Pentavalent organic arsenicals

Dimethylarsinic acid An organic pentavalent arsenical with the composition of (CH3)2AsO(OH), abbreviated DMA(V), see Figure B.4 (compare with dimethylarsinous acid, monomethylarsonic acid, and monomethylarsonous acid). 

Arsenic (As) has been reported In a variety of tissues, any of which are potentially useful as indexes to exposure. However, the organic pentavalent arsenicals are not accumulated in tissues and are rapidly excreted in urine ( - ). Therefore, urine generally is a particularly valuable index to applicator exposure. Exon et al. ( 5) reported both urine and feces were Important pathways of excretion in rabbits exposed to MSMA In their feed. They found 70 of ingested As had been excreted (54% in urine, 46% in feces) during a 17-week exposure period. Arsenic levels in liver, hair, and urine were the same as in controls after 12 weeks of MSMA exposure followed by 5 weeks of control rations. Indicating excretion was ultimately fairly complete. 

C) Dehydration, acidosis, and azotemia may cause death, b. Organic pentavalent arsenical feed additives... 

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. 

Generally, inorganic arsenic can occur in the environment in several forms but in natural waters and thus in drinking water, it is mostly found as trivalent arsenite or pentavalent arsenate. Organic arsenic species, abundant in seafood, are very much less harmful to health and are readily eliminated by the body5. 

Elemental arsenic and its insoluble compoimds are non-toxic, whereas soluble inorganic and organic forms of the element may be poisonous. Needless to say, the amount (or dose) matters a lot. Trivalent arsenic is often toxic, the most common form is arsenite (As03 ) salts. Pentavalent arsenates (AsO ) are less of a concern, many of them are insoluble. This is also tme in general the properties of a certain element (including toxicity) very much depend on the form (most commonly the oxidation state) found in the compound. Determining which of the possible forms occur in a sample is called speciation. 

Inorganic forms arsenic are more acutely toxic than the organic arsenicals and the toxicity depends upon the oxidation state of arsenic. Conversion between the oxidation states of inorganic arsenic have been shown to occur both in the environment and in the animal body. Recent studies (Vahter and Norin, 1980 Vahter, 1981) have suggested that the differences between the toxicities of trivalent and pentavalent arsenic depend upon the extent of vivo biotransformation to methylated metabolites. Environmental oxidation favors the conversion of trivalent arsenic to pentavalent arsenic. Pentavalent arsenic may be partially reduced vivo to trivalent arse-noxide (R As 0), but it is the vivo reduction of arsenate to arsenite which accounts for both toxicity and antimicrobial actions (Harvey, 1975). Rumen microflora obtained from Holstein cows reduced arsenate to arsenite (Forsberg, 1978). Ginsberg (1965) demon-... 

Inorganic arsenicals are more toxic than organic arsenicals, and trivalent forms are more toxic than pentavalent forms. 

Inorganic arsenic compounds are more toxic than organic arsenic compounds, and trivalent species are more toxic than pentavalent species. 

The degree of toxicity of arsenic is dependent on the form, either inorganic or organic, and the oxidation state of the arsenical. Inorganic arsenicals are generally more toxic than organic, and the trivalent forms are more toxic than the pentavalent. 

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