The article incorrectly said that corporate gold mines use mercury to extract gold from sediment or rock. U.S. gold mines stopped using mercury years ago. They emit mercury as a natural byproduct of refining ore. Artisanal miners in the developing world acquire and use mercury in gold mining.
Cleaner chlorine plants may be creating a mercury glut
Tuesday, November 17, 2009
Over the past decade, environmental groups have pressured U.S. chlorine plants to stop spewing mercury, the toxic heavy metal that settles in water and makes its way into the food chain by contaminating fish and shellfish. In the past four years, five such plants converted to mercury-free technology, cutting the industry's mercury emissions by 88 percent, according to the Environmental Protection Agency.
But this success has created a new environmental problem. Hundreds of tons of mercury acquired for use by the plants may be on the global market, where it could ultimately be used in small-scale unregulated "artisanal" gold mining. Such activity might create environmental and health hazards in developing countries.
Environmental stewardship is often a complicated balancing act, with solutions to one problem creating new and sometimes unforeseen issues -- for example, the planting of kudzu to control soil erosion and the introduction of voracious Asian carp to clean up aquaculture operations. In both cases, the invasive species wreaked havoc of their own.
Removing mercury from U.S. chlorine production could be another such example.
When the Erco Worldwide chlorine plant in Port Edwards, Wis., converted to mercury-free membrane technology this year, it sold 200 tons of mercury to a broker. Peter Maxson, a Brussels-based consultant who advises the European Commission on mercury, said it is likely some of that mercury ended up in a Dutch warehouse that distributes the metal worldwide. According to Maxson and various watchdog groups, significant amounts of globally traded mercury end up in artisanal gold mining in South America, Africa and Asia.
Erco President Paul Timmons and a spokeswoman for Olin Chemicals, which converted plants in Niagara Falls, N.Y., and Louisiana in recent years, say their brokers signed contracts that the mercury would not be sold for any use that emits the metal into the atmosphere. But critics say it is hard to track where globally traded mercury goes. "It's kind of like money laundering," Maxson said. "They can say they are doing the right thing and then wash their hands of it."
Four remaining plants
Mercury has been phased out of many industrial processes and products in the United States and Europe, though it is still used in fluorescent light bulbs and various scientific and manufacturing devices. The remaining four chlorine plants that use mercury account for only 2.5 percent of U.S. emissions, though they are major sources in their states: West Virginia, Ohio, Georgia and Tennessee.
Officially called chlor-alkali plants, they use cells full of mercury as cathodes in a reaction where salt brine is turned into chlorine gas and caustic soda, or lye. Chlorine is used to purify water in pools and municipal drinking systems, and to manufacture a wide range of products including paper, textiles and medicines. Caustic soda (potassium hydroxide or sodium hydroxide) also has many uses, such as titanium refining and cleaning products.
Mercury is also a convenient tool for extracting gold from sediment or rock, used by both large corporate gold mines and Third World miners selling lumps of gold for dollars a day.
The individual miners add mercury to silt or soil; after it binds with flecks of gold, this amalgamated ore can be sifted out. Heating evaporates the mercury, leaving only gold. The miner is directly exposed to mercury, and the metal is also usually released into the atmosphere in high concentrations.
"Many of them do it in a really wasteful, dirty processes, usually because they don't know better," said Glenn Wiser, a lawyer hired by the United Nations to give advice on ongoing treaty negotiations meant to curb the global mercury trade. "It has devastating health impacts on the miners and their families, and can get into water and have global impacts."
Bans on the horizon
U.S. and European policymakers are trying to limit the amount of mercury available to those miners. A European Union ban on mercury exports takes effect in 2011, and U.S. exports will be banned in 2013. The bans, affecting up to a third of the world trade, will probably mean rising mercury prices; that would make it less attractive for artisanal miners to use the toxic metal, or at least make them more likely to recapture and reuse mercury instead of releasing it. Until the ban takes effect, environmentalists have demanded that Erco and other companies store their mercury rather than sell it.