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United States Department of Agriculture

Agricultural Research Service

Arsenic Bad, Good or Both?
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Eric O. Uthus

Could it be that a little bit, but not too much, of a "bad" thing is actually "good" it appears to be that way with arsenic.

Since ancient time, compounds of arsenic (arsenicals) have been characterized by actions both beneficial and harmful. Medicinal virtues of arsenic have been acclaimed for nearly 2000 years. Hippocrates is said to have used arsenic sulfide as a remedy for ulcers and similar disorders. In 1905, Ehrlich first synthesized organic arsenicals and demonstrated their medicinal value against parasites that cause sleeping sickness. By 1937 more than 8000 arsenic compounds were examined as possible pharmaceuticals. Ehrlich’s compound 606 was the first to successfully treat syphilis and hence, was named the "magic bullet".

Arsenicals were considered at various times to be specific remedies in the treatment of certain nutritional disturbances, rheumatism, asthma, malaria, tuberculosis, diabetes, and skin diseases. The use of arsenic for treating these disorders has fallen into disrepute or has been replaced by more effective alternatives. Organic arsenicals were still used in the mid-1980s in the treatment of specific forms of sleeping sickness.

On the other hand, very early in the history of arsenic, it was found that some arsenic compounds were convenient, scentless and tasteless instruments for homicidal purposes. For about 1100 years, up to the last century, arsenic reigned as the king of poisons.

Around 1820, arsenic became equated with cancer. Even today, arsenic is often considered synonymous with "poison" and "cancer". Interestingly, arsenic is probably the oldest known chemical agent used to treat cancer. Very recently, there has been a resurgence in the use of arsenic in treating leukemia; it has been used to successfully treat acute promyelocytic leukemia.

Researchers at the Grand Forks Human Nutrition Research Center are looking at the possible beneficial nutritional role of arsenic. Their research indicates that arsenic is an essential element, but the specific biochemical reason for its importance in humans has not been found. Currently the effects of arsenic deficiency (ingestion of less arsenic than typically found in normal diets) on DNA methylation is being studied. DNA methylation, which is important for gene control, involves the addition of a molecule (methyl) to specific locations on the DNA chain; too little methylation of DNA is associated with an increased cancer incidence. Arsenic deprivation has been shown to reduce the concentration in liver of a compound very important for DNA methylation. Thus, present research is focused on the possibility that too little arsenic is associated with decreased DNA methylation and thus, increased cancer.

Arsenic is generally found at low concentrations in drinking water. Average daily dietary intake of arsenic by humans ranges from 12 to 40 micrograms. Seafoods, grains, and cereal products contribute the most arsenic to the diet. Based on animal studies, a calculated arsenic requirement for humans is 12 to 25 micrograms per day.

Last Modified: 4/4/2007
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