Arsenic Stress in Plants: An Inside Story - Crop Improvement: New Approaches and Modern Techniques - page 377

waste combustion generates particulate emissions of arsenic, that contribute to dry
(particles) and wet deposits (rain) (Melanen et al. 1999 ). Inorganic arsenic is a po-
tent human carcinogen, associated with increased risk for cancer of the skin, lungs,
urinary bladder and kidneys, as well as hyperkeratosis, pigmentation changes, and
effects on the circulatory and nervous systems. It is also known to generate oxida-
tive stress in humans (Benton et al. 2011 ).
DistributionofArsenicinWorld
Arsenic contamination has become a problem in many parts of the world. The World
Health Organization (WHO) has set a guideline of 10 µg As L -1 as the drinking water
standard (WHO 2008 ). However, As concentrations in the range of > 1,000 µg L -1
have been reported from various places throughout the world (Tuli et al. 2010 ).
Especially Australia, Canada, Japan, Mexico, Thailand, United Kingdom, United
States, Argentina, Bangladesh, Cambodia, Chile, China, Ghana, Hungary, Inner
Mongolia, Mexico, Nepal, New Zealand, Philippines, Taiwan, the United States
and Vietnam are reported as highly contaminated countries (WHO 2002 ).
In India sever contamination of arsenic in ground water has been reported in West
Bangal (69 times more arsenic than WHO standard) whereas Jharkhand, Assam, Bi-
har, Utter Pradesh, Manipur and Chhattisgarh are some other states well effected by
arsenic toxicity. In Rajasthan also, arsenic bearing groundwater has been reported
in the vicinity of Cu (Khetri) and Zn mines (Zawar). It has been reported that agri-
cultural land contains ≤ 10 mg kg -1 in non-contaminated soil whereas it increases
up to 1,000-3,000 mg kg -1 in contaminated soil (Panda et al. 2009 ). Growing crops
in arsenic contaminated soil and irrigation with arsenic contaminated water effects
the crops in terms of growth, yield, biomass production and arsenic accumulation
which can directly leads to food chain contamination.
ArsenicSpeciesFoundintheEnvironment
The oxidation states and electron orbital of arsenic is similar to those of phospho-
rus. Arsenic forms alloys with various metals and covalent bonds with carbon, hy-
drogen, oxygen, and sulfur. In nature, arsenic exists predominantly in inorganic
form as trivalent arsenite (III) or pentavalent arsenate (V). The major species found
in the environment are arsenite As(III), arsenate As(V), mono methylarsonic acid
(MMA), dimethyal arsenic acid (DMA), arseno betain and arseno choline (Tangahu
et al. 2011 ). In the environment arsenic is present in both organic and inorganic
forms. The inorganic species arsenate As(V) and arsenite As(III) are more abundant
in soil as compare to organic species, monomethyarsonic (MMA), Dimethylarse-
nic (DMM) etc. (Takamatsu et al. 1982 ). These forms have different physical and
chemical characteristics resulting in various degrees of mobility, bioavailability and