Once viewed merely as small adults, and therefore not requiring separate scientific studies, children have gradually risen to a priority status in environmental health research. More than twenty years ago, the NIEHS initiated its first studies into the effects of lead, PCB, and DDT exposure on the youngest and most vulnerable human beings. Today, the research focus is on determining which environmental substances can cause problems, learning how to identify susceptible children, and finding ways to intervene to prevent illness.
Their dynamic growth and development make children at all stages--fetuses, infants, toddlers, older children, and teens--especially susceptible to environmental contaminants. The cells in children's bodies are multiplying and organ systems are maturing so rapidly that exposure to environmental toxins at such critical stages can lead to permanent and irreversible damage in both DNA and tissues.
"We think there are some major public health needs and research opportunities in the area of children's environmental health," says Samuel Wilson, deputy director of the NIEHS. "I think the topic of children's environmental health is very important for us to continue to address and focus on in the future."
An April 1997 presidential executive order assigned high priority to addressing environmental health risks to children. As a result, the NIEHS and the EPA have allocated $10 million annually to jointly create the first federal research centers to study children's environmental health. "This is going to be a major new initiative," says Anne Sassaman, director of extramural research and training at the NIEHS. "But we already have a substantial portfolio on children, and have been a leader in research on lead, pesticide exposure, and asthma. The new thrust will just make all of these efforts much more visible as a priority."
Lead
Found in old paint, household dust, soil, and drinking water, lead has long topped the list of environmental hazards to children. In 1994, a
Journal of the American Medical Association
article estimated that in 1990 1.7 million U.S. preschool children had blood lead levels above the CDC's action level of 10 micrograms per deciliter (µg/dl). But despite efforts to reduce lead levels, about 57 million homes built before 1980 still contain three million tons of potentially dangerous lead, according to the 1992 U.S. census.
At high doses, lead is known to cause severe health problems in children, including muscle and abdominal pain, mental symptoms, paralysis, and even death. "You can kill a kid with lead at levels that would have no effect on an [adult] house painter, for example," says Walter Rogan, medical research officer in the epidemiology branch of the NIEHS. Lower doses have been associated with decreased IQ scores and impaired attention, behavior, and physical development. The NIEHS is supporting research into a possible link between lead exposure and attention deficit hyperactivity disorder (ADHD), lower high school graduation rates, and delinquency.
In Johnston County, North Carolina, NIEHS epidemiologist Andy Rowland is looking at the distribution of ADHD in schoolchildren and the possibility, among other hypotheses, that lead exposure may play a role in the disorder. "We'll be screening 7,000-8,000 kids over a two-year period," says Rowland. "Johnston County is a good location to study because it provides a diverse population that is fairly typical of many North Carolina counties; it includes children from rich and poor, black and white, and rural and urban environments. And what's innovative about our study is that we are trying to look at potential, preventable causes of ADHD in a population-based, rather than a small, clinic-based, sample."
In addition to lead exposure, researchers will consider the effects of preterm delivery, pregnancy complications, family history, and parental smoking and alcohol consumption on each child. Because no well-validated physical tests for ADHD currently exist, the NIEHS researchers will rely on information from teachers and parents to assess each child's symptoms. Children who behave as if they may have ADHD will have the opportunity to be further evaluated in a mobile school-based clinic staffed by physicians, nurses, and health educators from the University of North Carolina at Chapel Hill.
NIEHS-funded scientists have helped develop treatments to remove lead from the bodies of affected children, a process called chelation. The institute supported a study of dimercaptosuccinic acid (DMSA), also known as Succimer and marketed as "Chemet," which has been approved by the FDA for use in chelation of blood lead levels above 45 µg/dl. But because negative health effects have been detected at lower lead concentrations--between 10 and 25 µg/dl--the NIEHS is conducting clinical trials to test Succimer in children with lower blood lead levels. Researchers want to see if oral chelation reduces or prevents lead-induced developmental delay. "We still don't know if it matters if we reduce lead levels," says Rogan. "We don't know how lead causes the effects it does. We still don't know if abruptly dropping lead levels will make a difference."
PCBs and DDE
Partly as a result of NIEHS studies, polychlorinated biphenyls (PCBs) are now banned from use in commercial processes. But they have yet to disappear from the environment. Stable and persistent, PCBs are also fat-soluble, allowing them to concentrate in humans who consume contaminated foods, especially fish. Pregnant and nursing mothers can transfer PCB traces to their children through the placenta or breast milk. Fetal exposure to PCBs may translate into lower IQ, poor reading comprehension, memory problems, and difficulty in concentration.
NIEHS research on PCBs began in the mid-1970s, a time when little was known about PCB exposure and its effects, according to Rogan. "Exposure in infants was thought to come mainly through breast milk. But it's turned out the effects are mainly due to prenatal exposure. The quantities in prenatal exposure are smaller than in breast milk, but far more crucial."
In a landmark 1985 study, NIEHS scientists studied 117 offspring of Taiwanese women who were poisoned by eating PCBs in contaminated food in 1979. The children of these women have shown such defects as cavity-prone teeth, poor nail formation, and short stature. They also display behavioral problems and developmental delays that average 5-8 points on standard IQ scales. In addition, researchers discovered that children born up to six years after the exposure exhibit delays as severe as those in children born in 1979.
The pesticide DDT has also been banned in the United States and much of the world, but its metabolite, DDE, continues to persist in the environment. The effects of DDE on childhood disease and development are still not clear. NIEHS scientists followed more than 700 North Carolina children exposed to DDE via breast milk and found no related illness or lasting developmental abnormality. However, women with the highest levels of DDE in their milk were found to have been able to breast-feed their children over periods of time less than 40% as long as women with lower levels. A study in Mexico, where levels of DDE in milk are often higher, showed a similar decrease in length of lactation periods, at least among second and later children.
One current NIEHS study on the effects of PCBs and DDE is using blood samples collected from 50,000 pregnant women in a number of U.S. cities between 1959 and 1965. The samples had originally been taken to identify causes of cerebral palsy but few studies actually analyzed the blood. Frozen for nearly forty years, about 3,000 of the samples are now being thawed and tested. NIEHS scientists will compare PCB and DDE levels with information recorded on the women's children, including the presence of birth defects, the rate of neurodevelopment, and IQ scores.
"It's an incredible resource," says senior research investigator Matt Longnecker. "After the original samples were taken, the children were systematically examined for seven to eight years. Now we're looking at the response to that exposure. If we took the same specimens in the United States today, DDE levels would be 80% lower. PCB levels would also be a little lower than in the past. So, having these earlier samples gives us an especially informative population to study."
Childhood Asthma
Asthma affects millions of U.S. children. Children have narrower airways, a faster rate of respiration, and inhale more pollutants per pound of body weight than adults, making them especially vulnerable to air pollutants and allergens that cause and exacerbate asthma. In 1995, the American Lung Association reported that childhood asthma cases had increased by 42% between 1980 and 1987.
"Most sensitization to asthma occurs in childhood," says Darryl Zeldin, head of the asthma prevention program in the clinical studies section at the NIEHS. "Children are most susceptible to environmental factors that give rise to asthma, perhaps because their lungs and immune systems aren't fully developed. We still don't understand a lot about the development of the immune system, but we do believe it depends on a combination of the environment and genetic factors because even in the same family, one child might get the disease while the others might not."
Air pollution is not the only culprit in childhood asthma. Cockroaches and dust mites give off proteins, or allergens, that can cause an immune system reaction in children. Once children are sensitized to these allergens, reexposure can lead to the development of airway inflammation and asthma. Zeldin's group has recently begun a multiphase study on such allergens and their relationship to asthma. In the study's first phase, researchers will test different methods for eliminating roaches and mites from homes in several cities around the country. For a year, they will examine household dust before, during, and after the various methods have been applied, looking at which ones best eliminate the pests and their allergens.
"There's still a lot of disagreement over which techniques are the most effective," adds Zeldin. "For example, we'll be comparing the use of tannic acid [as a treatment] to steam cleaning of carpets to see which is most effective at reducing dust mite allergens. Until now, nobody has looked at which prevention techniques are the best."
Once the most effective techniques have been determined, the study's second phase will begin. Researchers will track about 500 children over a period of 7-8 years, watching for improvements in their respiratory health. Half of the children will be from homes where the allergens have been effectively treated, the other half will be from untreated homes. Scientists will compare the prevalence of asthma and allergies between the two groups, and will also look at lung function.
Pesticides and Birth Defects
Norway is the site of a five-year NIEHS research project into possible environmental and genetic causes of facial clefts in newborns. Norway has one of the highest rates of facial clefts in the world--two babies per 1,000 born in Norway have facial clefts--making it one of the most common birth defects in that country. The country's centralized health care system makes it easier for researchers to identify babies for the study; all surgery to correct the defect is performed at two hospitals. The NIEHS is collaborating with Norway's National Institute of Public Health in Oslo on the project.
"We're planning to enroll 600 babies with clefts and 100 control babies," says Allen Wilcox, chief of the epidemiology branch of the NIEHS and principal investigator on the project. "We'll be looking at pesticides and drinking water with the idea of studying genetic susceptibility to facial clefts. We're collecting cheek swabs and blood samples, for example, then looking at genes that might be related. For the pesticide hypothesis, we will look at metabolism genes. For drinking water contaminants such as fertilizers or halogenated by-products of fluorides, we will look at a different set of genes." Researchers will also measure the pesticide exposures of the affected children's parents, including exposure to pesticides on the job as well as to bug sprays and chemical treatments used to eliminate pests in the home.
On the other side of the globe, in the lower Rio Grande Valley region of south Texas, NIEHS-funded researchers are looking at possible environmental causes for a dramatic increase in neural tube defects in recent years. In one 36-hour period in March 1991, three babies were born in a Brownsville, Texas, hospital with anencephaly, one of the two forms of neural tube defects. Anencephaly causes the brain and skull to form improperly and the infant dies soon after birth. The second form is spina bifida, a congenital cleft of the vertebral column that requires considerable medical attention.
Although people of Mexican-American ancestry may have a higher risk for neural tube defects, this border region might normally experience two anencephalitic births in an entire year, according to Stuart Shalat, science coordinator for the Environmental and Occupational Health Sciences Institute at Rutgers University in Piscataway, New Jersey. "The community was very upset and we wanted to figure out what was going on," says Shalat. "We looked at a variety of factors, [including] recent weather changes that had caused a shift in agriculture. Several bad frosts in the valley had wiped out the citrus, leading farmers to switch to a different crop and different pesticides. Then they had a drought, which deprived them of water to dilute the pesticides." In addition, few residents of this area have air conditioning to filter air coming into the home.
Since 1993, Shalat's team has been studying soil, dust, and river sediment samples from the area looking for a possible connection between chemical exposures and neural tube defects. "We have discovered a vast array of chemicals, mostly in soils and surface water, not as much in drinking water," he says. "For example, we've found as many as 80-100 chemicals in some soil samples. The area is being increasingly industrialized and we've found over 400 identifiable chemicals in river sediments. We're just starting to analyze the data, but what's emerging is a very good picture of what's going on in the lower Rio Grand Valley."
Shalat is also interested in the discovery that infants with neural tube defects have folic acid deficiencies. His study is considering the hypothesis that environmental chemicals may compete for receptors of folic acid, preventing the fetus from absorbing folic acid taken by the mother in supplement form during pregnancy.
No longer viewed scientifically as miniature adults, children will continue to benefit from an intensified focus on the unique effects of environmental agents on their vulnerable health. At the same time, researchers are exploring genetic predisposition in an attempt to understand why some children become ill from exposure while others remain healthy. By studying which substances can cause problems, which children are most susceptible, and which methods best intervene to prevent illness, NIEHS scientists hope to brighten the future of children's health.
Rebecca Clay Haynes
Environmental health issues affect every person living on the earth, yet many people are not aware of exactly what "environmental health" means, or why they should be interested. So the NIEHS decided to publish a booklet aimed specifically at explaining environmental health to young people. The primary goals of the publication--meant to be a fun and informative teaching aid for schools (it's written at a sixth-grade reading level)--are to give examples of a number of environmental diseases and tell how they affect everyday people, and also to describe the work that the NIEHS does.
The publication,
Environmental Diseases from A to Z,
is a brightly illustrated, eight-page booklet that features information on environmental diseases from allergies to zinc poisoning. Some of the topics cover general areas of concern, such as job-related illnesses and waterborne diseases. Other topics, such as pneumoconiosis, describe specific diseases that arise from environmental exposures. The booklet is packed with facts, statistics, and even some intriguing bits of trivia about each disease. It also contains pronunciation guides for some of the more complicated disease names.
A first run of 20,000 copies was printed in July. In order to spread word of the booklet to its target audience, the NIEHS posted a press release on the World Wide Web. So far, over 500 respondents--including teachers, students, public health administrators, and reporters--have contacted the NIEHS Office of Communications for more information about the booklet, making it one of the institute's most popular outreach publications in recent years. A 13-state mailing to science teachers is planned for this winter. The mailing will be organized by Karen Hoffman, president of the North Carolina Association for Biomedical Research, a nonprofit organization based in Raleigh that, among other efforts, works closely with educators in an effort to foster scientific literacy among North Carolina schoolchildren. Along with her counterparts in 12 other states, Hoffman will send single copies of the booklet to approximately 13,000 middle school and high school teachers. Each teacher will have the opportunity to request up to 90 additional free copies.
The booklet was written by John Peterson, a public affairs specialist for the NIEHS. William Grigg, director of the Office of Communications and editor of the booklet, came up with the idea of an "A to Z" format. The illustrations were drawn by Donna McCullough, an artist at
The Washington Post. Peterson, who had long recognized the need for such a booklet and championed its publication, says that coming up with the single best environmental illness to match each letter of the alphabet was the most difficult challenge in creating the booklet. He searched through medical dictionaries and the NIH Health Information Index (a database of diseases studied by NIH constituents) for suitable topics, and solicited suggestions from scientists at the NIEHS. In the end, each letter was eventually paired with an appropriate entry.
A free copy of
Environmental Diseases from A to Z
may be obtained by writing to the NIEHS Office of Communications, MD EC-12, PO Box 12233, Research Triangle Park, NC 27709, Attention: John Peterson. The booklet may also be requested by sending an e-mail message to
booklet@niehs.nih.gov.
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Last Update: January 8, 1997