Summary
Elevated mercury (Hg) levels were found in the upper Nickerie and upper Coppename river, two pristine rivers
located in central and western Suriname, by Ouboter et al. (2012). Due to lacking upstream disturbance, Ouboter et
al. (2012) hypothesize that these high levels of mercury originate from anthropogenic mercury emissions. They
suggest that mercury emitted by the gold-mining industry in the east is transported to central and western
Suriname by the north-eastern (NE) trade winds. However, a view scholars argue that the effect of natural
geological Hg sources in the Amazon are underestimated and that geological variations may override regional
deposition effects (e.g. Lechler et al. 2000). This study aimed to assess the origin of elevated mercury levels in
pristine central and western of Suriname, by analyzing downstream pristine soils and sediments and comparing
these with downstream gold-mining impacted soils and sediments.
Mercury concentrations at three rivers have been investigated: the lower Nickerie river and lower Coppename
river, which are both considered to be pristine rivers, and the lower Saramacca river, which has upstream goldmining activities. To assess the potential origin of Hg in these areas, the spatial distribution of Hg throughout the
river system and the vertical distribution of Hg in each soil was analyzed. To gain insight into the spatial
distribution, soils and sediments were sampled along a transact downstream the river. Furthermore a distinction
was made between floodplain soils and less frequently flooded soils, to test the importance of fluvial transport on Hg
deposits in each area. The vertical distribution of Hg was studied by taking a look at Hg concentrations in relation
to soil depth. Soil samples were taken each 10 cm, down to 50 cm beneath the surface, taking into account soil
horizons. To explain the vertical distribution by Hg adsorption and retention of the soil, the following soil
characteristics were also analyzed: pH, EC, texture, amorphous Al, Fe and Mn oxides (Alox, Feox and Mnox),
crystalline Fe oxides (Fedi), total sulfur concentrations (Stot) and total organic carbon content (TOC).
Results for the Hg analysis revealed that the Nickerie river is not contaminated, demonstrating low levels of Hg that
match both global and Amazon background levels. The Saramacca river, which is directly impacted by the gold
mining industry, displayed significantly higher levels in sediments than in soils. Mercury concentrations in
sediments were above background Amazon levels, while Hg concentrations in soils matched background levels.
This could partially be explained by low retention of Hg in soils, due to high salinity levels which may lead to the
leaching of Hg. Highest concentrations were found at the Coppename river, at which soils were found that
contained more than 330 ng/g Hg, which was set as a reference norm to identify mining contaminated soils by
Santos-Francés et al. (2011).
Spatial and vertical distribution patterns of Hg concentrations indicated that the origin of Hg is mainly
anthropogenic. Surface horizons had a significantly higher burden of Hg than subhorizons in soils. This could
partially be explained by the positive correlation between Hg and TOC that was found in this study. Furthermore
most soils demonstrated decreasing Hg concentrations with soil depth, emphasizing the importance of surface
deposition on the Hg burden in those soils. At the Nickerie river, fluvial transport was not found to be dominant,
suggesting that atmospheric deposition is the most important driver of Hg input in the area. Spatial trends of Hg
concentrations at the Saramacca and Coppename river, suggest that Hg is mainly originates from contaminated
sediments that have been transported by the river. Given the lack of upstream disturbance at the Coppename river,
it is not precisely clear where Hg in these contaminated sediments originates from. It is difficult to directly link
elevated Hg levels to the gold-mining industry in the east, as hypothesized by Ouboter et al. (2012), because
erosion processes and forest fires may also enhance the release of Hg in the regional cycle. Further research into
the Hg burden of forest soils and the atmospheric budget of Hg is necessary to gain more insight into the
relationship between the gold-mining activities in the east and elevated levels of Hg in pristine western and central
Suriname.
Despite the origin of elevated Hg levels in Suriname, its detrimental effects are becoming increasingly clear. High
Hg concentrations have been found in women and children of tribal communities, that largely rely on fish for their
diets (Mohan et al. 2005). It is therefore important to raise awareness on Hg in Suriname and to control its use by
the gold-mining industry.
Keywords: Mercury, Distribution, Artisanal gold mining, River, Suriname, Soil, Sediment, Contamination