Health effects of disulfoton
Contents
Introduction
Disulfoton is a manufactured substance used as a pesticide (Health effects of disulfoton) to control a variety of harmful pests that attack many field and vegetable crops. Disulfoton does not occur naturally. The common trade names for disulfoton are Di-syston®, Disystox®, Frumin AL®, and Solvirex®. Pure disulfoton is a colorless oil with no identifiable odor and taste. The technical product is dark yellowish, and has an aromatic odor. It does not easily dissolve in water or evaporate to air. It is most likely to be present in hazardous waste sites with other wastes, either in drums or mixed with soil. Disulfoton is used to protect small grains, sorghum, corn, and other field crops; some vegetables, fruit, and nut crops; and ornamental and potted plants against certain insects. Although it is used primarily in agriculture, small quantities are used on home and garden plants. Small quantities also are used for other purposes, such as mosquito control in swamps. The use of disulfoton has decreased in recent years.
Pathways for disulfoton in the environment
Disulfoton enters the environment primarily when it is applied as a spray or as granules on field crops, vegetables, potted plants, and home gardens. Disulfoton also can enter the environment when it accidentally spills or leaks during storage and transport. Disulfoton may also enter the environment from hazardous waste sites. Environmental contamination by disulfoton mainly affects soil and water. Natural chemical reactions and bacterial attack remove disulfoton from soil and water. Such reactions form some by-products that are more toxic than disulfoton. Fish accumulate disulfoton in their bodies. The levels of disulfoton in fish can be hundreds of times higher than the level in water. Disulfoton binds moderately well to soil and typically does not travel deep into soil with rainwater. Disulfoton has been detected infrequently in groundwater from agricultural soil in California and Virginia. The estimated amount of time required for the concentration of disulfoton in river water to decrease to half of its initial level (half-life) is 7 days. The estimated half-life in soil ranges from 3.5 to 290 days, depending on the nature of the soil and climatic conditions.
Exposure to disulfoton
You may be exposed to disulfoton by breathing contaminated air, drinking contaminated water, and eating contaminated food. Disulfoton is rarely detected in air. In 1980, a low level of disulfoton was detected in 1 of 123 air samples collected from 10 locations in the United States. The average concentration at this site was 0.1 nanogram (ng) in 1 cubic meter of air (1 ng = 1/1,000,000,000th Billionth of a gram). Disulfoton has not been detected in drinking water. Low levels of disulfoton (0.05–1.0 milligram in a kilogram [mg/kg] of food) (1 mg = 1/1,000 Thousandth of one gram) are sometimes found in some grains, fruits, and vegetables treated with this pesticide. Because the levels in food are higher than levels in air and water, you are more likely to be exposed to disulfoton by eating contaminated food. The Food and Drug Administration (FDA) estimated that the average intake of disulfoton in food per day for a 14- to 16-year-old male in the United States from 1986 to 1991 was 0.2 ng/kg (nanograms per kilogram) of body weight. The FDA estimate for disulfoton intake from foods is 0.07% or less than 1/1,000th of the Food and Agriculture Organization/World Health Organization (FAO/WHO) acceptable daily intake (ADI) value of 300 ng/kg. The FAO/WHO ADI value is the maximum amount of a chemical which if ingested over a person's lifetime appears to be without appreciable health risk. Workers in industries that manufacture and formulate disulfoton are at a higher risk of exposure. Workers who spray the pesticide in fields and some farm workers who enter the fields following spraying also are at a higher risk of exposure than the general population. Among the general population, people who frequently use the pesticide in their homes and gardens are potentially at higher risk. People who live near hazardous waste sites that contain disulfoton also are potentially at a higher risk of exposure. Children playing at or near these hazardous waste sites may be exposed by touching and eating soil that contains disulfoton.
Pathways for disulfoton in the body
Disulfoton can easily enter your body when you breathe it in, swallow it, or have skin contact with it. The amount of disulfoton that enters your body depends on the amount in air, food, and water, and the length of time you are exposed to it. In an oily mixture, disulfoton may enter the body through the skin, lungs, or stomach more easily than it would in a water mixture. After disulfoton enters your body, the blood carries it to your organs and tissues. Disulfoton generally does not build up in your organs and tissues, but is initially changed to more harmful substances, which quickly break down to harmless by-products. The harmful breakdown products inhibit important enzymes (cholinesterases) in the nervous system, and this action can cause neurological effects. The harmless breakdown products do not have any known effects on the body. Studies in animals show that disulfoton and/or the breakdown products completely leave the body through the urine, feces, and exhaled air in about 10 days or less.
Health effects of disulfoton
You should know that one way to learn whether a chemical will harm people is to determine how the body absorbs, uses, and releases the chemical. For some chemicals, animal testing may be necessary. Animal testing may also help identify such health effects as cancer or birth defects. Without laboratory animals, scientists would lose a basic method for getting information needed to make wise decisions that protect public health. Scientists have the responsibility to treat research animals with care and compassion. Scientists must comply with strict animal care guidelines because laws today protect the welfare of research animals.
Additionally, there are vigorous national and international efforts to develop alternatives to animal testing. The efforts focus on both in vitro and in silico approaches and methods. For example, the National Toxicology Program (NTP) at the National Institute of Environmental Health Sciences (NIEHS) created the NTP Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM) in 1998. The role of NICEATM is to serve the needs of high quality, credible science by facilitating development and validation—and regulatory and public acceptance—of innovative, revised test methods that reduce, refine, and replace the use of animals in testing while strengthening protection of human health, animal health and welfare, and the environment. In Europe, similar efforts at developing alternatives to animal based testing are taking place under the aegis of the European Centre for the Validation of Alternative Methods (ECVAM).
In people, disulfoton mainly causes harmful effects to the nervous system. The harmful breakdown products of disulfoton inhibit cholinesterase activity in the nervous system, which results in neurological effects. Depending on the amount of disulfoton that enters the body, neurological effects, such as inhibited cholinesterase activity, narrowing of the pupils, vomiting, diarrhea, drooling, difficulty in breathing, tremors, convulsions, and even death may occur. These effects can occur if you breathe in, swallow, or have skin contact with disulfoton. Exposure to small amounts of disulfoton can sometimes inhibit cholinesterase activity without causing obvious neurological effects. If you take in disulfoton from food or water for long periods, you may also become nearsighted. You are less likely to die from skin contact with disulfoton than from swallowing it, but you may become weak and tired after skin contact.
Breathing in, swallowing, or having skin contact with high levels of disulfoton can cause similar neurological effects in animals. The neurological effects of disulfoton are the most common effects. Animals that swallowed disulfoton for long periods became nearsighted, and the structures of their eyes were further damaged. Results of animal studies suggest that female rats and mice are more sensitive to disulfoton than male rats and mice.
We do not know whether disulfoton causes reproductive or birth defects, or cancer in people. However, some studies suggest that disulfoton may cause reproductive effects in animals. Some animals that swallowed disulfoton during pregnancy had newborns with underdeveloped bones, damaged livers and kidneys, and underdeveloped testes. Animals that swallowed disulfoton for long periods did not develop cancer. Disulfoton has not been classified for carcinogenic effects by the Department of Health and Human Services (DHHS), the International Agency for Research on Cancer (IARC), or the EPA.
Medical tests for exposure to disulfoton
Disulfoton and its breakdown products can be measured in the blood, urine, feces, liver, kidney, or body fat of exposed people. In cases of occupational or accidental exposure to disulfoton, the breakdown products are often measured in the urine. The breakdown products are relatively specific for disulfoton and a few other similar organophosphate pesticides and can be detected in urine for up to one week after people were last exposed. Because disulfoton inhibits cholinesterase in blood and in blood cells, inhibition of this enzyme activity may also suggest exposure to disulfoton. Cholinesterase activity in blood and in blood cells may remain inhibited for as long as 1–2 weeks after the last exposure. Because other organophosphate pesticides also inhibit cholinesterase activity in blood and blood cells, this test is not specific for disulfoton. The measurement of cholinesterase in blood and blood cells and the amount of disulfoton breakdown products in the urine cannot always predict how much disulfoton you were exposed to. Your doctor can send samples of your blood or urine to special laboratories that perform these tests.
Further Reading
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