An Introduction to Environmental Chemistry

This would force iron oxide (Fe(OH) 3 ) to precipitate, but also remove some of

the dissolved arsenic as it adsorbs to the precipitating oxide surface. Trials at

water-treatment plants in the area have shown that water with 220mgl-^1 As,

can be reduced to around 40mgl-^1 As (below the Bangladesh drinking water

maximum) by this method. Longer-term mitigation strategies might include the

construction of shallower wells in the oxidized upper zone of the aquifer. What-

ever the long-term mitigation strategies are, it is clear that these wells are cur-

rently critical for the water supply of millions of people. As abandoning the wells

is not an option in many cases, short-term mitigation methods, even imperfect

ones such as aeration with a stick in a bucket, seem preferable to continued expo-

sure to high levels of arsenic.

It is worth noting that an ‘early warning’ of potential arsenic contamination

by reduction of iron oxide is given by high values of dissolved iron in reducing

drinking water wells. This element is simple to analyse, and routinely measured

during water quality analysis. It could therefore be used as a sign that arsenic

contamination is possible, prompting further analysis for dissolved arsenic.

5.8 Further reading

Baird, C.B. (1995) Environmental Chemistry. WH Freeman, New York.

Berner, K.B. & Berner, R.A. (1987) The Global Water Cycle.Prentice Hall, Englewood

Cliffs, New Jersey.

Harrison, R.M., deMora, S.J., Rapsomanikas, S. & Johnston, W.R. (1991) Introductory

Chemistry for the Environmental Sciences.Cambridge University Press, Cambridge.

Moss, B. (1998) Ecology of Freshwaters: Man and Medium, 3rd edn. Blackwell Science,

Oxford.

Stumm, W. & Morgan, J.J. (1996) Aquatic Chemistry, 3rd edn. Wiley, New York.

5.9 Internet search keywords

180 Chapter Five

water chemistry

freshwater chemistry

chemistry river water

chemistry groundwater

oxyanions

phosphorous natural water

silica natural water

weathering regimes

geochemistry Amazon

alkalinity

pH buffering

aluminium solubility

acid deposition

acid rain

acid mine drainage

landfill leachate

electron acceptors

nitrate water

phosphate water

eutrophication

heavy metal contamination

mercury contamination

groundwater contamination

arsenic contamination

ionic strength

Eh-pH

redox potential