Mercury in your 'maach'
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COMMENTS 
Most of the 264 fish samples picked up from different locations in West Bengal showed mercury contamination well above the stipulated safety level. Given the high consumption of fish in the state, local government bodies need to take the findings of the study seriously
A recent study concluded by the Kolkata-based NGO, DISHA, together with Toxics Link has revealed abnormally high levels of mercury in fish populations across West Bengal.
The fish samples were taken from five major markets in Kolkata, and several major water-bodies covering the north, central and southern parts of the state.
In all, 60 samples were picked up from the markets of Behala and Gariahat in south Kolkata, Manicktala in north Kolkata, and Sealdah and Sahababur Bazaar in central Kolkata.
Besides these, 204 samples were collected from the estuary of the Haldia and Hooghly rivers in the Haldia industrial belt; the Ganga feeder canal in Farakka; the Matla, Vidyadhari and Herobhanga rivers in Jharkhali in the Sunderban Biosphere Reserve; ponds in the East Kolkata wetlands; Mudiali, Dolua, Kanchanseri, Ranijjot and Ruidasa in Darjeeling; Jalpaiguri in North Bengal, and the Hugli agricultural belt. The surveyors also collected samples from the confluence of the Mahananda, Teesta and Balshon rivers in the North Bengal Mahananda barrage area, and the Korola river in Jalpaiguri district for this study.
Using the Provisional Tolerable Weekly Intake (PTWI) standards set by the Joint FAO/WHO Expert committee on Food Additives in 2004 (and reconfirmed by the same body in 2006), and the Prevention of Food Adulteration Act (PFA) Rules, 1954, the study found that the amount of methyl-mercury in fish vastly exceeds the limits set in terms of PTWI and PFA.
According to these standards, PTWI has to be within 1.6 microgramme per kg of body weight per individual. This means that it should be within 0.228571 microgramme/kg of body weight per day. As per PFA standards, the limit of mercury in fish is 0.5 parts per million (ppm) by weight and that of methyl-mercury is 0.25 ppm by weight. The study equated ppm to mg /kg or microgramme/g.
Elemental (metallic) mercury primarily affects health when it is breathed in as vapour and enters the bloodstream directly through the lungs. The effects of such exposure are: tremors, insomnia, neuromuscular changes, muscle atrophy, headaches, disturbances in sensations and nerve responses, and impairment of cognitive function. At higher exposures there may be kidney effects, respiratory failure and death.
The methylation of mercury occurs through microbial action and is a key step in the entrance of mercury into the food chain. Humans are most likely to be exposed to methyl-mercury through fish consumption. Incidentally, mercury in methylated form (methyl-mercury) has the greatest toxic significance. It is a known human toxicant and can cause neurological changes and neurotoxicity resulting in Mad Hatters’ Disease. The neurotoxic effects range from less immediately observable weakening of motor skills and sensory ability at comparatively low doses, to tremors, inability to walk, convulsions and death at very high exposures.
Results from Kolkata Market
Of the 60 samples collected from markets in Kolkata, 16 showed mercury levels in excess of the PFA stipulations, while 24 had methyl-mercury levels far above the PFA stipulations.
Of the 16 cases that contained mercury well above the safe level, two had mercury exceeding more than 100% above the PFA stipulations, while five had mercury exceeding the PFA stipulations by over 50%.
Out of 24 cases that recorded excess levels of methyl-mercury, seven cases showed methyl-mercury exceeding PFA stipulations by over 100%. Another 18 cases showed levels that were 50% above PFA stipulations.
Results from fishing locations in the rest of West Bengal
As regards the 204 samples taken from different parts of West Bengal, excluding Kolkata, 62 cases showed mercury levels well in excess of the PFA stipulations. Of these, 35 samples had mercury that was 50% above the safety levels, while 19 samples exhibited mercury at levels 100% above the PFA stipulations.
In 105 cases, methyl-mercury levels were well above the PFA stipulations. Of these, 18 cases were at levels 200% above the safe level. Another 45 cases exhibited levels that were 100% above, while 70 cases had levels higher than 50%.
Effects on the population
Out of the 43 four-member families surveyed in Kolkata and outlying areas with incomes ranging from Rs 8,000 to Rs 90,000 per month, the majority of the families were found to consume 300-500 gm of fish per week.
Using a conversion factor of 0.75 to estimate the amount of flesh in the fish purchased, the investigators concluded that typical weekly fish flesh consumption in West Bengal, particularly in the middle income groups, easily ranges between 300 to 400 gm, and may go up to 500 gm of fish per week. The combination of this high level of fish consumption with the comparatively high mercury levels detected raises substantial health concerns.
However, there is no proper system in place to follow up on the findings of this disturbing study. As State Expert Environmental Appraisal Committee chairman, Dr Kumar Jyoti Nath, makes amply clear, “Our Committee is in charge of appraising all new projects before any clearance is granted. But as regards existing industries, it is the respective municipalities, municipal corporations and the Pollution Control Board who are in charge. Mercury levels in food, and particularly the presence of methylated mercury, is dangerous. But issuing a blanket ban on the sale of all fish is well-nigh impossible. For this, it is important that the sources of mercury pollution be identified for necessary action.”
Even here, there are bureaucratic hurdles. The Pollution Control Board is in charge of water bodies, but health matters fall outside its purview. Hence, the health departments of the respective municipalities and corporations need to look into the matter.
Mercury generally finds its way into waterbodies from thermal power stations and chlor-alkali industries. But again, waterbodies in the vicinity of thermal power stations may not be contaminated. In this case, the fish catch from water bodies in the vicinity of the Kolaghat thermal power station were found to be uncontaminated.
“The direction in which the winds blow may be a major determinant in the manner in which mercury finds its way to major rivers and ponds,” points out DISHA secretary Santanu Chacraverti. “We are hence keen that the state government takes steps to pinpoint the reasons and identify the polluting industries responsible. This is imperative in the case of West Bengal where fish happens to be a staple ingredient in the daily diet of millions.”
(Rina Mukherji is a Kolkata-based journalist)
InfoChange News & Features, July 2009