The Toxicity of Arsenic

The toxicity of arsenic ranges from very low to extremely high depending on the chemical state. Metallic arsenic and arsenious sulfide [1303-33-9] AS2S2, have low toxicity. Arsine is extremely toxic. The toxicity of other organic and inorganic arsenic compounds varies (28). 

Arsenic compounds must be considered extremely poisonous. Dust or fumes irritate mucous membranes and lead to arsenical poisoning. When swallowed they irritate the stomach and affect the heart, Hver, and kidneys. Nervousness, thirst, vomiting, diarrhea, cyanosis, and coUapse are among the symptoms of arsenical poisoning (3). In spite of the toxicity of arsenic compounds, there is evidence that arsenic is an essential nutrient for several animal species (4). 

The toxicity of arsenicals conforms to the following order, from greatest to least toxicity arsines > inorganic arsenites > organic trivalent compounds (arsenoxides) > inorganic arsenates > organic pentavalent compounds > arsonium compounds > elemental arsenic. 

Bryant, V., D.M. Newbery, D.S. McLusky, and R. Campbell. 1985. Effect of temperature and salinity on the toxicity of arsenic to three estuarine invertebrates (Corophium volutator, Macoma balthica, Tubifex costatus). Mar. Ecol. Prog. Ser. 24 129-137. 

Earlier in this century the toxicity of arsenic was utilized in medicine and, later, in warfare. In 1909 Ehrlich developed salvarsan, the first effective antisyphilis agent and one of the first... 

Magnesium arsenate has lost its industrial importance because of the toxicity of arsenic. 

Arsenate, As043, is chemically similar to phosphate in size and geometry and in its ability to enter into biochemical reactions. However, arsenate esters are far less stable than phosphate esters. If formed in the active site of an enzyme, they are quickly hydrolyzed upon dissociation from the enzyme. This fact accounts for some of the toxicity of arsenic compounds.1... 

K.S. Squibb, and B.A. Fowler, The toxicity of arsenic and its compounds, in Fowler, B.A., ed., Biological and Environmental Effects of Arsenic, Amsterdam Elsevier Science, 233, 1983. 

The redox environment can also determine some of the properties of metallic and non-metallic species. For example, the toxicity of arsenic when present in oxic (oxidizing) environments such as As( V) is very low, whereas its reduced form, As(III), is highly poisonous. The opposite occurs with Cr(VI) that is much more toxic than its reduced counterpart, Cr(III). 

The toxicity of arsenic has been put into practical use in medicine. Ehrlich in 1909 developed Salvarsan, the trade name for arsphenamine (1), which was the first modem chemotherapeutic agent effective in the treatment of syphilis, which was eventually phased out by better organoarsenicals and latter by penicillin. Some specialist arsenical dmgs are still the treatment of choice for amoebic infections like glycobiarsol (2). ... 

The toxicity of arsenic compounds to living organisms is utilized in chemotherapy several organic compountis of arsenic liave been dis covered which are able to attack invading organisms, such as the spiro chete of syphilis, when taken in amounts smaller than the amount poisonous to man. 

The toxicity of arsenic is well-documented. Trivalent arsenic (arsenite) is almost always more toxic than the pentavalent species (arsenate)The differential toxicity is due to their different modes of action. The primary biological targets of trivalent arsenic are thiol-containing molecules, e.g. in active sites of enzymes (see below). Arsenate, on the other hand, is better tolerated (detoxified) at low concentrations and, at higher levels, competes with phosphate, an ubiquitous biological anion. Indeed the toxicity of pentavalent arsenic in vivo may be partly due to its intracellular reduction to the trivalent form . ... 

A number of different factors can influence the toxicity of arsenicals, including chemical structure, physical properties, mode of administration and species of organism. 

Speciation analysis of arsenic and selenium is veiyo active in the recent literature. The toxicity of arsenic varies widely and is dependent on the specific compounc present. Arsenic in its various forms is also widely distributed in the environment and the food that human eats. Speciation of arsenic in human depends both on th J... 

A mixture of dihydroxyacetone and inorganic arsenate may replace DHAP and this mixture has been used in syntheses by Wong and coworkers. A dihydroxyacetone arsenate monoester probably forms in the rate-determining step, and is consumed in a fast, irreversible aldol reaction. The irreversibility imposed by this method may be useful with slowly reacting substrates, but the toxicity of arsenate limits its usefulness. Vanadate does not operate as a phosphate mimic in FDP aldolase catalyzed reacdons. ... 

The importance of organic arsenic compounds as antiprotozoals faded with the development of penicillin. Because of the toxicity of arsenic compounds this branch of chemistry lost its importance for the next 40 years. 

The toxicity of arsenic compounds can be roughly described in the following decreasing order (Hindmarsh and McCurdy 1986) ASH3 > > AS2O3 > easily soluble As " compounds (e.g., K and Na arsenite) > less soluble arsenites (e.g., Cu arsenite) > arsenate > As-sulfides > metallic arsenic. 

There are many species and strain differences in the toxicity of arsenical compounds. The purity, physical form, and solubility of the compounds also influence toxicity. In a NRCC study (1978), the range of acute toxic values for fish was similar for arsenite and arsenate. Of seven tested fish species, LC50 values (median lethal dose) ranged from 13.3 mg (rainbow trout) to... 

---