Effect of industrial pollution on soil-to-plant transfer of plutonium in a Boreal forest

Plutonium in a forest ecosystem was studied at different distances from the copper and nickel smelter at Monchegorsk, Kola Peninsula, Russia. Soil and plant samples were collected 7 Žsite A., 16 ŽB., 21 ŽC. and 28 ŽD. km from the smelter and at a reference site situated in Finland, 152 km from Monchegorsk. The deposition of Cu in litter and in the organic layer decreased from 10 700 mg m2 at site A to 33 mg m2 at the reference site, the deposition of Ni from 14 300 to 29 mg m2. From the reference site to site A, the volume of the litter layer increased almost five-fold. Most of the 239,240Pu in soil was found in the organic layer and in the litter layer. When industrial pollution increased, the content of 239,240Pu in the litter layer increased Žfrom approx. 0.5 at site D to 15 Bq m2 at site A. whereas, that in the organic layer decreased Žfrom approx. 20 at site D to 5 Bq m2 at site A.. Four different plant species typical for the subarctic environment were collected at each sampling site: Deschampsia flexuosa Žforest hair grass.; Empetrum nigrum Žcrowberry.; Vaccinium myrtillus Žblueberry.; and Vaccinium itis idaea Žlingonberry.. The concentration of 239,240Pu increased with pollution in Deschampsia flexuosa Žfrom approx. 2 at site D to 7 mBq kg at site A., Empetrum nigrum Žfrom approx. 3 at site D to 14 mBq kg at site A. and Vaccinium myrtillus Žfrom approx. 1 at site D to 8 mBq kg at site A.. In Vaccinium itis idaea, the Pu concentration did not have any clear trend of association with pollution. With the exception of Vaccinium itis idaea, the aggregated transfer factors of plutonium Žm2 kg. for the plants studied increased almost ten-fold from site D to site A, the range being 3 10 5 3 10 4 m2 kg for Deschampsia flexuosa, 7 10 5 5 10 4 m2 kg for Empetrum nigrum and 3 10 5 3 10 4 m2 kg for Vaccinium myrtillus. The most likely explanation for the higher transfer factors of plutonium near the smelter is contamination of the plants by litter rather than root uptake