Aquatic Pollution and Coastal Management

Unit 5 : Heavy metal pollution

5.5.3.Arsenic
Arsenic is naturally occurring in the environment and accounts for small portion of the earth’s crust minerals. Arsenic is released into the environment by the smelting process of copper, zinc and lead as well as manufacturing of chemicals and glasses. Other sources are paints, rat poisons, fungicides and wood preservatives. Arsenic can volatilize into the atmosphere as a result of different biological transformations. It can be absorbed onto soil, washed away by surface runoff or leached into groundwater and be taken up by plants, subsequently entering the food chain. Arsenic and most of its compounds are solids that do not evaporate. They exist as small particles in the atmosphere. Burnt arsenic compounds exist as a gas. They will then settle into the soil or water depending upon where the air currents carry them.

Arsenic is not water-soluble, but many of its compounds are water soluble. Arsenic as a free element (0-oxidation state) is rarely encountered in natural waters. Soluble inorganic arsenate (+5-oxidation state) predominates under normal conditions since it is thermodynamically more stable in water than arsenite (+3 oxidation state). Fish generally contain lower concentrations of arsenic than other organisms indicating that it is not readily available for uptake an aquatic environments.

Potential Hazards to Fish, Wildlife and other Non-human Biota:
Plants can take up arsenic in a variety of ways, from fly ash, sludge and by manure dumped on the land. Animals are generally less sensitive to arsenic than plants. Arsenic is one of the most toxic elements to fish. Sediments contaminated with arsenic results in reduction in the abundance of polychaetes, molluscs and crustaceans.

Potential Hazards to Humans:
Arsenic has long been a concern to man because small amounts can be toxic to humans. Relatively high doses of arsenic have been reported to cause bone marrow suppression in humans. Inorganic arsenic in high quanties has been known for centuries as a fast acting human poison.
High levels of arsenic resulted in “Black foot” disease in Taiwan.