Soils with high Ni contents occur in several parts of the world, especially in areas with ultramafic rocks which cause serious environmental impacts. This book aims to extend the knowledge on the risks and problems caused by elevated Ni contents and to cover the existing gaps on issues related to various aspects and consequences of high Ni contents in soils and plants. Nickel in Soils and Plants brings together discussions on Ni as a trace element and as a micronutrient essential for plant growth and its role in plant physiology. It analyzes the biogeochemistry of Ni at the soil plant interface, and explains its behavior in the rhizosphere resulting in Ni deficiency or toxicity, or Ni tolerance of various Ni hyperaccumulators. Included are Ni resources and sources, the origin of soil Ni, its geochemical forms in soils and their availability to plants, a special reference on soils enriched with geogenic Ni, such as serpentine soils, and the special characteristics of those ecosystems. Recent advancements in methods of Ni speciation, including the macroscale and X- ray absorption spectroscopy studies as well as serious views on Ni kinetics, are also covered. Written by a team of internationally recognized researchers and expert contributors, this comprehensive work addresses the practical aspects of managing Ni in soils and plants for agricultural production, and managing soils with high Ni levels by using organic and inorganic amendments. The text also addresses practical measures related to Ni toxicity in plants, the removal and recovery of Ni from high Ni wastes, and offers environmentally friendly innovative processes for mining Ni from soils containing high Ni levels.

Abstract: Nickel (Ni) is a required element but may become toxic to plants, animals and humans if normal levels are exceeded. At very high levels of exposure, Ni salts are known to be carcinogenic. To assess the health and environmental effects of Ni, the bioavailable, not total, concentration of Ni in soil must be accurately measured. Urease has an absolute requirement for Ni to function, and this was used to develop a method to assess Ni bioavailability in soil. Bacteria with Ni-deficient urease were enriched from Spinks sandy soil by growing the cells in Luria Broth (LB) medium. This created a culture with high amount of potential urease activity but with low actual activity because of Ni limitations. Culture cells were equilibrated with different concentrations of Ni salt for four hours and the urease response to the added Ni was measured using steam distillation. When Ni concentration increased from 0 to 1.0 mM, urease activity also increased, proving that urease activity was positively correlated to bioavailability of Ni. To test bioavailability of Ni, not from added Ni salts but in soil, the bacterial culture was inoculated into a test soil that was composed of acid-washed Spinks sandy soil as a carrier soil and the soil with unknown Ni bioavailability. Nickel bioavailability was then measured using the urease bioassay optimized for conditions in terms of amount of culture, urea concentration, incubation time and THAM buffer pH. The following equation could be used to calculate Ni bioavailability from urease activity response when Ni bioavailability is in the range from 0 to 0.06 mM: Ni Bioavailability = Urease Activity/k/f where Ni Bioavailability has a unit of mM, Urease Activity has a unit of ug 30 mL−1 culture 2 h−1, k is equal to 15646 ug 30 mL1−1 culture 2 h−1 mM−1 , and f is the percentage of unknown soil in the test soil. The urease bioassay was able to detect as little as 1.99 mg kg−1 of bioavailable Ni in soil or 0.282 uM of bioavailable Ni in culture. The coefficient of variation for the urease bioassay was approximately 10%, indicating good precision. A significant correlation (r=0.9957**) was observed between Ni bioavailability measured using urease bioassay and Mehlich III extractable Ni. This indicates the bioassay method provided a relatively good indication of the bioavailable Ni content in the soil samples compared to chemical extraction. The urease bioassay was applied to measure the Ni bioavailability in soils with different properties and to evaluate the effects of soil pH and soil organic matter content on Ni bioavailability. Twenty soil samples that varied in soil pH and total C content were studied. The Ni bioavailability measured by urease bioassay in these twenty soils ranged from 19.9 to 68.3 mg kg−1 . Significant correlations were observed between bioavailable Ni measured by urease bioassay, Ca(N03)2 extractable Ni and Mehlich III extractable Ni. Nickel bioavailability decreased with the increase in total C content. When 1000 mg kg−1 Ni was added to soils with total C content ranging from 0.009% to 12.7%, Ni bioavailability decreased about 50%. Nickel bioavailability also decreased with increase in soil pH, and a change in soil pH from 4.15 to 9.94 decreased Ni bioavailability by 70%. Urease bioassay is recommended over chemical extraction methods to measure Ni bioavailability in soil because it is accurate, simple, sensitive, and directly measures biological response. Urease bioassay can be applied to soils with different properties, and can be used in most laboratories.

Future development in the Arctic and Subarctic region requires careful attention to the possible consequences of the development activities themselves, in relation to their environmental, socioeconomic and cultural impacts. A more thorough understanding of the impact of future activities, however, demands the dissemination and confrontation of results from different regions and different scientific traditions. This requires scientific cooperation, not only across disciplines but across border. Primarily it requires both consensus and innovations in regard to methods. This book confronts such differences in approaches and methods in relation to the analysis of socioeconomic and environmental consequences of large-scale mineral and energy development activities in the Arctic and Subarctic, establishing the common ground upon which future research activities can be based.