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Transgenic Trees Spread Mercury Poisoning
by Joe Cummins, Professor Emeritus,
University of Western Ontario
Recently, researchers tested trees genetically modified to remove ionic mercury from contaminated soil, then convert that to volatile elemental mercury which is released to the atmosphere. The researchers seem to believe that the atmospheric mercury will be relatively harmless. The field tests were undertaken in Danbury, Connecticut, and supported by the United States Environmental Protection Agency (EPA) and other interested parties. [1] Danbury is the home of mercury-polluted sites originating from hat-making. Mercury caused poisoning in workers, who get the “Danbury shakes.” The mercury “remediation” project will, however, simply move the pollution to the atmosphere, from which it will be redeposited over the cities of the Northeast and the lakes and waterways of the northern USA and Canada. Once deposited in waterways and streets, elemental mercury will be converted by microbes into organic mercury that will cause nerve damage and birth defects in humans and animals alike.
Worldwide, emissions of mercury from human activities are estimated at some 1900 tons, about three quarters from burning fossil fuels, particularly coal. Waste disposal sites, cement manufacture and waste incinerators make up the bulk of the remainder. Asian countries contribute over half the emissions while Europe and North America contribute less than a quarter. Gaseous elemental mercury makes up over half of the emitted mercury, while divalent mercury and particulate mercury make up the rest. [2] The emitted mercury tends to be deposited from the atmosphere in snow and rainfall, posing serious threats to humans and animals because elemental mercury is converted to ionic and organic mercury after ending up in the Arctic, in Canada and in Northeastern American cities. [3,4] If phytoremediation of mercury-polluted sites were undertaken on a large scale in North America, the global emissions of mercury could double in less than a decade.
The mercury phytoremediation scheme is based on introducing a bacterial gene, merA, into the genome of plants. For efficient genetic activity in plants, a synthetic merA gene with altered DNA sequence is used. [5–7]
Mercury-resistant microbes are also promoted as an efficient and inexpensive treatment for mercury-polluted water. [8] But the anticipated widespread application of such technology has not considered the consequences of atmospheric pollution from mercury remediation.
The mercury “remediation” project will…simply move the pollution to the atmosphere, from which it will be redeposited…
Phytoremediation and bacterial remediation both cause atmospheric release of elemental mercury but are being promoted by technologists and government regulators. Such “remediation” is no remediation at all; it is just moving the problem from one place to another! In fact, it is moving mercury from contained, contaminated sites to the streets of cities and the bodies of water that give us fish and drinking water.
Notes
1. Williams P. UGA researchers involved in first trial using transgenic trees to help clean up toxic waste site. University of Georgia News Release September 11, 2003 http://www.uga.edu/news/
2. Pacyna E. & Pacyna J. Global emissions of mercury from anthropogenic sources in 1995, Soil, Air and Water Pollution 2002, 137, 149-65.
3. Cummins J. “GM trees alert,” Science in Society 2002, 16, p.33; www.i-sis.org.uk
4. Renneberg A & Dudas J. Transformation of elemental mercury to inorganic and organic forms in mercury and hydrocarbon co-contaminated soils. Chemosphere 2001 45, 1103-9.
5. Rugh C, Wilde H, Stack N, Thompson D, Summers A & Meagher R. Mercuric ion reduction and resistance in transgenic Arabidopsis thanliana plants expressing a modified mer A gene. Proc. Natl. Acad. Sci USA 1996, 93, 3182–7.
6. Heaton A, Rugh C, Wang N, & Meagher R. Phtoremediation of mercury and methyl mercury polluted soils using genetically engineerd plants. Journal of Soil Contamination 1998, 7,497–509.
7. Kramer U and Chardonnens A. The use of transgenic plants in bioremediation of soils contaminated with trace elements. Applied Microbiology and Biotechnology 2001, 55, 661–72.
8. Wagner-Dobler I. Pilot plant for bioremediation of mercury-containing industrial wastewater. Appl. Microbiol Biotechnol 2003, 62, 124–33.
[5 apr 04]