Effect of Fasting on Toluene Metabolism: A Study of Hippuric Acid and O-Cresol Excretion

Abstract

A study of toluene metabolism was conducted among 34 workers during normal workdays, fifteen of these workers were also investigated during the month of Ramadan, when they had no food and water intake from sunrise to sunset (∼6 a.m. to ∼6 p.m.). The time-weighted average (TWA) concentrations of toluene in the breathing zone of workers were measured using passive dosimeters. Concentrations of urinary hippuric acid (HA) and Ortho-cresol (OC) were determined by high performance liquid chromatography and gas chromatography, respectively. Good correlations were observed for environmental toluene concentration, urinary HA, and urinary OC for normal workdays and fasting days. However, under similar exposure conditions, workers with no food and water intake excreted significantly less HA at the end of the shift (0.87 g per gram creatinine for a TWA exposure of 50 ppm toluene) than on normal workdays (1.42 g per gram creatinine). In contrast, the excretion of OC was much higher during the fasting days, with an estimated excretion of 1.17 mg per gram creatinine at 50 ppm toluene exposure as compared with 1.09 mg per gram creatinine. These differences suggest that dietary intake may influence the metabolism of toluene. When toluene metabolites are to be used for biological monitoring of exposure, dietary pattern may have to be taken into consideration. The toxicokinetics of toluene are also discussed in this article.