Chromium and Nickel

Nickel (Ni) and chromium (Cr) are elements naturally present in all rock 4 types and present in the pedosphere in a range from trace amounts to relatively high 5 concentrations, as compared to other trace elements. Particularly high Ni and Cr 6 concentrations are found in serpentine rocks and soils, originating from this rock 7 type and colonized by a specialized flora that may present some curious species 8 able of hyperaccumulating extraordinary high concentrations of Ni in their above- 9 ground parts. In recent decades, the large release of Cr and Ni by industrial activities, 10 mainly the manufacture of stainless steel, as well as the use of sewage sludge as soil 11 amendment in agricultural soils, have caused an impressive increase in the levels 12 of these two metals in the pedosphere and other environmental matrices. This has led 13 to increasing environmental concern as, while relatively low concentrations of 14 Ni and Cr are essential for plants and other living organisms including humans, 15 both the elements are toxic for all living organisms if present in excessive 16 concentrations. This chapter reviews the distribution and the geochemical behaviour 17 of Ni and Cr, their main dynamics in the soil environment, with regards to the natural 18 and anthropogenic sources. The relationships of Ni and Cr with the plants, in 19 particular with some Ni hyperaccumulator species are also discussed.