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All about mercury (Download pdf)

Spreading far and wide
Mercury is persistent and moves globally

Mercury travels far and wide and even after installing effective treatment systems to control emission from various point sources, it has been found to escape and contaminate the environment within and outside factory premises.

During the CSE’s rating of the chlor-alkali sector, effluent and soil samples were collected from various mercury-based caustic soda plants and from plants using its products and by-products. The results of these tests paint a threatening picture of mercury pollution, different from the one that is normally known.

Mobile killer
Once released, mercury persists in the environment where it circulates between air, water, sediments, soil and biota in various forms. Current emissions add to the global pool, and all of it is deposited on land and water, and re-mobilised.

The form of mercury released varies depending on its source and other factors. The majority of air emissions are in the form of gaseous elemental mercury, which is transported globally to regions far from the emission source.

The remaining emissions are in the form of gaseous inorganic ionic mercury (such as mercuric chloride) or are bound to emitted particles. These forms have a shorter atmospheric lifetime and will deposit on land or water bodies within roughly 100 to 1000 km of their source.

Elemental mercury in the atmosphere can transform into ionic mercury, providing a significant pathway for deposition. Once deposited, it can change (primarily by microbial metabolism) to methyl mercury, which has the capacity to collect in organisms (bioaccumulate) and concentrate in food chains (biomagnify), especially in the aquatic food chain (fish and marine mammals). Methyl mercury is, therefore, the cause of greatest concern.

(Source: Global Mercury Assessment, UNEP Chemicals, 2002)

First of all, almost all the treated wastewater samples of mercury-based caustic soda plants, tested by CSE’s Pollution Monitoring Lab, met regulatory norms. Therefore, as far as regulations are concerned, all mercury-based caustic soda plants met the existing wastewater regulations.

However, when soil samples within and outside caustic soda plants and wastewater and soil samples from plants using products and by-products of caustic soda plants were tested, the actual danger of mercury became clear. The results display the mobility of mercury and how it can contaminate the environment far away from where it is actually used.

Case studies
Soil samples were collected within and outside the premises of Hukumchand Jute and Industries Limited, Amlai and Bihar Caustic and Chemicals Limited, Daltonganj. Test results showed that the mercury content in the soil outside the plant premises were higher than that within the plant. The general trend was that as one moved away from the source of mercury pollution, there was an increasing amount of mercury in the soil. CSE had also collected soil and water samples from companies using products and by-products of mercury-based caustic soda plants and found mercury in the effluents and soil. Mahavir Spinning Mill, Hoshiarpur, uses diluted sulphuric acid (waste generated from chlorine liquefaction plants) and caustic soda from Punjab Alkalies & Chemicals Limited (PACL), Ropar. The wastewater samples of PACL were also tested.


Mercury content in soil samples
Sample Details Mercury content (ppm)
Soil near the mercury cell room — Hukumchand Jute & Industries Limited 0.028
Soil within the plant but away from the mercury cell room — Hukumchand Jute & Industries Limited 0.054
Soil about 1 km away from the plant premises — Hukumchand Jute & Industries Limited 0.174
Soil near the HCl Storage Tank — Bihar Caustic & Chemicals Ltd 0.006
Soil about 500 m away from the plant premises — Bihar Caustic & Chemicals Ltd 0.016
Source: Pollution Monitoring Lab, Centre for Science and Environment, New Delhi

The results clearly showed that the products and by-products from mercury-based caustic soda plants carry a significant mercury load and pollute the environment of the user unit. The treated wastewater sample of Mahavir Spinning Mill, Hoshiarpur, contained a level of mercury almost similar to that of PACL. This research conclusively proves that monitoring mercury pollution within the plant, as is the current regulation, has very little validity since mercury released from the plant travels great distances.

Mercury content in waste
Sample Details Mercury content
Treated wastewater sample — Punjab Alkalies & Chemicals Limited, Ropar 0.0125
Effluent from wastewater drain outside the mill — Mahavir Spinning Mill, Hoshiarpur. 0.0094
Source: Pollution Monitoring Lab, Centre for Science and Environment, New Delhi.


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