also and subsequently methylated to DMA. The metabolism of

also been reported in contaminated environments. These reactions also contribute to the protective and/or energy metabolisms of the bacteria from various Arsenic-induced stress condition. 

8­. 9. 10. 10

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19. 4,5. 20 21 or.

 23

 (Reference 4)

 

 

 

Human exposure to arsenic and pharmacokinetics.

 

Humans can be primarily exposed to Arsenic compounds through contaminated water and food but minor exposure through respiratory and dermal routes has also been reported.Toxicity of Arsenic to human body depends on its chemical form, oxidation state and solubility with inorganic forms (Arsenite)  being more toxic than the organic forms (Arsenate). Among the inorganic forms, the trivalent form (Arsenite) is considered more toxic than the pentavalent form (Arsenate). This can be attributed to the higher solubility of Arsenite in water than Arsenate 4. Arsenobataine is the most widespread form of Arsenic in marine biological systems, but is non-toxic to humans given the inability to be metabolised.

The absorption of Arsenic in gastrointestinal tract is highest among the heavy metals with 90% of Arsenic getting absorbed in alimentary canal. Arsenic gets accumulated in the liver, kidneys, muscle, bone, hair, skin, and nails. Enzyme inhibition is a common feature of Arsenic toxicity as inorganic arsenic species can restrain the activity of enzymes involved in DNA synthesis, cellular respiration and glutathione metabolism. It has been estimated that Arsenic affects about 200 enzymes by binding with thiol or sulfhydryl groups.

In humans Arsenate is converted to Arsenite and its subsequent metabolism is a complex process involving five different metabolites and initiated by its methylation. Arsenite is  metabolized into MMA and subsequently methylated to DMA.  The metabolism of Arsenic  leads to its expulsion through the urine and can therefore be used as an indicator of Arsenic exposure through the digestive and respiratory systems. Initial reports suggested methylation to be a part  of the detoxification process but recent evidence reveals that methylation may lead to increased toxicity in specific cases. Arsenic is known to bind with thiol or sulfhydryl groups of more than 200 enzymes.  Further pentavalent arsenate can replace phosphate group, which can affect various biochemical path­ways

 

.. , The separation and quantification of trivalent and pentavalent inorganic arse­nic, as well as that of MMA and DMA, is believed to be the most accurate indicator of a recent arsenic exposure 7.