Arsenic.pptx

About Arsenic

1. Arsenic SUBMITTED by - S akshi P atil

2. I ntroduction Arsenic (As), is a major threat to the lives of millions of people whose primary water source for drinking and farming . Responsible for groundwater pollution. Long-term exposure to trace levels of arsenic (As) in shallow groundwater used for drinking and irrigation puts millions of people at risk of chronic disease. Arsenic is found in the natural environment in some abundance in the Earth's crust and in small quantities in rock, soil, water and air.

3. contd... A tomic number - 33 A tomic weight - 74.92 It is a metalloid element. It is not found in nature as a free element, but exists in combination with other elements . G rey / Y ellow / B lack M ajorly found in grey colour ( 70% )

4. S peciation I norganic form A s 2 O 3 ( ars e nite ) and As 2 O 5 ( ars e nate ) which are soluble in water . A rs e nate used in agriculture Commonly found state : -3,0, + 3, + 5 -3 and 0 are non exit form . + 5 is the most stable form in pres e nce of ox i dizing condition ( adsorb s strongly into clay ). + 3 is most dominant in presence of reducing condition .

5. contd.. O rganic form M onomethylars o nic acid D imethylars i nic acid T rimethylars i n e acid M ost toxic form is +3

6. H istory C ontamination was first observed in W est B enagl in 1983. It is followed by B ihar and U . P . in plain of G anga , A ssam and M anipur in B rahmaputra and I mphal river , rajnandgaon village in chhattisgarh state chronically been exposed to drink in g contaminated hand tube wells . Drinking limits: permitted level 50 μ g/ L WHO limit 10 μ g/ L A rsenic affected river plain come from Himalaya region.

7. S ources N atural - V olcanic eruption - W eathering of rocks A nthropogenic - B urn i ng high arsenic coal - A rsenic mining - CCA tr eated wood - P ainting pigments ( As 2 S 3 , As 4 S 4 ) - M edicine and antibiotic

8. M inerals rich in As A rsenolite Cobaltite O livenite FeAsS ( Arsenopyrite ) - most abundunt form As found in earth . I norganic As +3 , As +5 and Organic MMA, DMA are present in great extent in natural sy s tem.

9. contd... C ontaminated for m A rsenous acid ( H 3 AsO 3 ) - acid of trivalent A rsenic acid ( H 3 AsO 4 ) - acid of pentavalent

10. F actors affecting mobility pH R edox potential D issolve organic matter A dsorbents , oxide and hydroxide of Fe ( III ) , Al ( III ) , Mn ( III ) H umic substances There are some bacteria that can mobilize As from sediments. examples: Shewanella algae, Shewanella oneidensis , Geobacter metallireducens

11. contd. There is an inverse relationship between As mobilization and pH. Carbonate and bicarbonate ions substitute As from sediment and As become mobilize. If pH is <2, Arsenious acid. If pH is 2-11, H 2 AsO4 - , HAsO4 2- If pH is 4-10 As (V) is - ve charged As (III) is neutral in charge.

12. M obili zation process R eductive dissolution ( anoxic pH-7) A lkali desorption (pH 8) G eothermal high temperature S ulphur oxidation ( oxic p H greater than 7)

13. contd.. B acteria - T. ferrooxidants work as catalyst . FeASs oxidized when exported to atmosphere releasing soluble As III , S ulphate SO 4 2- FeAsS + 13Fe 3 + + 8H 2 O = 14Fe 2+ + SO 4 2- + 13H + + H 3 AsO 4

14. B iological action Arsenic interferes with cellular longevity by allosteric inhibition of an essential metabolic enzyme pyruvate dehydrogenase (PDH) complex, which catalyzes the oxidation of pyruvate to acetyl-CoA by NAD+. With the enzyme inhibited, the energy system of the cell is disrupted resulting in a cellular apoptosis . Trivalent toxicity- As can bind with thiol group ( -SH), So cysteine rich proteins are vulnerable to As.

15. R emoval Methods C oagulation /Filtration A dsorption through iron oxide- get adsorbed on it A ctivated alumina - remove both +3 and +5 Io n exchange R everse osmosis E lecyrodialysis

16. Effects Initial stage of poisoning- can cause melanosis Middle stage of poisoning- Known as keratosis Last stage of poisoning- known as Arsenicosis or black foot disease. Arsenicosis is the effect of arsenic poisoning, usually over a long period such as from 5 to 20 years. Blackfoot disease (BFD) is a severe form of peripheral vascular disease (PVD), in which the blood vessels in the lower limbs are severely damaged, resulting eventually in progressive gangrene.

17. T hank you !