Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/5/2004
Publication Date: 11/10/2004
Citation: Kukier, U., Peters, C.A., Chaney, R.L., Angle, J.S., Roseberg, R.J. 2004. The effect of ph on metal accumulation in two alyssum species. Journal of Environmental Quality. 32(6):2090-2102. Interpretive Summary: Growing Ni hyperaccumulator plants has been shown to be a cost effective method to remove Ni from contaminated soils and to phytomine Ni from mineralized serpentine soils. A earlier paper reported that although acidifying soils increased the solubility of Ni in the soil solution, it reduced Ni uptake by hyperaccumulator plants, opposite the response found with many crop plants. Thus a new study was conducted to further characterize the effect of increasing soil pH on Ni accumulation and growth of two Alyssum species which can hyperaccumulate Ni very effectively. Soil extractions confirmed that raising pH reduced the solubility of Ni in each case. However, when Alyssum was grown on the pH-adjusted soils, shoot Ni concentration increased on two soils collected near a Ni refinery in Port Colborne, Ontario, Canada, reaching maximum levels at pH 7.5; but in the case of the serpentine soil, shoot Ni declined with increasing pH. We attribute this different response to the effect of pH on binding of Ni to organic matter Ni-binding sites and hydrous iron oxide Ni-binding sites in the soils. In the serpentine soil which contained 22% Fe, Ni adsorption greatly increased as pH rose above about 6.5, while with the organic matter rich muck soil from Canada, increased pH may increase the solubility of Ni bound to organic matter which would not necessarily reduce plant availability. Besides Ni, the other microelements (Zn, Cu, Co) were tested in soils and plants. The Alyssum had increased Ni with increasing pH on the Canadian soils, but increasing pH decreased both solubility and plant uptake of Zn, Cu and Co. Results are considered in terms of both phytoremediation (reduction in soil Ni burden), and phytomining (production of biomass high in Ni). The results provide more evidence of effective management practices for management of Ni hyperaccumulator plants on soils with varied chemical properties.
Technical Abstract: Nickel phytoextraction using hyperaccumulator plants offers a potential for profit while decontaminating soils, or while cropping mineralized soils which contain insufficient metal concentrations to support metal smelting using traditional technologies. Although soil pH is considered a key factor regulating metal uptake by crops, little is known about the soil pH effect on metal uptake by hyperaccumulator plants. Two Ni- and Co-hyperaccumulators, Alyssum murale and Alyssum corsicum, were grown in Quarry muck (Terric Haplohemist) and Welland (Typic Epiaquoll) soils contaminated by a Ni-refinery in Port Colborne, Ontario, Canada, and in the serpentine Brockman soil (Typic Xerochrepts) from, Oregon, USA. Soils were acidified and limed to cover pH from strongly acidic to mildly alkaline. Alyssum grown in both industrially contaminated soils exhibited increased Ni concentration in shoots as soil pH increased. An opposite trend, a decrease in shoot Ni concentration as soil pH increased, was observed in the serpentine soil. The highest fraction of total soil Ni was phytoextracted from Quarry muck (6.3%), followed by Welland (4.7%), and Brockman (0.84%). Maximum of Ni-phytoextraction was achieved at pH 7.3, 7.7, and 6.4 in the Quarry, Welland and Brockman soils, respectively. Cobalt concentrations in shoots increased with soil pH increase in the Quarry muck, but decreased in the Welland soil. Plants extracted 1.71, 0.83, and 0.05% of the total soil Co from Welland, Quarry and Brockman, respectively. The differences in uptake pattern of Ni and Co by Alyssum from different soils and pH were probably related to the differences in organic matter and iron contents of the soils.