Monitoring of mercury and other metals mobility by sequential fractionation in soils nearby an abandoned chlor-alkali plant in Managua (Nicaragua)

Lake Xolotlan (Nicaragua) is an important industrial area including heavy industries such as a fuel refinery and numerous industries that discharge their effluents to the lake. Mercury distribution was studied in soil samples from six different sites close to an old chloralkali plant (CAP) which has historically released mercury wastes to the lake and its surroundings. A Hg-specific sequential extraction procedure was used to assess Hg partitioning. Hg content was subdivided in operationally defined fractions named as labile mercury species, humic and fulvic complexes, elemental Hg and bound to crystalline oxides and bound to sulphide Hg and refractory species. The total mercury concentrations ranged between 1 and 123 mg kg(-1). Sequential extractions revealed that both humic and fulvic complexes and elemental Hg constituted the major forms of mercury in the most samples. Both fractions are related with the accumulation of mercury from both atmospheric deposition and sewage outflow. Moreover, accumulation of the elemental Hg in these soils decreased with the increasing distance from the CAP. In addition, the study of the distribution of other elements revealed a remarkable availability of Al, Ba, Ca, Fe, Pb, Sr, V and Zn that are commonly related to petroleum treatment and combustion. This suggests that these soils are also affected by the releasing of other pollutants from a nearby refinery.