Toxic effects of arsenic

DEFINITION: Toxic chemical element used industrially in the manufacture of glass, semiconductors, and wood preservatives as well as in insecticides and herbicides.

SIGNIFICANCE: Because arsenic is widespread in soil and water and has a number of industrial uses, many opportunities exist for human exposure to this element, which can lead to toxic effects. Both the effects and the mechanisms of exposure to arsenic can be subtle, and the symptoms of intoxication can be confused with those of other conditions.

Life- or health-threatening exposure to the toxic chemical arsenic can result from industrial contact, from deliberate poisoning, or from naturally contaminated food or drinking water. Arsenic poisoning may be acute or chronic, depending on whether a large dose is ingested at one time or smaller doses are taken over a lengthy period.

Acute arsenic poisoning is often associated with attempted murder of the victim. Ingestion of as little as two-tenths of a gram of arsenic trioxide (the arsenic compound most commonly used by poisoners, found in insecticides and weed killers) is followed by intense pain in the stomach and esophagus, followed by vomiting and diarrhea. Chronic poisoning by low levels of arsenic such as may be found in contaminated drinking water produces thickening of the skin (hyperkeratosis) of the hands and feet as well as white lines on the fingernails. Cancer of the bladder or other organs can result with long exposure. Neurological effects are also observed, including weakness in the hands and feet (peripheral neuropathy). These symptoms are not always recognized as arsenic-related unless suitable forensic tests are done.

Arsenic binds to proteins and exerts its toxic effects on the body by interfering with vital enzymes. The presence of arsenic in blood or urine can be confirmed through atomic absorption spectrophotometry, a method developed in the second half of the twentieth century. Previously, the primary method of detecting arsenic was a test developed in 1836 by James Marsh. The Marsh test was first used in Tulle, France, in the 1840 trial of Marie Lafarge, who was accused of murdering her husband.

Occasionally, arsenic poisoning may be suspected as the long after the person in question has died. In such a case, an expert can analyze a hair sample using neutron activation. In this process, the sample is subjected to a flux of neutrons in a nuclear reactor; the induced radioactivity can reveal arsenic, if it is present. This type of procedure has been used on samples from Napoleon I of France and US president Zachary Taylor, both of whom died in the nineteenth century. Many other long-ago deaths have also been revisited in this way, but a complicating element in such cases is the fact that arsenic was sometimes used in embalming procedures in the past.

Quantitative determination of the arsenic level present in a given person’s body is important because a certain amount of arsenic is to be expected from the naturally occurring traces of arsenic that appear in food and water. Elevation of a person’s arsenic level above this threshold may indicate accidental or deliberate poisoning. It is estimated that, in the United States, the average person’s diet contains 25-30 micrograms of arsenic per day. Excretion of more than 50 micrograms per day is cause for concern. Given that arsenic can exist in many forms of chemical combination, any urine analysis aimed at determining the body’s level of arsenic should distinguish between organic arsenic compounds and inorganic ones. The latter are more dangerous.

Arsenic Exposure

In the past, the dangers of arsenic were often treated casually, with the result that many people experienced unnecessary, sometimes dangerous, levels of exposure to the chemical. The use of arsenates as pesticides, now minimal in the United States, once was widespread. Fruit, vegetable, and tobacco crops were often sprayed with such pesticides, and high levels of arsenic were left in the soil and on the crops themselves. When humans suffered ill health as a result, forensic scientists needed to find the source of the trouble. In France, arsenate pesticide residues on grapes found their way into wine that poisoned hundreds of French sailors in 1932. Plants grown on contaminated soil can pick up enough arsenic content to be toxic for human or animal consumption, and residues on tobacco are eventually inhaled by smokers.

Chromated copper arsenate is still used as a wood preservative, but many products that formerly contained arsenic no longer do so. Arsenical pigments were long used in wallpaper and in paint, and this led to many poisonings. Research over many years revealed that wallpaper with pigments such as Paris green or Scheele’s green (both arsenicals) could generate arsenic-containing vapors (known as Gosio gas, for Italian physician Bartolomeo Gosio, who published his research on the topic in 1893) if moisture and certain microorganisms were present. This type of vapor, which caused some mysterious deaths in the 1890s, was eventually identified as trimethylarsine during the 1930s. In the 1950s, the US ambassador to Italy, Clare Boothe Luce, became the victim of arsenic poisoning when she absorbed a toxic dose from arsenic-contaminated chips of paint that fell from the ceiling of her bedroom in her embassy quarters. Her resulting health problems forced her to resign her post in 1956 and return to the United States.

Medicines based on arsenic are mostly of historical importance, with some exceptions. Arsenic trioxide has been approved for treatment of leukemia, and arsenicals continue to be used against some tropical parasitic diseases. All these remedies present some danger of arsenic poisoning, as do cosmetic preparations that contain arsenic.

Arsenic is probably an essential trace element in human nutrition in very small amounts. People in the Austrian state of Styria have been known to consume arsenic purposely for its supposed tonic effects. By habituating themselves to ever-increasing doses, they are eventually able to tolerate amounts that would normally be fatal.

Murder by Arsenic

Foul play may be suspected in the death of an otherwise healthy person who develops the symptoms of arsenic poisoning. When such a person dies, forensic testing done postmortem can substantiate toxic levels of arsenic in the liver and other organs, in the stomach contents, and in the blood. If high levels are found, investigators must try to find the source of the poison and its mode of delivery. Accidental or environmental sources must be considered; for example, the victim may have used medicines containing arsenic or taken herbal supplements with arsenic content. If malicious intent is suspected, the dietary habits of the victim may suggest how the poison could have been administered. Any remnants of food or drink known to be ingested by the victim should be tested for arsenic, and those who have had access to the victim or the victim’s food should be investigated to see if they have obtained poison or are currently in possession of some.

Bibliography

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