Uptake of Uranium, Thorium and Arsenic from Refinery Residue by Pinus Sylvestris L. and the Effect on Growth

Abstract

A preliminary experiment was carried out to determine the growth rate and survival of Pinus sylvestris L, (Scots pine) seedlings grown on Welcome Residue Area soil from Port Hope, Ontario, containing uranium, thorium and arsenic. This soil is silt loam in texture, and contains approximately 26 μg U/g, 5 μg Th/g, and 780 μg As/g. The control soil was Woodridge fine sand containing < 0.8 μg U/g, 3 μg Th/g and < 2 μg As/g. The control seedlings developed fascicle needles earlier than the treatment seedlings and the mean fascicle growth rate was 142 greater in the controls.

Chemical analyses indicated an acropetal (tip-ward) gradient of uranium, thorium and arsenic in the seedlings. The mean concentrations of uranium found in the roots, shoots and fascicle needles were 346, 9 and 4 μg/g dry plant, respectively, approximately 340, 4 and 2 times the quantities found in the control plants. The mean concentrations of thorium found in these plant parts were 4, 1.1 and 0.8 μg/g dry plant, respectively, approximately 10, 0.5 and 1 times the quantities found in the controls. The mean concentrations of arsenic found in the plant parts were 232, 68 and 47 μg/g dry plant respectively, > 23, 340 and > 2300 times the quantities found in the controls. There was, on the average, more uranium, thorium and arsenic found in the tissues of the dead seedlings than in those of the live seedlings.

Since the concentrations of both uranium and arsenic appear to be in the phytotoxic range and morphological differences found were due to chemical toxicity of these elements rather than radiation injury.