Biological monitoring by breath and urine analyses

A mathematical model developed previously has been used to study some aspects of biological monitoring of exposure to trichloroethylene (TRI) by the analysis of this solvent in alveolar air or of its metabolites, trichloroethanol (TCE) and trichloroacetic acid (TCA), in urine. Assuming that a biological control must be representative of the time-weighted average concentration (TWA), it was found that sampling for TRI and TCE analyses must be carried out the morning after the exposure being considered. On the other hand, for a TCA analysis, the timing of urine sampling is not a determinant factor. Theoretical limit concentrations have been set up for these biological indicators, but it is shown that their application must be restricted to exposures which are quantitatively reproducible from one day to the next. In all other cases, it appears that this monitoring method can lead to errors in the estimated exposure concentrations. A tentative method of biological monitoring is therefore proposed. It is based on the analysis of TCE in the urine or TRI in the alveolar air before and after the exposure being monitored. TCA is not considered to be sensitive enough to variations in the inspired concentration to be used as an indicator of a single exposure risk. Although numerous studies have been devoted to the biological monitoring of exposure to trichloroethylene (TRI), this remains a very controversial subject. Several authors have proposed the analysis of the urinary excretion of trichloroacetic acid (TCA) (Frant and Westendorp, 1950; Ahlmark and Forssman, 1951; Elkins, 1954; Grandjean et al., 1955), while others have recommended that of trichloroethanol (TCE) (Lowry et al., 1974), or the sum of these two metabolites (TTC) (Nomiyama, 1971; Ogata et al., 1971; Ikeda et al., 1972). Recently, the analysis of these two compounds in the blood (Muller et al., 1974; Vesterberg et al., 1975) and also that of the pulmonary elimination of TRI (Pfaffli and Backman, 1972; Stewart et al., 1974) were considered. Moreover, the biological limit values proposed for these different indicators (corresponding to an exposure at the TLV) vary considerably from author to author, and the timing of urine, blood or alveolar air sampling is still very arbitrary. We recently developed a mathematical model (Fernandez et al., 1977) which enables the absorp*Requests for reprints to Professor Fernindez. Received for publication 28 April 1977 Accepted for publication 25 July 1977 tion, distribution and excretion of TRI, and the kinetics of the formation and elimination of TCE and TCA to be satisfactorily described. This model is used here to study some aspects of the biological monitoring of exposure to TRI, as it enables occupational exposure to be simulated by repeating the absorption of TRI and varying the inhaled concentrations. U-nder such conditions, the influence of the different exposure factors on the relationship between degree of exposure and excretion of the biological indicators can be studied in the absence of distorting factors such as interand intraindividual differences, or analytical accuracy and sensitivity. This mathematical approach to exposure to TRI enables one to estimate the theoretical biological limit values corresponding to a repeated exposure at 100 ppm (TLV), for the urinary excretion of TCE and TCA and for the pulmonary elimination ofTRI. The possibility of applying these limits to the control of occupational exposure is then studied by varying the inhaled concentration of TRI during an exposure (hourly variations) and from one exposure to another (daily variations). Finally, on the basis of the results obtained, a tentative optimal method of biological monitoring is proposed. 35 group.bmj.com on April 12, 2017 Published by http://oem.bmj.com/ Downloaded from