Arsenic is a poisonous
metalloid that exists in inorganic as well as organic
forms. The major inorganic forms of arsenic include the trivalent arsenite (As3+)
and the pentavalent arsenate (As5+). The major organic forms are the
methylated metabolites monomethylarsonic acid (MMA), dimethylarsinic acid (DMA),
and trimethylarsine oxide (TMAO). The majority of humans are chronically exposed
to low levels of arsenic, principally through ingestion of food and water and to
some extent due to inhalation of arsenic in the ambient air. Inorganic
arsenic and its compounds are well-known human carcinogens (IARC, Group 1)
causing tumors of the lung, liver, bladder, skin, and kidney. The underlying
mechanisms of arsenic carcinogenicity are still not fully understood. Although
multiple pathways such as inhibition of DNA repair, methylation status, and
co-carcinogenesis with other environmental toxicants have been proposed, one
common theme that has emerged is the role of reactive oxygen species in the
pathogenesis of arsenic-induced diseases. It has been found that arsenic is not mutagenic but genotoxic in both animal and human systems. In
vitro chromosomal aberrations
(CA), sister
chromatid exchanges (SCE) and micronuclei (MN) assays
showed the clastogenic potential of arsenic in mammalian cells. Several
epidemiological studies also reported increased incidences of chromosomal
aberrarions (CAs), sister chromatid exchanges (SCE) and micronuclei (MN) in
human populations exposed to arsenic through drinking water.
For
further information see Wikipedia, the free encyclopedia
website:
http://en.wikipedia.org/wiki/Arsenic
Structures
of Arsenic compounds:
References:
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