Pesticides and Human Health

by Glen Andersen

July 1999
No.1

Pesticides play a vital role in ensuring the quality of the United States food supply-but the potential for pesticides to cause human and environmental harm has required the creation of numerous regulations. Pesticide use affects a large number of people the United States: the Environmental Protection Agency (EPA) estimates that approximately 100,000 pesticide poisonings occur annually. Pesticides have been detected in a large number of the nation's water bodies, including those that provide drinking water1. Congress, through the Food Quality Protection Act, has required the EPA to review and revise all pesticide residue limits to ensure that they adequately protect children. This review, which will impact the use of the most harmful pesticides, is an effort to ensure that regulations keep pace with the complex and changing science that determines pesticide safety. State laws that regulate pesticide use will need modification to account for federal rules and scientific advancement.

The importance of pesticides in world agriculture should not be understated, as their introduction in the 1940s began a trend marked by crop yields that continually increased in size and quality. This "Green Revolution," which relied heavily on chemical pesticides and fertilizers, led to healthier populations by providing an increasingly varied food supply, controlling food borne disease, and reducing malnutrition. Agricultural dependence on pesticides has steadily increased since their introduction-each year more than 2 million metric tons of pesticide products are used to control pests and diseases.

Although the use of pesticides to produce healthier and more abundant crops has been beneficial for human health, some aspects of pesticide use still trouble scientists, lawmakers and the public. Problems with pesticides were not widely known until the publication of the book Silent Spring by researcher Rachel Carson in 1962. Her book presented a detailed study of ecosystem damage caused by the indiscriminate use of pesticides. Later work by other researchers supported Carson's book, and suggested negative effects for humans as well. Due to mounting evidence against hazardous pesticides, the federal government banned DDT and chlordane.

Many modern pesticides are designed to break down into non-toxic substances with the passage of time. Pesticides are most potent just after application, but should break down to relatively safe levels by the time treated food reaches the table. If the pesticide has not had the required amount of time to break down, is applied too liberally, or a more persistent pesticide is used, some pesticide residue may still be in food at the time of consumption.

The U.S. Food and Drug Administration's Pesticide Program found that 60 percent of the fruits and 37 percent of the vegetables that were sampled in 1995 contained detectable pesticide residues. Approximately 2 percent of these fruit and vegetable samples contained residue amounts that exceeded maximum residue limits set by the EPA. The EPA sets the maximum residue limit (MRL) to be the maximum level of residue legally permitted in or on a crop in commerce. This level is set to insure that there are no adverse effects to the consumer over a lifetime of dietary exposure.

Under the 1996 the Food Quality Protection Act, many of the current MRLs are likely to change, largely since the new act requires that levels be reduced by 90 percent if uncertainty about effects on children exists. The EPA must review all pesticides and their health effects using current methodology, taking into account exposure to pregnant women and developing children, while also including exposures from other sources. Using this new data, EPA must set residue limits accordingly by the year 2000

Pesticides enter water resources in a variety of ways, including:

· Runoff from field application;

· Direct entry from spray operations;

· Sewage dumping;

· Settling from the atmosphere;

· Leaching from waste dumps;

· Leaching from field application through soils into groundwater.

The amount each of these methods of entry contributes varies, depending upon the environment and nature of the source. However, runoff and leaching tend to be the main pesticide pathways to water.

Groundwater, which supplies drinking water to approximately 50 percent of the U.S. population, was until recently thought to be safe from chemical pollution. However, researchers are detecting a greater variety of pesticides in a growing number of groundwater resources across the United States. In 1988, the EPA documented the presence of 46 pesticides in groundwater from 26 states. A 1990 study found one or more pesticides in 10.4 percent of community water systems. Contamination of these important water resources may threaten human health, since the millions of Americans who rely on groundwater use it without pre-treatment. Residues that reach groundwater may linger for long periods of time, or eventually find their way to surface waters by emerging through springs and lake bottoms. In 1986, EPA testing found pesticide residues in half of the 2,000 wells they tested in Iowa. Groundwater contamination can have long-lasting effects, since the cold temperatures and a lack of organic substances impede the decomposition of pesticide compounds.

In 1998, the U.S. Geological Survey finished the largest pesticides and water study ever conducted. Within the study regions, they found that 95 percent of streams and 50 percent of wells near agricultural and urban areas contain one or more pesticides. Although most did not violate current safe drinking water standards, these standards are valid only for exposure to individual pesticides, not to the mixtures of different pesticides that are present in most contaminated sources. For most of the streams tested-half of which supply drinking water-pesticide levels exceeded EPA's guidelines for aquatic life.

Workers can be exposed to pesticides through direct skin contact or inhalation during application. Such exposure also may occur when safety periods between application and harvest are ignored or when pesticides are overused or used improperly. Pesticides from aerial spraying may also drift into neighboring areas and expose residents.

In 1995, an international study conducted by the World Health Organization estimated that approximately 3 million cases of pesticide poisonings occur annually, including 220,000 pesticide-related deaths, mainly among those who use and apply pesticides.

The most common type of pesticide poisoning results from ingestion, inhalation, or skin absorbtion of relatively large amounts of pesticides. This type of acute poisoning is most common among agricultural workers. While much is known about the toxic effects of pesticides at these higher levels, uncertainty about long term low level exposures-similar to what one could experience through food and water consumption-remains.

The nature of a pesticide is to kill or otherwise adversely affect the target pest, be it fungus, insect, weed or rodent. Although efforts are made to design the pesticide in such a way that it affects only the target organism, pesticides do cause harm to non-target organisms. Toxic effects range from acute (poisoning occurring through single or a few exposures) to chronic (occurring through long-term exposure). In humans, pesticides can affect the nervous, reproductive and endocrine systems, and may cause cancer. Laboratory studies conducted on animals also have linked chronic exposure of pesticides to birth defects, tumor development and cancers. The EPA's has classified approximately 165 chemical pesticides as known, probable or possible human carcinogens.

New research suggests that some pesticides may disrupt the body's endocrine system-the set of glands, hormones and target cells that help control growth, development, reproduction and behavior. Endocrine disruptors interfere with this system, causing biological dysfunction. Some endocrine disruptors mimic hormones that occur naturally in the body, fooling the body into a response. Other endocrine-disrupting chemicals can inhibit or stimulate the body's production of hormones. Such disruption is known to cause birth defects in wildlife and laboratory test animals, and is suspected of causing cancer and birth defects in humans. Much is yet to be learned about the effects of pesticides on the human endocrine system, and research in this area is ongoing.

Children, in particular, are susceptible to pesticides for various reasons-they are still developing, have faster metabolisms and are involved in play activities that increase their exposure. A child's small size and quick metabolism means that he or she consumes more fresh produce, breathes more air, and drinks more water than adults relative to his or her body weight. They also play on the ground, swim in lakes and rivers and mouth toys and other objects, all of which lead to increased pesticide exposure. Additionally, a child's growing body is more sensitive to chemical exposures because development is taking place in the brain, nervous system and many other areas. Some studies have shown that children of parents who use pesticides occupationally or in the household are three to nine times more likely develop leukemia. (1, 2)

Determining the levels at which a pesticide causes harm is a complex, scientifically demanding task. Pioneering biomonitoring efforts by the Centers for Disease Control and Prevention have helped reduce the uncertainty involved in estimating human risk involved in pesticide and other chemical exposures. Biomonitoring involves the direct measurement of a toxic substance in blood or urine to assess exposure, and will help to determine which of the thousands of known chemical compounds cause birth defects, cancer and other diseases.

Reducing the human health threat of pesticides is possible through combined efforts in different areas, such as improved risk assessment and toxicity testing, better education and training for users of pesticides, and integration of farming practices that require fewer pesticides. Ways to reduce the potential hazards of pesticide use could involve the following.

• Crop rotation helps mitigate weed, disease and pest problems, increases soil nitrogen, and reduces the need for fertilizers. Monoculture-the practice of repeatedly growing one type of crop, such as corn, in the same field year after year-is a common practice throughout the United States. This practice promotes pest problems and depletion of soil nutrients.

• Natural predators and parasites can be used to control pests. Pesticides often destroy predators while the pest gradually grows more tolerant to the pesticide, requiring that increasing amounts of the pesticide be applied.

• Soil and water conserving tillage reduces runoff and helps maintain soil quality.

• Integrated pest management is encouraged by the EPA and U.S. Department of Agriculture. This approach to pest control uses the tactics mentioned above-such as crop rotation, biological controls, resistant varieties of plants, pheromones to attract beneficial insects, efficiently timed spraying-and other methods. Integrated pest management can be more economical because it minimizes the use of costly chemicals.

• The majority of children's pesticide exposure comes from home, lawn, and garden application-reducing this exposure requires a more prudent and controlled use of pesticides in private and public areas. (3)

In 1996, the United States exported 687 million pounds of pesticides, mostly to developing countries. Workers in developing nations such as Mexico often lack proper training and handle pesticides without masks or protective clothing. In the highly agricultural Culiacan Valley of Mexico, nearly 3,000 field workers are hospitalized for pesticide poisoning each year.

Ten million pounds of 1996 U.S. pesticide exports were pesticides that were banned or forbidden for use in the United States due to their hazardous nature. In addition, testing of produce imported into the United States has uncovered traces of banned pesticides. Chlordane and lindane, extremely hazardous pesticides that are banned for food use in the United States, have appeared in canola seed imports from Canada and carrot imports from Mexico. Adding to the safety uncertainties of imported produce is the decline in the testing of imported produce since the implementation of the North American Free Trade Agreement.

To address this growing problem, 95 countries have signed the Prior Informed Consent Convention. The convention contains provisions for the exchange of information among parties about potentially hazardous chemicals that may be exported and imported. This convention requires that 1) all chemicals designated for occupational use must be accompanied by an international safety data sheet; and 2) all chemicals that are banned or severely restricted domestically must have labeling that provides information with regard to risks and hazards to human health and the environment. The convention has been signed by the president, but has yet to be ratified by the Senate.

Several attempts have been made to address the problem in the United States through "Circle of Poison" legislation. These bills, none of which have passed, were designed to stop companies from exporting banned and unregistered pesticides, as well as to introduce tougher testing standards to keep these pesticide residues from showing up in consumers' food.

The United States has a complex set of chemical safety statutes and regulations that are administered by a number of federal agencies. The principal statutes are described briefly below.

Toxic Substances and Control Act (TSCA)-Regulates industrial chemicals, including heavy metals. Identifies and controls industrial chemical hazards that are toxic to human health and the environment. Administered by the U.S. Environmental Protection Agency.

Federal Insecticide, Fungicide and Rodenticide Act (FIFRA)-Also administered by the EPA, requires the agency to register all pesticides sold in the United States. FIFRA makes it a violation to use a pesticide in a manner inconsistent with its label, including the specified uses. FIFRA was revised and strengthened substantially by the Food Quality Protection Act in August 1996.

Federal Food, Drug and Cosmetic Act (FFDCA)-Regulates the establishment of pesticide tolerances (maximum residue levels). FFDCA was revised and strengthened substantially by the Food Quality Protection Act in August 1996. Administered by the EPA and the Food and Drug Administration.

Food Quality Protection Act (FQPA)-Amends both FIFRA and FFDCA to make a more consistent, protective regulatory system that is supported by sound science. It mandates a single, health-based standard for all pesticides in all foods and provides special protection for infants and small children.

Emergency Planning and Community Right-to-Know Act (EPCRA)-Requires local emergency planning for responses to industrial chemical or pesticide accidents; requires industries to notify their communities and states of releases; provides information from companies about possible industrial chemical or pesticide hazards in the facility's community; and mandates a national inventory of toxic chemical releases (Toxics Release Inventory [TRI]). Administered by the EPA.

Clean Air Act (CAA)-Establishes criteria and standards for regulating toxic air pollutants to safeguard public health and the environment. Administered by the EPA.

Clean Water Act (CWA)-Establishes criteria and standards for pollutants-including some pesticides-in surface water bodies to protect against chronic ecosystem effects. Administered by the EPA.

Safe Drinking Water Act (SDWA)-Establishes enforceable maximum contaminant levels (MCLs) for pesticides and health advisories. Major revisions strengthening SDWA were enacted in August 1996. Administered by the EPA.

Resource Conservation and Recovery Act (RCRA)-Requires appropriate handling and disposal of hazardous waste. Administered by the EPA.

Comprehensive Environmental Response, Compensation and Liability Act (CERCLA)-Covers incidents with hazardous materials and mandates the EPA Superfund program to clean up the highest priority sites contaminated by chemicals. The Agency for Toxic Substances and Disease Registry (ATSDR) evaluates data on the release of hazardous substances to assess effects on public health, initiates toxicological research, establishes and maintains registries for persons exposed to hazardous substances, and provides response to emergency release of substances.

Hazardous Materials Transportation Act (HMTA)-Ensures the safe and environmentally sound transportation of hazardous materials by all modes of transportation through a comprehensive, risk-based national program. Administered by the U.S. Department of Transportation (DOT).

Federal Hazardous Substances Act (FHSA) Consumer Product Safety Act (CPSA) and Poison Prevention Packaging Act (PPPA)-Regulates the safety of consumer products, including chemical safety. (Consumer Product Safety Commission)

Occupational Safety and Health Act (OSHA)-Regulates toxic chemicals related to occupational safety. Administered by the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH).

1. "Pesticides in Surface and Ground Water of the United States: Summary of Results of the National Water Quality Assessment Program" U.S. Geological Survey, (1998)

2. J.D. Buckley, L.L. Robison, R. Swotinsky, D.H. Garabrant, M. LeBeau, P. Manchester, M.E. Nesbit, L. Odom, J.M. Peters, W.G. Woods, and G.D. Hammond, "Occupational Exposures of Parents of Children with Acute Nonlymphocytic Leukemia: A Report from the Children's Cancer Study Group," Cancer Research 49, (1989): 4030-4037.

3. R.A. Lowengart, J.M. Peters, C. Cicioni, J. Buckley, L. Bernstein, S. Preston-Martin, and E. Rappaport, "Childhood Leukemia and Parents' Occupation and Home Exposures," Journal of National Cancer Institute 79, (1987): 39-46.

4. S.H. Zahm and M.H. Ward , "Pesticides and Childhood Cancer," Environmental Health Perspectives, 106 [Supplement 3] (June 1998):893-904