EFFECTS OF TIME AND TEMPERATURE ON THE SORPTION OF CADMIUM, ZINC, COBALT, AND NICKEL BY A SOIL

Several levels of cadmium (Cd), zinc (Zn), nickel (Ni), or cobalt (Co) were added to samples of a soil as solutions of nitrate salts. The sa mples were incubated at about field capacity for up to 30 days at diff ering temperatures and the concentration of the metal ions in the soil solution was estimated at 4 times for each temperature. The effects o f level of addition, time, and temperature on solution concentration w ere well described using a mechanistic model. The model suggests that the metals react with a differing range of soil components and that th e pathways for diffusion into the particles also differ. The change in solution concentration was slowest for Cd and fastest for Co and Ni b ut these were not significantly faster than Zn. These results suggest that the toxic effects of Cd added to soils will not decrease greatly with time whereas the effectiveness of fertilisers (Zn and Co), and po tential fertilisers (Ni), will decrease.