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

三甲基苯（TMB）在工业上用作溶剂和油漆稀释剂。TMB的阈值（TLV）已被确定为25ppm (ACGIH)，但其生物暴露指数（BEI）尚未被推荐。TMB由三个异构体组成；1,2,3-, 1,2,4-和1,3,5-三甲基苯。在这些异构体中，1,2,4-TMB（伪文献）主要存在于TMB溶剂中。已知1,2,4- tmb主要代谢为3,4-二甲基马尿酸（3,4- dmha），其代谢物排泄到大鼠尿液中。在本研究中，我们首先检测了职业暴露于1,2,4- tmb的工人尿液中3,4- dmha的排泄量，并评估了它是否可以作为1,2,4- tmb暴露的生物学指标。所得数据表明，尿3,4- dmha浓度与工人1,2,4- tmb暴露水平呈正相关。由此，我们证实尿3,4- dmha是生物监测1,2,4- tmb暴露最有用的指标之一。其次，我们调查了400名铅工人血浆中α -氨基乙酰丙酸（ALA）浓度与铅暴露程度的关系。结果表明，血浆ALA浓度是职业铅暴露生物学监测中最有用的指标之一。

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.