scientists to hypothesize that the fetus was sharing the mother's toxic load. "It looks as though being pregnant sort of protects the mother, because the fetus takes up some of the mercury, reducing the mother's exposure," says Weiss. The fetus receives at least the same doses as its mother--and the fetus has far greater susceptibility to toxic pollutants.

The Environmental Protection Agency (EPA) has measured dioxins and PCBs in samples from umbilical cord blood, placentas and other fetal tissue. Not only are the young exposed to toxic chemicals in the womb, mothers also unload toxics in their milk. In milk from species ranging from beluga whales to dairy cows, scientists have measured concentrations of chemicals including dioxins, PCBs and various pesticides. Children get 12 percent of their lifetime exposure to dioxin in their first year of life. Notes EPA toxicologist Linda Birnbaum, "On a daily basis, the infant is getting about 50 times the exposure an adult gets, during what may be a critical developmental stage." Of course, milk also provides important protection by passing along the mother's antibodies, and doctors still recommend nursing when possible. "The benefits still clearly outweigh the potential risks," says Birnbaum.

DAMAGED IMMUNITY: A few disturbing links between pollutants and human immune systems are currently under investigation. In the Canadian Arctic, Quebec community health researchers are attempting to tease out connections between unusually high rates of infectious disease among Inuit children and exposure to toxic chemicals. Even though no polluting industries operate near the region, contaminants enter the ecosystem in high-altitude winds and in migrant wildlife. As PCBs, pesticides and other organochlorines make their way up the food chain--from plants and fish to seals, whales, polar bears and humans--they accumulate in greater density in every link. Inuit women have seven times more PCBs in their breast milk than women from the urban, industrialized south of Quebec.

During their first year, Inuit babies suffer through 20 times more infectious diseases than babies in southern Quebec. Acute ear infections are rampant among the Inuit children, causing hearing loss for nearly one in four. And the usual childhood immunizations frequently don't seem to work on these kids; they apparently can't produce enough antibodies for vaccinations to take. Public-health workers stress that Inuit children are subject to many other risk factors--such as wood smoke in homes. That sort of complication is a common problem in human research. Researchers can't control for every factor, and they obviously can't deliberately expose humans to toxics. Frequently, scientists can't distinguish which chemical might be causing a problem, because people are exposed to so many all at once.

But in Quebec, data suggests that contaminants may be at least partly responsible for the health problems. In a 1993 study, Quebec community health researcher Eric Dewailly found that babies nursed by mothers with the highest contaminant levels in their milk are afflicted with more acute ear infections than bottle-fed Inuit babies. The babies with the highest exposures also produced fewer of the helper T cells that play an important role in ridding the body of bacteria and other harmful invaders.

On the other side of the Atlantic, in the Netherlands, researchers concluded in 1995 that even infants with mild exposures to contaminants may experience weakened immunity. A study published in the journal Pediatric Research found a correlation between PCB/dioxin exposures and suppressed levels of disease-fighting white blood cells. Doctors who examined the children concluded that while the immune-system changes were not extreme, they "could persist into later child- or adulthood and could presage difficulties"--including autoimmune diseases that provoke the body to attack itself.

LOWERED INTELLIGENCE: Not only are kids' metabolisms faster than those of adults, babies don't excrete contaminants or store them away in fat in the same ways that adults do. That means babies get continuous exposures at a time when all of their organs, including their brains, are still developing. 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 studies have found that developing brains of various wildlife species are far more sensitive to toxic insults than adult brains. In the late 1980s, for example, University of British Columbia zoologist Diane Henshel found gross asymmetries and other abnormal changes in brain structures of great blue heron hatchlings from dioxin-contaminated colonies in Canada.

Now evidence from an accidental PCB poisoning in Taiwan in 1979 is helping scientists establish that human children also are susceptible to such toxic effects. In the Taichung province of Taiwan, more than 2,000 people were exposed to PCB-contaminated cooking oil in what has come to be called "Yu-Cheng" or oil disease. In the first three years after the accident, many newborns died outright, and others developed blotchy patches of dark skin and deformities of their fingernails and toenails.

As these children grew, tests found that many were slower mentally than other kids their age, and they were frequently hyperactive or had other behavioral problems. According to National Institute of Environmental Health Sciences (NIEHS) medical officer Walter Rogan, who has studied the Yu-Cheng case, the developmental delays and IQ deficits did not go away as the children aged. "And moms continue to have kids with problems," Rogan says. "The kids born as late as 1985 were still affected as much as the kids born in 1979."

As Rogan explains it, a large portion of the PCBs these women consumed ended up stored in their fat, as happens with many toxic chemicals. Because women mobilize a lot of body fat during pregnancy to provide nourishment for their growing babies, the contaminants in the fat also are passed to the children--even, as in Yu-Cheng, when the pregnancy occurs years after the mother's exposure. The same mechanism also applies to low-level toxic exposures from food, air and water. Now researchers are finding that even these small amounts of pollutants--accumulated by women throughout their lives--can have lasting consequences for a child exposed to them in the womb.

The human evidence is not just from accidents where people were exposed to huge toxic doses, such as Yu-Cheng. "Low levels of some of these chemicals are turning out to be more hazardous than we thought," Rogan says, "And the longer we look, the more problems we find." A Michigan study published in The New England Journal of Medicine in 1996 found persistent intellectual deficits in children exposed before birth to much lower doses of PCBs than the Yu-Cheng children. In 1981, two Wayne State University psychologists, Sandra and Joseph Jacobson, measured PCB levels in mothers and newborn infants. Since consumption of fatty fish from contaminated water is a major source of PCBs, the Jacobsons selected mostly mothers who had eaten Lake Michigan salmon or lake trout regularly during the years before their children were born. To confirm exposure levels, researchers measured PCBs in umbilical cord blood soon after the birth of each child. The Jacobsons found that infants with the highest exposures grew more slowly than other babies, and at four years old, the high-exposure group had poorer short-term memory. By the time the group reached 11 years old, the 30 most highly exposed children had average IQs six points lower than the least exposed group. And of the high-exposure kids, 23 percent were two years behind in reading, while only 10 percent of children with low prenatal PCB exposure were two years behind.

Unlike the Yu-Cheng oil poisoning, these were environmental level exposures, the kind anyone, anywhere, could have--not just people who live near the Great Lakes. Somewhat to their surprise, the Jacobsons found that fish-free diets didn't necessarily guarantee lower PCB levels. "We had some very high-exposed children whose mothers didn't eat the fish," Jacobson says. One guess is that those exposures might have come from other fatty foods, such as butter, cheese, beef or pork--but there is no way to know the source. "This is a societal problem," Jacobson says. "We are all walking around with PCBs in us."

In New York, PCBs are buried in sediment in the Hudson River from Albany to the southern tip of Manhattan. PCBs were released into the river between 1946 and 1977 by two General Electric plants on the upper Hudson. As the PCBs move up through the marine food chain, they accumulate in striped bass, bluefish, crabs, eels and other predatory species. Dr. Landrigan warns that women who eat these fish during pregnancy could risk exposing their babies to the PCBs.

SEXUAL IMPAIRMENT: Sexual development in the growing fetus may be as sensitive as the brain to toxic effects. When certain chemicals bind to hormone receptors, they can interfere with the work of natural hormones in signaling the body to develop male or female organs. When that happens, studies in the laboratory and in the wild have shown that any number of reproductive disorders can result. These chemicals, known as endocrine disrupters, include PCBs, dioxins and many pesticides.

Scientists are uncertain about the extent of effects of these endocrine-disrupting chemicals in levels found in the environment. But again, the growing body of evidence suggests reason for concern. Among the Yu-Cheng children of Taiwan, boys with high PCB exposures tended to have smaller than average penises once they reached puberty.

In the early 1990s, University of Florida biologists documented the same phenomenon among alligators born in a lake poisoned by a pesticide spill. And in 1989, in the highly polluted St. Lawrence River, biologists were stunned when they examined what they thought was a male beluga whale only to find a fully developed set of female organs--ovaries and a uterus--in addition to the whale's male apparatus. Like other dead belugas recovered from the river, the hermaphrodite carried a tremendous load of contaminants in its blubber, including DDT, PCBs, and other chemicals that are capable of interfering with hormonal processes. It is impossible to determine whether the contaminants caused the hermaphroditic whale’s condition, or whether other factors were involved. As with humans, individual animals respond in different ways to toxic exposures. Some appear to be unaffected, whereas others may suffer serious health consequences.

According to a 1996 review by a team of U.S. and European scientists, birth data from several countries show "substantial increases" since the 1950s in the number of human boys born with undescended testicles and hypospadias, a condition where a shortened urethra causes the urinary opening to come out on the underside of a baby boy’s penis instead of at the end. According to data from the Centers for Disease control, the incidence of boys born with that condition has doubled since the 1970s. Another study in London found that 5.2 percent of low-birthweight boys born in the late 1980s had undescended testicles, compared with 1.74 percent of low-birthweight boys born 30 years earlier.

Testicular cancers are on the rise, increasing by 70% among older teenagers in the United States between 1973 and 1992, from one in every 1,550 boys to one in 820 boys. Public-health officials are concerned that these conditions may be somehow linked to toxic chemicals, but they are a long way from finding proof.

GREATER IMPACT ON BOYS: Recent research has uncovered another disturbing possibility; toxic chemicals may do more damage to male children than to girls. When scientists at the University of Minnesota looked at high rates of birth defects among the region's farm children, they found that boys had far more birth defects than girls. The 1996 study published in the NIEHS journal Environmental Health Perspectives, examined birth defect rates in western Minnesota--where wheat, sugar beet and potato farmers rely on insecticides and herbicides to protect their crops. Children of farm families had significantly higher rates of birth defects than the state's general population. The highest rates were among children conceived in the spring, when spraying is most intense.

Wildlife biologists have also noted instances where toxic exposures appear to do more damage to male offspring than to females. And Italian scientists say that dioxin contamination may explain a peculiar absence of male children born in the late 1970s and early 1980s to certain families in Seveso, Italy. After a 1976 industrial explosion spewed dioxin over the town, the 735 people living in the most contaminated area were evacuated, but not until two weeks after the accident. In the following eight years, women from that group gave birth to far more girls than boys. At the time, researchers did not notice the phenomenon; they were more concerned with whether the dioxin might eventually cause cancer. Then excess cancers did start turning up among Seveso's adults, and in the late 1990s, epidemiologists noticed in the data the strange scarcity of male children among the Seveso neighborhood’s previous residents.

Baby boys usually slightly outnumber girls; worldwide, there are about 106 boys to every 100 girls. But during the first eight years after the Seveso accident, mothers who had lived in the most contaminated zone gave birth to 48 girls and only 26 boys. Parents with the highest levels of dioxin had daughters but no sons at all. Perhaps, theorized University of Milan clinical pathologist Paolo Mocarelli in the British medical journal The Lancet, dioxin interferes with hormonal balances in developing embryos, either making normal male growth impossible or killing males.

Studies such as these have barely begun to sort out the human health effects that might be caused by the chemicals we all are exposed to in everyday life. Most of the more than 70,000 chemicals registered with the EPA have never been tested for safety – much less for their effects on the very young. Our children are the laboratory mice in a vast chemical experiment. And no one can say what the consequences for them might be.