Methanol Vial Cross-contamination Risk
May. 29 2019
Methanol vials have been adopted nationally for use in the preservation of soil samples for volatile organic compounds (VOCs), through both provincial and federal guidelines and regulations.
The benefits of methanol vials over the previously-used glass jars for sample collection include longer hold times, improved stability of target VOC parameters and improved extraction efficiency. However, methanol is exceptionally volatile and can pose a contamination risk to other samples during transport.
Should I be concerned?
Methanol contamination will only be an issue if you intend on testing for methanol. Aside from Alberta (Tier 1) and BC (CSR Schedule 3.1), methanol is not a regulated parameter in any other jurisdiction. Therefore, for samples sourced outside of Alberta and BC this may not be an issue. However, if sampling within Alberta or BC, or your project scope involves testing for methanol, this will be a concern.
Study Design and Observations
Performed at Bureau Veritas’ Calgary laboratory, the study was structured as follows:
- Two sample shipping coolers were placed in two separate cold-storage areas.
- A single standard methanol vial used in the collection of field-preserved soil samples was placed inside each cooler.
- Eight 100mL soil jars each containing 20mL of organic-free water were placed inside each cooler with their lids sealed.
- Half of each set of jars within each cooler were placed inside individual zipper sealed bags.
- The methanol vial within one cooler was loosened. This cooler was designated “Compromised” and the cooler containing the sealed methanol vial was designated “Uncompromised”.
- Along with an initial test of the water used in the study, all of the jars were analyzed and returned to the cooler following 1, 2, 4 and 7 days of storage at 2-6°C.
The purpose behind the two individual cooler test scenarios was to simulate both a standard sample shipment, and one where there was a limited introduction of methanol into the cooler interior. For the latter, the lid of the single vial was simply loosened. The loosened vial was not intended to represent a “worst-case scenario”, but instead that of a relatively commonplace occurrence where a vial cap was not adequately sealed due to the presence of dirt on the vial’s threads or on the sealing face of the cap. The jar lids, however, were all sealed appropriately.
Two graphs provide the average concentration of methanol observed within each of the four soil jar sets (refer to Figure 1). The graphs depict the same data set, but the methanol concentrations (y-axis) were plotted on both a linear and on a logarithmic scale.
As the decision to plot on two scales would suggest, the range of concentrations observed within the jars of each dataset were dramatically different. As one might expect, the sample jars that were sealed in bags and placed in a cooler with the sealed methanol vial recorded the lowest concentrations of methanol, whereas the non-bagged jars placed in the cooler with the unsealed methanol vial recorded the highest. What was not necessarily expected by those conducting the study was the degree of contamination within the “Compromised” cooler despite the jar lids being sealed and even when placed within a sealed bag. Perhaps even more alarming were the methanol detections within the “Uncompromised” cooler despite the methanol vial being sealed; even with the added protection of the jar enclosed within a bag.
Figure 1: Linear and Logarithmic Plots of Methanol Cross-Contamination Data Set
Conclusions and Recommendations
Although the concentration of methanol detected in each of these water samples cannot be adjusted to provide a specific soil concentration, it does adequately demonstrate the exposure risk. The results also indicate that the only guaranteed means to avoid cross-contamination of methanol between the supplied “field-preservation” soil vials and the contents of the soil jars would be to ship them in separate coolers. Other, more exhaustive measures can be undertaken and evaluated through the incorporation of appropriate project QC on a case-by-case basis. These may include the use of more vapor-impervious containers to isolate the vials from the other contents of the cooler.
On the basis of the study findings, Bureau Veritas Laboratories recommends the following procedures be followed for any project where methanol is, or may likely be, a test parameter:
- Make it clear to your Bureau Veritas representative that you will be testing for methanol. Package the field-preserved vials in a separate cooler from your VOC water vials and soil jars.
- Be sure to avoid cross-contamination in the field by keeping the soil vials away from the other containers. Be sure to replace your gloves after handling the vials. Consider filling the jars intended for methanol analysis before handling the soil vials.
- Consider using a Trip Blank (TB) and/or an Equipment Blank (EB) to monitor methanol exposure during sample transport, and sample collection, respectively. Soil jars filled with approximately 20mL of Organic-Free Water initially at the laboratory (TB) or in the field (EB) would serve this purpose. These would then be tested (as a water) upon returning to the laboratory. Ensure these are appropriately identified on the COC.
Above all, the most important “take home” message is to communicate your objectives with your Bureau Veritas representative and your field staff to ensure everyone is aware of the risk.