on. There is no evidence that malathion affects the ability of humans to reproduce. There is also no conclusive proof that malathion causes cancer in humans, although some studies have found increased incidence of some cancers in people who are regularly exposed to pesticides, such as farmers and pesticide applicators. The International Agency for Research on Cancer (IARC) has determined that malathion is unclassifiable as to carcinogenicity to humans.
To protect the public from the harmful effects of toxic chemicals and to find ways to treat people who have been harmed, scientists use many tests.
One way to see if a chemical will hurt people is to learn how the chemical is absorbed, used, and released by the body; for some chemicals, animal testing may be necessary. Animal testing may also be used to identify health effects such as cancer or birth defects. Without laboratory animals, scientists would lose a basic method to get information needed to make wise decisions to protect public health. Scientists have the responsibility to treat research animals with care and compassion. Laws today protect the welfare of research animals, and scientists must comply with strict animal care guidelines.
Studies in animals have observed the same effects that occur in humans after exposure to malathion. This is because malathion also affects the nervous system of animals. Some studies in animals suggest that malathion may produce subtle changes in the immune system, but there was no evidence indicating that those animals were more susceptible to infections than animals that were not given malathion. Some studies in male rats observed temporary alterations in the testes following short-term exposure to malathion, but there is no evidence that exposure to malathion affected the reproductive ability of these animals. A longer-term study that evaluated the ability of rats to reproduce did not detect any harmful effects. Most studies of cancer in animals have not shown evidence of carcinogenicity for malathion, or have shown evidence of cancer at doses considered excessive. Still, there is some disagreement among scientists on how to interpret the results. The EPA has determined that there is suggestive evidence of carcinogenicity for malathion in animals but it is not sufficient to assess potential carcinogenicity in humans. See Chapter 3 for more information on how malathion can affect your health.
How can malathion affect children?
This section discusses potential health effects from exposures during the period from conception to maturity at 18 years of age in humans.
Children can be exposed to malathion from food and drinking water, but these risks are low and not of concern. Because malathion is a widely used pesticide, greater concern exists from exposure following application to recreational areas, parks, and playgrounds and from home and garden uses of malathion. Children can also be exposed when malathion is sprayed, for example, to control mosquitos. Because children spend more time outdoors than adults, they may be at a greater risk of exposure to malathion than adults. Because of their smaller weight, children's intake of malathion per kilogram of body weight may be greater than that of adults. The EPA permits residues of pesticides to be present in crops used as food, and these amounts are considered to be safe. Children may be exposed also by dermal contact with contaminated surfaces or by placing contaminated objects in their mouths.
The main target of malathion toxicity in children is the nervous system, the same as in adults. Children who have accidentally swallowed high amounts of malathion or who had skin contact with high amounts of malathion experienced difficulty breathing, chest tightness, vomiting, cramps, diarrhea, watery eyes, salivation, sweating, headaches, dizziness, and loss of consciousness, and some died. We do not know whether or not children are more susceptible than adults to malathion toxicity. However, studies in animals have shown that very young animals are more susceptible than older ones when expos