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Mercury QA Oversight Program Intercomparison Study 2 Results

This document presents the results from Intercomparison Study 2 of the Mercury QA Oversight Program, showcasing the comparability and quality of data from different laboratories. The study evaluates THg and MMHg levels in water, sediment, and tissue samples.

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Mercury QA Oversight Program Intercomparison Study 2 Results

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  1. CALFED/California Bay-Delta AuthorityMercury StudiesQuality Assurance Oversight ProgramResults from Intercomparison Study 2November 2005 Presented by: Beverly H. van Buuren February 22, 2006 San Francisco Estuary Institute Third Annual Mercury Coordination Meeting Regional Water Quality Board, Oakland, California

  2. QA Oversight Program Goals Data that supports Decisions Develop Comparability Between Hg Projects Build Comparability with other Programs Performance Requirements Linked to Program Goals Data of Known and Documented Quality QA/QC Tools & Systems to Improve Efficiency

  3. How Intercomparison Studies Help • Comparability of Data (bias) • within current project schedule • year-to-year • other programs? • Alerts program/project/method/lab issues • Individual Lab Performance (esp. CRMs) • Data of Known and Documented Quality • CBDA since March 2000 (6 years!)

  4. Intercomparison Study Schedule

  5. Intercomparison Study 2 • 4 laboratories plus the referee lab • samples shipped 11/17, results back 01/15, draft report 03/06

  6. Evaluation of Laboratory Results

  7. THg in Water Results QA group and lab E are investigating systematically low-bias results to assess significance and causes

  8. MMHg in Water Results Difference between reference value and all lab results was less than 3 times the MDL (0.020 ng/L)

  9. THg in Sediment Results All laboratories employed different analytical methods, however results indicate good comparability of data

  10. MMHg in Sediment Results Significant high-bias in lab C results likely due to artifact resulting from distillation method. Other labs use extraction method.

  11. THg in Tissue Results Lab A “good” very close to “very good” Lab D and lab E do not perform THg tissue analysis for this project

  12. MMHg in Tissue Results Study results indicate good comparison of MMHg in tissue results across all participating labs

  13. Closing Remarks • The MMHg in sediment results submitted by lab C highlight the potential problem associated with the distillation of sediment samples…high-bias resulting from the methylmercury artifact. Projects using this method should have a specific plan for assessing if this method is appropriate to meeting project objectives (the QA group can help). • One intercomparison study with only one sample per analyte/matrix combination is not statistically significant. • Based on the results of this intercomparison study, comparability of data generated by laboratories is good across all matrix/analyte combinations.

  14. Contact Information Beverly H. van Buuren QA Manager beverly@vanbuurenconsulting.com Van Buuren Consulting, LLC 4320 Baker Avenue Northwest Seattle, WA 98107 (206) 781-1692 Other projects we’re working on: Surface Water Ambient Monitoring Program Training classes for Monitoring Design and QA/QC Holding Time Study on Low-level Nutrients Appropriate QA/QC for Physical Habitat and Bioassessment Studies Intercomparison for Pyrethroids in Sediment QA/QC for Citizen Monitoring QAPP Review for the SWRCB DFA SWRCB OIT CIWQS Database Expert Software System to draft QAPPs

  15. Milestone DMA-80 Hg Analyzer • Commercially available automated mercury analyzer • Uses thermal decomposition of sample followed by amalgamation onto gold trap and atomic absorption spectrophotometry (AAS) • Used for total mercury analysis of tissues and sediments • EPA Method 7473 was developed to cover analysis of THg using this instrument

  16. QA Considerations for the DMA-80 • Currently 3 laboratories participating in the program use this analyzer • EPA Method 7473 is vague regarding important practical details (such as how to perform matrix spikes) • Other QC parameters such as instrument calibration and accounting for carryover contamination must be detailed so they conform to the QC requirements of the CBDA Mercury Program • Important to address QC issues without losing benefit of analysis with this instrument (savings in time/labor)

  17. Resolution of QC questions for DMA-80 • Spoke with Milestone applications chemist, Dr. Skip Kingston, and Wes Heim (MLML) to resolve questions and develop QA policies • Calibration will consist of 10-point “primary calibration” performed every 2 weeks and 5-point “daily calibration performed before an analytical run • Matrix spikes can be performed by addition of standard directly to sample boat

  18. Resolution of QC questions for DMA-80 • Carryover contamination can occur after running greater than 250ng of Hg through the analytical system • Results will be reviewed after analysis to identify potential carryover

  19. Evaluation of Laboratory Results • Performance is evaluated through the use of z-scores • lab = the mean of the three values reported by the participating laboratory • xref = the reference value established for the study • ref = 0.05* xref to evaluate results 10% from the reference value

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