Long-term effects of sewage sludge application on the heavy metal concentrations in acid pine (Pinus sylvestris L.) forests in a climatic gradient in Sweden

The paper clarifies the effects of sewage sludge application on the heavy metal concentrations in soil and plant fractions of acid pine forests (Pinus sylvestris L.) on sandy soils in a south to north temperature gradient in Sweden. 20 t dw ha−1 of sewage sludge was applied in 50–60 year old pine forests from Brösarp in South Sweden to Jukkasjärvi in the northern parts of the country.Sewage sludge fertilization only to a minor degree effected the concentrations of heavy metals in the soil. However, in some of the research areas there was a limited increase of Cr, Cu, Ni, Zn both in the humus and in the upper mineral layers. The concentrations of most heavy metals in current pine needles were unaffected by application of 20 t ha−1 of sewage sludge. A limited uptake of Cu and Ni was found in current shoots of Vaccinium vitis-idaea L.

► Application of sewage sludge causes limited long-term accumulation in the mor layer of Cr, Cu, and in N. Sweden of Pb and Zn.
► The concentrations of most heavy metals in current pine needles are unaffected by application of 20 t ha−1 of sewage sludge.
► A limited uptake is found in current shoots of Vaccinium vitis-idaea, especially of Cu and Ni.
► Sewage sludge in the amount of 20 t dw ha−1 give limited effects on the accumulation of heavy metals in pine forests.