Dissolution half-times of nickel compounds in water, rat serum, and renal cytosol

Seventeen nickel compounds were incubated in water, rat serum, and rat renal cytosol for 72 hr at 37 degrees C. Concentrations of dissolved nickel were analyzed by electrothermal atomic absorption spectrophotometry, and dissolution half-times (T50) were computed by the Weibull equation. Eleven of the nickel compounds (Ni, beta NiS, amorphous NiS, alpha Ni3S2, NiSe, Ni3Se2, NiTe, NiAs, Ni11As8, Ni5As2, and NiFeS4) dissolved more rapidly in serum or cytosol than in water. Four of the compounds (NiO, NiSb, NiFe alloy, and NiTiO3) had no detectable dissolution in any of the media (i.e., T50 greater than 11 yr). One compound (NiAsS) had approximately equal T50 values in the three media; the T50 value of one compound (NiS2) could not be determined in serum or cytosol owing to precipitation. T50 value of 34 and 21 days for dissolution of alpha Ni3S2 in serum and cytosol, respectively, agree closely with the excretion half-time of 24 days derived from previously reported data for excretion of 63Ni in urine and feces of rats after intramuscular injection of alpha 63Ni3S2. These findings suggest that in vitro dissolution half-times of nickel compounds may be used to predict their in vivo excretion half-times, since the dissolution process is rate-limiting to their metabolism and excretion.