In a strongly worded declaration, many of the world's leading environmental scientists warned Thursday that exposure to common chemicals makes babies more likely to develop an array of health problems later in life, including diabetes, attention deficit disorders, prostate cancer, fertility problems, thyroid disorders and even obesity.
The declaration by about 200 scientists from five continents amounts to a vote of confidence in a growing body of evidence that humans are vulnerable to long-term harm from toxic exposures in the womb and during their first years.
Convening in the Faroe Islands in the North Atlantic, toxicologists, pediatricians, epidemiologists and other experts warned that when fetuses and newborns encounter various toxic substances, growth of critical organs and functions can be skewed. In a process called "fetal programming," the children then are susceptible to diseases later in life -- and perhaps could even pass on those altered traits to their children and grandchildren.
The scientists' statement also contained a rare international call to action. The effort was led by Dr. Philippe Grandjean of Harvard University and the University of Southern Denmark, and Dr. Pal Weihe of the Faroese Hospital System, who have spent more than 20 years studying children exposed to mercury.
Many governmental agencies and industry groups, particularly in the United States, have said there is no or little human evidence to support concerns about most toxic residue in air, water, food and consumer products. About 80,000 chemicals are registered in the United States.
Yet the scientists urged leaders not to wait for more scientific certainty and recommended that governments revise regulations and procedures to take into account subtle effects on fetal and infant development.
Chemicals with evidence of developmental effects include compounds in plastics, cosmetics and pesticides.
"Given the ubiquitous exposure to many environmental toxicants, there needs to be renewed efforts to prevent harm. Such prevention should not await detailed evidence on individual hazards," the scientists wrote in the four-page statement.
The scientists are particularly concerned that the newest animal research suggests that chemicals can alter gene expression -- turning on or off genes that predispose people to disease. Although the DNA itself would not be altered, such genetic misfires in the womb may be permanent, and all subsequent generations could be at greater risk of diseases too.
"Toxic exposures to chemical pollutants during these windows of increased susceptibility can cause disease and disability in childhood and across the entire span of human life," the scientists concluded.
The "Barker hypothesis," conceived by a British scientist in 1992, says human fetuses are "programmed" for diseases by their early environment. The scientists concluded that this is now well-documented for toxic exposures by a large collection of animal experiments and some human data.
"A sad aspect with many of these prenatal exposures is that they leave the mother unscathed while causing injury to her fetus," said Dr. Philip Landrigan, a pediatrician who chairs the Mount Sinai School of Medicine's Department of Community and Preventive Medicine. He was one of the statement's authors.
In a more optimistic vein, the researchers said that if contaminants do play a big role in human health problems, some diseases could be prevented.
"Reducing exposure would lead to tremendous benefits," said Dr. Bruce Lanphear, director of the Environmental Health Center at Cincinnati Children's Hospital Medical Center. "We shouldn't wait for an epidemic to fully mature before we develop policies to protect children."
For centuries, the basic rule of toxicology has been "the dose makes the poison." Now, the scientists say "the timing makes the poison" -- in other words, when a toxic exposure occurs is as important as the amount people are exposed to.
The fetus "is extraordinarily susceptible to perturbation of the intrauterine environment," they wrote.
The growing brain is the most sensitive. Mothers' exposure to mercury and polychlorinated biphenyls (PCBs) in fish and other seafood can cause slight declines in a child's IQ and motor skills. In addition, early exposure to pesticides might trigger Parkinson's and Alzheimer's diseases.
Also, children exposed to lead, organophosphate pesticides or cigarette smoke have greater risk of attention deficit hyperactivity disorder. One of every three cases -- or an estimated 560,000 children in the United States -- can be attributed to lead exposure or prenatal tobacco smoke exposure, Lanphear reported in a study published in December.
The immune, reproductive and cardiovascular systems also are vulnerable to early damage. Children exposed prenatally to PCBs have a high rate of infections and weak response to vaccinations. Many chemicals also can mimic hormones, and in animal tests, they feminize newborns, lowering sperm counts and promoting prostate, testicular, uterine and breast cancers.
In the newest area of research, metabolic systems, which control how nutrients are converted into energy, have been altered by chemicals administered in animal experiments -- changes that may contribute to obesity and diabetes.
"These adverse effects have been linked to chemical pollutants at realistic human exposure levels similar to those occurring from environmental sources," the scientists wrote.
Among the risky chemicals they named are bisphenol A, found in polycarbonate plastic food and water containers; the pesticides atrazine, vinclozolin and DDT; lead; mercury; phthalates used in some cosmetics and soft plastics; brominated flame retardants; arsenic, which contaminates some water supplies; and PCBs, banned but ubiquitous, particularly in fish.
Some of the chemicals have been regulated in the United States, but many have not. Moreover, the scientists said, tests for developmental effects are not routinely required, so "the potential for such effects is therefore not necessarily considered in decisions on safety levels of environmental exposures."
There is "an incredible gap," Landrigan said, because 80% of major chemicals in commerce have never been tested to see if they damage early development.
The conference was funded by the World Health Organization, National Institutes of Health, European Environment Agency and the Centers for Disease Control and Prevention.
Denmark's Faroe Islands, just south of the Arctic Circle, were the venue because the region is home to the longest-running human experiment analyzing prenatal toxic exposure. Since 1986, Grandjean and Weihe have tracked Faroese children from the womb to adolescence to monitor neurological effects of mercury in seafood. Their findings prompted U.S. advisories that children and women of childbearing age avoid swordfish and other highly contaminated fish.
In addition to Landrigan, three Californians and six other U.S. scientists served on the 28-member committee that wrote the consensus: Brenda Eskenazi of UC Berkeley, Irva Hertz-Picciotto of UC Davis, Beate Ritz of UCLA, Jerry Heindel and Kimberly Gray of the National Institute of Environmental Health Sciences, Larry Needham of the CDC, Terry Huang of the National Institute of Child Health and Human Development, David Bellinger of Harvard University and Howard Hu of the University of Michigan.