Improved Methods Reveal More Than Twice As Much Environmental Mercury

October 6, 2014- The preponderance of mercury is making news as scientists conclude the most comprehensive estimate of mercury in the environment.

The calculations, which account for mercury in consumer products and released by industrial processes, more than double the previous estimates of the amount of mercury that has been introduced to the environment since 1850.

Here are the highlights of a recent post on the subject, "More than Twice as Much Mercury in Environment as Thought," at the website ScienceMag.org:

• Although the calculations accounted for 540,000 additional tons of mercury in the environment, more than double the previous tallies, the researchers say that it doesn't indicate a greater risk to human health because scientists already know how much mercury most people are exposed to.

• The data shows how tighter regulations over the last 40 years have reduced the total amount of mercury released into the global environment, even as some industries in the developing world continue to expand.

• Mercury is a dangerous neurotoxin that becomes most harmful when microbes convert the element into the compound methylmercury, a form of the metal that accumulates in the food chain. Most people are exposed to mercury by its concentrations in fish. In developed countries, researchers monitor the amounts of methylmercury in fish and set consumption advisories.

• Scientists and public health advocates wanted to know how mercury is used and where it eventually ends up in the environment to help inform policy and regulations.

• It was estimated that about 720,000 metric tons of the element have been taken out of the ground since 1850, when major silver and gold rushes were under way. Mercury is particularly useful for extracting silver from pulverized ore, and a number of other industrial processes. It is also in many products and devices, such as thermometers and switches.

• Coal contains trace amounts of mercury, hence burning the fossil fuel places a lot of mercury into the atmosphere.

• Analysis of sediment cores and other research shows that background levels of mercury have risen threefold since the Industrial Revolution.

• Previous studies focused on atmospheric mercury, where roughly 100,000 tons of mercury pollution came from its use in silver mining, which peaked in the 1890s. Since that time, most atmospheric mercury has been emitted by power plants, smelters, and chlor-alkali plants, which use it to make chlorine and sodium hydroxide for industry.

• Environmental modeler Hannah Horowitz, a graduate student at Harvard University, and her colleagues accounted for all the uses of mercury over time. Her team found the largest peak in the 1970s, instead of the late 19th century. This timeframe matches what is seen in sample cores taken from lake sediments and peat marshes.

• One major source of mercury was latex paint, which used mercury compounds as a preservative. Its use in this fashion declined after the 1970s in the U.S. until it was finally banned by the Environmental Protection Agency in 1991.

• The researchers pointed to the production of vinyl chloride, an important ingredient in plastics and vinyl, as a continued source of mercury in the environment.

• Horowitz and her team say about 57% of the mercury released since 1850 continues to circulate in the environment; the remainder is locked away in sediments or landfills. She admits the uncertainty is quite large due to the difficulty in establishing an error range around the estimates. The post pointed to the latest Global Mercury Assessment, by the United Nations Environment Programme (UNEP), where the estimate of annual mercury emissions ranged by a factor of 4.

• This research "helps to fill some of the many holes in our understanding of mercury flows historically," says Peter Maxson, a consultant based in Brussels who advises the European Commission, UNEP, and others on mercury issues. "Once mercury is brought into the environment, it doesn't just go away but becomes everyone's problem for a very long time," says Maxson, who was not an author of the new paper.

• ScienceMag.org notes that one of the largest concerns today with mercury is small-scale gold mining in the developing world. "Environmentalists and public health advocates are pinning their hopes on an international treaty, agreed to in 2013, called the Minamata Convention, after a town in Japan where citizens suffered from severe mercury poisoning," they write in closing the post. "The treaty would require countries that ratify it to ban mercury in batteries, light bulbs, and other products, and cut emissions from power plants, incinerators, and factories."

Read the full ScienceMag.org post here.

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