Explaining Mercury Levels in Pristine and Gold Mining Impacted Aquatic Ecosystems of Suriname (South America)

摘要

Since 1985 a new gold rush has hit the eastern part of Suriname. Small-scale gold miners use mercury to amalgamate the gold. An estimated 40,000-200,000 kg of mercury is released into the environment annually. Measurements of total mercury in water, bottom sediment and fish in 53 localities spread all over Suriname showed high pollution levels in gold mining areas, but also in pristine Central and Western Suriname. The average mercury level in bottom sediment surpassed the Canadian standard for sediment in most localities, except the coastal plains. Of the predatory fish, 41 % had a mercury level above the European Union standard for human consumption. Core samples in floodplains showed a higher mercury level in the layers near the surface, indicating a recent anthropogenic source. High mercury levels in pristine areas can be explained by mercury being emitted and evaporated to the atmosphere in the mining areas, transported to the south-west by the prevailing north-eastern trade winds, and partly deposited in Central and Western Suriname, especially in areas with high precipitation. We hypothesize that a second mechanism is likely to impact the biological availability of mercury in the aquatic environment: mercury is easily bound to small sediment particles. Streams in mining areas are usually very turbid as a result of the mining activities. Part of the mercury released in these streams will bind to the suspended sediment. These sediment-mercury particles are too large to pass through biological membranes and are therefore less biologically available. This mechanism does not apply to pristine streams where turbidity is usually at a lower level. This could explain the significantly higher mercury levels in predatory fish in pristine streams compared to streams in gold mining areas. Mercury pollution in Suriname is causing elevated levels in the human population, with the highest values measured thus far being registered in a village far upstream of any gold mining.