Natural organic matter plays key role in making mercury toxic to living creatures

August 19th, 2009 - 2:00 pm ICT by ANI  

Washington, August 19 (ANI): Scientists have found that naturally occurring organic matter in water and sediment appears to play a key role in helping microbes convert tiny particles of mercury in the environment into a form that is toxic to most living creatures.

According to Duke University environmental engineers, this finding is important because it could change the way mercury in the environment is measured and therefore regulated.

This particularly harmful form of the element, known as methylmercury, is a potent toxin for nerve cells. When ingested by organisms, it is not excreted and builds up in tissues or organs.

In a series of laboratory experiments, Amrika Deonarine, a graduate student in civil and environmental engineering at Duke’s Pratt School of Engineering, found that organic matter and chemical compounds containing sulfur - known as sulfides - can readily bind to form mercury sulfide nanoparticles.

Since they are more soluble than larger particles, these nanoparticles may be the precursors to a process known as methylation.

“When the organic material combines with the mercury, it prevents the particle from accumulating with other mercury particles and growing larger,” said Deonarine.

“Since the mercury remains in a nanoparticle size, it can easily collect on the surface of microbes where any mercury that dissolves can be taken in by the microbes,” she said.

“Without the organic matter, the mercury sulfide nanoparticles would grow too large and become insoluble, thus reducing the availability of mercury for microbial methylation,” she added.

It is while inside the microbe that the mercury is converted into the harmful methylmercury form, according to the researchers.

These reactions can only take place in cold water environments with little to no oxygen, such as the zone of sediment just below the bottom of a body of water.

Other such anaerobic environments can also be found in waste water and sewage treatment systems, the researchers said.

Mercury is extremely toxic and can lead to kidney dysfunctions, neurological disorders and even death. In particular, fetuses exposed to methylmercury can suffer from these same disorders as well as impaired learning abilities.

There are many ways mercury gets into the environment, with the primary sources being the combustion of coal, the refining of such metals as gold and other non-ferrous metals, and in the gases released during volcanic eruptions. (ANI)

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