Dr. David Adamson is a Principal Engineer with GSI Environmental Inc. in Houston, Texas, with more than 19 years of environmental project experience in academic research and consulting. He has served as a Principal Investigator or co-Principal Investigator on multiple DoD-sponsored research projects, including those focused on 1,4-dioxane and PFAS fate and transport, innovative treatment and long-term monitoring strategies, MNA and enhanced remediation performance, and improved characterization and treatment methods for contaminants in low-permeability zones. He is a contributor to the ITRC teams on 1,4-dioxane and PFAS, and he also serves as a Lecturer at Rice University.
Trends in 1,4-dioxane analyses: implications for identification and characterization of contaminated sites
Our understanding of the environmental occurrence of 1,4-dioxane is strongly influenced by the quality of data being generated during site assessment and monitoring. Several analytical methods with varying levels of sensitivity are commercially available, and stakeholders must select a method based on site-specific considerations and lab guidelines (e.g., data quality objectives, added cost, regulatory requirements, co-occurring contaminants). Given the differences associated with these various options, method selection has significant implications. Evidence already exists that the environmental community has done an inadequate job of characterizing 1,4-dioxane by simply not looking for it at sites with suspected contamination. It is equally important to understand the adequacy of data being generated when we do look for 1,4-dioxane at sites. To-date, there have been no comprehensive studies to-date on how these analytical methods are being employed and how they are performing. The objective of this study was to examine trends in 1,4-dioxane analytical data in order to evaluate several specific hypotheses related to our ability to characterize and manage sites where this emerging contaminant is potentially present. This study compiled public sampling records from 2001 to 2019 that included > 90,000 analyses of 1,4-dioxane from 786 different sites in the state of California. The 1,4-dioxane detection frequency in the entire dataset (including all methods) was 45%, and the median concentration among detections was 12 ug/L, highlighting the dilute nature of 1,4-dioxane in environmental media and the importance of selecting a method with adequate sensitivity. The annual distribution of samples analyzed by each method type was used to confirm a shift towards methods designed for semi-volatile compounds (Method 8270 and Method 8270 SIM) that exhibited consistently lower reporting limits (median reporting limit for each year typically ? 1 ug/L). In contrast, the method designed for volatile compounds (Method 8260) declined significantly over time due to poor sensitivity for 1,4-dioxane (median reporting limit per year between 40 and 100 ug/L), with increasing use of the moderately sensitive Method 8260 SIM in later years. This shift contributed to an increase in the 1,4-dioxane detection frequency over time, with a strong correlation between the annual detection frequency and the median reporting limit. Sites where 1,4-dioxane was analyzed but not detected overwhelmingly used less-sensitive methods that were inadequate for the expected concentration levels. This indicates that a significant number of 1,4-dioxane contaminated sites have not been properly identified due to method selection bias, with an estimated false negative rate of approximately 10%. The trends in method selection suggest that future efforts are likely to rely on more sensitive methods. This is critical because data from this study identified 972 sites with detections of 1,1-DCA (an intermediate of 1,1,1-TCA degradation) that had not yet analyzed for 1,4-dioxane as of July 2019. Adoption of isotope dilution and other modifications to further improve sensitivity is key because the data also indicate that the reporting limits currently being achieved for 1,4-dioxane are insufficient for compliance with several recently-established regulatory limits.