Arsenic in Ground Water and Menopause

Question 1

a) .   Fertilizer on the fields would contain phosphates.   As arsenic and phosphate are in the same group in the periodic table they compete against each other in binding to iron (III) hydroxide.   Arsenic is replaced on iron (III) hydroxide by phosphorus and arsenic is released into surrounding water.   A rice field containing stagnant water would be an anaerobic environment and therefore a reducing one.   This environment enables anaerobic bacteria to metabolize arsenic particles into a soluble state by making them less oxidized.   Arsenic would also be contained in water used to irrigate these fields as it would come from wells nearby, making a vicious circle of arsenic contamination.

b) Sulfide minerals contain arsenic.   When minerals such as pyrite become oxidized, iron(III) hydroxide is produced and the arsenic contained in minerals binds to the surface of the iron (adsorbtion) and is carried into the groundwater.   Iron(III) hydroxide coats the grains of sediment in groundwater, storing arsenic until the right conditions allow its release.   The arsenic that had been adsorbed can be displaced back into the surrounding water by a chemical change which causes the coating of iron(III) hydroxide to break down.

c) The sediments from densely vegetated lands will have been in an anaerobic environment. The breaking down of dead plant materials by aerobic bacteria consumes all available oxygen in areas of stagnant water.   These sediments will contain arsenic in its most soluble, least oxidized form.   It will also contain iron(III) hydroxide and pyrite which will give rise to conditions for making arsenic available to the groundwater and as in all the above situations, able to filter through into the water in shallow wells.

Question 2

a) Three assumptions that need to be made in order for the data from West Bengal and Taiwan to be able to be applied to the case in Hanoi are:

-that the women of Hanoi are as susceptible to the effects of arsenic...