2014 brooks rand instruments interlaboratory comparison ......(v/v) bromine monochloride (brcl)...

2014 Brooks Rand Instruments

Interlaboratory Comparison Study for Total

Mercury and Methylmercury

(Intercomp 2014)

Joel Creswell, Ph.D

Julian Metz

Annie Carter

Colin Davies

Brooks Rand Instruments

4415 6th

Ave NW

Seattle, WA 98107 USA

[email protected]

www.brooksrandinc.com

April 23, 2014

http://www.brooksrandinc.com/

1

Table of Contents

Introduction ..................................................................................................................................... 2

Methods........................................................................................................................................... 3

Sample Collection and Distribution ............................................................................................ 3

Data Analysis and Calculations .................................................................................................. 5

Results ............................................................................................................................................. 8

Holding time data ........................................................................................................................ 9

Total mercury data, Site WH ..................................................................................................... 12

Total mercury data, Site UB ...................................................................................................... 17

Total mercury data, Site SP....................................................................................................... 22

Summary of total mercury scores .............................................................................................. 27

Methylmercury data, Site WH ................................................................................................... 29

Methylmercury data, Site UB .................................................................................................... 34

Methylmercury data, Site SP ..................................................................................................... 39

Summary of methylmercury scores ........................................................................................... 44

Discussion ..................................................................................................................................... 46

Method Data .............................................................................................................................. 48

Future Studies ............................................................................................................................... 52

Acknowledgements ....................................................................................................................... 52

References ..................................................................................................................................... 53

2

Introduction

The Brooks Rand Instruments Interlaboratory Comparison Study (Intercomp) for Total

Mercury (THg) and Methylmercury (MeHg), now in its fourth year, was initiated to take the

place of the Mercury Round Robin, which was conducted by the Florida Department of

Environmental Protection (DEP) on an annual basis between 2001 and 2009. This exercise

provides a reliable means for laboratories to test their competency in the analysis of total

mercury and methylmercury in natural waters, as well as a metric for assessing the

intercomparability of data generated by different laboratories. Brooks Rand Instruments

undertook the organization of the Intercomp in 2011, upon learning that the Florida DEP no

longer planned to continue the exercise.

Intercomp 2011 was organized to replicate, to the extent feasible, the methods followed

in the Mercury Round Robins organized by the Florida DEP. The four week analysis and

reporting period for methylmercury data, introduced and validated in Intercomp 2012 (Creswell

et al. 2012), was maintained in Intercomp 2014 (this study). The organization and methods of

Intercomp 2014 were kept as similar to Intercomps 2011-2013 as possible, with the goal of

producing a multiyear record of laboratory performance and data intercomparability.

Some of the key features of Intercomp 2014 were a broad invitation to participate;

anonymous data submission, analysis, and reporting; and the inclusion of analytical method

reporting. The initial invitation to participate was sent to Brooks Rand Instruments’ email

database of more than 3,000 unique addresses. 64 laboratories in 17 countries signed up to

participate and were sent samples (some of these laboratories registered twice and were sent two

sets). Participants submitted 63 sets of total mercury results and 41 sets of methylmercury

results. Intercomp 2014 had one less participant than Intercomp 2013, which was, to our

knowledge, the largest interlaboratory comparison study for total mercury and methylmercury in

un-spiked natural waters ever conducted.

By requesting participating laboratories to report detailed information about their

analytical methods, we were able to assess the performance of specific protocols, reagents, and

equipment. These data can help identify methods that should be widely used and those that

should be avoided.

3

Methods

Sample Collection and Distribution

Samples were collected on January 15, 2014 from a site in Woods Hole, Massachusetts,

and on February 1, 2014 from two sites in the western Washington State, USA. Site WH (Woods

Hole Oceanographic Institution; Woods Hole, Massachusetts) was sampled by Carl Lamborg

from the Woods Hole Oceanographic Institution Environmental Research Laboratory’s seawater

distribution system. Site UB (Union Bay Natural Area; Seattle, Washington) is a freshwater

wetland located within the Union Bay Natural Area on the University of Washington campus

(Figure 1). Although we did not conduct a detailed study of site hydrology for this exercise, the

main water source for this wetland appears to be nearby Lake Washington. We sampled this site

near the parking lot. Site SP (Sunset Pond; Bellingham, Washington) is an impoundment of

Squalicum Creek, a small stream draining a primarily suburban watershed (Figure 2). This site

was sampled from the park on James St.

Figure 1. Sampling site UB

Figure 2. Sampling site SP

At site WH, 20 L fluorinated polyethylene (FLPE) carboys were filled from the seawater

distribution system, after passing the sample through 0.45 µm inline filter capsules (Voss

Technologies, San Antonio, Texas). At sites UB and SP, samples were collected with two

peristaltic pumps, using the same filters and carboys as at site WH. We used FEP sampling lines

connected to silicone tubing through the pump head. The carboys were each tested for

contamination prior to use by analyzing blanks of deionized water that had been stored overnight

4

in each vessel. Only containers with blank concentrations lower than 0.4 ng/L were used for

sample collection. Ten percent of the filters in each manufacturer’s lot were checked for

contamination by analyzing DI water passed through them. The average total mercury level was

less than 10 pg per capsule. Filters were rinsed with sample prior to filling carboys. We followed

strict trace metal clean techniques (U.S. Environmental Protection Agency 1996) at the field sites

(UB and SP) to avoid sample inhomogeneity to the extent possible. Approximately 120 L of

water was collected at each of the three sites.

Samples from site WH were preserved prior to shipping to Brooks Rand by adding

concentrated (18M) Trace Metal Grade sulfuric acid to each carboy for a final acid concentration

of 0.2% (v/v) or approximately 36 mM. Samples from sites UB and SP were preserved upon

returning from the field, by adding concentrated (12 M) Trace Metal Grade hydrochloric acid to

each carboy, for a final acid concentration of 0.4% (v/v) or approximately 50 mM. We

distributed the samples into 500 mL FLPE bottles for shipment to laboratories the following day,

February 2, 2014. In an effort to maximize sample uniformity, we shook and transferred samples

from the field carboys into fluorinated HDPE 30 gallon (113.6 L) drums that had been cleaned

and tested in the same manner as the carboys (described above). We filled the 500 mL FLPE

bottles through a fluoropolymer spigot installed in the bottom of the barrel. These bottles were

all from the same manufacturer’s lot, and prior to use we tested a random selection of ten percent

of the cases received. Ten percent of the bottles from each case selected were filled with a 1%

(v/v) bromine monochloride (BrCl) solution, stored at room temperature overnight, and analyzed

the following day. All of these bottle blanks contained less than 0.4 ng/L total mercury.

The 500 mL FLPE sample bottles were placed in single plastic zip-top bags and stored in

shipping boxes overnight. 66 sets of samples were sent to 64 laboratories on Monday, February

3, 2014, by express courier. Most deliveries were completed within three days, but in a few

cases, international customs delays prevented timely delivery and samples were not delivered for

several days or even weeks. Participating laboratories were asked to analyze samples for total

mercury and/or methylmercury following their standard operating procedures, and were given no

further guidance on analytical methodology. All results were requested to be reported by March

3, 2014, four weeks after the samples were shipped; however, results were generally accepted for

samples analyzed by the March 3 deadline. This deadline is based on the results of the 2012

5

bottle storage study, which demonstrated that analyte concentrations did not change substantially

over a four week holding time (Creswell et al. 2012).

Three laboratories participated in a holding time study as part of Intercomp 2014. Brooks

Rand Labs, the “Jožef Stefan” Institute Department of Environmental Sciences, and the U.S.

Geological Survey Wisconsin Mercury Research Lab each received two replicate sets of samples

to analyze at the beginning and end of the reporting period. The results of these analyses were

used to determine whether the analyte concentrations changed over the course of the study.

All results were reported to an independent third party, EcoChem, Inc. (Seattle,

Washington, USA), a data validation company who had no role in the study other than data

management. At EcoChem, the dataset was compiled, and a unique identifier was assigned to

each laboratory, before it was transmitted to Brooks Rand. Following delivery of this report,

each participating laboratory received an e-mail containing their own unique identifier, but

identifiers were not disclosed to any other parties, including Brooks Rand Instruments. This

research design ensured that there would be no bias by the preparers of this report against any

participating laboratory and that participants could submit data without fear of embarrassment

from a possible low score.

Data Analysis and Calculations

Each laboratory was asked to report an analytical result, detection limit, and date

analyzed for each sample and analyte. These data are the basis of the scores in this report. In

addition, each laboratory reported information on sample preparation and analytical

methodology and equipment. These data were used to compile assessments of the performance

of various analytical methods, but were not used in laboratory scoring.

Statistical data analysis was carried out largely following the recommendations of Lin &

Niu (1998). Because a true value of the Intercomp samples was not known, it was necessary to

remove obviously outlying data points before calculating a grand mean. The method of modified

Z scores (Filliben 2012) was selected for outlier removal because it is robust for both small and

large sample sizes, and is not affected by the magnitude of extreme outliers. The modified Z

score is calculated as follows:

6

( ̃)

Zi Modified Z score for laboratory i

xi an individual measurement of a sample by laboratory i

̃ the median measurement of sample x across all laboratories and

replicates

MAD median absolute deviation = (| ̃|) across all

measurements of a given sample

Any measurement with a modified Z score greater than 3.5 was labeled as an outlier (Filliben

2012) and excluded from the calculation of the consensus mean and median and laboratory

performance scores, described below. For all calculations, individual samples were grouped by

site as shown in Table 1. If any of a lab’s results for a given site were flagged as outliers, that lab

received a score of 0 for that site, and its results were excluded from calculation of that site’s

statistics. A series of exploratory statistical plots was then generated to verify that the removal of

outliers resulted in a dataset with a normal (Gaussian) distribution. The method of outlier

removal used in this study did not always result in a normal distribution of data (e.g., Figure

13a), however outlier removal improved normality for every site.

Table 1. Sample identification table.

Site

Sample

Numbers

WH (Woods Hole Oceanographic Institution) 1, 4, 6

UB (Union Bay Natural Area) 2, 7, 9

SP (Sunset Pond) 3, 5, 8

Participating laboratories were requested to report undetected values as being less than

their detection limit. A value of half of the detection limit was substituted for any undetected

result, for the purpose of calculating a modified Z score. If that modified Z score was above the

outlier threshold (3.5), the undetected value was flagged as an outlier and the laboratory’s results

excluded from calculations of the consensus mean and median and performance scores for that

site. If the modified Z score for a substituted result was below the outlier threshold, that result

was included in subsequent calculations of the consensus mean and median and performance

7

scores. Scores generated by this substitution method are marked with asterisks in the data tables

below to indicate that they are at least partially based on speculative substitution of a result.

In order to assign a score to each laboratory’s performance, we calculated a t-statistic and

Cook-Weisberg distance (Cook and Weisberg 1980; Lin and Niu 1998; Niu and Tintle 2008; Niu

and Miller 2009) for the measurement of each analyte at each site by each participating

laboratory. For example, if a lab analyzed total mercury and methylmercury in all nine samples,

with no outliers, that lab would receive six scores: one for each analyte for each of the three sites.

If a lab that did not report results for all three samples from a given site, the lab did not receive a

score for that site. The t-statistic was calculated as follows:

̅ ̃

̃√ ⁄ ⁄

ti t statistic for lab i

̅ the mean measurement for site Y by lab i

̃ mean of all measurements by labs with no flagged outliers

̃ standard deviation of the residuals of all measured values for site Y

r number of replicates from site Y analyzed by lab i

n0 total number of measurements taken by laboratories with no

flagged outliers

The t-statistic reflects the distance of an individual laboratory’s mean value from the consensus

mean for the site.

The Cook-Weisberg distance (C-W distance) was calculated as follows:

( ̅ ̅)

Di C-W distance for lab i

r number of replicates of site Y analyzed by lab i

̅ mean of all measurements of site Y by lab i

̅ the consensus mean of site Y

p number of labs with no flagged outliers

s2 variance of the residuals of all measured values for site Y

The C-W distance reflects the influence that each laboratory’s average value has on the

consensus mean.

8

We assigned scores following the rating system of Niu and Tintle (2003; Table 2).

Table 2. Rating system for laboratory performance (Niu and Tintle 2003).

Rating t-value C-W distance

5 (Very good) 0.00 ≤ t-value ≤ 2.00 C-W distance < 3.00

4 (Good) 2.01 ≤ t-value ≤ 4.00 C-W distance < 3.00

3 (Satisfactory) t-value > 4.00 C-W distance < 3.00

2 (Questionable) t-value > 4.00 3.00 ≤ C-W distance ≤ 10.00

1 (Poor) t-value > 4.00 10.01 ≤ C-W distance

0 (Unacceptable) With one or more outliers With one or more outliers

Results

We received 65 unique sets of results. 63 of these contained total mercury data and 41

contained methylmercury data. Because some labs registered for more than one set of samples,

the results may include more than one submission from some participants. We accepted results

with analysis dates up to the reporting deadline of March 3, 2014.

Figure 3. Particulate matter visible in some samples. Photo courtesy of Joël Knoery.

Some participants reported small amounts of leakage or particulate matter in some of the

sample bottles (e.g. Figure 3). Although great care is taken to minimize sample inhomogeneity,

9

the occurrence of these two problems (leakage and precipitation) seems to be unavoidable. No

participants reported a correlation between observed leakage or precipitate and sample results.

Holding time data

Due to differences in sample receipt and preparation times, holding time samples were

not analyzed on the same dates by all three laboratories participating in the holding time study.

However, the dates of analysis shown in Figures 4 and 5 below span the majority of the reporting

period for both analytes. There are several instances in which one or more labs observed a

change in analyte concentration in a sample greater than ± 1 standard deviation of three replicate

measurements (indicated by error bars). However there is no trend of a consistent, directional (up

or down) concentration change over time in all results from any one lab. If a lab exhibited

increasing concentrations over time in all samples, this might indicate a contamination problem,

while the reverse might indicate poor sample storage conditions. The lack of any such trend

indicates that the changes over time in these holding time samples exemplify the variability that

can be expected in all samples over the course of the reporting period.

10

Figure 4. Holding time data for total mercury. Error bars are ± 1 standard deviation of replicate

measurements. Where error bars are not visible, they are smaller than the chart symbol to which

they pertain. Note that the vertical scales are not identical. BRL = Brooks Rand Labs; JSI =

“Jožef Stefan” Institute; USGS = U.S. Geological Survey.

50

55

60

65

70

75

80

85

90

95

100

2/10/14 2/15/14 2/20/14 2/25/14 3/2/14 3/7/14

Tota

l Me

rcu

ry (

ng/

L)

Date Analyzed

Site WH

BRLJSIUSGS

1.55

1.65

1.75

1.85

1.95

2.05

2.15

2.25

2.35

2.45

2/10/14 2/15/14 2/20/14 2/25/14 3/2/14 3/7/14

Tota

l Me

rcu

ry (

ng/

L)

Date Analyzed

Site UB

BRLJSIUSGS

5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

10

2/10/14 2/15/14 2/20/14 2/25/14 3/2/14 3/7/14

Tota

l Me

rcu

ry (

ng/

L)

Date Analyzed

Site SP

BRLJSIUSGS

11

Figure 5. Holding time data for methylmercury. Error bars are ± 1 standard deviation of

replicate measurements. Where error bars are not visible, they are smaller than the chart symbol

to which they pertain. Note that the vertical scales are not identical. BRL = Brooks Rand Labs;

JSI = “Jožef Stefan” Institute; USGS = U.S. Geological Survey. *In the Site WH graph, the

USGS concentrations were below the detection limit (0.04 ng/L). The plotted value is half of the

detection limit (0.02 ng/L) and the error bars span the range from 0 to the detection limit.

0

0.01

0.02

0.03

0.04

0.05

2/10/2014 2/15/2014 2/20/2014 2/25/2014 3/2/2014 3/7/2014 3/12/2014

Me

thyl

me

rcu

ry (

ng/

L)

Date Analyzed

Site WH BRLJSIUSGS*

0.1

0.11

0.12

0.13

0.14

0.15

0.16

0.17

0.18

0.19

2/10/2014 2/15/2014 2/20/2014 2/25/2014 3/2/2014 3/7/2014 3/12/2014

Me

thyl

me

rcu

ry (

ng/

L)

Date Analyzed

Site UB BRLJSIUSGS

0.08

0.09

0.1

0.11

0.12

0.13

0.14

0.15

0.16

2/10/2014 2/15/2014 2/20/2014 2/25/2014 3/2/2014 3/7/2014 3/12/2014

Me

thyl

me

rcu

ry (

ng/

L)

Date Analyzed

Site SP BRLJSIUSGS

12

Total mercury data, Site WH

Table 3. Laboratory performance for total mercury, site WH (samples 1, 4, 6). An asterisk

indicates that the lab mean includes at least one undetected value that was substituted with half

of that lab’s detection limit.

Consensus Mean = 76.49 ng/L, Consensus Median = 77.54 ng/L

Lab Mean t value C-W Distance Score

1 91.3 9.24 1.45 3

2 84.7 4.96 0.42 3

3 84.7 4.96 0.42 3

4 61.7 9.77 1.62 3

5 91.1 9.11 1.41 3

6 59.8 10.96 2.04 3

7 37.8 With outliers 0

8 137 With outliers 0

9 63.2 8.81 1.31 3

10 76.5 0.26 0.00 5

11 81.0 2.60 0.11 4

12 63.2 8.79 1.31 3

13 78.6 1.09 0.02 5

14 77.6 0.40 0.00 5

15 77.5 0.35 0.00 5

16 17.1* With outliers 0

17 80.2 2.10 0.07 4

18 99.9 14.71 3.67 2

19 67.8 5.83 0.58 3

20 72.0 3.14 0.17 4

21 83.6 4.28 0.31 3

22 83.5 4.22 0.30 3

23 59.7 11.06 2.07 3

24 81.8 3.15 0.17 4

25 87.6 6.87 0.80 3

26 73.4 2.28 0.09 4

27 78.2 0.79 0.01 5

28 80.4 2.25 0.09 4

29 80.2 2.12 0.08 4

30 86.5 6.12 0.63 3

31 67.8 5.85 0.58 3

32 69.7 4.66 0.37 3

Table continued on following page

13


33 71.4 3.52 0.21 4

34 71.9 3.22 0.18 4

35 88.1 7.17 0.87 3


37 81.1 2.68 0.12 4

38 68.8 5.21 0.46 3

39 73.2 2.37 0.10 4

40 77.8 0.58 0.01 5

41 95.1 11.66 2.30 3

43 79.7 1.76 0.05 5

44 58.3 11.92 2.41 3

46 80.6 2.38 0.10 4

47 74.7 1.42 0.03 5

48 79.3 1.50 0.04 5

49 71.1 3.76 0.24 4

50 68.7 5.26 0.47 3

51 98.0 13.49 3.09 2

52 89.8 8.28 1.16 3

53 72.9 2.58 0.11 4

54 68.6 5.32 0.48 3

55 84.9 5.09 0.44 3

56 66.9 6.45 0.71 3

57 74.8 1.34 0.03 5

58 80.4 2.22 0.08 4

59 91.2 9.13 1.41 3

60 72.7 2.73 0.13 4

61 67.3 6.15 0.64 3

62 Unreported values

63 84.8 5.07 0.44 3

64 66.5 6.68 0.76 3

65 59.8 10.96 2.04 3

14

Figure 6. Total mercury results from all participating laboratories for site WH.

Figure 7a. Histograms of reported total mercury concentrations for site WH. All concentrations

(left); non-outlier values (right).

0

20

40

60

80

100

120

140

160

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63

Tota

l Me

rcu

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on

cen

trat

ion

(n

g/L)

Lab

Site WH Total Mercury Results

Lab Results

Consensus Mean

15

Figure 7b. Box plots of reported total mercury concentrations for site WH. All concentrations


Figure 7c. Normal quantile-quantile plots of reported total mercury data for site WH. All

concentrations (left); non-outlier values (right).

16

Figure 7d. Density functions of residuals (residual = individual measurement - laboratory mean)

of total mercury data for site WH. All values (left); non-outlier values (right).

Figure 7e. Residual (residual = individual measurement - laboratory mean) vs. fitted value plots

of reported total mercury concentrations for site WH. All values (left); non-outlier values (right).

17

Total mercury data, Site UB

Table 4. Laboratory performance for total mercury, site UB (samples 2, 7, 9). An asterisk





1 2.56 6.82 0.86 3

2 1.83 0.57 0.01 5

3 1.90 0.13 0.00 5

4 1.93 0.40 0.00 5

5 1.88 0.10 0.00 5


7 2.39 5.10 0.48 3


9 1.50 3.90 0.28 4

10 1.98 0.89 0.01 5

11 1.93 0.43 0.00 5

12 1.21 6.82 0.86 3

13 1.93 0.47 0.00 5

14 1.67 2.23 0.09 4

15 1.84 0.44 0.00 5


17 1.67 2.19 0.09 4



20 2.28 3.96 0.29 4

21 1.94 0.50 0.00 5

22 1.76 1.28 0.03 5

23 1.11 7.86 1.14 3


25 1.98 0.95 0.02 5

26 1.95 0.67 0.01 5

27 2.06 1.78 0.06 5

28 2.00 1.14 0.02 5

29 1.88 0.04 0.00 5

30 1.67* 2.22 0.09 4

31 2.20 3.12 0.18 4

32 1.74 1.51 0.04 5


18


33 1.47 4.23 0.33 3

34 1.70 1.88 0.07 5

35 1.42 4.70 0.41 3


37 1.64 2.45 0.11 4

38 1.73 1.55 0.04 5

39 2.17 2.82 0.15 4

40 1.80 0.84 0.01 5

41 2.10 2.18 0.09 4

43 1.88 0.07 0.00 5

44 1.54 3.53 0.23 4

46 2.01 1.24 0.03 5

47 1.71 1.82 0.06 5

48 1.93 0.40 0.00 5

49 1.94 0.54 0.01 5

50 1.93 0.47 0.00 5


52 1.99 1.04 0.02 5

53 2.64 7.56 1.06 3

54 2.18 2.99 0.17 4

55 2.03 1.44 0.04 5

56 1.53 3.58 0.24 4

57 1.95 0.67 0.01 5


59 2.10 2.15 0.09 4

60 1.90 0.17 0.00 5

61 2.16 2.75 0.14 4


63 2.03 1.44 0.04 5

64 1.96 0.73 0.01 5

65 1.77 1.14 0.02 5

19

Figure 8. Total mercury results from all participating laboratories for site UB.

Figure 9a. Histograms of reported total mercury concentrations for site UB. All concentrations


0

5

10

15

20

25

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63

Tota

l Me

rcu

ry C

on

cen

trat

ion

(n

g/L)

Lab

Site UB Total Mercury Results

Lab Results

Consensus Mean

20

Figure 9b. Box plots of reported total mercury concentrations for site UB. All concentrations


Figure 9c. Normal quantile-quantile plots of reported total mercury data for site UB. All


21

Figure 9d. Density functions of residuals (residual = individual measurement - laboratory mean)

of total mercury data for site UB. All values (left); non-outlier values (right).

Figure 9e. Residual (residual = individual measurement - laboratory mean) vs. fitted value plots

of reported total mercury concentrations for site UB. All values (left); non-outlier values (right).

22

Total mercury data, Site SP

Table 5. Laboratory performance for total mercury, site SP (samples 3, 5, 8). An asterisk


of that lab’s detection limit. Consensus Mean = 6.16 ng/L, Consensus Median = 6.12 ng/L


1 8.00 8.89 1.41 3

2 6.00 0.67 0.01 5

3 6.00 0.66 0.01 5

4 6.51 1.78 0.06 5


6 5.77 1.77 0.06 5

7 6.41 1.31 0.03 5


9 5.30 4.00 0.29 3

10 5.82 1.52 0.04 5

11 6.17 0.16 0.00 5

12 5.51 3.02 0.16 4

13 6.03 0.50 0.00 5

14 6.21 0.33 0.00 5

15 5.69 2.12 0.08 4


17 5.77 1.77 0.06 5


19 6.97 3.97 0.28 4

20 6.94 3.84 0.26 4

21 6.00 0.66 0.01 5

22 6.88 3.54 0.22 4

23 4.47 7.96 1.13 3


25 6.88 3.57 0.23 4

26 6.24 0.49 0.00 5

27 6.30 0.76 0.01 5

28 5.95 0.90 0.01 5

29 5.94 0.94 0.02 5

30 7.22 5.18 0.48 3

31 5.53 2.92 0.15 4

32 5.65 2.31 0.10 4


23


33 5.83 1.45 0.04 5

34 5.36 3.70 0.24 4

35 5.71 2.04 0.07 4


37 6.66 2.50 0.11 4

38 5.20 4.48 0.36 3

39 6.57 2.05 0.08 4

40 5.89 1.17 0.02 5

41 6.77 3.03 0.16 4

43 6.42 1.35 0.03 5

44 5.00 5.44 0.53 3

46 6.23 0.44 0.00 5

47 5.76 1.80 0.06 5

48 6.42 1.34 0.03 5

49 6.08 0.27 0.00 5

50 7.07 4.45 0.35 3

51 7.62 7.08 0.89 3

52 6.21 0.33 0.00 5


54 8.00 8.91 1.42 3

55 6.78 3.07 0.17 4

56 5.49 3.11 0.17 4

57 6.18 0.22 0.00 5


59 7.03 4.29 0.33 3

60 5.81 1.56 0.04 5

61 4.49 7.88 1.11 3

62 4.61 7.29 0.95 3

63 6.52 1.85 0.06 5

64 5.90 1.15 0.02 5

65 5.79 1.66 0.05 5

24

Figure 10. Total mercury results from all participating laboratories for site SP.

Figure 11a. Histograms of reported total mercury concentrations for site SP. All concentrations


0

5

10

15

20

25

30

35

40

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63

Tota

l Me

rcu

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on

cen

trat

ion

(n

g/L)

Lab

Site SP Total Mercury Results

Lab Results

Consensus Mean

25

Figure 11b. Box plots of reported total mercury concentrations for site SP. All concentrations


Figure 11c. Normal quantile-quantile plots of reported total mercury data for site SP. All


26

Figure 11d. Density functions of residuals (residual = individual measurement - laboratory

mean) of total mercury data for site SP. All values (left); non-outlier values (right).

Figure 11e. Residual (residual = individual measurement - laboratory mean) vs. fitted value

plots of reported total mercury concentrations for site SP. All values (left); non-outlier values

(right).

27

Summary of total mercury scores

Table 6. Summary of total mercury scores. Scores range from 0 (unacceptable) to 5 (very good).

An asterisk indicates that the score is based on at least one result that was below the reported

detection limit and was replaced by half of the detection limit.

Lab

Site

WH

Site

UB

Site

SP Mean

1 3 3 3 3.00

2 3 5 5 4.33

3 3 5 5 4.33

4 3 5 5 4.33

5 3 5 0 2.67

6 3 0 5 2.67

7 0 3 5 2.67

8 0 0 0 0.00

9 3 4 3 3.33

10 5 5 5 5.00

11 4 5 5 4.67

12 3 3 4 3.33

13 5 5 5 5.00

14 5 4 5 4.67

15 5 5 4 4.67

16 0* 0* 0* 0.00

17 4 4 5 4.33

18 2 0 0 0.67

19 3 0 4 2.33

20 4 4 4 4.00

21 3 5 5 4.33

22 3 5 4 4.00

23 3 3 3 3.00

24 4 0 0 1.33

25 3 5 4 4.00

26 4 5 5 4.67

27 5 5 5 5.00

28 4 5 5 4.67

29 4 5 5 4.67

30 3 4* 3 3.33

31 3 4 4 3.67

32 3 5 4 4.00


28

Lab

Site

WH

Site

UB

Site

SP Mean

33 4 3 5 4.00

34 4 5 4 4.33

35 3 3 4 3.33

36 0 0 0 0.00

37 4 4 4 4.00

38 3 5 3 3.67

39 4 4 4 4.00

40 5 5 5 5.00

41 3 4 4 3.67

43 5 5 5 5.00

44 3 4 3 3.33

46 4 5 5 4.67

47 5 5 5 5.00

48 5 5 5 5.00

49 4 5 5 4.67

50 3 5 3 3.67

51 2 0 3 1.67

52 3 5 5 4.33

53 4 3 0 2.33

54 3 4 3 3.33

55 3 5 4 4.00

56 3 4 4 3.67

57 5 5 5 5.00

58 4 0 0 1.33

59 3 4 3 3.33

60 4 5 5 4.67

61 3 4 3 3.33

62 0 3 1.50

63 3 5 5 4.33

64 3 5 5 4.33

65 3 5 5 4.33

29

Methylmercury data, Site WH

Table 7. Laboratory performance for methylmercury, site WH (samples 1, 4, 6). An asterisk





2 0.0721 13.96 5.72 2

4 0.00250* 7.86 1.82 3

5 0.0100* 5.51 0.89 3

7 0.0243* 1.02 0.03 5


9 0.0200 2.38 0.17 4

10 0.0319 1.35 0.05 5


13 0.0533 8.07 1.92 3

15 0.0200* 2.38 0.17 4

17 0.0242* 1.07 0.03 5

18 0.0357 2.54 0.19 4

20 0.0233 1.33 0.05 5

21 0.0100* 5.51 0.89 3

22 0.0347 2.23 0.15 4

25 0.0100* 5.51 0.89 3

27 0.0200* 2.38 0.17 4

32 0.0250* 0.81 0.02 5

33 0.0100* 5.51 0.89 3



36 0.0100* 5.51 0.89 3

37 0.0125* 4.73 0.66 3

41 0.0153 3.84 0.43 4

42 0.0170 3.32 0.32 4

45 0.0250* 0.81 0.02 5

47 0.0250 0.81 0.02 5

48 0.0273 0.08 0.00 5

49 0.0701 13.33 5.22 2


55 0.0500* 7.03 1.45 3


30



57 0.0244 1.00 0.03 5

58 0.0591 9.89 2.88 3

59 0.0349* 2.31 0.16 4


61 0.0333 1.80 0.10 5


63 0.0300* 0.76 0.02 5

64 0.0151 3.93 0.45 4

65 0.0340 2.01 0.12 4

Figure 12. Methylmercury results from all participating laboratories for site WH.

0

0.5

1

1.5

2

2.5

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62

Me

thyl

me

rcu

ry C

on

cen

trat

ion

(n

g/L)

Lab

Site WH Methylmercury Results

Lab Results

Consensus Mean

31

Figure 13a. Histograms of reported methylmercury concentrations for site WH. All


Figure 13b. Box plots of reported methylmercury concentrations for site WH. All concentrations


32

Figure 13c. Normal quantile-quantile plots of reported methylmercury data for site WH. All



mean) of methylmercury data for site WH. All values (left); non-outlier values (right).

33


plots of reported methylmercury concentrations for site WH. All values (left); non-outlier values

(right).

34

Methylmercury data, Site UB

Table 8. Laboratory performance for methylmercury, site UB (samples 2, 7, 9). An asterisk





2 0.119 0.81 0.02 5

4 0.148 2.03 0.11 4

5 0.109 1.86 0.09 5

7 0.118 0.91 0.02 5

8 0.117 1.00 0.03 5

9 0.117 1.07 0.03 5

10 0.136 0.80 0.02 5


13 0.143 1.56 0.07 5

15 0.150 2.21 0.13 4

17 0.0944 3.26 0.29 4

18 0.113 1.43 0.06 5

20 0.154 2.61 0.18 4

21 0.0930 3.40 0.31 4

22 0.202 7.37 1.47 3

25 0.111 1.63 0.07 5

27 0.167 3.85 0.40 4

32 0.123 0.45 0.01 5

33 0.0433 8.29 1.86 3

34 0.120 0.74 0.01 5


36 0.096 3.11 0.26 4

37 0.146 1.85 0.09 5

41 0.148 2.02 0.11 4

42 0.135 0.70 0.01 5

45 0.221 9.24 2.30 3

47 0.126 0.15 0.00 5

48 0.0973 2.97 0.24 4

49 0.0537 7.27 1.43 3

54 0.100 2.74 0.20 4

55 0.110 1.73 0.08 5

56 0.0827 Unreported values


35


57 0.174 4.54 0.56 3

58 0.111 1.61 0.07 5

59 0.138 1.00 0.03 5


61 0.130 0.24 0.00 5

62 0.109 1.79 0.09 5

63 0.155 2.67 0.19 4


65 0.163 3.53 0.34 4

Figure 14. Methylmercury results from all participating laboratories for site UB.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62

Me

thyl

me

rcu

ry C

on

cen

trat

ion

(n

g/L)

Lab

Site UB Methylmercury Results

Lab Results

Consensus Mean

36

Figure 15a. Histograms of reported methylmercury concentrations for site UB. All


Figure 15b. Box plots of reported methylmercury concentrations for site UB. All concentrations


37

Figure 15c. Normal quantile-quantile plots of reported methylmercury data for site UB. All



mean) of methylmercury data for site UB. All values (left); non-outlier values (right).

38


plots of reported methylmercury concentrations for site UB. All values (left); non-outlier values

(right).

39

Methylmercury data, Site SP

Table 9. Laboratory performance for methylmercury, site SP (samples 3, 5, 8). An asterisk





2 0.0961 0.77 0.02 5

4 0.117 2.01 0.10 4

5 0.0947 0.96 0.02 5

7 0.108 0.84 0.02 5

8 0.126 3.13 0.25 4

9 0.0933 1.14 0.03 5

10 0.120 2.40 0.15 4


13 0.113 1.50 0.06 5

15 0.113 1.50 0.06 5

17 0.0766 3.34 0.29 4

18 0.101 0.15 0.00 5

20 0.124 2.95 0.22 4

21 0.0784 3.11 0.25 4

22 0.139 4.84 0.60 3

25 0.0867 2.02 0.10 4

27 0.143 5.46 0.76 3

32 0.100 0.26 0.00 5

33 0.0600 5.53 0.78 3

34 0.0382 8.41 1.81 3


36 0.0773 3.25 0.27 4

37 0.127 3.26 0.27 4

41 0.101 0.17 0.00 5

42 0.104 0.31 0.00 5

45 0.172 9.20 2.17 3

47 0.100 0.26 0.00 5

48 0.0903 1.53 0.06 5

49 0.102 0.05 0.00 5

54 0.0970 0.65 0.01 5

55 0.0667* 4.65 0.56 3

56 0.0605 Unreported values


40


57 0.137 4.58 0.54 3

58 0.0849 2.25 0.13 4

59 0.125 3.09 0.24 4

60 0.0324* 9.18 2.16 3

61 0.0767 3.34 0.29 4

62 0.118 2.07 0.11 4

63 0.119 2.25 0.13 4

64 0.0926 1.23 0.04 5

65 0.123 2.73 0.19 4

Figure 16. Methylmercury results from all participating laboratories for site SP.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62

Me

thyl

me

rcu

ry C

on

cen

trat

ion

(n

g/L)

Lab

Site SP Methylmercury Results

Lab Results

Consensus Mean

41

Figure 17a. Histograms of reported methylmercury concentrations for site SP. All


Figure 17b. Box plots of reported methylmercury concentrations for site SP. All concentrations


42

Figure 17c. Normal quantile-quantile plots of reported methylmercury data for site SP. All



mean) of methylmercury data for site SP. All values (left); non-outlier values (right).

43


plots of reported methylmercury concentrations for site SP. All values (left); non-outlier values

(right).

44

Summary of methylmercury scores

Table 10. Summary of methylmercury scores. Scores range from 0 (unacceptable) to 5 (very

good). An asterisk indicates that the score is based on at least one result that was below the

reported detection limit and was replaced by half of the detection limit.

Lab

Site

WH

Site

UB

Site

SP Mean

2 2 5 5 4.00

4 3* 4 4 3.67

5 3* 5 5 4.33

7 5* 5 5 5.00

8 0 5 4 3.00

9 4 5 5 4.67

10 5 5 4 4.67

12 0 0 0 0.00

13 3 5 5 4.33

15 4* 4 5 4.33

17 5* 4 4 4.33

18 4 5 5 4.67

20 5 4 4 4.33

21 3* 4 4 3.67

22 4 3 3 3.33

25 3* 5 4 4.00

27 4* 4 3 3.67

32 5* 5 5 5.00

33 3* 3 3 3.00

34 0* 5 3 2.67

35 0 0 0 0.00

36 3* 4 4 3.67

37 3* 5 4 4.00

41 4 4 5 4.33

42 4 5 5 4.67

45 5* 3 3 3.67

47 5 5 5 5.00

48 5 4 5 4.67

49 2 3 5 3.33

54 4 5 4.50

55 3* 5 3* 3.67

56


45

Lab

Site

WH

Site

UB

Site

SP Mean

57 5 3 3 3.67

58 3 5 4 4.00

59 4* 5 4 4.33

60 0 0* 3* 1.00

61 5 5 4 4.67

62 5 4 4.50

63 5* 4 4 4.33

64 4 0 5 3.00

65 4 4 4 4.00

Table 11. List of the 64 participating laboratories to which samples were sent.

Laboratory Name Country

ACZ Laboratories Inc. USA

AEP Dolan Chemical Laboratory USA

Alpha Analytical Laboratories, Inc. USA

ALS Environmental (Vancouver) Canada

ALS Environmental (Winnipeg) Canada

ALS Technichem Sdn Bhd Malaysia

American Assay Laboratories USA

Basic Laboratory, Inc. USA

Battelle Marine Sciences Lab USA

Brigham Young University Mercury Lab USA

Brooks Rand Labs USA

Caltest Analytical Laboratory USA

City of San Jose ESD Laboratory USA

Clean Water Services Water Quality Laboratory (Oregon) USA

CNR Institute of Atmospheric Pollution Research Italy

CSIRO Land and Water Australia

Dartmouth College Trace Element Analysis Lab USA

Desert Research Institute USA

Dr. Carol Ptacek Lab, University of Waterloo Canada

Duke University/Hsu-Kim USA

Environment Canada - Burlington Canada

Environment Canada PYLET Canada

Flett Research Ltd. Canada

Geosciences Environment Toulouse France

Gustavus Adolphus College USA

IAEA-Environment Laboratories Monaco

IFREMER/LBCM France


46

Laboratory Name Country

Institut FA Forel, University of Geneva Switzerland

Institute of Geology, ASCR, v.v.i. Czech Republic

Instituto de Quimica/UNICAMP Brazil

IVL Swedish Environmental Research Institute Ltd Sweden

Jozef Stefan Institute Slovenia

Kentucky Environmental Services USA

Laboratory of Environmental Chemistry, Univ. of Athens Greece

Lakehead University Environmental Laboratory Canada

LEEQ - Environment Canada Canada

Lumex Analytics GMBH Germany

Marine Environmental Monitoring Centre of Guangxi Province China

Metro Wastewater Reclamation District USA

Microbac Laboratories, Inc. - Chicagoland Division USA

NIVA (Norwegian Institute for Water Research) Norway

North Carolina DENR Laboratory USA

Oak Ridge National Laboratory USA

Pace Analytical USA

Southeast Laboratory San Francisco PUC USA

SRC Environmental Analytical Laboratories Canada

SRCSD-EL (Sacramento) USA

Texas Tech University/Dr. Danny Reible Lab USA

Trace Element Laboratory, University of Oulu Finland

TU Braunschweig, Inst. für Geoökologie, Umweltgeochemie Germany

UNIR/Laboratorio de Biogeoquimica Ambiental Brazil

University of Alberta, Biogeochemical Service Laboratory Canada

University of Illinois USA

University of Ottawa Environ. Geochem. & Microbiol. Lab Canada

University of South Carolina USA

University of Utah Geology & Geophysics USA

University of Western Ontario, Analytical Services Canada

USGS Menlo Park USA

USGS Middleton USA

USGS Southeast Ecological Science Center USA

WE-Energies USA

Westminster College USA

Wisconsin State Lab of Hygiene USA

Woods Hole Oceanographic Institution USA

Discussion

The performance of most laboratories was satisfactory (mean score of 3) or better. Of the

63 labs that submitted total mercury results, 50 (79%) received average scores of 3 or higher, 35

47

labs (56%) received average scores of 4 or higher, and 8 labs (13%) received the maximum

average score of 5 (Table 6). Of the 41 labs that submitted methylmercury results, 36 labs (90%)

received average scores of 3 or higher, 24 labs (60%) received average scores of 4 or higher, and

3 labs (8%) received the maximum average score of 5 (Table 10). The percentage of labs

receiving THg scores equal to or greater than 3 (satisfactory) has decreased from 2013 and

previous years, while the percentage of labs receiving MeHg scores equal to or greater than 3 has

increased since 2013 (Table 12). Because individual labs are not identifiable in these results, it is

impossible to know if a change in the percentage of labs achieving a given score is due to

improvements or declines in performance, differences in the participant pool from one year to

the next, or differences in the samples being analyzed. It is important to note that sample

variability can have a significant effect on the number of labs receiving satisfactory scores. If a

sample has high natural variability in one analyte, such as total mercury at site MP in Intercomp

2013, it will create a wide range of satisfactory concentrations, driving up scores for that site.

Table 12. Number and percentage of labs achieving scores greater than or equal to 3, 4, and 5 in

each of the four years of the Brooks Rand Interlaboratory Comparison Study.

2011 2012 2013 2014

n % n % n % n %

Mean THg Score ≥ 3 33 79 40 82 50 85 50 79

Mean THg Score ≥ 4 22 52 36 73 45 76 35 56

Mean THg Score = 5 10 24 13 27 18 31 8 13

Mean MeHg Score ≥ 3 25 83 33 92 36 84 36 90

Mean MeHg Score ≥ 4 22 73 28 78 20 47 24 60

Mean MeHg Score = 5 8 27 13 36 6 14 3 8

The fact that the majority of laboratories participating in this study achieved a

satisfactory score for total mercury and methylmercury suggests that the intercomparability of

data among the majority of the participants is good. In every case, laboratories with an average

score of less than three (i.e. large differences from the consensus mean) had outliers for one or

more sites, indicating a significant analytical problem. One of the aims of this study is to help

these laboratories identify their analytical problems so that they can isolate the causes and

eliminate them. Labs with scores greater than three but less than five (i.e. smaller differences

from the consensus mean) may be able to improve their scores by assessing different sample

48

digestion/preparation methods, renewing their analytical standards, or cleaning/servicing their

analytical system, but likely do not have significant problems.

Method Data

By collecting information on the methodology and equipment each laboratory used to

analyze the samples, we attempted to assess the effectiveness of different analytical approaches.

We compared methods using t-tests on mean performance scores from each lab (we only

compared groups with n ≥ 4, and used α = 0.05). In Intercomp 2014, as in previous years, there

were few instances in which any method underperformed relative to any other (Tables 13-17).

The reason for the lack of significant differences in performance is likely due primarily to the

size of this study. Although the study involved a large number of participants, the wide variety of

methods in use and inconsistencies in the reporting of method characteristics often resulted in

very small groupings of results for any one method attribute. In many cases, robust comparisons

of performance between methods will require a more targeted study. However, another

conclusion that can be drawn from the lack of significant differences between methods is that a

wide variety of methods and equipment are capable of producing acceptable data. Participants

must assess for themselves whether their score indicates a method problem or other analytical

issue.

We found a significant difference between total mercury analysis using an automated

system (“automated” was defined as having an autosampler) vs. a manual system (p = 0.04;

Table 13), with automated instruments performing better; however, there was no significant

difference between automated and manual methylmercury systems (p = 0.12).

Table 13. Comparison of automated and manual systems. Automated systems are defined as

those with an autosampler. Manual systems are defined as all others. n = number of labs.

THg Median Score THg n MeHg Median Score MeHg n

Automated 4.00 44 4.17 28

Manual 3.83 18 4.00 11

49

Unlike in Intercomps 2012 and 2013, in Intercomp 2014, there was no significant

difference between total mercury amalgamation methods (dual gold, single gold, or no

amalgamation; Table 14), although the median score for analysis with no amalgamation is lower

than the others. There were also no significant differences between detector manufacturers

(Table 15), however the vast majority of the participants used Brooks Rand and Tekran

instruments, making it difficult to compare the performance of other instrument manufacturers.

Table 14. Comparison of total mercury amalgamation methods. n = number of labs.

Median Score n

Dual Gold 4.00 36

Single Gold 4.00 19

No Amalgamation 3.33 7

Table 15. Comparison of detector manufacturers. n = number of labs.

THg Median Score THg n MeHg Median Score MeHg n

Agilent (ICP-MS) 1.50 1 3.75 2

Analytik Jena 4.17 2

Brooks Rand 4.00 28 4.00 23

CETAC 4.33 4

Home-made 4.33 1

Leeman 4.67 3

Lumex 1.33 1

Nippon 3.33 1

PerkinElmer (ICP-MS) 4.33 2

PS Analytical 3.00 3

Tekran 4.17 18 4.33 9

Thermo (ICP-MS) 3.33 1 2.00 2

There were no significant differences between sample preparation methods for

methylmercury analysis (Table 16), although distillation-based methods have higher median

scores. As in previous years, the vast majority of labs continue to use distillation, following EPA

Method 1630, however an increasing number of labs are using non-distillation methods. In

Intercomp 2014, 11 labs (of 41 that submitted methylmercury results, 27%) did not distill

methylmercury samples; in Intercomp 2013, that number was 16%; in Intercomp 2012, 25%; in

Intercomp 2011, 20%.

50

Table 16. Comparison of methylmercury sample preparation procedures and reagents. n =

number of labs.

Median Score n

DCM Extraction 4.67 1

All Distillation 4.33 28

Distillation / APDC 4.33 10

Distillation / CuSO4 3.67 5

Distillation / KCl/H2SO4 4.50 2

Distillation / L-cysteine 4.33 5

Distillation / No reagents 4.17 6

Direct Ethylation 3.67 6

Other Non-Distillation 3.50 4

The majority of labs performing methylmercury analysis use packed GC columns (71%;

Table 17). Every lab that reported their packing material is using 15% OV-3 on Chromosorb

W/AW, the material specified in EPA Method 1630. Four labs reported using packed columns

but did not report their packing material. Of the labs using capillary columns, the majority are

using a DB-1 x 15 m length x 0.53 mm inner diameter x 5 µm coating thickness, the standard

column in a Tekran automated methylmercury system. The other capillary column type reported

was HP-5. One lab reported using a capillary GC column but did not describe it. One lab is using

ion chromatography (liquid chromatography) to separate mercury species. There were no

significant differences between packed and capillary GC columns, or between any specific

column types.

Table 17. Comparison of methylmercury separation methods. n = number of labs.

Median Score n

All Capillary Column 4.33 9

DB-1 x 15 m x 0.53 mm x 5 µm 4.50 6

HP-5 x 15 m x 0.32 mm x 0.25 µm 0.00 1

HP-5 x 15 m x 0.53 mm x 1.5 μm 4.67 1

All Packed Column 4.00 29

15% OV-3 on Chromosorb W/AW 4.33 25

Ion Chromatography (Dionex CG-5A) 4.50 1

51

To investigate possible links between storage conditions and measured total mercury

results, we collected data on the length of time and storage temperature between when BrCl was

added to total mercury samples and analysis. There were effectively no correlations between

storage time and measured concentrations for all three sites (Figure 15). The correlation

coefficients were small and insignificant at the 95% level. There were also no significant

correlations between storage temperature and measured concentrations (Figure 16). Some sample

types have been shown to require more rigorous oxidation than others in order to achieve

complete recovery of total mercury (Olson et al. 1997; Pyhtilä et al. 2012). However either these

samples are not sufficiently complex to require extra oxidation or they require a stronger

digestion than that provided by added time or temperature.

Figure 15. Plot of measured total mercury concentrations (lab means) vs. storage time after BrCl

addition to the samples. Holding times reported as > x hours were not included. Where a range of

values was reported (e.g. 8-12 hours), the mid-point was used.

R² = 0.0308

R² = 0.0061

R² = 0.0178

1

10

100

0 100 200 300 400 500

Me

an T

Hg

Co

nce

ntr

atio

n (

ng/

L)

Storage time (hours)

Site WH

Site UB

Site SP

52

Figure 16. Plot of measured total mercury concentrations (lab means) vs. sample storage

temperature after BrCl addition. Room temperature was assumed to be 20 °C. Where a range of

temperatures was given, the midpoint was used. If samples were held at a higher temperature for

several hours, followed by a lower temperature, they are plotted at the higher temperature.

Additional method data beyond what we include in the report did not reveal any

significant differences and were omitted for brevity.

Future Studies

Brooks Rand Instruments conducts this study on an annual basis. Any feedback on this

year’s study or interest in participating in future studies should be directed to Joel Creswell

([email protected]).

Acknowledgements

This study was made possible by the dedicated effort and input of many people. Carl

Lamborg at the Woods Hole Oceanographic Institution collected sample WH. Michela

Hernandez at EcoChem, Inc. received, organized, anonymized, and archived all of the data.

Kristina Obu Vazner, Vesna Fajon, Ermira Begu, and Milena Horvat at the “Jožef Stefan”

Institute and John DeWild at the U.S. Geological Survey Wisconsin Mercury Research Lab

generously performed extra analysis for the holding time study. The Hg Group at Brooks Rand

R² = 0.0034

R² = 0.0094

R² = 0.0044

1

10

100

-5 0 5 10 15 20 25 30 35 40 45 50 55 60 65

Me

an T

Hg

Co

nce

ntr

atio

n (

ng/

L)

Storage Temperature (°C)

Site WH

Site UB

Site SP

53

Labs (Becky Thorsness, Ashley Pittenger, Ian Joslin) performed holding time analysis and

analyzed site screening samples. James FrederickLindenfelser, Jennie Kim, and Candace

Kittleson packed and shipped sample bottles to participants. Brittany Nelson, Nathan Andersen,

and Frank McFarland provided insight and advice into the statistical analysis. In addition to the

participation fees, additional funding for this study was provided by Brooks Rand Instruments.

We thank everyone involved for helping make this study possible.

References

Cook, R. D., and S. Weisberg. 1980. Characterizations of an empirical influence function for detecting

influential cases in regression. Technometrics 495–508.

Creswell, J., V. Engel, A. Carter, and C. Davies. 2012. 2012 Brooks Rand Labs Interlaboratory

Comparison Study for Total Mercury and Methylmercury (Intercomp 2012). Brooks Rand Labs.

Filliben, J. J. 2012. Chapter 1. Exploratory Data Analysis, In C. Croarkin and P. Tobias [eds.],

NIST/SEMATECH e-Handbook of Statistical Methods.

http://www.itl.nist.gov/div898/handbook/eda/section3/eda35h.htm. Accessed 4/22/14.

Lin, P. E., and X. F. Niu. 1998. Statistical Analysis of Environmental Laboratory Data. Technical Report

LAB012. LAB012 Florida Department of Environmental Protection.

Niu, X.-F., and D. Miller. 2009. Statistical Analysis and Summary of the HgRR9 Mercury Round Robin

Data. Technical Report LAB027. LAB027 Florida Department of Environmental Protection.

Niu, X.-F., and A. Tintle. 2003. Statistical Analysis and Summary of the HgRR3 Mercury Round Robin


Niu, X.-F., and A. Tintle. 2008. Statistical Analysis and Summary of the HgRR8 Mercury Round Robin


Olson, M. L., L. B. Cleckner, J. P. Hurley, D. P. Krabbenhoft, and T. W. Heelan. 1997. Resolution of

matrix effects on analysis of total and methyl mercury in aqueous samples from the Florida

Everglades. Fresenius J. Anal. Chem. 358: 392–398.

54

Pyhtilä, H., P. Perämäki, J. Piispanen, M. Niemelä, T. Suoranta, M. Starr, T. Nieminen, M. Kantola, and

L. Ukonmaanaho. 2012. Development and optimization of a method for detecting low mercury

concentrations in humic-rich natural water samples using a CV-ICP-MS technique.

Microchemical Journal 103: 165–169.

U.S. Environmental Protection Agency. 1996. Method 1669: Sampling Ambient Water for Trace Metals

at EPA Water Quality Criteria Levels.

2014 brooks rand instruments interlaboratory comparison ......(v/v) bromine monochloride (brcl)...

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