Using 12-day sampling periods for estimating long-term ambient air exposures to dioxins/furans

Long-duration and 24-hour dioxin/furan air samples were collected as part of a two-year, multi-media environmental exposure assessment for a resource recovery facility in a predominantly rural area. The extended samples were collected over 12-day periods to improve the detection frequency of the 2,3,7,8-substituted compounds used to calculate TEQ values. The long-duration samples were collected using the standard TO-9 method, with minor modifications to the sampling apparatus. The air sampling rate was not decreased relative to the 24-hour samples, and was approximately 250 L/min. The high-resolution GC/MS analytical procedures were unchanged. The 12-day samples showed a significant improvement in the frequency of detection of 2,3,7,8-substituted compounds, with no breakthrough indicated. Typical contributions to the overall TEQ values for detected compounds were about 80%, versus 10% for 24-hour samples (all TEQs were calculated using a half-detection-limit substitution for non-detected compounds). The total masses of congeners commonly detected in the 24-hour samples (e.g., OCDD, OCDF) did not increase in direct proportion with the volume sampled in the 12-day samples. The experience in this study showed that long-duration dioxins/furans sampling is a workable approach that can provide more realistic information for input into evaluations of human health risk.