Despite arsenic's reputation as a poison, it actually has fairly low toxicity in comparison with some other metals, although with chronic exposure there is some concern about arsenic's effect on chromosomes and its carcinogenicity. In fact, arsenic may even be essential and functional in humans in very small amounts. It has been shown to be essential in rats and other animals, though it is found in higher concentrations in them than in humans.
Organic arsenic as arsenates (+5 form of arsenic) and elemental arsenic both found naturally in the earth and in foods do not readily produce toxicity. In fact, they are handled fairly easily by the body and eliminated by the kidneys. The inorganic arsenites or trivalent forms of arsenic, such as arsenic trioxide used industrially and found as a food contaminate, seem to create the problems. They accumulate in the body, particularly in the skin, hair, and nails, but also in internal organs. On the average, there is about 10-20 mg. of arsenic in the human body; higher levels may lead to problems. Arsenic can accumulate when kidney function is decreased. Luckily, absorption of arsenic is fairly low, usually less than 5 percent, so most is eliminated in the feces and some in the urine.
Hair and blood levels are currently the best way to evaluate arsenic levels. They will usually show increased levels when higher amounts are present in the body.
Sources: Arsenic is present in small amounts in soil and therefore is present in our food. It is present in the ocean, so there is some arsenic in most seafood, especially the filtering mollusks, such as clams and oysters. Some arsenic is present as a contaminant in meats as well.
Arsenic is also found in many fuel oils and coal, so it is added to the environment when these are burned. Weed killers and some insecticides (particularly the lead-arsenate sprays) are the main sources of contamination with arsenic. This use of arsenic is responsible for a twentyfold increase in the level found in humans since ancient times. Even so, this in itself is not a great cause for concern about wide-range toxicity.
Methods of toxicity: Though there is some suggestion that arsenic may be useful in the human body, no clear biological function has yet been proved. In some studies, arsenic has been shown to promote longevity in rats. The importance of arsenic in cardiac function in humans is being studied. Though arsenic can displace phosphorus and phosphates in some reactions in the body, this is not known to lead to any definite physiological change.
Symptoms of toxicity: These are not clearly known. The average intake of arsenic is estimated at 1 mg. per day, mainly from food, but this is not toxic arsenic; this organic arsenic bound in food is generally well tolerated. Elemental arsenic can accumulate in the body and be a problem, and the oxidized forms of arsenic are toxic in large amounts. Arsenic trioxide is used industrially and is the strongest poison of the arsenics. Below 7-10 ppm of arsenic in hair is a relatively safe level.
Amounts leading to toxicity: There is no clear picture of arsenic deficiency or toxicity in humans. Possible effects of arsenic toxicity include hair loss, dermatitis, diarrhea and other gastrointestinal symptoms, fatigue, headaches, confusion, muscle pains, red and white blood cell problems, neurologic symptoms, and liver and kidney damage. Acute arsenic exposure may cause a rapid series of symptoms. Arsine gas exposure is very toxic to the lungs and kidneys and is often fatal. Death from low-level, chronic arsenic exposure has the appearance of death from natural causes, very good for mystery books.