This overview is the first in a series of articles to be published concerning children's environmental health. Additional articles will appear in the run-up to "Children's Environmental Health II: A Global Forum for Action," scheduled for September 8–11, 2001. This conference is sponsored by the Children's Environmental Health Network and the Canadian Institute of Child Health and will take place at Georgetown University in Washington, D.C.
(July 2001) Children living in industrialized countries today inhabit a world fundamentally different from that of generations past. The traditional infectious diseases have largely been controlled: smallpox is eradicated, polio is nearly gone, measles is under control, diphtheria and tetanus are rarities, and cholera has virtually disappeared. In the United States, the expected life span of a baby born today is more than two decades longer than that of an infant born at the beginning of the 20th century.
Children in less affluent parts of the world are not so fortunate. In less developed countries, especially in the least developed countries, infectious diseases — particularly dysentery, pneumonia, malaria, measles, and AIDS — remain the leading causes of pediatric morbidity and mortality. Infant mortality is high. Life expectancy at birth in the United States is 76.5 years, yet in the least developed countries three out of four people are dying before the age of 50, according to the World Health Organization's (WHO) World Health Report 1998.
The environment children face today includes hazards that were neither known nor suspected a few decades ago. They are at risk of exposure to over 85,000 synthetic chemicals, most of which have been developed since World War II. In the United States, they are most likely to be exposed to the 15,000 high-production-volume (HPV) chemicals that the U.S. Environmental Protection Agency estimates are produced in quantities of over 10,000 pounds per year. These chemicals are the most widely dispersed in foods, household products, and pesticides, but only 43 percent of them have been tested for their potential human toxicity, according to the National Academy of Sciences (NAS). And although children are now recognized to be especially vulnerable to chemicals in the environment, only 7 percent of these HPV chemicals have been examined for their potential toxicity to children.
Chemical exposures are expected to become an increasingly serious problem in less developed regions as hazardous industries relocate there, both to take advantage of globalization and to escape stricter labor and environmental laws in more developed countries. The danger that this process poses to communities in less developed countries includes not just increases in everyday exposures, but also catastrophic accidents at production facilities. The chemical explosion in Bhopal, India, that claimed more than 2,000 lives in 1984 may unfortunately be a harbinger of future environmental catastrophes in less developed countries.
An Array of Threats to Children
In industrialized countries, a number of chronic diseases — including asthma, cancer, and certain developmental disorders — have replaced infectious diseases as the principal causes of illness and death in childhood. While this development is due partly to the control of traditional infectious diseases in more developed countries, it also stems from the increasing incidence of chronic illnesses. Environmental toxins contribute to a number of these chronic diseases, either as a primary cause (as in lead poisoning) or as contributing factors (as in asthma). In other cases, such as cancer, the precise cause of spreading disease remains unclear, but environmental factors are suspected of playing a role.
Examples of the "new pediatric morbidity" include the following:
The frequency of asthma among children under age 18 years has more than doubled over the past decade in the United States and other industrialized countries. The increasing incidence of asthma is particularly evident in urban centers, where it has become the leading cause of admission of children to hospitals and the principal cause of school absenteeism.
Ambient air pollutants, especially ground-level ozone and fine particulates of automotive origin, appear to be important triggers of asthma. Asthma frequency declines when levels of these pollutants drop. Indoor air pollution, including insect dust, mites, molds, and environmental tobacco smoke are additional triggers.
Sharp discrepancies in asthma by socioeconomic and racial/ethnic status have been noted. In New York City, hospital admission rates for asthma are 21 times higher in the poorest as compared to the wealthiest communities. In 1997, 8 percent of non-Hispanic black children living in families with incomes below the poverty level had asthma, as opposed to 5 percent of all children nationwide.
The reported incidence of cancer among children under 18 years of age in the United States has increased substantially in the past two decades. Although death rates are down, thanks to improved treatment, the incidence of acute lymphoblastic leukemia (ALL), the most common pediatric malignancy, increased by 27 percent from 1973 to 1990, from 2.8 cases per 100,000 children to 3.5 per 100,000. Since 1990, the incidence of ALL has declined in boys, but it has continued to rise in girls. Between 1973 and 1994, the incidence of primary brain cancer (glioma) increased by 40 percent, with nearly equal increases in boys and girls. And in young white men, 20–39 years of age, although not in black men, incidence of testicular cancer increased by 68 percent. While the causes of these increases are not known, environmental factors could play a role. The known and suspected environmental causes of childhood cancer include benzene, radiation, arsenic, and pesticides.
Despite a 94 percent decline in blood lead levels since 1976, caused principally by the removal of lead from gasoline, the Centers for Disease Control estimated in 1998 that 930,000 preschool children in the United States still had elevated blood lead levels (10 micrograms per deciliter or above) and suffered from lead toxicity. These children are at risk of diminished intelligence, behavioral disorders, school failure, delinquency, and diminished achievement. Rates of lead poisoning are highest among poor minority children in urban centers. New immigrants are at high risk, because they tend to live in poor quality housing, are not aware of the dangers of lead-based paint, and may bring medications or cosmetics containing lead from their home countries.
Developmental disorders, including autism and attention deficit disorder, are widespread and affect 5 percent to 8 percent of the 4 million children born each year in the United States. The causes are largely unknown, but exposures to lead, mercury, PCBs, certain pesticides, and other environmental neurotoxins are known to contribute. An expert committee convened by the U.S. National Academy of Sciences concluded in July, 2000 that 3 percent of all developmental disorders in American children are the direct consequence of toxic environmental exposures, and that another 25 percent are the result of interactions between environmental factors and individual children's susceptibility.
Endocrine disruptors are chemicals in the environment that have the capacity to interfere with the body's hormonal signaling system. The effects of these chemicals have been well documented in experimental animals exposed in the laboratory as well as in wildlife populations in contaminated ecosystems such as the Great Lakes.
While data on the human health effects of endocrine disruptors are still scant, it appears that the embryo, fetus, and young child are at greatest risk of adverse consequences following early exposure to these chemicals. Human reproductive and endocrine systems undergo complex development in fetal life and are thus are highly vulnerable to toxic influences at that stage of development. It has been hypothesized (but not proven) that endocrine-disrupting compounds may be at least partly responsible for several disconcerting trends in children's health. These include increases in incidence of testicular cancer, a recently reported doubling in incidence of hypospadias (a birth defect involving the shortening of the urethra in baby boys), and the increasingly early onset of puberty in young girls.
The Global Perspective
The first major international development in children's environmental health was a declaration issued in Miami in 1997 by the Group of 8 (G-8) countries (Japan, France, the United Kingdom, Germany, Canada, Italy, the United States, and Russia). The Miami declaration expressed the commitment of these countries to children's environmental health and included specific commitments to remove lead from gasoline, improve air quality, and improve the quality of drinking water.
The Miami declaration has also sparked interest in children's environmental health among international organizations and the nongovernmental (NGO) community. In 2000, the WHO established a working group on children's environmental health. This group has been active in bringing together participants from industrialized as well as less developed countries. The WHO recognizes that diseases of toxic environmental origin are becoming increasingly important in less developed countries as they industrialize and gain control over the classic infectious diseases. In this context, one particularly important issue in less developed countries is their use of highly toxic pesticides, many of which are banned in more developed countries. Another key problem is the extensive use of asbestos — exposure to which can cause an aggressive form of lung cancer — as a construction material. A third issue is the continuing use of lead in gasoline. The United Nations Environment Programme (UNEP), the World Bank, and the United Nations Education and Children's Fund (UNICEF) are currently in the early stages of joining with the WHO to combat these problems.
The international NGO community is also becoming active in children's environmental health. A new umbrella organization, the International Network on Children's Health, Environment and Safety (INCHES), has been formed to link together grassroots organizations in various countries. INCHES was created at the First International Conference on Children's Environmental Health, held in Amsterdam in August 1998. The U.S. Children's Environmental Health Network and the Canadian Institute of Child Health will host a follow-up conference, "Children's Environmental Health II: A Global Forum for Action," on September 8–11, 2001, in Washington, D.C. This effort should help build greater interest in children's environmental health, but our work is just beginning on what promises to be a critical issue in the 21st century.
Philip J. Landrigan is a pediatrician and chairman of the Department of Community & Preventive Medicine of the Mount Sinai School of Medicine. He is also director of the Mount Sinai Center for Children's Health and the Environment (www.childenvironment.org). Dr. Landrigan chaired the National Academy of Sciences Committee that in 1993 produced the landmark report, Pesticides in the Diets of Infants and Children.
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Children's Unique Vulnerability to Toxicants in the Environment
A detailed analysis undertaken by the U.S. National Academy of Sciences (Pesticides in the Diets of Infants and Children, Washington, DC: National Academy Press, 1993) has established that children are uniquely vulnerable to the toxicants in the environment. This vulnerability arises from four sources:
- Children have disproportionately heavy exposures to environmental toxicants. Pound for pound of body weight, children drink more water, eat more food, and breathe more air than adults. Thus children have substantially heavier exposures to any toxicants in water, food, and air. Two additional factors that further magnify children's exposures are their normal hand-to-mouth behavior and their play close to the ground.
- Children's metabolic pathways, especially in the first months after birth, are immature. Children's ability to detoxify and excrete pollutants is different from that of adults. In many instances, children are less able than adults to deal with toxic compounds.
- Children are undergoing rapid growth and development, and these developmental processes are easily disrupted. During embryonic and fetal life as well as in the first years after birth, a child's brain, endocrine system, reproductive organs, immune system, and respiratory organs are undergoing rapid growth, development and differentiation. If these developmental processes are disrupted by lead, mercury, solvents, endocrine disruptors, or other environmental toxicants, there is high risk of injury, and such injury is frequently irreversible.
- Because children have more future years of life than most adults, they have more time to develop chronic diseases that may be triggered by early exposures. Early exposure to carcinogens, for example, can lead to increased risk of cancer in adult life. Exposure to ionizing radiation as a child has particularly been linked the development of cancer during adulthood.
Insights and Uncertainties
The most important new insight in children's environmental health is the formal recognition in national and international policy circles of the vulnerability of children. Although understanding of children's vulnerability had existed for many years among pediatricians, recognition of children's special vulnerability among policymakers did not develop until after the 1993 publication of the NAS report, Pesticides in the Diets of Infants and Children. The initial impact of that publication was felt principally in the United States, where it helped lead to the 1996 passage of the Food Quality Protection Act (a new federal law on pesticides containing provisions specifically intended to protect the health of children). More recently, recognition of the special vulnerability of children has grown internationally, as shown by the increasing attention devoted to the issue by the World Health Organization and nongovernmental organizations.
Despite the scientific advances that have been made, much uncertainty remains about the extent to which toxic environmental factors influence the health of children. In the case of developmental disabilities, for example, it is known that certain chemicals such as lead, methyl mercury, and polychlorinated biphenyls (PCBs) have harmful effects on the developing brain and thus increase risk of disability. However, the full extent of this problem is not yet clear. Pesticides have the capability to contribute to neurodevelopmental impairment, but data on the chronic toxicity of pesticides are only beginning to be gathered. Considerable uncertainty also exists about the contribution of environmental toxins to rising rates of childhood cancer.
The most dangerous misconceptions in the field of children's environmental health are those that underestimate the seriousness of the threat to the well-being of children. For example, some industry-sponsored analysts have argued that the evidence for children's heightened vulnerability to environmental threats is weak, and have dismissed altogether the notion of endocrine disruption. While it is true that data linking endocrine disruptors to human health are still scant, the evidence for endocrine disruption in wildlife species and in laboratory systems is well established. It appears reasonable that in due course human effects will be identified.
The danger that air pollution poses for child health has also been downplayed by industry. The connection between air pollution and childhood asthma, in particular, has been questioned despite ample evidence that ozone, oxides of nitrogen, and five airborne particulates can exacerbate and trigger asthma. Asthma rates in children have also been shown to decline when levels of air pollutants are reduced.
The scientifically unsound claim that the results of toxicity testing in animals have little relevance to human health represents another important misconception in the field. This claim is contradicted by the fact that every known human carcinogen has been shown to cause cancer in animal species. It is belied further by the close genetic similarity that has recently been demonstrated between humans and other species.
Future Needs and Opportunities
Children's environmental health is a rapidly developing area. New training opportunities are being developed; the Ambulatory Pediatric Association has recently established a national training fellowship program in the United States in environmental pediatrics. The American Academy of Pediatrics is increasing its efforts to train practicing pediatricians in the recognition of diseases of toxic origin, and in 1999 the Academy published a Handbook of Pediatric Environmental Health. The international efforts developing under the aegis of the World Health Organization will likely lead to passage of child-protective legislation in various countries.
There is also great need for a new approach to risk assessment that recognizes the unique vulnerabilities of children. This new approach should incorporate:
- child-specific data on patterns of exposure;
- epidemiologic and toxicologic data on the susceptibility of infants and children;
- biological data that describe the unique mechanisms of toxicity of environmental chemicals to infants and children;
- protective defaults that activate automatically when exposure data or hazard data for children are lacking.
More toxicity testing and new approaches to this testing are also needed. Current testing typically involves administration of a chemical to adolescent animals who are then observed for only a limited period of time. The 1993 NAS report, Pesticides in the Diets of Infants and Children, called for lifetime toxicity testing in which chemicals would be administered in utero or shortly after birth and the animals followed over their entire life span. This approach would permit examination of the delayed effects of early exposure. Tests of a wider range of bodily function should also be incorporated into toxicity tests.
A proposed U.S. national longitudinal study offers a splendid opportunity to advance the field. This prospective study would involve approximately 100,000 children, and its goal would be to examine the consequences of early exposures to environmental toxins. Children would be enrolled into this study as early as possible in pregnancy through interviews conducted with their parents during prenatal visits. Biological samples would be obtained from the mother of each child to assess levels of environmental chemicals in the mother's body during pregnancy, including lead, PCBs, mercury, and pesticides (many of these toxic chemicals can cross the placenta from mother to fetus and affect development). The mother and the father of each child would complete an extensive questionnaire on possible toxic exposures as well as on lifestyle, socioeconomic, behavioral, and health factors that could influence development. Each child will be evaluated at birth, and biological samples will be obtained to assess exposures to environmental chemicals. Children will be assessed repeatedly throughout childhood and adolescence with annual or biannual physical examinations. Preliminary study funding has been appropriated by the U.S. Congress, and planning is being coordinated by the National Institute of Child Health and Human Development. Data from this study are expected to yield invaluable insights into the environmental causes of pediatric disease. Initial results will be available in 2004–2005.
An increasing amount of information on children's environmental health is available both online and in print:
Children's Environmental Health Network: www.cehn.org
Children's Health Environmental Coalition: www.checnet.org
Center for Children's Health and the Environment of the Mount Sinai School of Medicine: www.childenvironment.org
Office of Children's Health Protection, U.S. Environmental Protection Agency: http://yosemite.epa.gov/ochp/ochpweb.nsf/content/homepage.htm
Handbook of Pediatric Environmental Health (Washington, DC: American Academy of Pediatrics, 1999).
Environmental Health Perspectives, a journal published monthly by the U.S. National Institute of Environmental Health Sciences, carries many articles on children's environmental health and runs a special supplement on children's environmental health each June.
U.S. National Academy of Sciences, Pesticides in the Diets of Infants and Children (Washington, DC: National Academy Press, 1993).
Neurotoxicology 21, no. 6, December 2000. This issue of Neurotoxicology is devoted entirely to "Children's Health and the Environment."