Environmental sources of arsenic exposure include food, water, soil, and air.
Arsenic is ubiquitous in the environment. It is released into the air by volcanoes, through weathering of arsenic-containing minerals and ores, and by commercial or industrial processes. In industry, arsenic is a by-product of the smelting process for many metal ores such as
lead, gold, zinc, cobalt, and nickel. Other potential sources of arsenic exposure are
Natural sources: arsenic-containing mineral ores and groundwater (especially near geothermal activity).
Commercial products: wood preservatives, insecticides, herbicides (weed killers and defoliants), fungicides, cotton desiccants, cattle and sheep dips, paints and pigments, antifouling paints, leaded gasoline, and fire salts (multicolored flame).
Food: wine (grapes sprayed with arsenic-containing pesticides), tobacco (plants sprayed with arsenic-containing pesticides), and seafood (especially bivalves, certain cold water and bottom-feeding finfish, and seaweed).
Industrial processes: purifying industrial gases (removal of sulfur), burning fossil fuels, burning wood treated with arsenic preservatives, electronics manufacturing (microwave devices, lasers, light-emitting diodes, photoelectric cells, and semiconductor devices), hardening metal alloys, preserving animal hides, bronze plating, and clarifying glass and ceramics.
Medicinals: Fowler's solution (potassium arsenite), antiparasitic drugs (carbasone), Donovan's solution, folk remedies ("Asiatic pill," kushtay, yellow root), kelp-containing health foods, some naturopathic remedies.
Arsenic exists in three common valence states: As(0) (metalloid arsenic, 0 oxidation state), As(III) (trivalent state, such as arsenites), and As(V) (pentavalent state, such as arsenates). Arsenic-containing compounds vary in toxicity to mammals according to valence state, form (inorganic or organic), physical state (gas, solution, or powder) and factors such as solubility, particle size, rates of absorption and elimination, and presence of impurities. Inorganic arsenic is generally more toxic than organic arsenic. However, animal studies have shown that methyl and phenyl arsenates can produce health effects similar to those produced by inorganic arsenic. The toxicity of As(III) is several times greater than that of As(V), due to greater cellular uptake. At equivalent intracellular levels, As(III) and As(V) compounds are equipotent. Metalloid arsenic is generally regarded as nonpoisonous due to its insolubility in water and body fluids. Arsine gas (AsH3), used commercially in the microelectronics industry and encountered accidentally in metallurgical and mining processes, produces a clinical syndrome which is very different from syndromes produced by other arsenic compounds, and is the most toxic arsenical.
The relative toxicity of an arsenical depends primarily on inorganic or organic form, valence state, solubility, physical state and purity, and rates of absorption and elimination.
Until the 1940s, arsenicals (Salvarsan and Fowler's solution) were widely used in the treatment of various diseases such as syphilis and psoriasis. Arsenicals are still used as antiparasitic agents in veterinary medicine, and, in some countries, they are occasionally used to treat trypanosomiasis and amebiasis in humans. Arsenic is also found in some homeopathic and naturopathic preparations, and in folk remedies such as kushtay, a tonic used in Asian cultures to cure various sexual disorders.
Arsenic production has greatly decreased in the United States, but imports have increased steadily and substantially in recent years.
Arsenic production has greatly decreased in the United States, but imports have increased steadily and substantially in recent years. Currently, the principal use of arsenic is in products used for wood preservation. Most of the rest is used in the production of insecticides, herbicides, algicides, and growth stimulants for plants and animals. Gallium arsenide (GaAs) is used in integral components of discrete microwave devices, lasers, light-emitting diodes, photoelectric chemical cells, and semiconductor devices. The use of arsine gas (AsH3) as a dopant in the production of semiconductors is also expected to increase, although substitutes of lower toxicity such as tributylarsine have recently been used. A source of arsine exposure is accidental release during manufacture, transport, or use of the gas. More often, however, arsine forms unexpectedly when acid or other reducing substances are added to arsenic-containing compounds, such as metals in which arsenic is a low-level contaminant.
In the general population, the main route of arsenic exposure is via ingestion of arsenic-containing food. Intake from air, soil, and water is usually much smaller. It has been estimated that the average daily dietary intake of arsenic by adults in the United States is 11 to 14 milligrams per day. Meat, fish, and poultry account for 80% of dietary arsenic intake. Fish, seafood, and algae also contain high concentrations of arsenic in the form of arsenobetaine and arsenocholine, sometimes referred to as "fish arsenic." Fish arsenic has low toxicity to humans and is rapidly excreted in urine. Wine made from grapes sprayed with arsenic-containing pesticides may have appreciable levels of arsenic.
Smokers may also inhale small amounts of arsenic as a result of pesticide residue on tobacco leaves.
Well water contaminated by natural sources such as arsenic-containing bedrock has been reported to be the cause of arsenic toxicity throughout the world, including areas of the United States, Germany, Argentina, Chile, Taiwan, and the United Kingdom. The areas in the United States with the highest natural groundwater concentrations of arsenic are the Southwest, the Northwest, Alaska, and other areas near geothermal activity. Groundwater may also contain elevated concentrations of arsenic due to contamination from runoff of arsenical pesticide. Arsenic has been detected in both surface water and groundwater, at average concentrations of 40 and 47 parts per billion (ppb), respectively, at about 15% of hazardous waste sites studied. The U.S. Environmental Protection Agency's (EPA) maximum contaminant level for arsenic in drinking water is 50 ppb. Both the trivalent and pentavalent forms of inorganic arsenic can be found in drinking water. Because arsenic is a natural part of the environment, low levels are present in soil.
The patient described in the case study lives in the wooded foothills of the Cascade range in northwest Washington. His activities have consisted mainly of building new wood-frame housing, with occasional renovation of older structures. He has used lumber from these projects to fuel the stove and fireplaces in his home. Drinking water is obtained from an artesian well located on his property. What are the potential sources of arsenic exposure for the patient described in the case study?
What steps can be undertaken to identify sources of the patient's arsenic exposure?
