October 2017
08/12/2019
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08/13/2019

Why in news?

  • Recently researchers have found that despite a decrease in seawater concentration of methyl mercury, the amount of mercury found in fish is different among different species
  • A joint research conducted by the Indian Institute of Technology, Hyderabad (IIT-H), Harvard University, and Fisheries and Oceans Canada (a Canadian government agency) has found that though there has been a decrease in the levels of mercury emission, the concentration of mercury in fish varies across different species.

Highlights of the research

  • There have been global efforts to reduce the amount of mercury entering the ocean to reduce the amount of mercury found in fish and other marine animals.
  • Working in this direction, the researchers focused on whether these and other environmental measures alleviated or exacerbated the problem of increased mercury levels in fish.
  • For the study, they chose the Gulf of Maine, a well-studied but also exploited marginal sea in the Atlantic Ocean, to understand the trends in mercury accumulation in fish.
  • The researchers used three decades of data on ecosystem and mercury concentrations and developed a model for mercury bio-accumulation.
  • How Mercury accumulates in Fish

    There are three factors that result in mercury accumulation in fish

    • Overfishing: which leads to dietary changes among marine animals.
      • Cod relied more on lobsters and other large invertebrates (which are low in mercury), while the dogfish went for more squid and other cephalopods (which tend to be high in mercury).
      • Hence cod ended up with lower mercury levels than the dogfish.
    • Variations in the temperature of the sea water: This leads to changes in fish metabolism that gears towards survival rather than growth.
      • Fish metabolism is temperature-dependent, so as ocean temperature increases, fish experience higher metabolism and more energy obtained from food are spent on maintenance rather than growth, leading to more methyl mercury getting concentrated in predatory fish.
    • Changes in the amounts of mercury: found in sea water as a result of pollution.

    Why Mercury is a problem

    • Mercury is a naturally occurring heavy metal. It can build up in the bodies of fish in the form of methyl mercury, which is highly toxic.
    • It’s released into the environment in several ways, including through industrial processes like burning coal or natural events like eruptions.
    • Three main forms exist — elemental (metallic), inorganic, and organic.
    • People can be exposed to this toxin in a number of ways, such as breathing in mercury vapors during mining and industrial work.
    • You can also be exposed by eating fish and shellfish because these animals absorb low concentrations of mercury due to water pollution.
    • Over time, methyl mercury — the organic form — can concentrate in their bodies.

    Health effects

    • Pregnant women, breastfeeding mothers, young children, and those who regularly consume large amounts of fish have a higher risk of problems related to mercury exposure.
    • Higher levels of mercury can harm brain function and heart health.
    • Exposure to mercury – even small amounts – may cause serious health problems, and is a threat to the development of the child in uterus and early in life.
    • Mercury may have toxic effects on the nervous, digestive and immune systems, also on lungs, kidneys, skin and eyes.
    • Mercury is considered by World Health Organisation (WHO) as one of the top ten chemicals or groups of chemicals of major public health concern.
    • People are mainly exposed to methyl mercury (an organic compound) when they eat fish and shellfish and are more vulnerable to Minamata disease.
      • Minamata disease: A disorder caused by methyl mercury poisoning that was first described in the inhabitants of Minamata Bay, Japan and resulted from their eating fish contaminated with mercury industrial waste.
    • The disease is characterized by peripheral sensory loss, tremors, ataxia, and both hearing and visual loss.
    • Methylmercury is very different to ethyl mercury. Ethyl mercury is used as a preservative in some vaccines and does not pose a health risk.
    • However, the health benefits of eating fish may outweigh these risks as long as you limit your intake of high-mercury fish.

    Minamata Convention

    • The Minamata Convention on Mercury is a global treaty to protect human health and the environment from the adverse effects of mercury.
    • It was agreed at the fifth session of the Intergovernmental Negotiating Committee on mercury in Geneva, Switzerland in January 2013 and adopted later that year on 10 October 2013 at a Diplomatic Conference (Conference of Plenipotentiaries), held in Kumamoto, Japan.
    • The Minamata Convention entered into force on 16 August 2017, on the 90th day after the date of deposit of the 50th instrument of ratification, acceptance, approval or accession.
    • The Convention draws attention to a global and ubiquitous metal that, while naturally occurring, has broad uses in everyday objects and is released to the atmosphere, soil and water from a variety of sources.
    • Controlling the anthropogenic releases of mercury throughout its lifecycle has been a key factor in shaping the obligations under the Convention.

    Bio Accumulation and Bio Magnification:

    • Few toxic substances especially non- biodegradable (which cannot be metabolized by the living organism) ones, often present in the industrial waste have the ability to move through the various trophic level. Higher concentration of these elements in the food chain creates a lot of serious problems and may even cause life-threatening diseases like cancer.
    • The process of movement of toxic elements is of two types Bio-accumulation and Bio-magnification.

    Bio-Accumulation:

    • Process by which certain toxic substances (such as heavy metals and polychlorinated biphenyls) accumulate and keep on accumulating in living organisms, posing a threat to health, life, and to the environment.
    • Example- The air pollution which is caused due to various factors including the vehicular emission, progresses to an accumulation of toxic elements like PM2.5 and PM10 inside an organism and can have dangerous impacts on humans as well as other organisms.

    Bio- Magnification:

    • Process by which a compound (such as a pollutant or pesticide) increases its concentration in the tissues of organisms as it travels up the food chain.
    • Biomagnification can be seen in the case of Mercury or DDT. The concentration of Mercury/DDT increases at the successive trophic levels. DDT concentration in zooplankton gets magnified when DDT contaminated water is consumed by the Zooplanktons. In the successive trophic levels like, small fish, big fish, and at top carnivore, the magnification is much higher, which proves the event of Biomagnification.
    • A pollutant having properties like long life, mobile, soluble in fat, biologically active will lead to the process of biomagnification.
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