Scientists predict bleak future for mercury pollution.
Corbitt, ES, DJ Jacob, CD Holmes, DG Streets and EM Sunderland. 2011. Global source–receptor relationships for mercury deposition under present-day and 2050 emissions scenarios. Environmental Science and Technology http://dx.doi.org/10.1021/es202496y.
These vastly different scenarios illustrate how levels of industrial activity and pollution controls influence future emissions, according to a new computer study published in the journal Environmental Science and Technology.
In the study, scientists predict that by the year 2050, mercury falling onto the United States may increase by up to 30 percent unless factors – including fossil fuel use – change. Levels could drop if actions are taken to reduce releases.
Mercury is a toxic pollutant that enters the atmosphere from both human activities – especially coal combustion and mining – and natural sources, such as volcanoes and erosion. Over the past 200 years, mercury deposited onto the earth’s surface has tripled due to human activities. Once in the atmosphere, mercury can fall back to Earth within days, where it is deposited locally onto land and water. But some mercury stays aloft for months, allowing it to travel far from its origin until it is eventually deposited.
In water, bacteria transform mercury into the more dangerous methylmercury. This type readily enters the food chain and makes its way into plankton, fish, wildlife and humans.
Human exposure to the pollutant is mostly through eating fish and seafood. Long-lived fish high on the food chain can accumulate mercury and pass it on to people who eat them. Sufficiently high doses of methylmercury can cause neurodevelopment problems in children and have been linked to cardiovascular and immunological changes in adults.
Some technologies lower the amount of mercury emitted from human activities. For example, scrubbers and other control measures reduce emissions from coal-fired power plants. Power plants contribute up to 50 percent of mercury pollution in the United States, according to the U.S. Environmental Protection Agency. New national rules to reduce coal plant pollution – including up to 90 percent of mercury emissions – were announced recently by the agency.
Additionally, the use of alternative energy sources instead of fossil fuels would reduce the amount of mercury emitted into the atmosphere.
Researchers used a computer model to simulate global mercury cycling now and in the year 2050 to better understand how mercury emissions will change in the future. Mercury cycling refers to how mercury is emitted and moves around the world, circulating through the atmosphere to the earth's surface – moving between land and water – and back into the atmosphere again.
They examined the relationship between mercury emissions and where it will be deposited to quantify how human activities may affect future levels of mercury contamination. Estimating future mercury pollution patterns will help guide current policies regulating its release.
They predicted mercury emissions and its movements around the globe under four scenarios that had different economic development and environmental regulations. They included a "worst-case scenario" with high mercury emissions due to an intense use of coal and limited emission controls. A "best-case scenario" mimicked lower mercury emissions that could follow a major shift away from fossil fuels to other energy sources and increased controls.
Some of the mercury deposited onto the earth’s surface is recycled back into the atmosphere where it can continue its long-term travels. This mercury recycling essentially increases its lifetime in the atmosphere, allowing it to continue to be a potential source of pollution. The authors call this a "legacy source" of mercury.
Even with the far-traveling legacy sources, the findings indicate that mercury tends to land within the same hemisphere from where it was emitted.
By 2050, when anthropogenic emissions alone are considered, mercury deposition is expected to increase by 30 percent in the United States. This was considered the the worst-case scenario. In the best-case scenario, U.S. mercury deposition is expected to decrease by 10 percent, which means levels will be similar to what they are today.
In all scenarios, Asia emits the most mercury and is projected to increase its contribution throughout the world, contributing over one-half of all anthropogenic emissions. In the worst-case scenario, Asia will more than double its current mercury emissions by 2050. Much of these increased emissions from Asia are due to India's growing use of coal.
Worldwide mercury pollution is expected to increase dramatically by 2050, unless major policy changes are implemented.
The results of this study suggest that increasing or decreasing mercury emissions due to human activities can have dramatic effects on global mercury levels. The growing use of coal in India and other Asian countries without reductions in the United States and elsewhere will contribute to the higher worldwide levels of mercury. On the other hand, strict controls can keep levels steady or perhaps even reduce them well into the future.
Of the predicted scenarios, it is difficult to know which one will be the closest to reality. However, unless major policy changes are implemented, mercury emissions will most likely increase. Currently, human activities account for two-thirds of the pollutant worldwide. New mercury emissions from human activities make up one-third of the total global emissions. Legacy sources and natural sources each contribute one-third.
Even the best-case scenario suggests major actions will only dent mercury deposition to the United States, decreasing it by only 10 percent. This small reduction involves major changes that won't come easily. It demands a shift from fossil fuel use and a large increase in the use of emissions control technologies. EPA's tough, new national standards to restrict mercury emissions from power plants are a step toward that goal.
These findings show that mercury will continue to be a problem but that reduction efforts may work to diminish environmental levels.
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