Mercury
 

 

One of the main problems of the waters of the Amazon, is the buildup of Mercury.

Mercury is found to be strongly linked to the Gold mining carried out in the ranforest. Mining releases Mercury both into the atmosphere and into the rivers. At times, the rate of production of Gold equals the rate of production of Mercury and it is found that Bioaccumulation occurs, where the animals in the water slowly accumulate Mercury in their systems which is passed to the other animals that eat them, eg. fish, and eventually humans living off the fish in the rivers have above normal levels of Mercury in their blood. Even the miners themselves have been victims to mercurialism or Mercury-poisoning. Mercury in the water must be oxidised before it can be converted by Methylation to Methylmercury. However some bacteria are able to convert this poisonous form of Mercury back into its original state (¹).

At the same time however, as one moves further and further down steam the rivers of the Amazon,  it is expected that the concentrations of pollutants would generally decrease. A study done by Donna Mergler and Marc Lucotte both of the University of Quebec, Montreal, in 1992 found that the levels of Mercury of the waters in the Amazon did not follow this rule.

The study was done on the Tapajos River, a major tributary in the Amazon. Its aim was to map the gradient of the Mercury levels in the river, so logically, believing that the source of Mercury in the rivers was the mining operations, the researchers selected locations 50km and 400km from mining sites. Contrary to the rule stated above, the amount of Mercury in the river was found to be unchanged at 50km and 400km from the mining site. Similarly, the levels of Mercury in the sediment and the land were also observed to defy reasoning.

Mergler and Lucotte reasoned then, that there was another source supplying Mercury to the river. Knowing that  the soils of the Amazon are ancient (close to 1 million years old), they came up with the theory that the Amazon soils had been accumulating Mercury for millenia,  and that deforestation was causing more Mercury to be added to the waters via erosion etc. Mercury is rather stable while in the soils as it is bound to organic matter and other substances there, but on release to the aquatic system, the Mercury becomes methylmercury which is the cause of most of the Mercury poisoning in the Amazon.

Other researchers have said that their research shows that the expected Mercury gradient, is observed when the natives are tested for Mercury, but Mergler and Lucotte counteracted by noting that the diet of the natives has an important part to play in that method of Mercury measurement (²).

If Mergler and Lucotte are correct, it would mean that the gold miners actually play very minute parts in the mercury poisoning of the waters of the Amazon. Mining does add mercury to the soils also however, and it does leave trenches in the soils where mosquitos are able to breed and spread the malaria disease. As rain fills these trenches, the stagnant water in them acts as a harbour for insect vectors. So while the Mission 2006 Team may not have to focus too much of our efforts on the mercurial effect of mining, we still must keep in mind that the dangerous malaria disease is promoted by mining. We would also have another point to use to convince any parties necessary of the dangers of deforestation.

If however, Mergler and Lucotte have incorrect data, our original beliefs about the enormous effects of mining would still stand.
 
 
 

---Source.1: M Veiga and J Meech (University of British Columbia), 'Heuristic Approach to Mercury Poisoning in the Amazon'
 

---Source.2: Randall C. Willis, 'Mercury Rising', Today's Chemist at Work, March, 2001.
 

Ryan F Allard(Class of 2006)
 
 

Send inquiries to: furness@mit.edu