to the environment, usually from spraying on crops or in wide urban/residential areas, droplets of malathion in the air fall on soil, plants, water, or man-made surfaces. While most of the malathion will stay in the areas where it is applied, some can move to areas away from where it was applied by rain, fog, and wind. Malathion stays in the environment from a few days to several months, but is usually broken down within a few weeks. It is broken down to other chemical compounds by water, sunlight, and bacteria found in soil and water. Malathion does not tend to stick to the soil and is rapidly broken down by bacteria; thus, it is unlikely that malathion will reach groundwater in significant amounts. In water, malathion breaks down quickly by the action of the water and the bacteria in the water. In air, malathion is broken down by reacting with other chemicals formed naturally in the air by sunlight, to form a more toxic product called malaoxon. If malathion is present on dry soil or on man-made surfaces such as sidewalks, pavements, or playground equipment, it usually does not break down as fast as it would in moist soil. For more information, see Chapters 4, 5, and 6.
How might I be exposed to malathion?
Most people are not exposed to malathion in the air that they breathe or on things that they touch, unless they live near areas being sprayed. The people who are at the greatest risk of being exposed to malathion are those who work with this chemical. These include farm workers, chemical sprayers, and people who work in factories that make malathion or other products that contain the chemical. They are exposed to malathion on things they touch where it can pass through their skin, or by breathing it after it has been sprayed. Other people who are at risk of being exposed to malathion are those who use it near their homes and in their gardens, and people living in areas where malathion is sprayed to control medflies or mosquitos. Overexposure to malathion may cause severe poisoning or death. Persons may be exposed to dangerous amounts if they go into fields too soon after spraying. The people most likely to be exposed to malathion can be protected by wearing special clothing and breathing equipment and by staying out of sprayed fields for the appropriate amount of time for the job that they are going to do in the field; this amount of time can be up to 6 days.
Individuals can also be exposed to malathion if they live near landfills where malathion has been dumped or near water containing malathion that washes off nearby land or that is accidentally spilled. The greatest amounts of malathion are expected to be present near or on the farms where malathion is used. After spraying, some malathion can be transported by the wind or fog to areas away from where it is used, but the amounts present at these locations are not expected to be at dangerous levels. In a collection of data gathered by the EPA for the years 1971-1991, it was reported that malathion was only found in a total of 12 groundwater monitoring wells in three states. The most that was found in any of the wells was 6.17 parts of malathion per billion parts of water (ppb); this was found in a county in Virginia that is made up mainly of agricultural and forested land. More recent studies of water samples taken near where malathion was sprayed indicate that malathion is not usually found in groundwater. The risk of exposure to malathion from drinking groundwater appears to be low. For more information, see Chapter 6.
Malathion is approved for use on crops, in homes and gardens, in urban/residential areas where mosquitos or medflies pose a problem, and at agricultural sites. The maximum amount of malathion residue allowed by the FDA and EPA on crops used as food is 8 ppm of malathion. The FDA has monitored the food supply for pesticides for a number of years. FDA purchases many kinds of foods through Total Diet Studies (also called Market Basket Surveys) and analyzes them for residue levels of pesticides. These FDA studies allow scientists to estimate the daily in