Aquatic Pollution and Coastal Management

Unit 5 : Heavy metal pollution

5.3.1.b) Industrial Waste Waters
A number of heavy metals are used by various industries and a good proportion of them finds the way into the effluents. A few metals may also be disposed off as by products, while some are released during the industrial combustion of coal or other materials.
eg. Mercury cells used in caustic soda production.

Pit dumping and sanitary landfills allow the leaching of significant quantities of heavy metals into surface and ground waters.

Input Routes:

• a) Atmospheric input
• b) River input
• c) Direct discharges of industrial and other wastes by pipelines, by dumping sewage sludge and industrial waste.

Agricultural Activities:
Agricultural soils are usually rich in heavy metals as a result of the use of various fungicides, herbicides, fertilizers, organic manures and the presence of decaying plant and animal residues.A agricultural run off together with soil erosion is the potential source of water pollution.

Mining Activities:
Most mineral ores contain varying quantities of different heavy metals that tend to become free in the environment by mining and ore processing activities.
The waste rock left at the sites of mining and the surface exposed after the mining is over, are liable to greater weathering and oxidation that release most of the metals in free state.

Mode of Transport/Environmental Fate:
Metals may enter the aquatic environment via three pathways

Transport by Air:
Metals introduced into the atmosphere may be carried to the land surface/water body by precipitation and dry fallout. Metals readily adsorb on to many sediments types, wind borne sediments is a potential route.

Land Runoff:
Agricultural chemicals, fossil fuel and domestic and industrial effluent from land drainage during rainy seasons are another route for the input of metals.

Leaching:
Some of the dissolved metals are transported through ground water

Direct Discharge:
Direct discharge of industrial effluents and urban sewage into aquatic systems.