Copper Bioavailability to Beans (Phaseolus vulgaris) in Long-Term Cu-Contaminated Soils, Uncontaminated Soils, and Recently Cu-Spiked Soils

Abstract

Copper solubility and its bioavailability to Phaseolus vulgaris in long-term copper-contaminated soils, uncontaminated soils, and copper-spiked soils were studied. The role of plant factors, total copper load in soils, and/or the aging effect on the uptake of copper was explored so as to assess health risks through contamination of the food chain associated with growing the crop on such soils. Contaminated soils and clean soils were collected from coffee-growing fields in Kilimanjaro and Arusha, Tanzania. Two bean seeds were sown per pot, replicated three times, and arranged in a randomized design in a glass house. Copper spiking significantly increased extractable copper, as expected. For all of the treatments except for the Mwanga and Arumeru control soils, the addition of CuSO4 did not significantly increase the humic-acid-bound copper, but it significantly increased the fulvic-acid-bound copper (p = 0.05). Moshi soils had significantly higher concentrations of copper in the bean shoots than was the case with other treatments (p = 0.05). For the respective soil types, there was no significant difference in the concentrations of copper in bean leaves between spiked and unspiked treatments (p = 0.05). Bean shoots did not accumulate copper beyond the normal concentrations.