Acclaimed as the ‘Pearl of the Indian Ocean’ as well as the ‘Granary of the East’ Sri Lanka is renowned for its proud agricultural tradition. Such titles reflect upon the significance of Sri Lanka’s major sources of income and livelihoods; agriculture and fisheries. Though agriculture and fisheries may not be on top of the list of industries contributing to the GDP of the country, the bond that these two industries have with the Sri Lankan culture is undeniable.

Farming and fishing no longer enjoy the status of two of the major livelihoods as they did decades ago. But it is these livelihoods that still ensure food security. Sri Lankans from all walks of life still relish a full plate of warm rice with a red-hot fish curry to spice it up. But the truth is that these very relishes hide a silent killer in their savour.

Put in a nutshell they contain toxicants. Oxford dictionary defines toxicants as ‘any toxic substance introduced to the environment.’ It does not require rocket science to realize that the environment around us contains a cocktail of toxicants from various sources. But the burning question is where these toxins that get into our food chain come from.
Some toxicants are naturally produced. Many plants and animals produce toxicants as a defensive mechanism; a prime example is the poison produced by snakes in the form of venom. On the other hand there are toxicants of inorganic origin present mainly in soil as reserves in atomic or molecular form; heavy metals such as mercury, copper, cadmium and lead and their molecular for example. The names of these toxicants may seem so commonplace at a first glance that it may be hard to comprehend how they can act as deadly poisons hidden in the daily plate of rice. The catalyst that has turned these metals poisonous is Climate Change.

The link between climate change, toxicants and the impact it’s making on a simple plate of food is somewhat complex. Climate change refers to drastic changes in several environmental parameters at global scale. These changes attribute to increasing global atmospheric temperature and atmospheric carbon dioxide, increasing intensity and frequency of extreme weather events such as droughts and floods and changes in precipitation patterns. This in turn leads to prolonged drought conditions followed by high-intensity rainfalls paving way to disastrous floods. In fact, what’s happening in Sri Lanka is a classic example for climatologists prediction that ‘dry areas are getting drier and wet areas are getting wetter, as a result of climate change.’

To link these basic theories of climate change with the impact of toxicants, it is necessary to consider some of the predictions made in the reports of Intergovernmental Panel on Climate Change (IPCC) on the rate of run-offs of toxicants such as mercury, organochlorines and sulphates. According to this, organic matter run-offs are expected to increase by 15 to 20 per cent by the end of the century. Global temperatures that are expected to rise to uppermost limits predicted, will undoubtedly make matters worse. Meanwhile, all climate change triggering activities such as industrial and technological changes, economic growth, population growth and fossil energy consumption will continue to happen sans control measures.

The technological advancement that the world is going through at present, coupled by the exponential population growth have proven to be major triggers of climate change and its impacts, especially considering the amount of energy it requires. The fact that a greater part of energy channelled into above mentioned activities come from burning of fossil fuel is noteworthy when considering the by-products produced through energy generation using fossil fuels, especially coal power, which is commonly used in developing countries.
Scientific research has proven coal combustion to be the major source of anthropogenic mercury emissions. IPCC predictions for 2050, based on current data regarding anthropogenic mercury emissions have an alarming revelation showing that Asia is the leading contributor to current global mercury emissions and a 240 per cent increase from current trends by 2050, owing to the increased coal combustion in China and India, the global population hubs.

Deposition of atmospheric mercury refers to deposition of gaseous mercury atoms released mainly from coal combustion, in terrestrial and marine sinks. Soil which acts as the principle sink for terrestrial atmospheric deposition of mercury retains mercury and other equivalent toxicants. With rain, these deposits are washed-off and get into ground water, inland water bodies and eventually the ocean.

Most of the time, toxicants, mainly mercury, are retained in soil for a period long enough for it to undergo various changes. For example, soil microbial action on mercury converts it to its organic form, methylmercury. This retention time has its own pros and cons depending on the type of toxicant. Some toxicants undergo bioremediation during the time it is retained in soil, which involves breaking down of the toxicants to non-toxic substances.

To a great extent this bioremediation is carried out by plants which involves uptake of toxicants by plants, a process referred to as phytoremediation. Some of these toxic substances are metabolized by plants into less toxic substances. Unfortunately some toxins accumulate in the plant tissues in the toxic form itself – bioaccumulation, ultimately getting into the food web.

Large volumes of water are received in the form of intense rainfall coming just once or twice a year leading to disastrous floods and landslides. Prolonged drought conditions means toxicants are retained in soil for a longer period of time before being washed away, which gives toxicants a greater time to get absorbed by bioaccumulating plants.
Sri Lanka, being an agricultural country, is highly dependent on not only rice but on a number of other crops as well. Burdened by heavy debts, constantly struggling in a fluctuating market, faced by extreme weather and climate change related problems, Sri Lankan farmers depend heavily on agrochemicals. Agrochemicals are another source of toxicants, adding a cocktail of toxicants to soil. Toxicants are retained in the soil for long periods, getting concentrated and being absorbed into food crops due to prolonged drought conditions.

The severity of this heightens with biomagnification which is the process through which toxicants accumulated in food crops enter the human body through food chains in ever increasing concentrations, worsening the impact.

Prolonged drought conditions followed by high intensity rainfalls lead to a greater volume of water falling on Earth’s surface, increasing the rate of run-off of toxicants deposited in soil. As a result more toxicants make their way into water bodies, ultimately ending up in the ocean. This process is significant in relation to mercuric deposits in soil. Mercury released from anthropogenic sources deposit in soil both in elemental and divalent forms. Divalent mercury is highly water soluble resulting in direct wet deposition in water bodies and ground water close to its source. But sparingly soluble elemental mercury has a greater lifetime ranging over months, which causes it to remain in its toxic form even after being retained in soil over a long period. This elemental mercury accumulated in soil getting concentrated over long drought periods gets washed off in its full dose of toxicity with exposure to heavy rainfalls following the droughts.

Mercury thus washed into the oceans make its way into aquatic organisms through food chains, especially into carnivorous fish in the top levels of the food web. Specially types of tuna, which are top predators in food webs of marine fish, being pelagic fish inhabiting the surface layers of the ocean runs a higher risk of exposure to mercury because toxic run-offs mostly deposit on surface waters.

Experiments conducted by a Swedish group of scientists have a new revelation to add to this. According to their study increased levels of organic run-offs cause addition of extra steps to marine food webs. Each extra step in food a web increases the biomagnification of toxicants through the food web, by up to seven-folds. In this manner biomagnified mercury and other toxicants accumulated in the fish body muscles slowly makes way into human bodies in increasing concentrations.

Toxicants thus entering human bodies through their seemingly harmless meals are the major culprit for a number of health related issues. Although Minamata disease, (a neurological disorder resulting in crippling of limbs, muscle weakness and vision impairment and speech), which comes first in the list of diseases caused by mercury poisoning is not that famous in Sri Lanka, chronic kidney diseases is not far behind. The fact that children are at extremely high risk of mercury poisoning is a tragic truth that should be kept in mind.

Signing of Minamata Convention by the Sri Lankan Government in 2014 does not prove to be an adequate step to curb this trend. It requires the implementation of an integrated management plan with the involvement of all relevant parties.

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