Vinyl chloride loss during laboratory holding time

Because vinyl chloride is a potent human carcinogen, it is important that analytical results from groundwater samples accurately reflect levels of exposure to groundwater users. This study investigated the current allowable holding time of 14 days to determine if vinyl chloride is lost from samples during this time. Samples containing an initial concentration of 2 microg/liter of vinyl chloride showed progressive, increasing losses when held for 1, 2, 7, and 14 days. Due to the inherent variability of low-level laboratory results, the most statistically significant loss (alpha = 0.05) was seen for samples held for 14 days. No statistically significant differences in degradation pattern were noted between analytical detectors used (PID versus Hall) or sample type (lab versus field). There also was a loss of vinyl chloride observed during sample collection and handling. These results suggest that analytical variability at low concentrations and the establishment of health-based guidelines near the analytical detection limit require multiple samples be collected from a single location when highly accurate results are needed. These findings should be considered in public health exposure assessments and the implementation of health-based recommendations at sites with vinyl chloride groundwater contamination.