Epsilon Archive for Student Projects

Abstract

High mercury concentrations in freshwater fish compose a serious environmental problem in
Sweden and a threat to human health. Mercury is accumulated in the food chain as
methylmercury which is a potential nervous toxin, especially harmful for prenatal life. Due to
anthropogenic emissions, mercury concentration in the atmosphere has increased, which has led
to faster deposition rates and a storage of mercury in forest soils. Inorganic mercury is
transformed into methylmercury by sulphur reducing bacteria in anoxic environments like
wetlands and lake sediment and enters aquatic systems by runoff. Lately studies have shown
that catchments subject to forestry practices have had an increased methylmercury load in
runoff compared to undisturbed catchments. In Balsjö, northern Sweden a project is started to
study the impacts of forestry on mercury levels in three forested catchments. This study is part
of the baseline assessment as a characterisation of the study area with respect to mercury
occurrence. Methyl- and total mercury concentrations in soil pore water have been measured
using isotope dilution, gas chromatography-inductively coupled plasma mass spectrometry. The
results have been compared with results from other studies in Sweden and show very low
concentrations in the Balsjö area which may be due to the way the sampling was carried out.
There were no significant differences in pre-treatment conditions between the catchments.
Methylmercury concentrations are not controlled by total mercury but rather by the potential for
methylation within the catchment. The lack of relationship between methylmercury
concentrations seen in soil and water shows that it is not a simple equilibrium but indicates that
other factors are involved where the binding to organic material could be one.