agency comments on erm proposal for hrms reanalysis … · agency comments on erm proposal for hrms...
TRANSCRIPT
1
AGENCY COMMENTS ON ERM PROPOSAL FOR HRMS REANALYSIS
28 April 2015
ERM has proposed that all samples of solid media (soil, sediment) collected from the inner PRIs
in the Phase 1A/B investigation be analyzed for dioxins/furans/PCBs by Low Resolution Mass
Spectroscopy (LRMS), and that, depending on the results of the LRMS analysis, a subset would
be re-analyzed by High Resolution Mass Spectroscopy (HRMS). In accord with EPA
suggestions, ERM has proposed a trigger for HRMS reanalysis that is intended to ensure that
samples with HQ values for TEQ nearing a decision threshold would be identified for reanalysis.
The specific rule proposed is that samples with OCDF concentrations lower than 40 ug/kg be
reanalyzed by HRMS. Given typical concentration ratios of TEQ risk drivers to OCDF, ERM
indicated that samples with 40 ug/kg or higher of OCDF would have detectable levels of most
TEQ risk drivers, and HQ values for TEQ would be well above the level of concern. If so,
results of the LRMS analysis would likely be adequate for risk assessment and risk management
decision making.
This approach is conceptually sound, but there is a potential problem. ERM evaluated the range
of expected HQ values based on the lowest RBC available (0.00012 ug/kg). This might seem to
be appropriate, but it is actually anti-conservative to focus on the lowest RBC. This is because
the higher the RBC, the lower the HQ values, and the more samples that approach the “grey
zone” (HQ values close to the decision threshold) for decision-making. In this regard, the RBCs
for exposure of mammalian ecological receptors (fox, shrew) to TEQ derived during the
refinement step are in the range of 0.02 to 0.3 ug/kg, substantially higher than the value of
0.00012 ug/kg used in ERM’s assessment. The RBC values for humans exposed to TEQ are
likely to be even somewhat higher, depending on site-specific and PRI-specific exposure
assumptions. The current default recommended by EPA headquarters1 for an outdoor worker is
0.8 ug/kg.
The basic problem is illustrated in Figure 1. Panel A plots HQ values based on mammalian2
TEQ for the historic data using the proposed RBC of 0.00012 ug/kg, and Panel B plots the values
using an RBC of 0.8 ug/kg. As seen, if the RBC were 0.00012, then HQ values at an OCDF
trigger of 40 ug/kg would be well above the grey zone. However, if the RBC is 0.8 ug/kg, then
most HQ values at the trigger are in the grey zone. Based on this, EPA believes the selection of
a trigger for HRMS needs to be based on a consideration of the expected results using the
highest, not the lowest, RBC value that is likely to be applicable.
1 http://epa-prgs.ornl.gov/cgi-bin/chemicals/csl_search 2 For avian receptors, TEQ is dominated by HCB. All TEQ values used in this discussion are based on
mammalian TEFs.
2
Granted that the RBC value is based on the highest reasonably expected, the next critical step is
deciding how to recognize a sample when a reanalysis is needed. EPA proposes that the basic
rule is: reanalysis is needed when the difference between LRMS and HRMS becomes
significant for decision-making (i.e., LRMS yields a different decision than HRMS). Based on
this, EPA feels the most informative data that are presently available are the set of 8 samples that
were analyzed by both LRMS and HRMS as part of the DMA. The basic approach is to plot the
HQ value for workers (RBC = 0.8 ug/kg TEQ) based on both LRMS and HRMS as a function of
OCDF, and see where the difference between the two becomes large enough that the LRMS
would not be considered optimal and HRMS would be needed.
This, in turn, raises a question as to how ND congeners in the LRMS analysis will be treated in
the calculation of TEQ. For simplicity, substitution of ND=1/2DL has been used to date3.
The results are shown in Figure 2. Although a data set of only 8 samples is too small to be
highly confident, the main conclusions seem to be:
1. At high values of OCDF (e.g., above 5,000 ug/kg), there is not much difference between
LRMS and HRMS, and LRMS results will likely be adequate.
2. As OCDF levels decrease, a difference begins to emerge, with the LRMS samples
tending to yield higher TEQ and HQ values than the HRMS.
3. The concentration at which the difference begins to become important is difficult to judge
with such a limited data set, but it seems likely it is in the range of 500 to 5,000 ug/kg
OCDF. Above this range, risk conclusions are likely to be the same by both methods,
while below this range, risk conclusions based on LRMS TEQ would likely be biased
high.
Based on this, EPA has concluded that an OCDF trigger of about 500-1000 ug/kg is needed to
prevent substantial overestimation of hazard from samples in the low end of the risk range.
3 EPA Region 8 has also briefly investigated the use of EPA’s KM TEQ calculator spreadsheet
tool, but it appears the results are generally similar to the ND=1/2DL approach.
3
FIGURE 1
HQ vs OCDF FOR LOW AND HIGH RBC VALUES
BASED ON HISTORIC DATA
Panel A: RBC = 0.00012 ug/kg
Panel B: RBC = 0.8 ug/kg
0.01
0.1
1
10
100
1000
10000
100000
1000000
0.01 0.1 1 10 100 1000 10000
HQ
OCDF (ug/kg)
0.01
0.1
1
10
100
1000
10000
100000
0.01 0.1 1 10 100 1000 10000
HQ
OCDF (ug/kg)
OCDF = 40
OCDF = 40
4
FIGURE 2
COMPARISON BETWEEN LRMS AND HRMS ESTIMATES OF HQ
BASED ON PAIRED SAMPLES FROM THE DMA
0.1
1
10
100
10 100 1000 10000
HQ
OCDF (ug/kg)
LRMS ND=1/2DL
HRMS ND = 1/2DL
OCDF = 500OCDF = 40
1
AGENCY COMMENTS ON ERM PROPOSAL FOR HRMS REANALYSIS
28 April 2015
ERM has proposed that all samples of solid media (soil, sediment) collected from the inner PRIs
in the Phase 1A/B investigation be analyzed for dioxins/furans/PCBs by Low Resolution Mass
Spectroscopy (LRMS), and that, depending on the results of the LRMS analysis, a subset would
be re-analyzed by High Resolution Mass Spectroscopy (HRMS). In accord with EPA
suggestions, ERM has proposed a trigger for HRMS reanalysis that is intended to ensure that
samples with HQ values for TEQ nearing a decision threshold would be identified for reanalysis.
The specific rule proposed is that samples with OCDF concentrations lower than 40 ug/kg be
reanalyzed by HRMS. Given typical concentration ratios of TEQ risk drivers to OCDF, ERM
indicated that samples with 40 ug/kg or higher of OCDF would have detectable levels of most
TEQ risk drivers, and HQ values for TEQ would be well above the level of concern. If so,
results of the LRMS analysis would likely be adequate for risk assessment and risk management
decision making.
This approach is conceptually sound, but there is a potential problem. ERM evaluated the range
of expected HQ values based on the lowest RBC available (0.00012 ug/kg). This might seem to
be appropriate, but it is actually anti-conservative to focus on the lowest RBC. This is because
the higher the RBC, the lower the HQ values, and the more samples that approach the “grey
zone” (HQ values close to the decision threshold) for decision-making. In this regard, the RBCs
for exposure of mammalian ecological receptors (fox, shrew) to TEQ derived during the
refinement step are in the range of 0.02 to 0.3 ug/kg, substantially higher than the value of
0.00012 ug/kg used in ERM’s assessment. The RBC values for humans exposed to TEQ are
likely to be even somewhat higher, depending on site-specific and PRI-specific exposure
assumptions. The current default recommended by EPA headquarters1 for an outdoor worker is
0.8 ug/kg.
The basic problem is illustrated in Figure 1. Panel A plots HQ values based on mammalian2
TEQ for the historic data using the proposed RBC of 0.00012 ug/kg, and Panel B plots the values
using an RBC of 0.8 ug/kg. As seen, if the RBC were 0.00012, then HQ values at an OCDF
trigger of 40 ug/kg would be well above the grey zone. However, if the RBC is 0.8 ug/kg, then
most HQ values at the trigger are in the grey zone. Based on this, EPA believes the selection of
a trigger for HRMS needs to be based on a consideration of the expected results using the
highest, not the lowest, RBC value that is likely to be applicable.
1 http://epa-prgs.ornl.gov/cgi-bin/chemicals/csl_search 2 For avian receptors, TEQ is dominated by HCB. All TEQ values used in this discussion are based on
mammalian TEFs.
2
Granted that the RBC value is based on the highest reasonably expected, the next critical step is
deciding how to recognize a sample when a reanalysis is needed. EPA proposes that the basic
rule is: reanalysis is needed when the difference between LRMS and HRMS becomes
significant for decision-making (i.e., LRMS yields a different decision than HRMS). Based on
this, EPA feels the most informative data that are presently available are the set of 8 samples that
were analyzed by both LRMS and HRMS as part of the DMA. The basic approach is to plot the
HQ value for workers (RBC = 0.8 ug/kg TEQ) based on both LRMS and HRMS as a function of
OCDF, and see where the difference between the two becomes large enough that the LRMS
would not be considered optimal and HRMS would be needed.
This, in turn, raises a question as to how ND congeners in the LRMS analysis will be treated in
the calculation of TEQ. For simplicity, substitution of ND=1/2DL has been used to date3.
The results are shown in Figure 2. Although a data set of only 8 samples is too small to be
highly confident, the main conclusions seem to be:
1. At high values of OCDF (e.g., above 5,000 ug/kg), there is not much difference between
LRMS and HRMS, and LRMS results will likely be adequate.
2. As OCDF levels decrease, a difference begins to emerge, with the LRMS samples
tending to yield higher TEQ and HQ values than the HRMS.
3. The concentration at which the difference begins to become important is difficult to judge
with such a limited data set, but it seems likely it is in the range of 500 to 5,000 ug/kg
OCDF. Above this range, risk conclusions are likely to be the same by both methods,
while below this range, risk conclusions based on LRMS TEQ would likely be biased
high.
Based on this, EPA has concluded that an OCDF trigger of about 500-1000 ug/kg is needed to
prevent substantial overestimation of hazard from samples in the low end of the risk range.
3 EPA Region 8 has also briefly investigated the use of EPA’s KM TEQ calculator spreadsheet
tool, but it appears the results are generally similar to the ND=1/2DL approach.
3
FIGURE 1
HQ vs OCDF FOR LOW AND HIGH RBC VALUES
BASED ON HISTORIC DATA
Panel A: RBC = 0.00012 ug/kg
Panel B: RBC = 0.8 ug/kg
0.01
0.1
1
10
100
1000
10000
100000
1000000
0.01 0.1 1 10 100 1000 10000
HQ
OCDF (ug/kg)
0.01
0.1
1
10
100
1000
10000
100000
0.01 0.1 1 10 100 1000 10000
HQ
OCDF (ug/kg)
OCDF = 40
OCDF = 40
4
FIGURE 2
COMPARISON BETWEEN LRMS AND HRMS ESTIMATES OF HQ
BASED ON PAIRED SAMPLES FROM THE DMA
0.1
1
10
100
10 100 1000 10000
HQ
OCDF (ug/kg)
LRMS ND=1/2DL
HRMS ND = 1/2DL
OCDF = 500OCDF = 40