Mercury poisoning: Growing concern of

Unchecked and unregulated, certain anthropogenic activities are increasing the levels of the heavy metal mercury in environment. Scientists are ringing alarm bells as the threat is reaching a global scale. 

Their findings report an urgent need for stringent regulations and definition for safety levels, for mercury accumulates in the tissues causing irreversible neurological damages. Traces of mercury are naturally found in the environment due to emissions from volcanoes, forest fires or weathering of metallic rocks. 

However, far greater amounts of this toxin is added into the atmosphere by human activities such as burning of fossil fuels, emissions from coal-fired power plants, gold mining, jewellery works and metal processing.

Different routes of entry: Mercury is a potent neurotoxin and affects almost every part of the body, causing neurological, behavioural and developmental anomalies. According to the World Health Organisation, mercury is listed as one among the top 10 chemicals of major public concern. There is a lack of awareness as people unknowingly expose themselves to the toxin. Once emitted, mercury spreads through air, water and land, contaminating them. Bacteria and plankton transform it into an organic form called methylmercury. This bioaccumalates or is collected in fish that ingest them. From here, mercury gets biomagnified in the food chain when the larger predatory fish consume the smaller species, and in humans who consume fish and seafood.

Humans are contributing far greater mercury burden affecting the level of exposure from mild to moderate to chronic.  Apart from emissions, inorganic mercury salts are entering our system through processed foods. 

Researcher Renee J Dufault reports in a study that these additives — used as taste enhancers and preservatives — cause mineral imbalances disrupting the process of their elimination from the body, in turn leading to accumulation of mercury.

In the dark: India currently lacks regulations to measure and monitor the limits of mercury exposure. In addition, there is a need for adequate studies to bring to light the exposure levels in the population.In one such attempt, a pilot study by researchers at IIT, Hyderabad, gives a cross sectional view of the situation. They investigated 668 volunteers from three coastal cities in southern India for mercury levels. They integrated several variables like dietary habits and patterns, fish and rice consumption, proximity to coal-fired power plants, occupational exposure to mercury and others. The examination shows that the total mercury levels were higher in populations from the high emission zone, in high-frequency fish consumers and gold artisans who use mercury compared to the other categories. 

Even the vegetarian rice consumers from the emission zone had higher levels of mercury compared to other regions. Although it could not be ascertained if the rice was grown locally, the contamination was evident. The study is indicative of the need to assess and develop an exhaustive, case by case database across India.

Realising the hidden perils, in 2017, more than 150 countries gathered in Geneva to enter into a treaty called the UN Minamata Convention on Mercury, to protect human health and the environment from the adverse effects of mercury. They called for banning and phasing out of mercury mining, regulating the use of mercury in dental fillings, lamps and gold artisan works and primarily checking the emissions from coal-fired power plants.

India, with its vast number of coal-fired power plants, is one of the top mercury emitting countries in the world with an urgent need to arrest the growing contamination. Reported, keen on an active role,  the Ministry of Environment, Forests and Climate Change has entered into an agreement with IIT Hyderabad for strengthening the capacity on the mercury situation in India. While these efforts are underway, a latest research has warned that there is more than that meets the eye. Just basic regulations may not suffice, as overfishing and climate change together are affecting the mercury burden. They report indicates that though the direct concentration of methylmercury in ocean water has decreased per se, the accumulated toxin in higher order fish have altered due to these two activates.

Dramatic changes

The global team observed the dramatic changes in methylmercury levels in fish by curating available records of three predatory fish species over a 30-year collected data in the Gulf of Maine.  Along with this, they simulated models to demonstrate how the dietary patterns of fish were changing, Predatory fish like cods are opportunistic feeders. So, when the supply of one type diminishes due to overfishing, consumption of another variety increases, thereby altering the mercury levels in their body. This percolates up the food web changing the mercury burden.

Also, fish being cold-blooded, are sensitive to temperature changes and when oceans warm up, their metabolic activities change. They were found to expend energy in maintenance rather than growth, thereby increasing the bioaccumulation of methylmercury in their body, which is again projected on to the food chain.“There is a stronger need for adopting stringent controls and regulations on both carbon and mercury emissions, to protect the ecosystem and human health, avers Asif Qureshi, professor at IIT-H who is involved in both the studies.

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