Arsenite poisoning

Figure 17.20. Arsenite Poisoning. Arsenite inhibits the pyruvate dehydrogenase complex by inactivating the dihydrolipoamide component of the transacetylase. Some sulfhydryl reagents, such as 2,3-dimercaptoethanol, relieve the inhibition by forming a complex with the arsenite that can be excreted.

Arsenite poisoning. The effect of arsenite on the experimental system of problem 14 was then examined. Experimental data (not presented here) showed that the amount of citrate present did not change in the course of the experiment in the absence of arsenite. However, if arsenite was added to the system, different results were obtained, as shown in the following table. 

Using a burette or a pipette with a safety pump (this is necessary owing to the poisonous properties of the solution) measure out 25.0 mL of the arsenite solution into a 250 mL conical flask, add 25-50 mL of water, 5g of sodium hydrogencarbonate, and 2 mL of starch solution. Swirl the solution carefully until the hydrogencarbonate has dissolved. Then titrate slowly with the iodine solution, contained in a burette, to the first blue colour. 

Arsenic is historically the poison of choice for many murders, both in fiction and reality (e.g., Christie 1924 CNN 1998). The element is considered a metalloid (having both metallic and nonmetallic properties) and is widely distributed in the earth s crust. Arsenic occurs in trace quantities in all rock, soil, water, and air (WHO 2001). Under reducing conditions, arsenite (As ") is the dominant form, while arsenate (As ) generally is the stable form in oxygenated environments. Arsenic salts exhibit a wide range of solubilities, depending on pH and the ionic environment. 

Symptoms of poisoning by arsenite (trivalent arsenic) Include dermatitis and a variety of neurologic manifestations. Including painful paresthesias (tingling and numbness in the extremities). 

Colloidal saccharated iron is sometimes used in place of ferric hydroxide as an antidote in arsenical poisoning, but its adsorptive capacity depends on the alkalinity of the medium.4 Thus a commercial preparation containing 0-75 per cent, of sodium hydroxide was found to adsorb 12-57 per cent, of arsenious oxide (reckoned on the amount of iron present) addition of alkali increased the adsorption until, with 1-28 per cent, of sodium hydroxide present, there was a maximum adsorption of 27 per cent. The addition of acid correspondingly diminished the adsorption. A gel of ferric magnesium hydroxide, if prepared without boiling, also adsorbs arsenic from sodium arsenite solutions.5... 

The important inorganic toxic compounds to be considered in the following pages are arsine, arsenic trichloride, white arsenic, arsenites and arsenates and arsenic sulphides. Metallic arsenic itself is not poisonous, and the intravenous injection of a colloidal solution of this substance has been found 8 to benefit greatly a case of bone sarcoma of the femur which did not respond to X-ray treatment. 

The poisonous action is influenced by the solubility of the compound in water. Lethal doses of sodium arsenate for goats and rabbits are found to be approximately 0-11 and 0-05 g. per kg. body weight,8 and the following doses which produced death of sheep not earlier than the second day have been observed,9 the figures in brackets being nontoxic doses sodium arsenite, 0-86 g. (043 g.) arsenic acid, 0-86 g. (0-43 g.) lead arsenate, 3-9 g. (2-6 g.) emerald green, 1-3 g. 

Experiments with house flies pointed to a considerable buffering action in the intestine.3 Solutions of arsenious acid and of the stoichiometric quantities of sodium hydroxide and arsenious oxide to form normal sodium arsenite, containing 15 g. of sucrose per 100 c.c., were fed to adult flies. The pH values of the former solutions were 6-58 to 6-96 and of the latter 11-3 to 11-4, but the toxicities were equal, being 0-14 mg. As per g. body weight—a large value for an insect. None of these solutions was repellent to the flies, but if the pH was increased beyond 11-4 repellent action was observed house fly bait therefore should not contain more alkali than is necessary to hold the arsenic in solution. The eradication of the tsetse fly by similar means is difficult. There is not much chance of a poisonous dose being taken from the skin of a dipped animal, but a toxic dose can be taken up from an arsenic-impregnated area by means of the proboscis.4... 

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