Engineering and Analysis Division Brian Englert Office of Science and Technology 202-566-0754

04/15/2010

Summary:

Malcolm Pirnie compared polychlorinated biph enyl (PCB) congener data from the Cooperating Parties Group (CPG) 2008 Low Resolution Coring Program and split 1 samples collected by

Malcolm Pirnie for the U.S. Environmental Prot ection Agency (USEPA) as part of the lower Passaic River oversight program. 2,3 Both laboratories used Method 1668A when performing PCB congener analyses.

In their assessment, Malcolm Pirnie select ed all PCB homologues and total PCBs for comparison. Malcolm Pirnie also selected six PCB congeners to represent the trichloro to octachloro homologue groups (congeners 18, 52, 110, 153, 187 and 195), and four additional congeners that will be modeled to examine futu re surface sediment concentrations (congeners 31, 77, 105 and 118), and included them in the analyses. For all PCB congener data, only samples for which the two laboratories’ reported concentrations were at least five times the sample-specific quantitation limit (SSQL) were considered.

Malcolm Pirnie used a combina tion of graphical methods and st atistical analyses to assess

whether there was a consistent bias between the two laboratories. While statistically significant

differences were observed for some of the P CB congeners, the medians of the differences

between the two laboratories’ results were mos tly within 20 percent, and all were within 30

percent.

While the purpose of the Malcolm Pirnie assessment was to determine whether there was a bias between the two laboratories analyzing the Passaic Ri ver samples, these data also may be used to summarize the performance of Method 1668A. Ther efore, a separate assessment of the split sample data was performed across all congeners and coeluting congener groups to assess the between-laboratory variability. Both laboratories also analyzed various types of QC samples. A subset of these QC data, including matrix spike/matrix spike duplicate (MS/MSD) results, laboratory duplicate results, and standard refe rence material (SRM) results, were used to estimated the precision and bias of the method. Other QC data reported for the Passaic River assessment, such as laboratory control samples (LCS) and labeled recoveri es in study samples, has previously been used in evaluations a nd modifications of Method 1668 QC acceptance criteria, and therefore were not included in this assessment.

Comparison of USEPA and CPG Split Samples :

A total of 30 split samples were analyzed as part of the Lower Passaic River assessment. For each sample, both analytical laboratories perfor med PCB congener analyses using EPA Method 1668A. A total of 151 individual PCB congeners or congener groups were reported by both

laboratories with the same coelu tion structure. For these congen ers and coeluting groups, results from the two laboratories could be compared fo r each sample. While the statistical analyses performed by Malcolm Pirnie were chosen to determine whether there was a bias between laboratories, this would not necessarily indicate an issue with the method itself. However, an examination of the distribution of relative per cent differences (RPDs) can be used to assessEngineering and Analysis Division Brian Englert Office of Science and Technology 202-566-0754

04/15/2010 whether appropriately similar results between the two laboratories can be obtained using the

method.

For each congener or congener group, descriptive sta tistics of the RPDs of each split sample pair

were calculated. To be consistent with the Ma lcolm Pirnie assessment, only pairs for which both laboratories’ results exceeded 5 times their SSQLs were included. Additionally, one sample that was removed by Malcolm Pirnie due to suspecte d matrix heterogeneity also was excluded for

this assessment. RPDs also were summarized ac ross congeners in each le vel of chlorination, and

across levels of chlorination.

Across all congeners, there were 1,500 pairs fo r which both laboratorie s’ results exceeded 5 times their sample-specific quantitation limits. When calculated across these pairs, the pooled RPD (calculated as the square root of the mean of the squared RPDs) was 27.5%, and the median RPD was 13.5%. Only 21.3% of the pairs acro ss all congeners yielded RPDs exceeding 30%, and only 6.8% of the pairs yielded RPDs exceeding 50%. Generally, pairs were more precise in chlorination levels 4-7, and were the less precise for chlorination levels 1-3 and level 8. This was likely due to the lower concentrations observe d in the lower-weight chlorination levels. As concentrations approach the sample-specific quan titation limit, relative va riability (as expressed by an RPD) tends to become larger, therefore th ese higher RPDs indicate a concentration effect rather than a method performance issue.

Performance of USEPA QC Samples:

The laboratory analyzing the USEPA split samples reported results of NIST SRM samples and laboratory duplicates. These results can be used to assess the bias and precision of the method, based on the laboratory’s performance. Th ese assessments are described below.

Bias : The QAPP used by USEPA in this project re quired that laboratory results for the SRM samples be within 30 percent of the certified NI ST values, with no more than 35 percent of the congener recoveries exceed ing this criterion. When these data were validated as part of the original project, the validator applied a more stringent accep tance limit of 20%. The SRM results were all within 15 percent of the certified values.

Precision : Internal laboratory precision for the sa mples was assessed by evaluating the results from the two laboratory duplicate pairs analyzed by the laboratory working for USEPA. Among duplicate pairs for which both the sample and duplicate result each exceeded 5 times their SSQLs, all but 30 PCB congeners in one of the pairs (12.7% of the 236 congener pairs) where less than 40%. The overall pooled RPD for pairs with results exceeding 5 times the SSQL was

27.1%.

Quality Review of CPG QC Samples:

Although not a requirement of Method 1668A, th e laboratory performing the CPG sample analyses analyzed MS and MSD samples as part of the Lower Passaic River project. These data were used to assess the bias and precision of the method, and the result s are described below.Engineering and Analysis Division Brian Englert Office of Science and Technology 202-566-0754

04/15/2010

Bias: Results from 33 MS/MSD pairs were reported for a subset of the PCB congeners. Mean MS/MSD recoveries were calculated for each congen er. An MS/MSD pair was included in this calculation only if the spike level exceeded th e concentration measured in the background sample. While pairs for which this was not the ca se would tend to have worse recoveries, this was due to the inappropriateness of the spike level for assessing bias, rather than a method performance issue.

A total of 1,240 MS or MSD recoveries were calculated for native PCB congeners. Mean recoveries of the native congeners ranged betw een 90% and 124%, with an overall mean of 105%. Only 4.7% of these MS or MSD recoveri es fell outside the 70-130% bound that was used

to assess the SRM results. Recoveries were more likely to fall outside this window for congeners in chlorina tion levels 8-10.

Precision : Precision was assessed by calculating the RP D of the matrix spike and matrix spike duplicate result for each pair. RPDs were th en summarized by congener, and across all congeners. Congener-specific pooled RPDs range d between 4.2% and 22.6%, with an overall pooled RPD of 13.9%. Among the 859 pairs, only six duplicate pairs (m ost for congeners 206 and 208) yielded RPDs exceeding 40%.

References :

1 Split refers to government oversight split samples (referr ed to as “USEPA split samples”) which were collected from 4 percent of the CPG samples, yielding 30 split sa mples plus two field duplicates. The purpose of the split sample program was to provide an independent analytical dataset that can be compared to the CPG samples to investigate precision, accu racy, and potential bias.

2 Statistical Comparison of 2008 Low Resolution Split Sample Sediment Data. Lower Passaic River Restoration Project. W912DQ-08-D-0017, Task Order 0010. Malcolm Pirnie. October 5 th , 2009.

3 Quality Review of CPG 2008 Low Resolution Sediment Coring Data. Lower Passaic River Restoration Project. W912DQ-08-D-0017, Task Order 0010. Malcolm Pirnie. September 23, 2009.