Validation of handheld X-ray fluorescence for in situ measurement of mercury in soils

- A field and laboratory validation study was conducted to test the performance of a handheld X-ray fluorescence device for measuring Hg in contaminated soils.
- Field samples were used to develop a site-specific calibration.
- The method achieved a detection limit of 7.4 mg/kg Hg, sufficient for detecting mercury at generic risk assessment screening levels.
- The method achieved accuracy and precision that was comparable to the traditional laboratory Method 7471A.

Handheld X-ray fluorescence (XRF) devices hold promise for quick field screening of contaminated sites, but so far, these devices have not been successfully used for mercury screening because of poor sensitivity and questionable accuracy. This paper describes a site-specific calibration method and demonstrates the successful field use of XRF for measuring mercury in the soils of contaminated sites. The method achieved a detection limit of 7.4 mg/kg Hg with a 60-s analysis time. This improves upon earlier attempts and is sufficient for detecting mercury at generic risk assessment soil screening levels (23 mg/kg Hg). The study also demonstrated levels of accuracy and precision for the method that rivaled traditional laboratory methods. In a split-sample comparison with laboratory Method 7471A, field XRF results agreed with an R2 of 0.93 and a median coefficient of variation of 15%. Precision estimates from duplicate and triplicate samples were not statistically different between the two methods and were constrained by sample heterogeneity and not method capabilities. This study demonstrates that handheld XRF can be successfully used at contaminated sites to achieve high quality Hg results that are accurate, precise, and at a level of sensitivity that is commensurate with generic risk assessment screening levels.