Essentiality of nickel and homeostatic mechanisms for its regulation in terrestrial organisms.

Nickel (Ni) is a naturally occurring element with many industrial uses, including in stainless steel, electroplating, pigments, and ceramics. Consequently, Ni may enter the environment from anthropogenic sources, resulting in locally elevated concentrations in soils. However, Ni is a minor essential element, and, therefore, biota have established systems that maintain Ni homeostasis. This paper discusses the role of Ni as an essential element and reviews storage, uptake, and transport systems used to maintain homeostasis within terrestrial biota. The bioaccumulation and distribution of metals in these organisms are also addressed. In all cases, information on Ni essentiality is very limited compared to other essential metals. However, the available data indicate that Ni behaves in a similar manner to other metals. Therefore, inferences specific to Ni may be made from an understanding of metal homeostasis in general. Nevertheless, it is evident that tissue and organ Ni concentrations and requirements vary considerably within and between species, and metal accumulation in various tissues within a single organism differs as well. High rates of Ni deposition around smelters indicate that Ni in acidic soils may reach concentrations that are toxic to plants and soil decomposers. However, with the exception of hyperaccumulator plants, Ni does not biomagnify in the terrestrial food web, suggesting that toxicity to higher trophic levels is unlikely. [ABSTRACT FROM AUTHOR]