Generation of Radioactive Mercury Vapor and its Application in an Exposure System

Abstract

Investigation of the toxicokinetics of mercury upon inhalation of the vapor (Hg°) requires an exposure system characterized by rapid development and stability of preselected Hg° concentrations, continuous operation over variable exposure times, easy monitoring of Hg° concentration in air, and ready determination of Hg in organs and carcasses. This can be realized by generating Hg° from the reduction of Hg²⁺ labeled with radioactive ²⁰³Hg²⁺. Since the commonly used reducing agents stannous chloride (SnCl₂) or sodium borohydride (NaBH₄) gave unsatisfactory results, the reducing properties of hypophosporous acid (HPH₂O₂) were tested. Continuous measurement with atomic absorption spectrometry (AAS) showed that rise time of Hg° concentration was below 10 min and that the plateau was stable and higher than with the other reductants. The concentration of Hg° in air was linearly correlated to that of Hg²⁺ in solution. Concentrations of ²⁰³Hg in the wasted solution were below 5% of that of the initial Hg²⁺ solution, i.e., vaporization of Hg was nearly complete. The time to attain 90% of the steady-state Hg° concentration in the exposure chamber can be calculated to be 3.7 min, which is in accordance with 4.6 min actually measured. Body burden and organ distribution of Hg were determined after exposure to 0.5, 1.0, and 2.0 mg Hg°/m³ for 1, 2, and 3 h. Under these conditions Hg uptake was linearly correlated to exposure time or concentration.

Key Words: :

• Mercury vapor
• Inhalation
• Rat
• Hypophosporous acid