Toxicokinetics of nickel in rats after intratracheal administration of a soluble and insoluble form

Abstract

Ninety day laboratory studies were performed to determine the whole body distribution of two chemical forms of nickel in female Wistar rats. A single injection of 15 µCi of ⁶³Ni, either NiCl₂ as a solution or NiO as a suspension, 100 nmoles in each case, was administered intratracheally. Rats were sacrificed at post-exposure intervals of 0.5, 2, and 8 hours, 1, 3, 7, 15, 30, 60 and 90 days, and major organs and tissues were analyzed for ⁶³Ni by liquid scintillation counting technique. The soluble NiCl₂ was readily distributed throughout the body, and rapidly cleared from the tissues. The insoluble NiO was distributed slowly to other organs from pulmonary tissues. The rate of decline of ⁶³Ni from various organs in the case of NiO was similar to that of NiCl₂, with notable exceptions being the lung and associated lymph nodes. After NiO administration, these organs showed a high retention of nickel after 90 days. Results indicated that Ni in soluble form was rapidly absorbed from the site of deposition following pulmonary exposure, whereas, Ni in its oxide or insoluble form was retained in lungs and related lymphatics for a considerable period. The amount of Ni in other organs following NiO exposure, though initially low in all tissues, declined in a fashion similar to organs following NiCl₂ exposure. This suggests that NiO was possibly converted to a soluble form of Ni before it was translocated from lungs to other organs, and that low environmental levels of insoluble forms of nickel, which persist in the lung and lymph nodes, do have the potential for assimilation in these tissues.