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Trouble on the Farm
Growing Up with Pesticides in Agricultural Communities


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Chapter 2

SUSCEPTIBILITY AND UNEQUAL EXPOSURE: CHILDREN AT RISK

"…while children from socio-economically disadvantaged communities may be disproportionately impacted by our public health and regulatory policies, it is important to emphasize that many toxicants represent greater threats to all children than to adults due to both biological and behavioral differences."
-- Dr. Kenneth Olden, Director, National Institute of Environmental Health Sciences[66]


Scientists and health professionals are finding that human exposure to toxic chemicals in the environment is highly variable, and that susceptibility to exposures also varies greatly. It is incorrect to assume that exposures are homogenous across the population, and that risk assessments performed for the typical study group, healthy adult males, will apply to other members of our society. Genetic variability, age, gender, overall nutritional and health status, and size and weight are all relevant to the risks that any individual faces from toxic chemicals in the environment. Good science requires that we look at population subgroups to quantify their exposures and their susceptibility in order to develop policies that adequately protect children's health.


All Children Are at Greater Risk

There is growing understanding in the field of public health that children are disproportionately susceptible to toxic exposures in their environment.[67] A recent NRDC report entitled Our Children at Risk outlined the scientific evidence that children are particularly impacted by various environmental health threats, including pesticides.[5] U.S. EPA has recognized this problem in their report "Environmental Health Risks to Children," released in the fall of 1996, and has followed up the report with the creation of a new Office of Children's Health Protection in February 1997.[68] The Administration also issued an Executive Order in April 1997 requiring that risks to children must be considered in all government decisions.[69]

Children and infants are uniquely at risk from pesticides both because of physiological susceptibility and greater relative exposure. Three major factors are particularly important:

  • Children often have greater contact with environmental contaminants because of activities that involve contact with dirt and floor surfaces, and because of hand-to-mouth behavior.

  • Children drink more fluids, breathe more air, and eat more food per unit of body weight than adults; they also eat a more limited selection of foods.

  • Children's bodies and brains are immature and still developing, they are more susceptible to certain cancers and reproductive problems, and they have a longer expected lifetime in which to develop illness after an exposure. Thus environmental toxicants can have more serious effects on children.


Unequal Distribution of Exposures to Environmental Toxicants

Scientific investigations of exposures in the environment have repeatedly found something quite curious about human exposures. If you measure the exposure of hundreds or thousands of people and plot their exposures along a line of increasing dose, no matter what the chemical, the distribution of the exposure intensity has a characteristic skewed shape. The curve rises steeply to a peak, and then has a long, slow decline at the high doses. This signifies that some people are exposed at doses much greater than the ‘average' person, sometimes more than a hundred times greater. Public health professionals look at those skewed exposure curves and ask, "who are those people at the upper end of the curve? Why are they exposed to so much more of this chemical compared with the rest of the population? What can we do to decrease their exposures?" In many cases, those people at the top end of the exposure curve are workers and poor people who, for example, rely on subsistence fishing for food (high exposures to mercury, PCBs), or who live in old, sub-standard housing (lead exposures). There is evidence that, for pesticides, farm children are near the top of the exposure curve. We need to investigate why that is true and what can be done about it.


Children Are More Exposed

The National Academy of Science report, Pesticides in the Diets of Infants and Children, outlined how children's eating patterns and physiology place them at particular risk from pesticides in their diet.[70] The most important factor determining children's increased risk from pesticides is their greater exposure. Compared to adults, children, on a body-weight basis, consume more food and water, ingest more dust and soil, and breathe more air. The skin surface area of an infant per unit of body weight is double that of an adult.[70] The normal relative respiratory volume of a resting infant is twice that of a resting adult. Caloric consumption by infants per unit of body weight is approximately two-and-a-half times higher than for adults. Any contamination of food, water, air, soil, or dust will result in increased child exposures compared to adults.

A child's diet is far less varied than an adult's. In particular children consume large quantities of milk, fruit, and fruit juices. The average one-year-old drinks twenty-one times more apple juice, eleven times more grape juice, and nearly five times more orange juice per unit of body weight than the average adult.[71] Infants and children also drink two-and-a-half times more water daily than adults do as a percentage of their body weights.[72] Fruit, fruit juice, and water frequently contain pesticide residues.

Because of their higher rate of breathing, children are more highly exposed to pesticides that remain in indoor air. Children living in homes with indoor air contaminated with the pesticide pentachlorophenol (PCP) were found to have nearly twice as much PCP in their blood as their parents.[73] The breathing zone of young children is closer to the floor, and often contains higher pesticide levels than the breathing zone of adults.[74] Children have greater hand-to-mouth activity, increasing opportunities for direct ingestion of pesticide residues in dirt or dust.


Children Are More Susceptible

Human and experimental animal data suggest that children are more vulnerable than adults to the neurotoxic effects of pesticides. In several cases of human poisoning by organophosphate insecticides, fatality rates were higher in children than in adults.[70] Two decades of scientific research has demonstrated repeatedly that immature laboratory animals are more susceptible than adults to the neurotoxic effects of organophosphate insecticides.[75], [76]

According to the National Academy of Sciences, concern about children's exposure to pesticides is valid because "exposure to neurotoxic compounds at levels believed to be safe for adults could result in permanent loss of brain function if it occurred during the prenatal and early childhood period of brain development."[70] In addition, children have a longer potential lifetime during which latent health effects from low-level exposures may be expressed.

Infants and children are sometimes less able to eliminate toxins from their bodies. Infant kidneys, for example, are immature and cannot excrete foreign compounds such as drugs as quickly as adult kidneys.[70] In immature animals, the lethal dose of some organophosphate compounds is only 1 percent of the lethal dose in adult animals.[77] In the infant rat, the maximum tolerated dose of chlorpyrifos was one-sixth the maximum tolerated dose in the adult.[78]

Genetic differences are also a determinant of susceptibility to pesticides. For example, the activity of the enzyme paraoxonase affects the metabolism of organophosphate pesticides, thereby influencing the ultimate toxic response in an individual.[79] Researchers have documented that the body's ability to detoxify organophosphate insecticides is dependent upon adequate production of this enzyme, which differs within the human population by a factor of 15. Children in the first few months of life have very low levels of the enzyme.[79][82] Thus all infants, and those children and adults with genetically low production of paraoxonase, are likely more susceptible to the effects of organophosphates.

Many scientists agree that public health protection efforts should focus on those children who are most exposed and most susceptible, rather than on the average adult, or even the average child.[83] The children most exposed to pesticides are farm children.


Farm Children Face Even Higher Risks

Scientific data strongly suggest that children who live on, or adjacent to, agricultural land and children whose parents work in the fields have significantly greater pesticide exposure than non-farm children. Farm children have exposure to pesticides through the usual routes common to the general population and in addition, via routes particular to their location and the employment of their family members.

Farm children are exposed to pesticides through food at levels similar to or higher than the general population. Higher levels of foodborne exposure in some agricultural areas may be due to the shorter transport time from field to table, which allows less time for degradation of residues on the food. Farm children also face potential exposures from "take home" residues on their parents' clothing, from contaminated water, from playing in contaminated soil on or near the fields, from pesticide drift, and from dust and indoor air in the home. In addition, there is extensive evidence that many children accompany their families to the fields, where they may face exposures at occupational levels whether or not they are working.[84] The Children's Health Protection Advisory Committee (CHPAC) to the U.S. EPA recognized the disproportionate risks faced by farm children. The Committee's final report to EPA found that, "Children may be exposed to pesticides through employment in farm work, by eating fruits and vegetables directly from the fields while at work, or by drift from field applications to neighboring residential areas and schools. Pregnant and lactating women who work in farm fields or reside in neighboring areas can also expose fetuses and neonates to pesticides. The current farm Worker Protection Standard has not considered these pesticide exposures to children."[85] As a result, CHPAC recommended that the Worker Protection Standard be re-evaluated in order to make sure it adequately protects the health of farm children. CHPAC did not point out how little enforcement there currently is of the weak Worker Protection Standard's basic health and sanitation regulations. In California, less than 3 percent of all farms are inspected each year by the state and in many other states the inspections are even rarer. Without strong enforcement of existing standards, violations are likely to be common.

The Food Quality Protection Act (FQPA) recognizes the disproportionate susceptibility and exposures of children. This law requires U.S. EPA to consider children's vulnerability and exposure when setting tolerances for pesticides on foods. Unfortunately, as described in a recent NRDC report entitled Putting Children First, U.S. EPA's usual testing requirements for pesticides do not adequately quantify their particular impacts on the health of the fetus and infant, particularly the development of the brain.[86] Furthermore, the record shows that U.S. EPA has failed to adequately consider the extensive evidence that children are exposed to significant amounts of pesticides through sources other than food, and that farm children are exposed to agricultural pesticides in their environment. Thus U.S. EPA is flying blind when trying to protect children from pesticides. To account for these data gaps while awaiting more research, an additional safety factor should be added to pesticide tolerances to account for uncertainties about childhood susceptibility and exposure.


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