Ectomycorrhizal heavy metal accumulation as a contributing factor to heavy metal levels in organic surface soils

Samples from the top organic layer of coniferous forest soils were collected at several locations in Southern Norway, a region with high surface soil levels of Pb, Cd and Zn. Soil samples and samples of different morphological types of ectomycorrhiza were analyzed with respect to Zn, Pb, Cu and Cd. Despite low levels in surface soils in the area, Cu showed a remarkable degree of concentration in mycorrhizas, reaching values of ∼800 ppm. The mean Cu concentration in mycorrhiza was 337 ± 140 μg/g mycorrhiza. A very low degree of Pb accumulation was found in mycorrhizas (arithmetic mean = 35 ± 6 μg/g mycorrhiza), indicating that Pb is almost excluded by the mycorrhizas. Mean Zn and Cd concentrations in mycorrhizas were 456 ± 201 and 4.6 ± 1.9 μg/g mycorrhiza, respectively. A comparison of the organic topsoil and the fungal heavy metal contents revealed that all Cu in the organic surface soil layer may be accumulated in ectomycorrhizas. Heavy metal accumulation in the fungal biomass may further account for ∼38%, 33% and 2% of the soil levels of Zn, Cd and Pb, respectively.