Biology Question #623

Kim Yonda, a 20 year old female from Winnipeg, Mb asks on February 1, 2002,

I'm doing a project on mercury in water. I was wondering if and how you get mercury out of lakes. Is it possible?

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The answer

Michael Ross answered on April 30, 2002

Sources of mercury potentially affecting water resources in North America include: old mining sites (where mercury rich materials are often present in tailings), untreated industrial mercury waste from industrial processes, dental amalgam detritus, and scientific laboratories. This contamination of our environment has gone on so long and is so prevalent in North America that the average Canadian or American have levels of mercury in the blood stream, which tend to be higher than those of populations of less industrialized countries.

The 'best' approach to cleaning up mercury is to safely treat and collect waste and/or spilled mercury before it is discharged down the drains of countless industrial plants, dental office and scientific laboratories in which mercury or amalgams are used on a daily basis. There is a wide variety of cost-effective decontamination solutions storage and disposal units, and spill control kits available to safely handle, store and clean-up mercury before it is released into the environment. Although the regulation of mercury and the use of mercury safety systems and solutions is growing, there is still a great deal to be done in educating the public and influencing users to incorporate safe mercury handling products and procedures.

Once mercury has gravitated to the bottom of a lake, it is extremely difficult to decontaminate and/or remove. However, it can be done by 'suction' dredging and water filtration with various filter mediums, keeping in mind the following factors, which would require cautious, site-specific solutions:

* THE DEGREE OF BOTTOM TURBULENCE AND/OR DISTURBANCE. Due to its high specific gravity, mercury tends to rest at or near the bottom of other lake sediment. If there is little disturbance to the lake bottom by currents, mechanical agitation, aquatic life and gas formation, an argument can be made that it safer to leave the mercury sediment in a relatively undisturbed state rather than risk stirring it up so that is available again for methylation and distribution in an extended fashion.

* THE RATE OF METHYLATION. Mercury will combine with organic materials, creating methyl mercury compounds, which are significantly more toxic than elemental mercury. In those lake where the level of methylated mercury is high and/or climbing (as evidenced through careful water and sediment test sampling), or where is there is evidence of high levels of biological contamination; the layer of mercury sludge should be carefully removed.

In sum, yes - mercury at the bottom of a lake can be removed by a combination of 'suction' dredging, filtration, treatment and disposal by a qualified remediation services contractor. However, given that almost any type of environmental clean-up tends to be an expensive undertaking, the pivotal question is: Do we reduce and or eliminate more 'available' mercury from our environment by cleaning up lake bottoms (where the sludge may be relatively undisturbed and inactive under layers of sand, mud and other sediment); or do we achieve more by ensuring that mercury and mercury compounds which are used daily in manufacturing processes, the neon industry, mining, dental and scientific laboratories are handled and stored safely?

There is no simple answer to any of this, but my inclination would be to: (a) Take appropriate steps to ensure that mercury safety procedures are implemented as widely as possible such that our industries and offices don't continue to add to the existing load of mercury in our environment, and (b) Extend the strategic monitoring of water resources and biological species in order to identify sites where there is the active generation and release of mercury in its most lethal form, organic mercury, so that 'hot' sources of mercury can be traced, contained and eradicated.

Michael Ross is a principal of EPS CHEMICAL, INC., a U.S. mercury decontamination products company.

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