Date: Wed, 3 Jul 2002 08:02:45 -0400 Sender: Sustainable Agriculture Network Discussion Group From: jcummins Subject: soil phytoremediation using transgenic trees July 2, 2002 Prof. Joe Cummins e-mail: jcummins@uwo.ca "Soil mercury remediation by transgenic trees" Soil mercury pollution can be a major chronic pollution hazard. Most of the sites are historical industrial sites , gold mining, in particular , may still use primitive "quicksilver" gold extraction that pollutes soil and waterway. In many areas the soil pollution may be of geological origin rather than a result of human activity. Currently, atmospheric deposition of mercury is a leading pollution problem in the cities and wild lakes of the northern countries. Most of the problem is associated with fossil fuels and medical waste incineration. Plots of land that are polluted with high levels of mercury are planned to be Phytoremediated using trees that are modified to take up the ionic mercury or organic mercury, convert it to less toxic elemental mercury then expel it the atmosphere where it will be safely diluted before it is diluted (1,2,3). The environmental risk assessment by the proponents of transgenic phytoremediation argued that mercury emissions from the treated sites would be below the current emission levels for elemental mercury, elemental mercury is retained in the atmosphere for up to two years during which time it is diluted to "non toxic" levels before precipitation (4). The proponents also argued that would negligible in comparison to fossil fuel burning and hospital waste incineration (4). Finally, the proponents argued that feeding animals would be exposed to less mercury than from conventional plants because elemental mercury was so rapidly released from the plant tissue (4). The proponents believed that the genes from mercury emission would not be transferred to non-transgenic plants (4). The proponents risk assessment seemed very uncritical and quite unrealistic. Elemental mercury does remain in the atmosphere for up to two years but always precipitates in rain and snow. The arctic acts as a trap to condense the fallen mercury but all of the northern communities including large eastern North America cities suffer growing mercury accumulation from precipitation. It is clear that the precipitated elemental mercury is rapidly converted to ionic and organic mercury once it is deposited. What phytoremediation will do is to relocate soil mercury from contaminated soil sites in southerly communities and redistribute the mercury to the northern communities. There are a large number of sites with mercury contaminated soil and sediment along with the geological areas of high mercury content. For example, the crude gold mining techniques used along the Amazon left elevated soil mercury levels. If that area were to be phytoremediated the mercury released to the atmosphere would likely precipitate in the cities on northern United States and Canada and impact heavily in the Arctic. Emitted mercury condensed in the ocean will reappear on the dinner tables of the world from bioaccumulation through the food chain. Based on the current experience with transgenic crops it is certain that some transgenic pollen and seed will escape. Populating expansive areas of geological mercury pollution with mercury transgenic trees ( which would be selected for) could lead to a global catastrophe. The US EPA seems rather schizophrenic in supporting the research on mercury phytoremediation by air emission while supporting major projects in reducing atmospheric mercury deposition. The United Nations should play a major role in regulating the global atmospheric deposition of mercury and other volatile pollutants. References 1. Rugh,C,Senecff,J,Meagher,R and Merkle,,S "Development of transgenic yellow poplar for mercury phytoremediation" 1998 Nature Biotech 16,925-6 2. Bizily,S,Rugh,C and Meagher,R "Phytoremediation of hazardous organomercurials by genetically engineered plants" 2000 Nature Biotech. 18,213-5 3. Kramer,U and Chardonnens,A "The use of transgenic plants in the bioremediation of soils contaminated with trace elements" 2001 Appl Microbiol Biotechnol. 55,661-72 4. Pilon-Smits,E and Pilon,M "Breeding mercury-breathing plants for environmental cleanup"2000 Trends in Plant Science 5,235-6