CALFED/California Bay-Delta AuthorityMercury Studies
Quality Assurance Oversight ProgramResults from Intercomparison Study 2
November 2005
Presented by: Beverly H. van Buuren
February 22, 2006
San Francisco Estuary InstituteThird Annual Mercury Coordination Meeting
Regional Water Quality Board, Oakland, California
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Data that supports Decisions
QA Oversight Program Goals
Performance RequirementsLinked to
Program Goals
Develop Comparability Between Hg Projects
Build Comparabilitywith other Programs
Data of Known and Documented Quality
QA/QC Tools & Systems to Improve Efficiency
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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!)
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Intercomparison Study Schedule
Analyte and Matrix Date Samples Ship Date Final Report
THg Water
MMHg SedimentJune 2005
April 2006
April 2007
Nov. 2005
June 2006
June 2007THg Water
MMHg Water
THg Tissue
MMHg Tissue
THg Sediment
MMHg Sediment
Nov. 2005
Nov. 2006
July 2007
March 2006
Feb. 2007
Nov. 2007
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Intercomparison Study 2
Analyte and Matrix Sample Concentration
THg Water spiked lake water 5.56 ng/L
THg Sediment IAEA-SL-1 130 ng/g
THg Tissue IAEA-407 222 ng/g
MMHg Water spiked lake water 0.173 ng/L
MMHg Sediment ERM-CC580 75 ng/g
MMHg Tissue IAEA-407 200 ng/g
• 4 laboratories plus the referee lab
• samples shipped 11/17, results back 01/15, draft report 03/06
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Evaluation of Laboratory Results
Ιz-scoreΙ Versus Reference Value
Rating
≤2 ±10% Very Good
>2 and ≤5 >10% and <25% Good
>5 >25% Poor
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THg in Water Results
Laboratory Intercomparison Study Summary Total Mercury in Freshwater QC
Parameter Lab A Lab B Lab C Lab D Lab E
Freshwater Reference Material
Mean Value
5.90 ng/L 1.3% RSD
n = 3
5.62 ng/L 0.1% RSD
n = 3
5.19 ng/L 4.1% RSD
n = 3
5.05 ng/L 2.7% RSD
n = 3
4.19 ng/L 2.2% RSD
n = 3
Ι z-score Ι 1.223 0.204 1.343 1.823 4.916
ratings very good very good very good very good good
QA group and lab E are investigating systematically low-bias results to assess significance and causes
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MMHg in Water Results
Laboratory Intercomparison Study Summary Methyl Mercury in Freshwater QC
Parameter Lab A Lab B Lab C Lab D Lab E
Freshwater Reference Material
Mean Value
0.175 ng/L 12% RSD
n = 3
0.158 ng/L 6.8% RSD
n = 3
0.15 ng/L 3.9% RSD
n = 3
0.194 ng/L 4.7% RSD
n = 3
0.201 ng/L 2.8% RSD
n = 3
Ι z-score Ι 0.231 1.696 3.044 2.466 3.237
ratings very good very good good good good
Difference between reference value and all lab results was less than 3 times the MDL (0.020 ng/L)
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THg in Sediment Results
Laboratory Intercomparison Study Summary Total Mercury in Sediment QC
Parameter Lab A Lab B Lab C Lab D Lab E
Sediment Reference Material
Mean Value
119 ng/g 0.8% RSD
n = 3
129.5 ng/g 0.8% RSD
n = 3
120.3 ng/g 0.5% RSD
n = 3
114.7 ng/g 0.9% RSD
n = 3
100.9 ng/g 1.9% RSD
n = 3
Ι z-score Ι 1.692 0.077 1.487 2.354 4.477
ratings very good very good very good good good
All laboratories employed different analytical methods, however results indicate good comparability of data
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MMHg in Sediment ResultsLaboratory Intercomparison Study Summary
Methyl Mercury in Sediment
Lab
QC Parameter
Lab A Lab B Lab C Lab D Lab E
Sediment Reference Material
Mean Value
66.1 ng/g 5.7% RSD
n = 3
70.9 ng/g 20.2% RSD
n = 3
112.3 ng/g 46.5% RSD
n = 3
75.5 ng/g 22.3% RSD
n = 3
83.1 ng/g 9.7% RSD
n = 3
Ι z-score Ι 2.364 1.106 9.956 0.145 2.151
ratings good very good poor very good good
Significant high-bias in lab C results likely due to artifact resulting from distillation method. Other labs use extraction method.
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THg in Tissue Results
Laboratory Intercomparison Study Summary Total Mercury in Tissue QC
Parameter Lab A Lab B Lab C Lab D Lab E
Sediment Reference Material
Mean Value
246 ng/g 2.1% RSD
n = 3
235.7 ng/g 2.4% RSD
n = 3
240.3 ng/g 0.2% RSD
n = 3
no results submitted
no results submitted
Ι z-score Ι 2.162 1.237 1.652 n/a n/a
ratings good very good very good n/a n/a
Lab A “good” very close to “very good”
Lab D and lab E do not perform THg tissue analysis for this project
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MMHg in Tissue Results
Laboratory Intercomparison Study Summary Methyl Mercury in Tissue
Lab
QC Parameter
Lab A Lab B Lab C Lab D Lab E
Sediment Reference Material
Mean Value
176 ng/g 1.1% RSD
n = 3
200.2 ng/g 3.0% RSD
n = 3
186 ng/g 4.6% RSD
n = 3
193 ng/g 1.7% RSD
n = 3
217 ng/g 4.3% RSD
n = 3
Ι z-score Ι 2.400 0.023 1.367 0.653 1.667
ratings good very good very good very good very good
Study results indicate good comparison of MMHg in tissue results across all participating labs
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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.
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Contact Information
Beverly H. van BuurenQA [email protected] Buuren Consulting, LLC4320 Baker Avenue NorthwestSeattle, 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
van buuren consulting, llcwww.vanbuurenconsulting.comslide# 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
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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)
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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
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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
van buuren consulting, llcwww.vanbuurenconsulting.comslide# 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
ref
reflab xscorez