Health effects of carbon tetrachloride
Contents
- 1 Introduction
- 2 Pathways for carbon tetrachloride in the environment
- 3 Exposure to carbon tetrachloride
- 4 Pathways for carbon tetrachloride in the body
- 5 Health effects of carbon tetrachloride
- 6 Reducing risk of exposure to carbon tetrachloride
- 7 Medical tests for exposure to carbon tetrachloride
- 8 Further Reading
Introduction
Carbon tetrachloride is a clear liquid that evaporates very easily. Most carbon tetrachloride that escapes to the environment is therefore found as a gas. Carbon tetrachloride does not easily burn. Carbon tetrachloride has a sweet odor, and most people can begin to smell it in air when the concentration reaches 10 parts carbon tetrachloride per million parts of air (ppm). It is not known whether people can taste it or, if they can, at what level. Carbon tetrachloride is a manufactured chemical and does not occur naturally in the environment. Carbon tetrachloride has been produced in large quantities to make refrigeration fluid and propellants for aerosol cans. Since many refrigerants and aerosol propellants have been found to affect the earth's ozone layer, the production of these chemicals is being phased out. Consequently, the manufacture and use of carbon tetrachloride has declined a great deal. In the past, carbon tetrachloride was widely used as a cleaning fluid (in industry and dry cleaning establishments as a degreasing agent, and in households as a spot remover for clothing, furniture, and carpeting). Carbon tetrachloride was also used in fire extinguishers and as a fumigant to kill insects in grain. Most of these uses were discontinued in the mid-1960s. Until recently, carbon tetrachloride was used as a pesticide, but this was stopped in 1986. (Health effects of carbon tetrachloride)
Pathways for carbon tetrachloride in the environment
Because carbon tetrachloride evaporates easily, most of the compound released to the environment during its production and use reaches the air, where it is found mainly as a gas. It can remain in air for several years before it is broken down to other chemicals. Small amounts of carbon tetrachloride are found in surface water. Because it evaporates easily, much of it will move from surface water to the air within a few days or weeks. However, it may be trapped in groundwater for longer periods. Carbon tetrachloride is not expected to stick to soil particles. If spilled onto the ground, much of it will evaporate to the air. Some of it may also go into groundwater, where it can remain for months before it is broken down to other chemicals. It is not expected to build up in fish. We do not know if it builds up in plants.
Exposure to carbon tetrachloride
Very low background levels of carbon tetrachloride are found in air, water, and soil because of past and present releases. Concentrations in air of 0.1 part carbon tetrachloride per billion parts of air (ppb) are common around the world, with somewhat higher levels often found (0.2-0.6 ppb) in cities. Carbon tetrachloride is also found in some drinking water supplies, usually at concentrations less than 0.5 ppb. Exposure to levels of carbon tetrachloride higher than these typical "background" levels is likely to occur only at specific industrial locations where carbon tetrachloride is still used or near chemical waste sites where emissions into air, water, or soil are not properly controlled. Exposure at such sites could occur by breathing carbon tetrachloride present in the air, by drinking water contaminated with carbon tetrachloride, or by getting soil contaminated with carbon tetrachloride on the skin. Young children may also be exposed if they eat soil that contains carbon tetrachloride. Carbon tetrachloride has been found in water or soil at about 26% of the waste sites investigated under Superfund, at concentrations ranging from less than 50 to over 1,000 ppb.
People who work with carbon tetrachloride are likely to receive the greatest exposure to the compound. The National Institute for Occupational Safety and Health (NIOSH) estimates that 58,208 workers are potentially exposed to carbon tetrachloride in the United States. The average daily intake of carbon tetrachloride for the general population is estimated to be 0.1 microgram (µg per kg of body weight). The estimated average daily amount that the general population may drink in water is 0.01 µg per kg of body weight.
Pathways for carbon tetrachloride in the body
Carbon tetrachloride can enter your body through your lungs if you breathe air containing carbon tetrachloride, or through your stomach and intestines if you swallow food or water containing carbon tetrachloride. Carbon tetrachloride can also pass through the skin into the body. When you inhale carbon tetrachloride, over 30-40% of what you inhale enters your body, where most of it temporarily accumulates in body fat. Some can enter the kidney, liver, brain, lungs, and skeletal muscle. When you drink water contaminated with carbon tetrachloride, about 85-91% of it can enter your body. Much of the compound that enters your body when you breathe it or drink water contaminated with it leaves your body quickly, and a lot of it can be found in your breath within a few hours. Animal studies have shown that under differing conditions, 34-75% of carbon tetrachloride leaves the body in expired air, 20-62% leaves the body in feces, and only low amounts leave the body in the urine. Animal studies also suggest that it may take weeks for the remainder of the compound in the body to be eliminated, especially that which has entered the body fat. Most of the carbon tetrachloride is eliminated from your body unchanged, but some of it may be changed to other chemicals before removal from the body (for example, chloroform, hexachloroethane, and carbon dioxide). Chloroform and hexachloroethane may themselves cause harmful effects.
Health effects of carbon tetrachloride
Scientists use many tests to protect the public from harmful effects of toxic chemicals and to find ways for treating persons who have been harmed. 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).
Most information on the health effects of carbon tetrachloride in humans comes from cases where people have been exposed to relatively high levels of carbon tetrachloride, either only once or for a short period, for example, by accidental poisoning or by working with the chemical in a confined space without ventilation. Experiments have not been performed on the effects of long-term exposure of humans to low levels of carbon tetrachloride, so the human health effects of such exposures are not known.
The liver is especially sensitive to carbon tetrachloride since it contains a large amount of the enzymes that change the form of the chemical. Some of the breakdown products may attack cell proteins, interfering with the functions of the liver cells. Products that attack cell membranes may result in the death of the cells. In mild cases, the liver becomes swollen and tender, and fat builds up inside the organ. In severe cases, liver cells may be damaged or destroyed, leading to a decrease in liver function. Such effects are usually reversible if exposure is not too high or too long.
The kidney is also sensitive to carbon tetrachloride. Less urine may be formed, leading to a buildup of water in the body (especially in the lungs) and buildup of waste products in the blood. Kidney failure often was the main cause of death in people who died after very high exposure to carbon tetrachloride. Long-term breathing exposure to carbon tetrachloride worsened age related kidney disease in rats.
Fortunately, if injuries to the liver and kidney are not too severe, these effects eventually disappear after exposure stops. This is because both organs can repair damaged cells and replace dead cells. Function usually returns to normal within a few days or a few weeks after the exposure has stopped.
After exposure to high levels of carbon tetrachloride, the nervous system, including the brain, is affected. Such exposure can be fatal. The immediate effects are usually signs of intoxication, including headache, dizziness, and sleepiness perhaps accompanied by nausea and vomiting. These effects usually disappear within 1-2 days after exposure stops. In severe cases, stupor or even coma can result, and permanent damage to nerve cells can occur.
Carbon tetrachloride also causes effects on other tissues of the body, but these are not usually as common or important as the effects on the liver, kidney, and brain.
There have been no studies of the effects of carbon tetrachloride on reproduction in humans, but studies in rats showed that long-term inhalation may cause decreased fertility.
Studies in animals have shown that swallowing or breathing carbon tetrachloride over a period of years increases the frequency of liver tumors. Mice breathing carbon tetrachloride also developed tumors of the adrenal gland. Studies have not been performed to determine whether swallowing or breathing carbon tetrachloride causes tumors in humans, but it should be assumed that carbon tetrachloride could produce cancer. The Department of Health and Human Services (DHHS) has determined that carbon tetrachloride may reasonably be anticipated to be a carcinogen (i.e., cause cancer). The International Agency for Research on Cancer (IARC) has classified carbon tetrachloride in Group 2B, possibly carcinogenic to humans. EPA has determined that carbon tetrachloride is a probable human carcinogen.
Many reported cases of carbon tetrachloride toxicity are associated with drinking alcohol. The frequent drinking of alcoholic beverages increases the danger of organ damage from carbon tetrachloride exposure. This enhanced effect has been shown in situations in which a group of workers were exposed to carbon tetrachloride in air, but only those who were heavy consumers of alcohol became ill.
Health effects in children
This section discusses potential health effects in humans from exposures during the period from conception to maturity at 18 years of age.
Children and adults may be exposed to low levels of carbon tetrachloride in drinking water. Small children who live near factories that produce or use carbon tetrachloride could accidentally eat some of the chemical by putting dirty hands in their mouths, but the amount of carbon tetrachloride in the soil is thought to be too low to be harmful. Carbon tetrachloride is no longer used in consumer products, but children could breathe in vapors if households are still using old supplies.
It is not known if the way in which carbon tetrachloride is absorbed into and eliminated from the body is different in children than it is in adults, but the processes are likely to be similar. Compared to adults, young children have lower amounts of the enzyme that converts carbon tetrachloride to a harmful chemical. The health effects of carbon tetrachloride have not been studied in children, but they are likely to be similar to those seen in adults exposed to the chemical.
There is no direct evidence that maternal exposure to carbon tetrachloride has a harmful effect on the fetus in humans. A few human survey-type studies suggest that maternal drinking water exposure to carbon tetrachloride might possibly be related to certain birth defects, such as low birthweight and small size at birth. Information from animal studies indicates that carbon tetrachloride may cause early fetal deaths, but does not cause birth defects in babies surviving to term. However, these animal studies did not test for neurological damage in exposed newborn babies.
One study calculated that carbon tetrachloride is likely to pass from the maternal circulation into breast milk. Thus, it is possible that children could be exposed to carbon tetrachloride from breast feeding, but the levels of exposure are likely to be low.
Reducing risk of exposure to carbon tetrachloride
If your doctor finds that you have been exposed to substantial amounts of carbon tetrachloride, ask whether your children might also have been exposed. Your doctor might need to ask your state health department to investigate.
Although most consumer uses of carbon tetrachloride have been banned, children may be exposed to carbon tetrachloride in old consumer household cleaning products. Removing these old containers will reduce your family's risk of exposure to carbon tetrachloride. Household chemicals should be stored out of the reach of children to prevent accidental poisonings and skin burns. Always store household chemicals in their original containers. Never store household chemicals in containers that children would find attractive to eat and drink from, such as old soda bottles. Keep your poison control center's number next to your phone.
Sometimes older children sniff household chemicals in an attempt to get high. Your children may be exposed to carbon tetrachloride by intentionally inhaling products containing it. Talk with your children about the dangers of sniffing chemicals.
Medical tests for exposure to carbon tetrachloride
Several very sensitive and specific tests can detect carbon tetrachloride in exposed persons. The most convenient way is simply to measure carbon tetrachloride in exhaled air, but carbon tetrachloride can also be measured in blood, fat, or other tissues. Because special equipment is needed, these tests are not routinely performed in doctors' offices, but your doctor can refer you to where you can obtain such a test. Although these tests can show that a person has been exposed to carbon tetrachloride, the test results cannot be used to reliably predict whether any bad health effects might result. Because carbon tetrachloride leaves the body fairly quickly, these methods are best suited to detecting exposures that have occurred within the last several days.
Further Reading
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