Biological monitoring of carbon disulphide: kinetics of urinary 2-thiothiazolidine-4-carboxylic acid (TTCA) in exposed workers

Abstract

The objectives of this study was to establish the kinetics of urinary 2-thiothiazolidine-4-carboxylic acid (UTTCA) for workers exposed to carbon disulphide (CS2) and to investigate the effects of volume and creatinine adjustment methods for urine measurement. Ten workers in the spinning department of a rayon factory were individually monitored for airborne CS2 concentrations, with consecutive urine samples collected for 24-38 hours after termination of exposure. The U-TTCA, urine volume and creatinine level were measured for each sample. First-order and biphasic kinetics were determined using the curve-fit method, for the measurement series. For the first-order kinetics linearity fit, statistically significant correlation coefficients of 0.74-0.98 and 0.86-0.99 were derived for the volume- and creatinine-adjusted methods, respectively. For the biphasic kinetics approach, the overall correlation coefficients were 0.544-0.999 and 0.171-0.999 for the first and second phases of the creatinine-adjusted method, respectively. A post-shift U-TTCA of 3.0 mg/g Cr. equivalent, 40% below the current BEI setting at nearly PEL exposed level, was found. In conclusion, first-order kinetic response was confirmed for U-TTCA. Both volume- and creatinine-based urine adjustment are satisfactory for TTCA assessment as a biomarker of individual CS2 exposure although the correlation for creatinine-based measurement was modestly superior to the volume-based analogue. Based on the results of this study, we recommend a re-evaluation of the current biological exposure index of 5 mg/g creatinine at a CS2 exposure level of 10 ppm.