Potassium biological variability

The extractable nickel content of soil affects the uptake of nickel by plant roots. Extracta-bility of nickel from soil is influenced by physical factors (e.g., texture, temperature, and water content), chemical factors (e.g., pH, organic constituents, redox potential), and biological factors (e.g., plant species variability, microbial activity) (NAS 1975, Wallace et al. 1977, Heale and Ormond 1982, Hazlett et al. 1983). Extractable nickel concentrations in soils, measured by treating soil samples with solutions of potassium chloride, ammonium acetate, acetic acid, or EDTA, usually range from <0.01 to... 

Rubidium is eliminated only very slowly from the body with Rb studies showing urinary and fecal excretion to be 68% and 32%, respectively [43]. The daily excretion of rubidium is variable [44] and is dependent on the dietary intake of both rubidium and potassium. However, the urinary Rb/K ratio remains fairly constant [43,44]. This consistent ratio is further evidence of the metabolic relationship between rubidium and potassium. Overall when rubidium is administered orally as RbCl, its biological half-life ranges from 30 to 60 days [45-48]. 

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