however,hippuric has limited specificity since levels can be modified by benzoic acid which is used as an antifungal preservative in pharmaceutical preparation and foods. Beside, the level can also be modified by co-exposure to other chemicals, such as ethyl benzene and styrene. for o-cresol, the levels are influenced by smoking habit. At present, BEL of toluene based on measuring urinary o-cresol or toluene either in blood or urine.