Highlands County Aerial
July 1998
Malathion mixed with bait has been applied by air to eradicate Mediterranean or Mexican fruit fly infestations in Florida. This summary answers questions about the safety of these pesticide applications. It presents findings of the California Department of Health Services 1990-1991 health risk assessment.
A: Yes. During the 1989-1990 campaign to eradicate the Mediterranean fruit fly (Medfly) in southern California, the Department of Health Services (DHS) was asked to evaluate the safety of the aerial application of malathion- bait. DHS spent a full year conducting a thorough health risk assessment. This included evaluating the health effects information in the scientific literature, the monitoring data from spraying, and the potential for exposure to malathion from the eradication program. In February 1991, DHS issued both a scientific report and a summary. The DHS report concluded that the health of the general population is not at significant risk from the applications of malathion-bait.
A: Yes. In 1990, DHS formed the Malathion Public Health Effects Advisory Committee (MPHEAC). This committee consisted of local health officials and scientific experts outside state government as well as community members. Its job was to ensure an open scientific review and evaluation of the potential health effects of malathion. This committee met 14 times in meetings open to the public during the course of the risk assessment and provided an essential review function. The MPHEAC endorsed the findings of the DHS risk assessment and presented additional recommendations for further scientific studies in a report issued in March 1992.
A: Malathion is perhaps the most commonly used home and garden insecticide. Malathion is used in 33 counties in Florida, including Lake County, for mosquito abatement. Insects lack the enzymes that quickly breakdown malathion in animals. This makes insects much more susceptible to malathion than humans. Thus, malathion can be used at low concentrations against insects with little risk to humans.
In aerial application for medfly eradication, malathion is mixed with a bait made from corn protein, to attract the fruit flies, and applied at the rate of 12 fluid ounces (1 « cups) per acre. The mixture consists of about 20% malathion and 80% bait. Small droplets of the mixture quickly fall to the ground and kill the fruit flies when they eat them. Because there is almost no vaporization and most of the droplets are too large to enter the lungs, there is very little chance of exposure to malathion from breathing. As a general precaution, people should stay indoors during the application to avoid contacting it.
A: The Food Quality Protection Act requires EPA to reevaluate the safety of all pesticides that are used on food products. EPA has selected four classes of compounds with the greatest potential for adverse effect for evaluation in the first phase of this review, including organophosphate pesticides. Malathion is an organophosphate pesticide. Malathion is much less toxic than the other organophosphate pesticides because humans and other animals rapidly metabolize malathion to chemicals that are less toxic and excreted from the body.
A: During the 1982 Medfly eradication campaign in Santa Clara County, two large epidemiological studies compared women who lived in areas where aerial bait had been applied with women in areas where there had been no aerial application of malathion. The first study was of 39,000 births and the second of 7500 pregnancies. Neither found evidence for a consistent association between increased birth defects and malathion-bait application. The first one also looked at low birth weight and found no evidence that malathion was associated with low birth weight.
Five studies conducted with rats and two with rabbits using relatively high doses of malathion failed to show an excess risk of birth defects. Therefore, on the basis of human and animal evidence, DHS does not consider malathion to pose a risk of birth defects.
A: These chemicals have not caused cancer in a number of experiments with animals. One study in animals suggests that malaoxon (a breakdown product of malathion) may increase thyroid gland tumors when given at very high dose. However, scientists in DHS, the MPHEAC, and the U.S. EPA who reviewed the studies found that the results were uncertain. The U.S. EPA has required more cancer studies and will review all the studies for malathion and malaoxon under the Food Quality Protection Act. Even if a tumor increase is confirmed in later studies, MPHEAC concluded that any potential cancer risk would be negligible based on the small amounts used in fruit fly eradication programs.
A: There is no convincing evidence of lasting visual impairment from chronic exposure to malathion. We looked into reports of eye damage in Japan where large amounts of several highly toxic pesticides were sprayed by airplane in farming areas in the 1970s. These reports did not implicate malathion or its decomposition products, although they did suggest that other, more toxic, organophosphate pesticides may cause eye problems. MPHEAC concluded that at the low levels likely to result from the malathion-bait application, no visual problems were anticipated.
A: When tested in animals or preparations of immune system cells in the laboratory, malathion has produced both increases and decreases in immune response, but there has been no definitive pattern to the results of these tests. Skin sensitization (or allergy) has been reported in some animal studies and in one human study. In the human study, a common impurity of malathion, diethyl fumarate, is thought to be involved. Overall, the tests indicate a potential for skin sensitization from exposure to malathion. This would mean that after initial exposure, subsequent exposure to malathion could induce a stronger skin reaction.
A: We do not expect that chromosome damage would result from the low doses of malathion which the public would receive from aerial malathion-bait application. Malathion, at relatively high doses in laboratory experiments, has the ability to change the normal structure of chromosomes, which carry the genetic material DNA. Some chromosome changes are causes of cancer, birth defects, or aging; others have no effect, and may also occur naturally. In any case, as indicated above, the evidence does not suggest that malathion causes birth defects or cancer.
The only studies on humans to date are not relevant because they were on pesticide applicators who received high exposures to malathion and other pesticides. Some showed chromosomal damage.
A: DHS estimated how much of the malathion people might actually receive internally from breathing it, through skin contact, and consuming malathion-bait on home-grown fruits and vegetables. DHS found that there is a theoretical possibility of two kinds of adverse effects in situations where people have a high exposure to malathion- bait. Such situations would be, for example, an adult working outdoors all day doing gardening, or a child wearing only shorts and playing outdoors several hours on the morning after an application. The possible health effects are skin irritation and lowered activity of an enzyme called acetylcholinesterase (AChE). AChE is a chemical involved in transmitting nerve signals through the body. If AChE activity is slightly lowered from the malathion exposure, the effect would be temporary and would not produce observable symptoms. Furthermore, the chance of these effects occurring is slight.
A: The signs of poisoning from high doses included pinpoint pupils, salivation, vomiting, diarrhea, and depressed levels of AChE as determined by laboratory testing. Before aerial spraying was conducted in California, physicians and hospitals were reminded of these signs so any such cases could be reported. None were. No cases of malathion poisoning have been recognized or reported by physicians during Medfly eradication in Florida. During the eradication campaign, however, some people called a specially advertised hotline and reported symptoms such as nausea, diarrhea, vomiting, rashes, and upper respiratory problems. These symptoms are also common to flu, colds, and other illnesses.
We feel that levels of malathion that the general public was exposed to would not cause any lowering of AChE sufficient to cause these symptoms. Indeed, two surveys DHS conducted in 1981 in Santa Clara County could show no increase in illness symptoms after aerial malathion-bait applications began.
A: A clinical study was conducted by the Los Angeles County Health Department with 42 volunteers out of 254 people who reported skin rashes to the specially advertised hotline during the 1989-90 Medfly campaign. These individuals were tested with separate skin patches containing malathion and the corn protein bait since it was possible that the bait caused an allergic reaction in some individuals. Of the 42 people, six showed some skin irritation but none developed skin rash in response to malathion. One individual reacted to the bait. This study failed to confirm that skin rash actually occurs after aerial applications of malathion-bait.
During recent eradication programs in Lake and Manatee Counties in Florida, a few people have reported similar skin rashes. Confirmation testing would be required to determine if the rashes resulted from exposure to the malathion-bait mixture.
A: DHS considered whether there were identifiable "sensitive" individuals or groups who, because of pre-existing illness, allergic sensitization, drug therapy, or other reasons, would be more susceptible to the relatively small doses of malathion expected in the Medfly aerial malathion-bait program. DHS identified several different conditions and drugs as theoretically contributing to increased susceptibility, and took this into account when making their risk calculations.
Because there were a number of complaints about subjective symptoms during the 1989-90 Los Angeles Medfly Eradication Program, DHS arranged for direct medical examinations and testing for a number of people with complaints. With the exception of a few cases of relatively mild allergic or irritant reaction, DHS did not have any solid evidence of any instances in which malathion-bait has caused illness in any of the identified "sensitive" people discussed in the risk assessment.
A few people have reported an exacerbation of respiratory symptoms after the malathion-bait spraying in Lake and Manatee Counties. People with respiratory problems, eg asthma or emphysema, should take extra precautions such as limiting exposure; remaining in closed, air conditioned buildings during and for four hours after spraying; or leaving the spray area until four hours after the spraying is completed. Further testing will be needed to determine if this increase in respiratory symptoms is the result of malathion, the bait, or neither.
A: Malathion has been widely used for more than 50 years in agriculture, mosquito control, and homes and gardens. Although the scientific data on its effects are about as extensive as for any pesticide, there are gaps in the data. When there are gaps in the scientific information, we made assumptions that were designed to err on the side of safety because of the large number of potentially exposed people.
A: Although DHS and the MPHEAC concluded that the malathion-bait did not pose a significant risk to public health, they noted that the anger and anxiety that aerial spraying may cause are important public health considerations in themselves, and that some people continue to believe their health has been affected. DHS and MPHEAC therefore recommended that aerial malathion- bait eradication be used only when no other method was practical. The Florida Department of Health agrees and recommends that aerial application in residential areas be done at night whenever possible to further reduce the risk and public concern.
The Florida Department of Health also agrees with DHS that if aerial spraying is required, people should use common sense measures to minimize their exposure. As a general principle, unnecessary exposure to pesticides should be avoided under any circumstances. Simple precautions should be taken such as remaining indoors during applications, rinsing off outdoor play areas, washing skin and clothing promptly if contact occurs, and washing home-grown produce before eating it. Such common sense measures should provide adequate protection to all individuals.
A: There is no need to relocate during aerial applications of malathion-bait. Nevertheless, individuals who believe that their physical or psychological health would be impaired by remaining in the spray area during a malathion-bait application should discuss their concerns with their physician and decide for themselves.
A: People who are sick and believe that malathion might be contributing to their symptoms should see their personal health care provider for an appropriate evaluation of their symptoms and consideration of all likely causes. Area residents and physicians are encouraged to report suspicious adverse health effects to the Highlands County Health Department at 386-6040. Health officials are interested in documenting any adverse health effects thought to be related to aerial spraying of malathion. However, symptoms that might be caused by malathion poisoning are like those caused by many illnesses and are very common in their occurrence in any community. Physicians who suspect that malathion may be responsible for a patient's symptoms may wish to consider appropriate laboratory tests.
A: We do not think that your child will suffer any damage to health from such behaviors. Typical exposures like this were taken into account in our health risk calculations, and a significant health risk was not found. Nevertheless, any unnecessary exposures to pesticides should be avoided, and we recommend that people take simple precautions to prevent contacting them whenever possible.
A: The available evidence indicates that malathion does not cause birth defects or other problems with pregnancy.
A: Studies in California tested for malathion in houses after aerial application. Malathion concentrations in houses under normal living conditions were more than 100 times below the levels that cause adverse effects in humans. People with preexisting respiratory conditions should take extra precautions such as limiting exposure; remaining in closed, air conditioned buildings during and for four hours after spraying; or leaving the spray area until four hours after the spraying is completed.
A: No. Many substances that are not hazardous to health such as eggs, cola, and acidic fruit, can blemish or discolor paints.
A: Yes. Wash them first, just as you should wash any produce.
A: Malathion is an organophosphate chemical, developed in the early 1940s. It is a popular home-garden insecticide that is used worldwide. Besides being used on home gardens and landscapes, it has widespread use on dairy farms, chicken ranches, and on orchards and commercial food crops. It is used on pets and livestock to protect them from fleas and biting flies. It has been marketed in shampoo to treat children for head lice. It is used regularly in urban areas for mosquito abatement. Malathion has a record of safe and effective use in past exotic pest eradication programs in Florida and California.
A: Toxicity is dose related. No chemical can be said to be absolutely "safe". Safety pertains to how one handles a material. Even highly hazardous materials can be used safely. Relatively large doses are necessary for malathion to be toxic to humans or other animals. The amount applied for fruit flies, and the manner in which it is applied (in a bait), does not expose members of the public to a significant toxic risk. The small amount of malathion people might come in contact with as it is applied, either from the ground or by air, is well below what is known to be toxic for humans. Concentrated solutions of malathion are sold for use by home gardeners in many neighborhood stores that carry gardening supplies.
A: The Florida Department of Agriculture and Consumer Services, in cooperation with the USDA, has developed an eradication program which uses malathion mixed with a protein bait that attracts flies. The mixture is applied to trees where Medflies may live. Adult flies are killed when they are attracted to the bait and eat it. As little as 12 fluid ounces of the mixture applied per acre is adequate to achieve eradication. In addition to killing mature flies that may have already mated, flies emerging from pupae require nutrients before they begin to mate. If malathion is present in bait as they emerge, immature flies that eat the bait are eliminated before having a chance to reproduce.
The procedure used to apply malathion from aircraft is designed to minimize human exposure. Most of the droplets reach the ground within a few minutes after application aircraft pass overhead. Only scattered slowly-falling droplets might be detected for a short while. After 30 minutes, settling is no longer visibly detectable.
A: The malathion used in this program is 96.8% pure. When malathion is produced (manufactured) a number of impurities remain in the final concentrate. While these impurities contribute to overall toxicity, they are present when the toxicity of malathion is tested, and are therefore accounted for.
A: The amount of malathion that is in swimming pool water after spraying would not cause any adverse health effects. Toxicologists have calculated the exposure from swimming pool water using assumptions that over-predict the exposure. If a 22 pound child was exposed to the malathion in over 2 quarts of swimming pool water, the dose would be too low to produce an effect. They also evaluated the risk if all the malathion was converted to malaoxon. A child could be exposed to all the malaoxon in over four ounces of water and not have any effects. People should use common sense about swimming after malathion is sprayed in the pool. It is always best to keep your exposure to pesticides as low as possible. If there is visible bait on the surface of the pool, it should be removed before anyone swims in the pool.
A: The protocol used for the aerial application of malathion includes steps to prevent malathion application to major bodies of water, because fish and other aquatic animals are more sensitive to the effects of malathion than are humans. The standard for malathion in surface water, which has been set to protect aquatic life, is 1600 times lower than the drinking water standard for malathion. Small ponds, streams, canals etc may have malathion sprayed over them during aerial application. This may result in toxicity to some aquatic animals, particularly if these animals are already stressed by other factors, such as low oxygen content in the water. Every effort is made during aerial application to prevent toxicity to aquatic animals.
A: Diazinon is applied directly to the soil under trees or plants that have fruit or vegetables containing Medfly larvae. The only way to be exposed to diazinon from this program is to come into direct contact with the soil that has been treated. This is unlikely. If there is incidental contact with the soil containing diazinon, the small dose of diazinon received is very unlikely to cause any adverse effects in humans.
A: If you have additional health questions about malathion, please contact the Highlands County Health Department at 386-6040