Mercury exposure in urban Southern India: A baseline study

K L, Subhavana (2016) Mercury exposure in urban Southern India: A baseline study. PhD thesis, Indian Institute of Technology Hyderabad.

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Abstract

The toxic pollutant mercury (Hg) is emitted through a number of natural and anthropogenic sources and, with a residence time of about 0.7-1.4 years in the atmosphere, is widely distributed in the atmosphere and deposited in terrestrial environments. Mercury exists three main species groups in the environment: elemental mercury [Hg(0)], divalent mercury [Hg(II)] and Methylated mercury (MeHg). Emissions of mercury are primarily in Hg(0) and Hg(II) forms, which are then deposited. In aquatic systems, divalent mercury is converted into Methyl mercury(MeHg) which is highly toxic and is bio-accumulated in aquatic food-chains. Concentrations in high tropic level fishes can be as high as 1,000,000 times than in water. Consumption of high MeHg containing food may result in neurological and cardio vascular diseases in humans, and more particularly in the human foetuses. Three long term cohort studies (Faroes Island, New Zealand and Seychelles) support the aforementioned statement. Harmful effects of acute exposure have also been observed in Minamata, Japan, an example of extreme exposure. Globally, fish consumption has been identified as the most relevant exposure pathway for common people; rice exposure has been identified to be also important in China.India is a major emitter of mercury into the atmosphere. Major sources of mercury to atmosphere are thermal (coal-based) power production, zinc production, iron and steel production, chlor-alkali production, cremation, and waste incineration. India also has a vast coastline and 14% of its population is concentrated in the coastal districts. In several locations, fish forms a staple portion of human diet and may be an exposure pathway for MeHg. Other localized pathways include occupational exposure like artisanal small scale gold mining, and e-waste recycling. While a sizeable portion of Indian population (possibly order of millions) may be exposed to MeHg due to dietary exposure, there is little data on mercury levels in humans, male, females and pregnant women in India. Even baseline information (that is, mercury levels in non-exposed or vegetarian population) is missing.

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