Arsenic compounds and cancer

ROC STATUS: Known human carcinogen since 1980

ALSO KNOWN AS: Arsenic pentoxide, arsenic trioxide, arsenic acid

RELATED CANCERS: Lung cancer, kidney cancer, bladder cancer, liver cancer, prostate cancer, colon cancer, certain types of skin cancer

DEFINITION: Arsenic occurs in small concentrations in earth and minerals. The leaching effects of water and wind erosion continuously release trace amounts. These can be transported over long distances via windblown dust, surface water, and groundwater flow.

Inorganic arsenic compounds are naturally occurring combinations of arsenic and oxygen, sulfur, or chlorine. These complex minerals they are associated with are generally water soluble and appear as white, odorless solids. They typically have high melting and boiling points and can be highly toxic, even fatal, if inhaled or ingested in large quantities.

Exposure routes: Arsenic compounds in the form of dust and fumes can be absorbed through the dermal layers of the skin or inhaled and absorbed into respiratory passageways. It can also be ingested orally as a contaminant in food or water.

Where found: Arsenic is a naturally occurring material in soil, water, and various ores, especially copper and lead. Therefore, arsenic compounds are found throughout the environment. Arsenic combines with other elements, including sulfur, oxygen, and chlorine, to create relatively stable inorganic arsenic compounds. Often the most concentrated environmental forms of arsenic are released into the atmosphere via volcanoes and mineral and ore erosion. Because arsenic compounds cannot be destroyed, a relatively constant level of toxic inorganic compounds of arsenic always exists in the environment, either in soil, water, or airborne particulate matter. Because most arsenic compounds are soluble in water, airborne arsenic may be transported great distances before being removed via precipitation to return to soil and water.

At risk: Compounds of inorganic arsenic are used to manufacture semiconductors and as a wood preservative. They are also used to make special glass. People involved in these industries are especially at risk because of direct occupational exposure. Because many arsenic compounds occur in ores, people who work in metal smelters are often exposed to higher levels of arsenic. Similarly, carpenters, contractors, and others may be exposed to the fumes of burning wood treated with an arsenic preservative or inhale sawdust from treated lumber. The most common arsenic poisoning incidents occur among workers involved in the production of arsine, an extremely toxic gas produced by combining arsenic and hydrogen. Finally, people living in areas with high levels of arsenic in rock or water are at greater risk.

Etiology and symptoms of associated cancers: Studies conducted on humans testing positive for high levels of inorganic arsenic compounds show significant correlations with various cancers, including skin, liver, lung, and bladder cancer. Studies show a robust positive correlation between an increase in toxicity levels of arsenic in air, soil, and water and an increase in nonmelanoma skin cancer. Internal cancers, including liver, kidney, and bladder cancer, probably result from exposure to arsenic via ingestion of food and liquid contaminated with high levels of inorganic arsenic and its compounds. As plants fairly readily absorb inorganic arsenic and its compounds, plants in habitats with high levels of arsenic will be contaminated with higher-than-normal amounts of this highly toxic mineral. Digestion of plant food in the gastrointestinal tract increases exposure to and absorption of certain arsenic compounds, which then are carried to the liver, kidney, aorta, and skin before they are transferred to the bladder for excretion. Note that this list of exposed organs equates to the more common types of arsenic-induced cancers.

The two most common types of nonmelanoma skin cancers associated with toxic arsenic levels are basal cell carcinoma and squamous cell carcinoma. Basal cell carcinoma begins in the lowest layer of the epidermis, called the basal cell layer. It is highly unusual for basal cell cancer to spread to lymph nodes or to distant parts of the body. However, if basal cell cancer is left untreated, it can grow into nearby areas and invade the bone or other tissues beneath the skin. Squamous cell carcinomas tend to be more aggressive than basal cell cancers. They are more likely to invade fatty tissues just beneath the skin and slightly more likely to spread to lymph nodes or distant parts of the body, although this is still uncommon. Symptoms include skin texture, size, or color changes, and the area may become sore or ooze.

Very high levels of arsenic exposure and absorption via all routes may lead to a decrease in blood cell production, lymphatic cancer, brain damage, and, in women, infertility and miscarriages.

History: In industry, inorganic arsenic compounds were used as pesticides as early as the middle of the nineteenth century. However, the use of such compounds was curbed within the next century because of noticeable environmental effects. Similarly, arsenic-containing compounds were used in pesticides in the United States until 2013. The most common use for inorganic arsenic since the 1980s is in wood preservation. Pressure-treated wood is made by immersing wood in chromated copper arsenate (CCA) or applying it to the wood under pressure. The arsenic component helps protect the treated wood from weather damage, insects, and decay. Beginning in 2003, CCA has no longer been used for residential projects but is used for industrial buildings. Although the United States has not produced arsenic since 1985, it is still the world’s leading arsenic consumer. This puts people at risk in nontraditional ways. For example, people with decks and other housing structures constructed with preserved wood are automatically at increased risk of arsenic exposure.

In medicine, diseases such as syphilis and psoriasis, leukemia, and asthma were commonly treated with inorganic arsenic solutions until the 1970s. Even in the twenty-first century, it is still used as an antiparasitic agent in veterinary medicine, especially in many countries outside the United States.

Arsenic can appear in foods grown in soil. Rice, a global staple, has higher levels of arsenic as it is produced in saturated terrain and is porous. The amount of rice needed to be consumed by an adult to be dangerous is too high to be a realistic concern. Nonethess, some advocate that babies not be fed rice, or rice products, for this reason. Other foods with higher levels of arsenic include seafood, mushrooms, poultry, and some fruit juices.

Continued use of arsenic in all its forms has increased environmental levels in soil, water, and air—a trend that is likely to continue with increased industrial demands for this highly valuable but also highly toxic mineral.

Bibliography

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