Studies of Childhood Exposure to Environmental Pollution

horizontal rule

Sick Child The cliché is true: Children are our future. And, besides, we love 'em. Both statements are good reasons to focus considerable medical research on kids.

But there is an important additional reason for such a focus in health research related to the environment: The growth, development and rapidly reproducing cells of fetuses, infants, toddlers, older children and teens make them particularly susceptible to environmental insults. Thus, the effects on children of lead, chemical dump sites, pesticides, PCBs, benzene, environmental estrogens and both outdoor and indoor air contaminants are a particular focus of environmental health research. We want to know what substances can cause problems, how to spot susceptible kids -- and how to intervene to prevent illness.

Here is a sampling of some of the child-oriented studies conducted or financed by the National Institute of Environmental Health Sciences, one of the National Institutes of Health:

LEAD POISONING -- At high doses, lead (commonly found in old paint, household dust, soil, pipe solder and some ceramics) has long been known to cause severe health problems -- muscle and abdominal pain, mental symptoms, paralysis and even death. Until recently, however, we have not appreciated the devastating effect of low exposures early in life.

Basic research financed by the NIEHS has shown the adverse effects of lead on children's IQ and physical development at levels previously considered safe. Based on these and other findings, public health officials declared lead the #1 environmental hazard to American children and the federal Centers for Disease Control and Prevention lowered what is considered to be "acceptable" blood lead levels.

Research by NIEHS grantees has helped to show the sources of lead in the environment and to design public health prevention efforts, as well as treatments to remove lead from affected children, a process called chelation.

To help improve this treatment, NIEHS supported the study of dimercaptosuccinic acid (DMSA). Known generically as Succimer and trade-named Chemet, it has the advantage over previously used intravenous therapies that it can be given by mouth, without hospitalization.

Succimer is approved by the Food and Drug Administration for use at lead levels above 45 micrograms per deciliter of blood. However, a treatment may be needed for even lower lead concentrations, because there are measurable effects between 10 and 25 micrograms per deciliter.

  bulletTo meet this need, NIEHS is conducting a clinical trial to test Succimer in children whose blood lead concentrations are within this lower range. Inner-city hospitals are participating in this trial in Cincinnati, Ohio; Newark, N.J., Philadelphia, Pa., and Baltimore, Md. The National Institutes of Health's Office of Research on Minority Health also is helping to support this trial. The aim is to see if oral chelation reduces or prevents lead induced developmental delay. Eight hundred kids are now being followed.

 

Additionally:

  bulletRecent studies supported by NIEHS suggest that a young person's lead burden is not only linked to lower IQS and lower high school graduation rates but to increased delinquency.

 

bulletPreliminary data from two other grantees' studies indicate that girls exposed to lead store the metal in their bones. This lead can be released when they become pregnant years later, exposing their fetuses.

 

NIEHS continues to perform and support research on lead's effects. The research is important in its own right and because lead may represent a model of how other environmental hazards can hurt the fetus or developing child and adolescent, even at relatively low levels of exposure. For example:

PCBs AND INTELLIGENCE -- Reduced intelligence also results from another common contaminant, polychlorinated biphenyls, or PCBs. Partly as the result of NIEHS studies, PCBs have been barred from their past uses in electric transformers, paper recycling and other commercial processes. But they are stable, persistent compounds that remain wide-spread in the environment and, being fat soluble, concentrate in animal foods and in the people eating these foods.

NIEHS studies have shown that nursing mothers can transfer their own internal supply of PCBs to their infants through breast milk or, earlier, to the developing fetus. Fetal exposure translates into lower IQ, poor reading comprehension, memory problems and difficulty in concentration -- good reasons for the FDA and state advisories warning against women of child-bearing age and children under 15 to avoid fish taken from contaminated waters.

In one follow-up, the University of Albany is studying the exposure PCBs and subsequent physical, mental and behavioral growth of 400 Mohawk children, 10 to 16.

NIEHS' scientists have also studied 117 offspring of women poisoned by PCBs in a 1979 food contamination in Taiwan. The PCBs were heat-degraded and thus partly converted to polychlorinated dibenzofurans (PCDFs). The children show such defects as carious teeth, poor nail formation and short stature. They average worse for conduct and hyperactive behavior and have persistent developmental delay averaging 5 to 8 points on standard IQ scales. The delay is as severe in children born up to six years after exposure as it was for those born in 1979.

CHILDHOOD ASTHMA AND OTHER LUNG PROBLEMS -- Asthma affects up to 20 million Americans. Its prevalence and severity appear to be increasing among children, particularly Hispanics of Puerto Rican origin and African Americans.

The benefits from emission controls on motor vehicles have been very nearly negated by increases in the numbers of our cars and trucks. And the use of tall stacks to disperse sulfur dioxide from large coal burning plants, while reducing sulfur dioxide at ground level, has increased the proportion of sulfur dioxide that is converted into sulfuric acid within the air, so acid aerosol concentrations have not declined much in recent years.

Chronic exposure to these current levels of acidic aerosol has been associated with respiratory symptoms in children. Environmental health scientists are concerned that acidic aerosol can trigger acute asthmatic reactions and, often, result in hospitalization.

  bulletFor many years, the NIEHS has funded the Six Cities and 24 Cities studies at the Harvard University's Kresge Center for Environmental Health. The studies have shown a strong and consistent relationship between elevated indoor concentrations of oxides of nitrogen and lower respiratory tract symptoms.

 

bulletRecent findings also suggest that exposure to sulfur dioxide, particulate matter and acid aerosols (in urban (outdoor) air) is associated with bronchitis in children.

 

bulletA related study is assessing the degree of risk of minority and/or disadvantaged children from such things as air contaminants from kerosene heaters.

 

ESTROGENS IN MEDICINE AND PESTICIDES -- NIEHS studies helped show the effects on the children of women who took the potent synthetic estrogen DES in pregnancy to prevent miscarriage. NIEHS and other research organizations have done many studies of pesticides -- including those containing chemicals that may mimic estrogens or disrupt the "chemical message system" of the body's hormones during a child's development.

DDT was banned when estrogenic effects were observed -- such as the thinning of the eggshells which threatened the survival of the Bald Eagle. But what of DDE, the form of DDT that persists in the environment? The Institute's scientists followed more than 700 North Carolina children exposed to DDE in breast milk and found no related illness or lasting developmental abnormality. However, the women with the highest levels of DDE in their milk breast-fed their children less than 40 percent as long as women with lower levels. A study in Mexico, where DDE in milk was often higher, showed a similar decrease in length of lactations, at least among second and later children. This may be related to the estrogenicity of DDE, since even very low doses of contraceptive estrogens can interfere with milk production.

Despite the research that has been done by NIEHS and others, the prestigious National Academy of Sciences says in the recent report "Pesticides in the Diets of Infants and Children" that there remains a knowledge gap as to the possible effects of pesticides on the development of the immune, nervous and reproductive systems from fetal, newborn and childhood exposures.

The academy recommended a significant research effort regarding these and other possible effects.

In one response, NIEHS is conducting a complex series of experiments with experts from the Environmental Protection Agency's Health Effects Research Laboratory. The experiments, which will require three years, will evaluate the effects in generations of rodents of common pesticides about which the academy expressed particular concern: carbaryl, parathion, chlorpyrifos, atrazine and trichlorfon.

CHILDHOOD LEUKEMIA -- Clusters of childhood leukemia appear to occur around hazardous waste facilities, including Superfund sites. Studies supported by NIEHS at the University of California-Berkeley are attempting to determine what environmental exposures, including tobacco smoke and poor diet, may lead to leukemia and how to identify those at risk.

A relatively new technique called fluorescence in situ hybridization, or FISH, has shown for the first time that people working with benzene, a chemical in gasoline, develop chromosome aberrations specifically related to leukemia. This work was conducted in China, but the same UC-Berkeley team has recently demonstrated that FISH can detect these markers of leukemia risk in children in a low socioeconomic area of the San Francisco Bay area.

This work is being supported by the Superfund Research Program, which NIEHS administers.

'MOST VULNERABLE POPULATION' REQUIREMENTS -- The above research on PCBs and lead and other substances led Congress to require in the new Food Quality Protection Act and in reauthorizing other regulatory law such as the Clean Water Act that the population "most vulnerable" to a substance must be identified and that risk assessment and regulations must be based on that population.

TO EMPHASIZE THE VULNERABILITY OF CHILDREN, the NIEHS Superfund Basic Research Program cosponsored the national symposium Preventing Child Exposures to Environmental Hazards: Research and Policy Issues in Washington, D.C., in 1994, with the participation of the U.S. Surgeon General.

The Children's Environmental Health Network at UC-Berkeley, has supported the First National Research Conference on Children's Environmental Health: Research, Practice, Prevention, Policy, Feb. 21-23, 1997, in Washington.