Arsenic
Arsenic is an element that is widely distributed in the earth's crust. Elemental arsenic is ordinarily a steel grey metal-like material that sometimes occurs naturally. However, arsenic is usually found in the environment combined with other elements such as oxygen, chlorine, and sulfur. Arsenic combined with these elements is called inorganic arsenic. Arsenic combined with carbon and hydrogen is referred to as organic arsenic. Organic forms of arsenic are usually less harmful than inorganic forms.
Presently about 90 percent of all arsenic produced is used as a preservative for wood to make it resistant to rotting and decay. The preservative is chromated copper arsenate (CCA) and the treated wood is referred to as "pressure-treated." In the past, arsenic was primarily used as a pesticide, most often on cotton fields and in orchards. Inorganic arsenic compounds can no longer be used in agriculture. However, organic arsenicals, namely cacodylic acid, disodium methylarsenate (DSMA) and monosodium methylarsenate (MSMA), are still used as pesticides, principally on cotton. Small quantities of arsenic metal are added to other metals to form metal mixtures or alloys with improved properties. The greatest use of arsenic in alloys is in lead-acid batteries used in automobiles. Other common uses of arsenic compounds include manufacturing of glass, semiconductors and light-emitting diodes.
Arsenic is a known human carcinogen with toxic effects on nearly all organ systems (ATSDR 2000d). Studies of people who drink tap water with high levels of arsenic show increased risk for cancers of the skin, bladder, lung, kidney, liver and colon (National Toxicology Program (NTP) 2002a). In laboratory animals, arsenic causes cancer when exposure occurs early in life, producing malignant, benign and precancerous lesions in adulthood at multiple sites including the lung, liver, adrenal gland and ovary (Waalkes 2003). In addition, arsenic causes proliferative lesions in the uterus and oviduct in exposed animals.
In 2001, a report by the National Academy of Sciences concluded that people who consume drinking water with three parts per billion (ppb) arsenic daily would have about a 1 in 1000 increased risk of developing bladder or lung cancer. At 10 ppb, the risk is even greater (National Research Council (NRC) 2001). Since 2006, EPA has decreased the highest allowable level, called a maximum contaminant level (MCL), of arsenic in drinking water from 50 ppb to 10 ppb (USEPA 2003c; USEPA 2006a). In 2004, the California Environmental Protection Agency established a long-term objective (called a public health goal) for a maximum drinking water concentration for arsenic of four parts per trillion, 2500 times lower than the EPA's MCL of 10 ppb. Four parts per trillion is a level of arsenic in drinking water that would not be expected to pose a significant human health risk (California Environmental Protection Agency 2004).
Long-term ingestion of arsenic in drinking water results in pronounced vascular changes, peripheral vascular insufficiency and adverse effects on bone marrow (ATSDR 2000d). Studies of communities with high drinking water levels, such as in Bangladesh, India and Taiwan, show that arsenic is associated with increased risk of diabetes (Longnecker and Daniels 2001; Tseng 2002), high blood pressure and heart disease (Tseng 2003; Wang 2002), skin disorders, neurological problems, chromosome damage (Mahata 2003), respiratory problems and birth defects. Arsenic has also been linked with harmful developmental effects in children (California Environmental Protection Agency 2004).
In 2004, the U.S. EPA's Toxics Release Inventory (TRI) reported that in 2002, U.S. industrial facilities released 1,842,882 pounds of arsenic and 403,580,936 pounds of arsenic compounds into the environment, mostly to the land (such as landfills, surface soil, spills and holding ponds) (USEPA 2009i). |