New indicators useful for biological monitoring of organic solvent and lead exposures

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Trimethylbenzene (TMB) is used in industry as solvents and paint thinners.The threshold limit value (TLV) of TMB has been set at 25 ppm (ACGIH) and, however, its biological exposure index (BEI) has not been recommended yet. TMB consists of three isomers ; 1,2,3-, 1,2,4-, and 1,3,5-trimethylbenzene. Of these isomers, 1,2,4-TMB (pseu-documene) is mainly contained in the TMB solvent. It is known that 1,2,4-TMB is mainly metabolized to 3,4-dimethylhippuric acid (3,4-DMHA) and its metabolite is excreted into urine in rats.In the present study, we first examined the urinary excretion of 3,4-DMHA in workers occupationally exposed to 1,2,4-TMB and evaluated whether it is useful as a biological indicator of 1,2,4-TMB exposure. The data obtained indicated that the concentration of urinary 3,4-DMHA had a positive correlation with the level of exposure to 1,2,4-TMB in workers. From this result, we confirm that urinary 3,4-DMHA is one of the most useful indicators for biological monitoring of 1,2,4-TMB exposure.Secondly, we investigated the relationship between plasma delta-aminolevulinic acid (ALA) concentration and the degree of exposure to lead in about 400 lead workers.The data obtained indicated that plasma ALA concentration was one of the most useful indicators for the biological monitoring of occupational exposure to lead.