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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
(ppm) |
| 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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