Arsenic Toxicity in Emergency Medicine 

Arsenic, element 33, has a long and nefarious history; its very name has become synonymous with poison. In the 15th and 16th centuries, the Italian family of Borgias used arsenic as their favorite poison for political assassinations. Some even have suggested that Napoleon was poisoned by arsenic-tainted wine served to him while in exile.

The metal was reported as the causative agent in an outbreak of food-borne illness after a church gathering in which the coffee urn was apparently criminally contaminated with arsenic. This highlights the need for an index of suspicion when multiple individuals present to an emergency department temporally related and with similar symptoms and circumstances.^[1]

Arsenic is typically considered a heavy metal and shares many toxic characteristics with the other heavy metals (eg, lead, mercury). Arsenic is ubiquitous in the environment. It ranks 20th in abundance in the earth's crust, 14th in seawater, and 12th in the human body.^[2] In nature, arsenic exists in the metallic state in 3 allotropic forms (alpha or yellow, beta or black, gamma or grey) and several ionic forms.

Arsenic has been used as a medicinal agent, a pigment, a pesticide, and an agent of criminal intent. In the form of chromated copper arsenate (CCA), it was used until recently as part of the treatment to render architectural wood immune to pest infestation. This product was banned for use in the United States by the Environmental Protection Agency (EPA) in 2003. A great deal of the treated wood continues to exist in the form of decks and other structures exposed to the elements. Data suggest that a significant quantity of arsenic may leach out from such wood into landfills and into the interiors of homes with existing CCA-treated decks.^{[3, 4, 5]} The durability of the CCA-treated wood suggests that such exposures may continue for decades. There is evidence in the rodent model that exposure to this compound, CCA, may produce significant renal pathology. Today, arsenic is primarily used in the production of glass and semiconductors.

Arsenic may be found as a water or food contaminant, particularly in shellfish and other seafood, and often contaminates fruits and vegetables, particularly rice.

Today, arsenic poisoning occurs through industrial exposure, from contaminated wine or moonshine, or because of malicious intent. The possibility of heavy metal contamination of herbal preparations and so-called nutritional supplements must also be considered. There has been a resurgence of interest in arsenic as a medicinal agent for treatment of acute promyelocytic leukemias, multiple myeloma, myelodysplastic syndromes, and assorted resistant solid tumors.^[6]

An association between exposure to arsenic and the development of Alzheimer disease has been proposed.^[7] In addition, an apparent link exists between arsenic exposure and gestational diabetes and potential long-term effects on the infants born to mothers consuming arsenic-contaminated water among other during pregnancy.^{[8, 9]}

Because arsenic has been involved in geopolitics, an estimated 100 million people are at risk of exposure to unacceptable arsenic levels in either well water or ground water. Numerous "outbreaks" of excessive arsenic in water and food from an assortment of natural and anthropological causes have occurred. This has become a major public health issue in the developing world, primarily Bangladesh and surrounding countries, where many thousands of individuals have precancerous arsenic-related disease.

Inorganic forms of arsenic are more toxic than organic forms. The trivalent forms are more toxic and react with thiol groups, while the pentavalent forms are less toxic but uncouple oxidative phosphorylation. Very few organ systems escape the toxic effects of arsenic.

Trivalent inorganic arsenic inhibits pyruvate dehydrogenase by binding to the sulfhydryl groups of dihydrolipoamide. Consequently, conversion of pyruvate to acetyl coenzyme A (CoA) is decreased, citric acid cycle activity is decreased, and production of cellular ATP is decreased. Trivalent arsenic inhibits numerous other cellular enzymes through sulfhydryl group binding. Trivalent arsenic inhibits cellular glucose uptake, gluconeogenesis, fatty acid oxidation, and further production of acetyl CoA; it also blocks the production of glutathione, which prevents cellular oxidative damage.

Effects of pentavalent inorganic arsenic occur partially because of its transformation to trivalent arsenic; toxicity proceeds as outlined above. More importantly, pentavalent arsenic resembles inorganic phosphate and substitutes for phosphate in glycolytic and cellular respiration pathways. Consequently, high-energy phosphate bonds are not made, and uncoupling of oxidative phosphorylation occurs. For example, in the presence of pentavalent arsenic, adenosine diphosphate (ADP) forms ADP-arsenate instead of ATP; the high-energy phosphate bonds of ATP are lost.

Arsenic has been shown to produce oxidative stress. In a small pilot study of environmentally exposed children, arsenic altered monocyte superoxide anion production and inhibited nitric oxide production.^[10]

Arsenic trioxide has been shown to cause a significant prolongation of cardiac action potential duration at many levels of repolarization producing conduction delay and increased triangulation. Electrolyte imbalance appears to enhance this toxicity.^[11] The drug appears to inactivate endothelial nitric oxide synthase, leading to a reduction in production and bioavailability of nitric oxide. It also has been associated with inducing/accelerating atherosclerosis, increasing platelet aggregation and reducing fibrinolysis.^[12]

Arsenic is listed as a presumed carcinogenic substance based on the increased prevalence of lung and skin cancer observed in human populations with multiple exposures (primarily through industrial inhalation).

Frequency

United States

According to the American Association of Poison Control Centers' (AAPCC) National Poisoning Data System (NPDS), in 2010, there were 927 human exposures related to arsenic (excluding pesticides) and 67 exposures related to arsenic-containing pesticides. The majority of the pesticide exposures occurred in children younger than 5 years (43 [65%] of 67), whereas more than 58% of the nonpesticide exposures occurred in adults (539 of 927).^[13]

International

Worldwide, up to 100 million people are at risk of exposure to arsenic from excessive arsenic in drinking water. In Bangladesh, more than 95% of the water supply to over 138 million people is potentially arsenic contaminated at levels exceeding the US EPA and WHO action limits.^[14] If international efforts at elimination of the risk are unsuccessful, it is estimated that a substantial proportion of the Bangladesh population will develop arsenic-related diseases such as pulmonary and skin cancers as well as cardiovascular and renal disease.

In addition to the concentration of arsenic in the water, the prevailing diet existing in the affected areas may place the citizens at increased risk for toxicity from the arsenic. The population was recently surveyed and those individuals who had diets deficient in certain B vitamins and antioxidants appeared to have greater risk of arsenic dermatoses. An inverse correlation was found between consumption of vitamins A, C, and E, riboflavin and folic acid, and the existence of dermatological manifestations or chronic arsenic exposure.^[15]

Mortality/Morbidity

According to the American Association of Poison Control Centers' (AAPCC) National Poisoning Data System (NPDS), 6 individuals suffered major effects and 3 died from exposure to nonpesticide arsenic exposure in 2011. Two of the 3 deaths were the result of suicides. There were no serious effects seen in the pesticide exposures.

Sex

Men are more likely to experience industrial arsenic exposure than women.

Age

As in many reported cases of poisoning, the majority of reports of exposure to arsenic-containing pesticides occur with children younger than 6 years as the victim (274 of 379 in the NPDS 2007 data), whereas, when nonpesticide arsenic exposure is involved, the majority are in adults older than 19 years (645 of 1165).^[13]