Introduction

Pesticides are designed to kill and because their mode of action is not specific to one species, they often kill or harm organisms other than pests, including humans. The World Health Organization estimates that there are 3 million cases of pesticide poisoning each year and up to 220,000 deaths, primarily in developing countries. The application of pesticides is often not very precise, and unintended exposures occur to other organisms in the general area where pesticides are applied. Children, and indeed any young and developing organisms, are particularly vulnerable to the harmful effects of pesticides. Even very low levels of exposure during development may have adverse health effects.

Pesticide exposure can cause a range of neurological health effects such as memory loss, loss of coordination, reduced speed of response to stimuli, reduced visual ability, altered or uncontrollable mood and general behavior, and reduced motor skills. These symptoms are often very subtle and may not be recognized by the medical community as a clinical effect. Other possible health effects include asthma, allergies, and hypersensitivity, and pesticide exposure is also linked with cancer, hormone disruption, and problems with reproduction and fetal development.

Pesticide formulations contain both "active" and "inert" ingredients. Active ingredients are what kill the pest, and inert ingredients help the active ingredients to work more effectively. These "inert" ingredients may not be tested as thoroughly as active ingredients and are seldom disclosed on product labels. Solvents, which are inert ingredients in many pesticide formulations, may be toxic if inhaled or absorbed by the skin.

Children are at greater risk from exposure to pesticides because of their small size: relative to their size, children eat, drink, and breathe more than adults. Their bodies and organs are growing rapidly, which also makes them more susceptible; in fact, children may be exposed to pesticides even while in the womb.

Insecticides

Organochlorines

Acute ingestion of organochlorine insecticides can cause a loss of sensation around the mouth, hypersensitivity to light, sound, and touch, dizziness, tremors, nausea, vomiting, nervousness, and confusion.

In 1975, over 70 workers manufacturing Kepone, an organochlorine insecticide, in Hopewell, Virginia, developed a variety of neurological symptoms, the most prominent of which became known as the "Kepone shakes." The workers' symptoms started about 30 days after their first exposure to Kepone. Subsequent testing also revealed decreases in sperm count and motility. In 1976, Kepone was discontinued and substituted with organophosphates.

Organophosphates and Carbamates

Acute organophosphate and carbamate exposure causes signs and symptoms of excess acetylcholine, such as increased salivation and perspiration, narrowing of the pupils, nausea, diarrhea, decrease in blood pressure, muscle weakness, and fatigue. These symptoms usually decline within days after exposure ends as acetylcholine levels return to normal.

Some organophosphates also have a delayed neurological reaction characterized by muscle weakness in the legs and arms. During Prohibition, people consumed a homemade alcoholic drink made out of Jamaican ginger that was contaminated with the organophosphate triorthocresyl phosphate (TOCP). More than 20,000 people were affected by a condition called "Ginger Jake paralysis." Later research found that these effects could be reproduced in animals, and the US government required that organophosphates be tested for delayed effects during the registration process. The human toxicity of organophosphates caused a decline in their use and spurred the search for new alternatives.

Pyrethroids

Among the most promising alternatives to organophosphates were synthetic pyrethroids. However, pyrethroids can cause hyper-excitation, aggressiveness, uncoordination, whole-body tremors, and seizures. Acute exposure in humans, usually resulting from skin exposure due to poor handling procedures, usually resolve within 24 hours. Pyrethroids can cause an allergic skin response, and some pyrethroids may cause cancer, reproductive or developmental effects, or endocrine system effects.

Herbicides

Herbicides are generally less toxic to mammals than insecticides. Most herbicides interfere with plant hormones or enzymes
that do not have any direct counterpart in animals. The most serious human health concerns have been related to chemical contaminants in the active ingredient. Military personnel and others exposed to Agent Orange, a mixture of the herbicides 2,4-Dand 2,4,5-T that was contaminated with dioxin (TCDD), reported birth defects, cancers, liver disease, and other illness. These concerns lead to improvement in the manufacturing process of 2,4,5-T to reduce TCDD contamination and ultimately lead to cancellation of 2,4,5-T and reduction in use of 2,4-D. However, some herbicides may cause cancer, reproductive or developmental effects, or endocrine system effects.

There is also concern that some herbicides may affect wildlife, especially aquatic organisms. For example, atrazine, a persistent herbicide, may adversely affect frogs. Concerns about the effect of atrazine on amphibians resulted in its ban in the European Union, but atrazine remains one of the most widely used herbicides in the US (over 70 million pounds used per year). Persistent herbicides may also contaminate surface water and groundwater.

Next: Integrated Pest Management (IPM)

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