Monitoring of Occupational Exposure to Methylene Chloride: Sampling Protocol and Stability of Urine Sample

A sampling protocol for biomonitoring of the volatile solvent methylene chloride (MeCl2) by analysis of urine from exposed workers was established. Storage temperature, sample volume in headspace vial (HSV), and time to sealing HSV on determination of MeCl2 in urine were evaluated. MeCl2 was analyzed by a solid-phase microextraction technique combined with gas chromatography. Volume of urine in HSV has no effect on MeCl2 analysis. Delays of 30 and 60 min from collection of urine until sealing the HSV caused 14.47 plus or minus 6.98% and 26.17 plus or minus 9.57% decreases from baseline concentration, respectively. MeCl2 concentration in spiked urine samples stored in sealed HSVs decreased on day 2 and then remained stable for 2 weeks. Refrigeration did not improve recovery although it seems to be associated with less variability. MeCl2 in urine samples of seven exposed workers was in the range of 0.02-0.06 mg/L. Sampling of MeCl2-containing urine should include collection of urine in closed plastic bottles, transfer to HSV within 15 min, sealing and clamping of HSV within 15 s, and storage of HSV in refrigeration until analysis, but no longer than 2 weeks. Standard samples should be prepared on the day of test sample collection and handled under the same conditions.