Abstract
The solubility of two types of commercial nickel oxide particles in five kinds of solvents and in the mouse respiratory tract were examined to estimate the feasibility of an in vitro chemical dissolution test as an alternative method to predict the actual solubility of particulate matter in the human respiratory tract . Green nickel oxide particles, which were well crystallized and contained less oxygen by weight, were completely insolulbe when incubated for 7 days at 37°C under 5% CO2 and 95% air in distilled water, physiological saline, Hank's balanced salt solution, and Eagle's mini mum essential medium with or without fetal calf serum . On the other hand, black nickel oxide particles, which contained more oxygen by weight, dissolved in all the five solvents under the above conditions, and their solubilities were 25-40%, depending on the solvent. The solubility of these particles in the C3H mouse respiratory tract following intratracheal injection, estimated from nickel kinetic parameters such as lung retention and redistribution to other organs, was 22.3-55.6 and 64.6-76.9% for the green and black nickel oxide particles, respectively. The difference in solubility between the green and black nickel particles, and the difference in solubility observed between the in vitro dissolution test and the mouse respiratory tract are discussed with respect to the physico-chemical characteristics of the particles.
