Minamata Convention: World perspective on mercury pollution


Mercury and mercury compounds have long been known to be toxic to humans, other organisms and the environment.

Considering that mercury bio-accumulates in the environment, its adverse impacts on the environment were evident in countries like Japan causing the Minamata disease as well as the Niigata Minamata disease.

The negative impacts of mercury gave rise to the promulgation of the Minamata Convention on Mercury of October 2013.

The convention is an international treaty designed to protect human health and the environment from anthropogenic emissions and releases of mercury and mercury compounds.

The convention was a result of international action aimed at managing mercury in an efficient, effective and coherent manner, while member states work towards its total elimination.

Zimbabwe is one of the 147 countries which signed the convention and is working towards ratification.

The document obliges member states to ensure there is informed consent from the receiving state in relation to the trade in mercury or mercury-based products.

Trade in mercury or mercury-based products will be restricted to allowed purposes under the instrument and also domestic law, and only in quantities needed for those purposes.

The instrument will also put restrictive measures on the use of mercury especially in the mining sector.

There is a need for the development of sustainable technologies to extract gold in preparation for the restrictions that will be imposed on trade in mercury.

Once ratified, the main benefit, of the document is that it will be a reference point or provide direction on how national legislation can be developed to  tackle the on-going problem of controlling the use and influx of mercury into the country and prevent the possibility of Zimbabwe being a dumping ground of such hazardous substances.

Miners are at risk since they do not use appropriate personal protective equipment when handling mercury.

The hazardous substance is not well-labelled and miners lack knowledge on the health risk associated with exposure to mercury considering that its effect is not acute but chronic.

Emerging evidence indicate that artisanal and small-scale gold mining related mercury contamination in Africa is contributing to serious health and ecological impacts and has raised concern among environmentalists.

UNEP estimates that 3, 5 million people are at risk of health impacts in artisanal and small-scale gold mining sector of which 2, 5 million are in Africa.

The effects of mercury to the environment
A very important factor in the impacts of mercury to the environment is its ability to build up in the organisms and up along the food chain.

Although all forms of mercury can accumulate to some degree, methylmercury is absorbed and accumulates to a greater extent than other forms.

Inorganic mercury can also be absorbed, but is generally taken up at a slower rate and with lower efficiency than is methylmercury (US EPA, 1997).

The biomagnification of methylmercury has a most significant influence on the impact on animals and humans.

The term bioaccumulation refers to the net accumulation over time of metals within an organism from both biotic (other organisms) and abiotic (soil, air, and water) sources.

The term biomagnification refers to the progressive build up of some heavy metals (and some other persistent substances) by successive trophic levels – meaning that it relates to the concentration ratio in a tissue of a predator organism as compared to that in its prey (AMAP, 1998).

At the top levels of the aquatic food web are fish-eating species, such as humans, seabirds, seals and otters.  Methylmercury is a central nervous system toxin, and the kidneys are the organs most vulnerable to damage from inorganic mercury.

Severe neurological effects were already seen in animals in the notorious case from Minamata, Japan, prior to the recognition of the human poisonings, where birds experienced severe difficulty in flying, and exhibited other grossly abnormal behaviour.

Significant effects on reproduction are also attributed to mercury.

The health effects of mercury to humans
The mercury in household products is trapped and usually does not cause any health problems.

However, when a thermometer breaks, a significantly high exposure to mercury through breathing will occur for a short period of time while it vaporises.

This can cause harmful effects, such as nerve, brain and kidney damage, lung irritation, eye irritation, skin rashes, vomiting and diarrhoea.

Mercury has a number of effects on humans, that can all of them be simplified into the following main effects:
– Disruption of the nervous system
– Damage to brain functions
– DNA damage and chromosomal damage
– Allergic reactions, resulting in skin rashes, tiredness and headaches
– Negative reproductive effects, such as sperm damage, birth defects and miscarriages

Damaged brain functions can cause degradation of learning abilities, personality changes, tremors, vision changes, deafness, muscle incoordination and memory loss.

Chromosomal damage is known to cause Down syndrome.

Most people can continue to look to fish as a healthy, low‐fat source of protein and other nutrients.

However, pregnant women, women who may become pregnant within the next several years, children less than six years old and people who consume unusually large quantities of freshwater fish, may be impaired by mercury.

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