Impact Of Mercury And Persistent Organic Pollutants In The Tibetan Plateau

The Issue

The Tibetan plateau north of the Himalayas is home to the largest mass of snow and ice outside of the poles and plays an important role in the climate of Asia and the rest of the northern hemisphere. Climate change is having a negative impact on the glaciers and snowpacks of this region and understanding pollutant storage and transport through hydrological cycles is vital in protecting downstream ecosystems and human populations from accumulation of toxic methylmercury and persistent organic pollutants (POPs).

Why it Matters

The Tibetan Plateau (TP) includes the largest concentration of alpine glaciers in mid-latitude and is home to vast areas of high-altitude permafrost and snow cover. This region is also warming faster than other non-polar regions. This large mass of snow and ice at such high altitude strongly influences atmospheric circulation and the climate of Asia as well as the rest of the Northern hemisphere. This region is known as the water tower of Asia as glacial and snow meltwater feeds over 10 river systems and is the source of critical drinking water supply for 1.4 billion people. However, this region is also polluted with persistent organic pollutants (POPs), and a higher mercury content than seen at either of the poles. This has potential impacts on high mountain lake ecosystems as well as the human populations who eat fish from those lakes, rely on products from animals who graze at high altitudes, as well as the humans who rely on water supplies from meltwater.

State of Knowledge

Methylmercury and POPs are toxic pollutants that are stored in the fat of animals and accumulate over an animal’s lifetime as well as up through the food chain. Mercury is a byproduct of human activities such as metal smelting and coal combustion and becomes methylated due to biotic processes. It is this methylmercury that acts as a neurotoxin in humans and animals, causing reproductive and behavioral problems. POPs comprise a variety of chemicals that are used for disease and pest control, agriculture, and industrial purposes. The most well-known are DDT, PCBs, and dioxins. Persistent organic pollutants (POPs) and mercury are known to be semi-volatile, meaning they may volatilize in warmer regions and then can be transported through the atmosphere where they are condensed and deposited over cold regions. The Himalayas are thought to be particularly at risk for being polluted this way because of its steep slopes and high altitudes, concentrating pollutants into high altitude lakes formed from glacier runoff where POPs can accumulate and Mercury can become methylated.

Evidence shows that mountainous regions have higher than expected pollutant concentrations and deposition rates of certain POPs. Elevated levels of organochlorinated compounds were reported in fish from the Canadian Rocky Mountains and toxaphene levels in fish were found to increase with altitude. This evidence suggests that mountain regions may function as convergence zones for POPs and given that the Himalayas are the tallest mountain range in the world as well as host the largest source of ice and snow outside of the poles, scientists are concerned this effect is stronger in this region.

Where Science is Headed

More studies looking into the effects of POPs and mercury on the downstream ecosystems of the Tibetan plataue are needed to fully understand the unique phenomena of pollutant storage and transport that occurs in the highest mountain range in the world. Many studies are limited to smaller mountain ranges in other regions of the world.

What Policies Should Be Implemented

Given that the Tibetan plateau and Himalayan range are surrounded by heavily populated, industrialized nations, and the meltwater is of vital importance to downstream ecosystems, it is imperative that policies are enacted that protect this region from toxic pollutants. India has signed the Stockholm Convention which is aimed at phasing out the production and emission of twelve known POPs. Accelerated industrial growth in the United States during the 1950’s-1990’s lead to high rates of mercury deposition in the Rocky Mountain range. Regulation during the 1980s resulted in an 85% decline in mercury deposition indicating that similar policies in Asia could have a positive impact on mercury deposition in the Tibetan plateau.