Biological monitoring for trimethylbenzene exposure: a human volunteer study and a practical example in the workplace

This paper presents data from both a human volunteer study looking at exposure to 1,3,5-trimethylbenzene (TMB) and an occupational hygiene study of a printing firm using screen wash containing technical grade TMB. The biomarkers measured were TMB in blood and breath, and urinary dimethylbenzoic acids (DMBAs). The volunteer (N = 4) study showed that TMB was rapidly absorbed into the bloodstream reaching a mean level of 0.85 micromol l(-1) during a 4 h exposure to 25 p.p.m. TMB. There was little decline 1 h post-exposure possibly indicating storage of TMB in adipose tissue. Breath TMB levels peaked within an hour of exposure commencing and averaged 137 nmol l(-1) during exposure. Elimination of TMB in breath was biphasic with an initial half-life of 60 min. Peak excretion of urinary DMBA occurred 4-8 h after the end of exposure and averaged 40 mmol mol(-1) creatinine. Elimination of DMBA in urine was biphasic with half-lives of 13 and 60 h indicating that accumulation of body burden throughout the working week is likely if exposure is repeated. The occupational hygiene study demonstrated an excellent correlation between personal air TMB levels and post-shift urinary DMBA levels (r = 0.997) collected on the third working day. The regression equation from this study indicates that 8 h exposure to 25 p.p.m. TMB would result in a urinary DMBA level of 206 mmol mol(-1) creatinine. All workers showed pre-shift levels of DMBA from exposure to TMB on previous days. Both urinary DMBA and breath TMB levels can be used as biomarkers of TMB exposure. Urine samples should be taken post-shift towards the end of the working week as significant body burden accumulation throughout the working week can be expected. Breath sampling is more suited to task or single-shift monitoring.