BREATH, URINE, AND BLOOD MEASUREMENTS AS BIOLOGICAL EXPOSURE INDEXES OF SHORT-TERM INHALATION EXPOSURE TO METHANOL

Due to their transient nature, short-term exposures can be difficult t o detect and quantify using conventional monitoring techniques. Biolog ical monitoring may be capable of registering such exposures and may a lso be used to estimate important toxicological parameters. This paper investigates relationships between methanol concentrations in the blo od, urine, and breath of volunteers exposed to methanol vapor at 800 p pm for periods of 0.5, 1, 2, and 8 h. The results indicate factors tha t must be considered for interpretation of the results of biological m onitoring. For methanol, concentrations are not proportional to the ex posure duration due to metabolic and other elimination processes that occur concurrently with the exposure. First-order clearance models can be used with blood, breath, or urine concentrations to estimate expos ures if the time that has elapsed since the exposure and the model par ameters are known. The 0.5 to 2-h periods of exposure were used to est imate the half-life of methanol. Blood data gave a half-life of 1.44 /- 0.33 h. Comparable but slightly more variable results were obtained using urine data corrected for voiding time (1.55 +/- 0.67h) and brea th data corrected for mucous membrane desorption (1.40 +/- 0.38 h). Me thanol concentrations in blood lagged some 15-30 min behind the termin ation of exposure, and concentrations in urine were further delayed. A lthough breath sampling may be convenient, breath concentrations refle ct end-expired or alveolar air only if subjects are in a methanol-free environment for 30 min or more after the exposure. At earlier times, breath concentrations included contributions from airway desorption or diffusion processes. As based on multicompartmental models, the desor ption processes have half-lives ranging between 0.6 and 5 min. Prelimi nary estimates of the mucous membrane reservoir indicate contributions of under 10% for a 0.5-h exposure and smaller effects for longer peri ods of exposure.