Urinary 2-Thiothiazolidine-4-Carboxylic Acid as a Biological Indicator of Exposure to Carbon Disulfide: Derivation of a Biological Exposure Index

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Abstract
The current American Conference of Governmental Industrial Hygienists (ACGIH) Biological Exposure Index (BEI) for carbon disulfide (CS2) is 5 mg of 2-thiothiazolidine-4-carboxylic acid (TTCA)/g creatinine in a urine sample collected at the end of the workshift. The BEI, based on studies of viscose rayon workers, corresponds to an 8-h time-weighted average (TWA) inhalation exposure at the 1991–1992 Threshold Limit Value (TLV) (ACGIH, Cincinnati, Ohio) of 10 ppm CS2. Reduction of the CS2 airborne permissible exposure limit (PEL) from 20 ppm to 4 ppm in 1989 by the Occupational Safety and Health Administration, coupled with new experimental human-exposure studies from the published literature, prompted us to reexamine the literature and derive a new BEI. This reexamination led to the following observations: (1) Inhalation exposures of humans at rest, under laboratory conditions, to 10 and 4 ppm CS2 8-h TWA, produced urinary increases of 2.7 and 1.1 mg TTCA/g creatinine, respectively. (2) Viscose rayon workers, exposed to 10 ppm CS2 TWA, experienced an increase of 4.8 mg TTCA/g creatinine for postshift versus preshift urine voids. (3) About 38 percent of the TTCA concentration could be ascribed to increased inhalation at an estimated 50-watt (W) workload. (4) The 56 percent increase of 2.7 mg TTCA/g creatinine in urine excreted by workers constituted the TTCA concentration produced had the workers been at rest. If the increase in the urinary TTCA concentration is not greater than that measured for workers at rest exposed to CS2 air concentrations at or below the TLV-TWA, these concentrations should be protective. We recommend that BEIs for CS2 exposures be based on human-volunteer inhalation studies, conducted at rest, because these BEIs will protect workers at any level of physical activity, assuming no interactions.