The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has re‐evaluated the biological tolerance value at the work place (BAT value) for xylene and its isomers, considering xylene in blood and methylhippuric (toluric) acid (all isomers) to characterize the internal exposure. Xylene can easily pass through the skin, so biological monitoring is necessary for a valid individual risk assessment.
Xylene shows a fast elimination in the blood compartment. Thus, the concentration of xylene in blood is halved 30 minutes after the end of exposure. Therefore, sampling should be performed directly at the end of exposure. This is, however, difficult to realize in practice. Therefore, the BAT value for xylene (all isomers) in blood was withdrawn. Methylhippuric (toluric) acid in urine is available as a diagnostically specific parameter. The BAT value for methylhippuric acid is confirmed.