An Interlaboratory Comparison for Total Mercury and Methylmercury in Water at Environmentally Relevant Concentrations

Creswell, J. E.; Carter, A.; Engel, V. L.; Metz, J. A.; Davies, C. A.

An Interlaboratory Comparison for Total Mercury and Methylmercury in Water at Environmentally Relevant Concentrations

2015

Creswell, J. E. | Carter, A. | Engel, V. L. | Metz, J. A. | Davies, C. A.

We have conducted an interlaboratory comparison study for total mercury and methylmercury analysis in natural (unspiked) water samples annually for the past 4 years. The samples were primarily freshwater, with the exception of one coastal seawater sample in 2014. The study provided participants with an opportunity to assess the quality of their measurements and the intercomparability of their data with their peers. Data on analytical methods used were collected and used to determine whether any methods yield biased results and should be discontinued. The majority of participants received performance scores of 3 or higher, indicating satisfactory performance and results close to the consensus means. However, the coefficients of variation between labs were greater than 20 % in most cases, which may not be sufficiently precise for multilaboratory environmental research, where the processes being studied may vary by 20 % or less. Total mercury analysis methods that do not use gold amalgamation were shown to be underperforming relative to those that do. No significant correlation was observed between sample storage time or temperature and total mercury recovery. Methylmercury analysis methods that do not use distillation performed poorly relative to those that use distillation.

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