9.9 Mining: Social and environmental impacts

Seventy percent of the mining in Goa occurs in forested areas. The state has around 1 billion tonnes of ore rejects in dumps, and several abandoned mines as pits. Every year
36-40 million tonnes of rejects are added to dumps. This causes environmental problems and threatens biodiversity in forests and rivers.

Groundwater and rivers

Mining lowers the groundwater level, leading to water scarcity. Springs dry up, affecting the supply of water to rivers. Biodiversity in forests and rivers is harmed.

Runoff from the mines during the monsoon carries large quantities of material to the rivers. Tributaries passing through mining zones contain higher concentrations of total suspended matter than do other streams. During the early monsoon the river and estuarine waters contain very high concentrations of such matter. The high turbidity reduces the amount of light to plankton, affecting the overall biological productivity of the water.

Mine materials and mine tailings settle in the estuarine zone (280,000 tonnes per year in the
Mandovi and Zuari in Goa), changing the geomorphology of the estuarine bed and increasing saline water intrusion upstream. The silt makes the bed shallow and suffocates the fauna living on it.

The silted water contains less oxygen, adversely affecting fisheries and lowering employment in fisheries. In Goa, many fisherfolk are displaced by silting of ponds and river beds.

Groundwater and rivers

Toxic chemicals

Various micro-organisms, including nitrogen fixers, ammonifiers celluloytic bacteria and phosphorus solubilizing bacteria recycle essential nutrients and make them available to plants. Toxic mining rejects harm these microorganisms, reducing the nutrient supply to plants and affecting the food chain and plant and animal biodiversity.

Assessing impacts

Environmental impact assessments must be carried out before mining is undertaken. Care has to be taken to include social costs while calculating the cost/benefit analysis of a proposed mining project.

The deforestation and erosion of soil in India has resulted in loss of 6,000 million tonnes of soil. This corresponds to Rs 7,000 million in terms of nitrogen, phosphorus and potassium lost due to mining and other development activities.

Important heavy metals

Iron (Fe)
Manganese (Mn)
Chromium (Cr)
Nickel (Ni)
Cobalt (Co)
Zinc (Zn)
Lead (Pb)

Agriculture

Mining harms dams and irrigation schemes by reservoirs with silt and clogging canals. Sediment covers fields, lowering soil fertility, reducing bioproductivity and forcing farmers to incur the cost of desilting.

The toxic effects of rejects also lead to the production of kernel-less rice. In Goa, mining has reduced rice output by over 60% in the mining belt. More farmers have lost their livelihood due to mining than there are workers employed by the mining industry.

Agriculture

Noise and dust

Mining activities, especially explosions, may scare away animals and birds. Dust from mining, ore transportation and deposition causes respiratory problems in humans and lowers the rate of photosynthesis of plants. This affects animal and plant health and hence biodiversity.

Laterization

The Western Ghats have a large number of lateritic plateaus. Wherever such plateaus are exposed by deforestation for any reason, including mining, the process of laterization begins. The laterite becomes harder and harder.

Laterization

Plants cannot grow on such a surface.

Measuring pollution

The extent of pollution of rivers and estuaries can be measured using the index of geoaccumulation. This index compares the level of an element (such as a heavy metal) with the general level prevailing in the environment.

Igeo = Index of geoaccumulation
Cn = Measured concentration of element
Bn = Geochemical background value
(post-archean average shale)

Heavy metal pollution
Mandovi and Zuari rivers, Goa

High Cr values are associated with high Fe values

Prepared by Dr. Joe De Souza, Dr. G. N. Nayak.