Peat and needle samples were collected from an old Cu, Zn and Ni ore-prospecting experiment at Alkkia, SW Finland. The element rates applied were 100–400 kg ha−1 for Ni and 100–1000 kg ha−1 for Cu and Zn. The heavy metal toxicity of Scots pine stand was estimated primarily on the basis of stand mortality during 28 yr. The tolerance limit values were applied to pine stands growing along a Cu-Ni deposition gradient (0.9–10 km) at Harjavalta copper smelter, SW Finland. Very high heavy metal concentrations in the pine needles and strong accumulation in the surface humus and uppermost peat layers were found. A Cu concentration of 840, Ni 180 and Zn 220 mg kg−1 in peat 0–10 cm, and a Cu concentration of 50, Ni 30 and Zn 175 mg kg−1 in the current needles of the uppermost whorl are proposed as toxicity limits for peatland forests at Harjavalta. According to the heavy metal amounts in peat 0–20 cm, the toxicity area for Cu extended to a distance of 2.0 km, for Ni about 1.0 km and for Zn 0.4 km to the west of the emission point source.