HEALTH HAZARDS OF PESTICIDES

"Late in the afternoon of April 1, 1990, a three-year-old girl playing in front of her trailer home in California’s San Joaquin Valley suddenly lost control of her body and began foaming at the mouth. By the time the girl arrived at the local emergency room, she was near death. She recovered eventually. A report filed with the California Department of Pesticide Regulation concluded the child had been poisoned by aldicarb, a highly toxic insecticide that works the same way on people as it does on bugs -- like nerve gas. ‘Somebody had parked a tractor with pesticide material on it right in front of the play area,’ said Michael O’Malley, the author of the report and a physician at the University of California, Davis."
-- Matt Crenson, Associated Press, December 9, 1997

Pesticides are specifically formulated to be toxic to living organisms, and as such, are usually hazardous to humans. Most pesticides used today are acutely toxic to humans. Pesticides cause poisonings and deaths every year and are responsible for about one out of every sixteen calls to poison control centers.^[18] Chronic health effects have also been reported from pesticides, including neurological effects, reproductive problems, interference with infant development, and cancer.

Acute Impacts

Acute pesticide poisonings frequently involve organophosphate pesticides, or sometimes their close relatives, the n-methyl carbamates. These pesticides were originally derived from chemical warfare agents developed during World War II. Some common organophosphates in use today include chlorpyrifos (Dursban®), diazinon, azinphos-methyl (Guthion®), malathion, and methyl-parathion. Aldicarb (Temik®) and carbaryl (Sevin®) are common n-methyl carbamates. They kill by blocking the enzyme that breaks down a critical nerve-impulse-transmitting chemical known as acetylcholine. The result is that certain nerve impulses are over-expressed, resulting in an array of acute toxic symptoms. Symptoms of organophosphate or carbamate poisoning include blurred vision, salivation, diarrhea, nausea, vomiting, wheezing, and sometimes seizures, coma, and death. Mild to moderate pesticide poisoning mimics gastroenteritis, bronchitis, or intrinsic asthma, and even astute clinicians may not link these symptoms to pesticides.

The American Association of Poison Control Centers reported 97,278 calls about pesticide poisonings in 1996. Half of the reported poisonings involved children under six years of age.^[18] Occupational pesticide poisonings are required to be reported in California, and there are approximately 1,500 reported cases per year.^[19], ^[20] Efforts to extrapolate to national occupational pesticide poisonings result in estimates of anywhere between 10,000 and 40,000 physician-diagnosed pesticide illnesses and injuries annually among agricultural workers.^[21] These estimates do not include children of agricultural workers.

Research has shown that current estimates based on occupational surveillance or poison control centers may greatly underestimate the problem of pesticide poisonings. A study in California that involved active surveillance, with extensive physician education and recruitment, revealed that this intervention significantly increases the number of reports of pesticide illness. A follow-up evaluation of poisoned workers discovered that 40 percent of the exposure incidents also involved co-workers who did not seek medical treatment for various reasons, suggesting that the total burden of illness is grossly underreported.^[19] Poison control centers are commonly called after accidental ingestions or spills of pesticides in the home, but are less frequently called when illnesses occur after routine agricultural pesticide exposures.

Mild signs of acute pesticide poisoning, such as nausea, vomiting, diarrhea, or wheezing are often not recognized as being potentially linked to pesticide toxicity. Rashes and other skin reactions are another major manifestation of pesticide toxicity that is often misdiagnosed.^[22] Even Dr. Lynn Goldman, Assistant Administrator of the Office of Prevention, Pesticides and Toxic Substances of the U.S. EPA, has publicly admitted, "Medical problems caused by pesticide exposure are often overlooked or misdiagnosed by health care providers."^[23]

Even severe pesticide poisoning is frequently misdiagnosed. In one review of the medical records of 20 severely pesticide-poisoned infants and children transferred to a major medical center from other hospitals, 16 of the 20 children had been wrongly diagnosed at the time of the transfer. Diagnoses of the children’s symptoms included brain hemorrhage, head trauma, diabetic acidosis, severe bacterial gastroenteritis, pneumonia, and whooping cough, although all of the children later turned out to have pesticide poisoning.^[24] In this series, five of the children, all infants, were poisoned after home application of a pesticide. Another child was poisoned after mowing a lawn that had recently been sprayed with an organophosphate. Although these cases did not involve farm children, they demonstrate that all children can be overexposed to pesticides in their home environment. Among infants, only a small dose is required to have potentially devastating health consequences. Furthermore, there is some evidence from animal studies that undernourished individuals are more vulnerable to poisoning by organophosphates, implying that poor and undernourished children may be at greater risk.^[25]

Chronic Impacts

"Twenty-two years that I have been working in the fields, I’ve seen more illnesses, more children being born ill, more families that miss work because every day they have more problems, headaches. Sometimes their children are sick and they have to miss work. . . . We live in a depression. We don’t know if it’s because of the chemicals."
-- Laura Caballero, Lideres Campesinas (Salinas, CA Public Meeting July 25, 1996)

Chronic effects of pesticide exposure may include adverse effects on neurological function, cancer, reproductive harm, reduced growth and development, and birth defects. Much of the evidence of chronic effects is based on studies of adult workers who are exposed to a mixture of chemicals every day, making it difficult to pinpoint specific pesticides. The effects of individual pesticides during specific periods of fetal life, infancy, and early development have been studied in laboratory animals. Little research on the chronic effects of pesticides has been done directly on children, and even less on farm children.

Neurological Effects

In adults, exposures to insecticides and herbicides have been reported to confer an approximately fourfold increased risk of early-onset Parkinson’s disease.^[26], ^[27] Other long-term neurological problems, particularly shortened attention span and reduced coordination, have been reported in adults overexposed to organophosphate pesticides.^[28] Although such studies have not been done in human children, animal studies have revealed that some pesticides appear to target the developing brain during the critical period of cell division, thereby leading to lasting behavioral aberrations.^[29], ^[30] Not only do organophosphate pesticides interfere with a critical nerve-impulse transmitter, but they also can permanently change the number of receptors in the brain for this neurotransmitter. This mechanism may explain the subtle, permanent effects observed in animals.^[31]

Subtle neurological effects may also occur in human children. A recent study compared preschool children in two farming communities in Mexico, one with heavy pesticide use and one with little or no pesticide use. The children living in the area with heavy pesticide use had strikingly impaired hand-eye coordination, decreased physical stamina, short-term memory impairment, and difficulty drawing, compared with the less exposed children. Furthermore, observers of the exposed children noticed increased aggressive and anti-social behavior compared to their less exposed counterparts.^[32] Studies have shown that lead, a known neurotoxicant, has lasting effects on attention span, intelligence, and behavior. Infants and children are more susceptible to the toxic effects of lead than are adults, probably because their brains are still developing.^[33]–^[35] Similarly, it appears that infants and children are also more susceptible to other neurotoxicants, including pesticides.

Childhood Cancer

"There were three funerals in a row here in this neighborhood for children that died of cancer. There was a day when some of the children got together [across from] our house. They were playing with the Barbies. They were picking flowers . . . and they were burying the Barbie. I said ‘What are you kids doing?’ Cause they were burying the Barbie and they were crying and crying and crying . . . they said that Barbie died of cancer. It had cancer in the leg and it died. . . . I was always wondering ‘Is my daughter going to be next after having her so ill?’ . . . When I went to the room, she was having another seizure and she kept saying, ‘My dollies are dying of cancer mom, please help me, please help me.’"
-- Marta Salinas, McFarland, CA^[14]

According to Dr. Lynn Goldman of the U.S. EPA, at least 101 pesticides in current use are probable or possible human carcinogens.^[36] Examples of pesticides which are known carcinogens in animals and are still used around humans today include pentachlorophenol, 1,3-dichloropropene (Telone II®), and dichlorvos (DDVP).^[37] Studies of farm populations indicate that adults exposed to pesticides may be at increased risk for cancers of the lymphatics and blood, stomach, prostate, testes, brain, and soft tissues.^[37], ^[38] Several human studies and studies of household dogs have consistently reported a particular association between exposure to the common herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and non-Hodgkin’s lymphoma.^[39]–^[41]

There is evidence of associations between parental or infant exposures to pesticides and childhood brain tumors, leukemia, non-Hodgkin’s lymphoma, sarcoma, and Wilm’s tumor.^[42]–^[46] In many of the reports, children’s increased cancer risks were of greater magnitude than the risks reported in studies of adults.^[47] Five of the nine human studies that evaluated the risk of childhood leukemia after parental exposures to pesticides found an increased risk, while four out of five studies looking at postnatal exposures to pesticides also found a link with acute leukemia.^[48] In one California study, children with leukemia were three to nine times more likely to have a parent who reported using pesticides in the home or garden during pregnancy or lactation.^[49] Eight of the nine studies evaluating the link between childhood brain tumors and pesticide use showed an association, with three reaching statistical significance.^[48]

Reproductive and Developmental Toxicity

Numerous pesticides are known or suspected reproductive toxicants. Examples include the fungicides benomyl (Benlate®) and vinclozolin (Ronilan®), as well as the fumigants methyl bromide and metam sodium.^[50] People who live in agricultural regions or undergo occupational exposure to pesticides are at increased risk of a variety of adverse reproductive outcomes. An investigation of stillbirths and neonatal deaths in California reported that maternal occupational exposure to pesticides was associated with more than a doubling of the risk of stillbirth due to congenital anomalies, and a slightly increased overall risk of all types of stillbirth.^[51] Numerous types of birth defects, particularly limb-reduction defects, have been associated with pesticide exposures in human studies.^[52]–^[54] A Minnesota study indicated an association between paternal employment as a pesticide applicator and a variety of birth defects in offspring, including abnormalities of the lungs, heart, musculoskeletal system, and urogenital system. Furthermore, the general population of agricultural regions of the state had an increase of birth defects, with the peak incidence among children conceived in the spring, when spraying is most intense.^[55]

Endocrine Disruption

Many currently used pesticides are now known to interfere with normal hormonal function in animals. For example, vinclozolin and iprodione, popular fungicides, both break down into a metabolite that interferes with testosterone and other androgens.^[56] Several organochlorine pesticides, including DDT, methoxychlor, endosulfan, and dicofol, mimic estrogen.^[57], ^[58] Lindane, which is sometimes used to treat head lice in children, acts as an anti-estrogen, and is also toxic to the nervous system.^[59], ^[60] Atrazine, a popular herbicide, can disrupt ovarian function, cause mammary (breast) tumors in animals, and interferes with the binding of steroid hormones and the breakdown pathway of estrogen.^[61]–^[63] Although no human studies have been done involving the endocrine effects of these chemicals, the endocrine system in animals is nearly identical with the human, making it likely that effects observed may be relevant to human health. In humans and animals, the endocrine system is critical to life. Disruption of hormone function can permanently alter normal development of the fetus and child.^[64] Some pesticides have also been reported to be toxic to the immune system in animals. ^[65]

Nearly all of the epidemiological studies on children’s health and pesticide exposures were done on the general, non-farming population. These studies would likely underestimate the health impacts that would be expected for highly exposed subpopulations of children such as farm children. Some studies did look at children of parents who work in jobs that may involve pesticide exposure; however the child’s exposure was almost never directly assessed, but was indirectly estimated based only on the parent’s job title. Such a technique is likely to lead to misclassification of exposures and underestimation of the health impact. Thus health impacts among farm children are likely much greater than those described in most of the scientific research to date. Because of the health impacts of pesticides, it is important to identify the sources and levels of exposure to these chemicals in order to protect the most highly exposed children from these dangerous substances.

http://www.nrdc.org/health/kids/farm/chap1.asp