The legacy of the mill : a metal polluted forest soil in Gusum

Abstract: Soils in a metal contaminated site on Stångberget in Gusum in southeastSweden were investigated and compared to relatively unaffected soils a fewkilometres away. Pollution came from historical release of untreated flue gasesfrom a brass mill. The objective was to find information on how high the metalconcentrations are, if metals from the polluted soil affect the surroundings andif the metal contamination affects the microbial community. The soil wasinvestigated using several different methods, such as field XRF measurements,chemical analysis of metal, carbon and nitrogen content, pH, acid neutralizingcapacity, texture, soil depth, field leach tests, sequential extraction and microbialfunctional profiles. The study showed that copper and zinc concentrationswere above Swedish Environmental Protection Agency guidelines for lesssensitive land use on the entire investigated area. Copper showed the highestconcentrations in relation to guideline values, 50 times the guideline in theworst affected sample point, followed by zinc, lead and cadmium, in thatorder. A pH raising effect caused by the release of metal oxides, that hadpreviously been shown could not be seen and pH on Stångberget was nowsimilar to that of a natural Swedish forest soil. Results could not show that thepH drop had caused increased leachability, instead the leachability was lowerthan in previous studies. Leaching from Stångberget did not seem to affectmetal concentrations in the soil nor be a major source of metals to surroundingsoils and waters. Microorganisms from the visibly affected part of Stångbergethad an increased specific respiration compared to the reference but the differencebetween the forested part of Stångberget and the reference area was notas clear even though metal concentrations were severely elevated also in theforested part. The effect on microorganisms could to a large extent be explainedby the metal contamination. The size of the bare part of Stångbergethad increased over the last 50 years and there was no sign of a decrease.