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Just clearing out old emails. I cannot recall whether Chris interesting message "provoked" a response. I must admit I had not appreciated the %ADE pathway and the killer dust contribution.
Happy New Year.
Adam
CL:AIRE Bulletins on CWAC for Benzene and Benzo(a)pyrene
Many thanks to Paul, the LQM Team and CLA:IRE for publishing these bulletins.
I’ve had a general read through of benzene and BaP, so thought I’d dive in and start a discussion. I know Paul is always up for some robust debate.
RB15 & RB16 for BaP & Benzene
1% versus 6% SOM
Does anybody actually use organic SGV/GACs based on 6% SOM on any site, let alone sites impacted by coking works processes?
Reading between the lines of RB15/16 comments on made ground: as most urban and previously developed sites are likely to include shallow made ground deposits (all likely to be relatively low in SOM), are LQM of the view that a more cautious default 1% SOM is more appropriate for all UK published GAC/SGV?
We would agree with this stance – all our assessments already use GACs/SGVs based on 1% SOM as we do not believe that 6% SOM is justifiable for GACs based on the range of SOMs we typically see.
RESIDUAL PHASE CONTAMINATION
A position we often come across is a very simplistic one – “The modelling outputs are above saturation limits, therefore there might be free product, therefore CLEA/RTM can’t be used”. And this can be on sites with observed site concentrations well above RTM/CLEA sat limits and no separate phase contamination!
How to deal with separate phase contamination (including defining the terms) and the applicability of the CLEA/RTM algorithms is a broad issue that really needs to be dealt with more thoroughly/directly/clearly by the UK risk community (SoBRA?). But that’s for another day.
PATHWAY CONTRIBUTION
This is something that has been brought up JISCMail a number of times, so I’m surprised that LQM has adopted the CLEA 1.06 ‘Distribution by Pathway %’ outputs as a means to discuss the relative significance of each pathway (though there is some discussion about ‘contribution’ to the CWAC for inhalation wrt BaP).
The CLEA Distributions by Pathway are based on pathway intake/uptake (mg/day). However, the best way to understand the actual pathway significance is via %ADE (average daily exposure) contribution to the GAC/SGV/SAC. Unfortunately, the CLEA 1.06 does not give these outputs.
Using %ADE paints a more illuminating/accurate picture for BaP & benzene GACs at 1% SOM:
Bap Distribution by Pathway % in LQM Reports
Ingestion soil/dust: 45%
Home Grown (combined):25%
Outdoor dermal: 29%
Indoor Dermal: 1%
Indoor Dust: 0.14%
Indoor Vapour 0.02%
Bap %ADE by Pathway
Ingestion soil/dust: 30.6%
Home Grown 17%
Home Grown (soil attached): 0.4%
Outdoor dermal: 19.7%
Indoor Dermal: 0.8%
Indoor Dust: 27.7%
Indoor Vapour 3.4%
Outdoor surface 0.4%
And we all know why indoor dust is at 28% ADE for BaP – via the combination of Indoor Air Dust Loading and the Soil to Dust Transport factors.
Benzene Distribution by Pathway % in LQM Reports
Home Grown (combined):35%
Indoor vapour 65%
Bap %ADE by Pathway
Home Grown 70%
Indoor vapour 30%
Ingestion soil/dust: 0.2%
Home Grown (soil attached): 0.0%
From the above, the actual significance of the pathways for benzene are reversed from that alluded to in the LQM report.
INDOOR AIR VAPOUR CORRECTION FACTOR FOR BENZENE
I’m surprised LQM didn’t vary this parameter. Did the LQM team come to any conclusion about the data/research discussed in the CIRIA VOCs handbook?
VOLATILITY ASSESSMENT FOR BAP
Although overall vapour inhalation %ADE for BaP is small at 3.8%, did LQM consider ruling out vapour inhalation pathways for BaP using the Sufficient Volatility/Toxicity tests discussed in the CIRIA VOCs handbook?
PROBABILISTIC MODELLING
In general, it seems a lot of effort has been expended by adopting a probabilistic approach, with no apparent gain in revising the current GACs. Could LQM have seen this as a likely outcome of the exercise or quickly established this with a few test runs, thinking about the algorithms or parameter sensitivity analysis? See specific comments at end with regard to benzene.
I really hope the CL:AIRE RB documents do not mark a return to widespread use of a probabilistic approach in UK human health modelling. The last thing we need is added complexity for no benefit. However, as a technical review exercise, the documents do provide a useful additional resource for assessors to draw upon in generating SAC for materials impacted by coking works processes.
The biggest issue I see from the typical use of probabilistic modelling is that selected PDFs are adopted for specific parameters, 1000s of iterations run, and then 5th percentile adopted as the CWAC, thereby removing all the potential benefits of the probabilistic approach.
As the general approach of the EA SR documents was to adopt average/typical values in the SR CLEA CSMs, did LQM consider a different approach to the outputs from the probabilistic modelling, rather than the 5th percentile adopted in the withdrawn CLR-10/CLEA 2002?
WHAT DO RB15 & RB16 CHANGE FOR IMPACTS FROM COKING WORKS PROCESSES
BENZENE
Not a lot is changed by the CWAC, as acknowledged by LQM.
The existing GAC for 1% SOM is 0.08 mg/kg, with the CWAC 0.1 to 0.24 mg/kg. Essentially the same low concentration. I don’t envisage assessors adopting the higher numbers as GACs, though it’s good to have the 0.1 to 0.25 mg/kg range as a technical basis to possibly screen out lower concentrations as unlikely to be of concern.
The small potential increases in the CWAC should have been obvious to LQM from the start and they could have avoided probabilistic modelling altogether as the change in the CWAC for benzene is driven by indoor air as they decreased plant uptake.
The only parameter varied for indoor air was Koc and then the 5th percentile is taken at the end of the modelling process. The Agency SGV uses a Koc of 68, the LQM 5% percentile (ish) Koc is around 100, so the best you could hope for is a c. 30% increase in the indoor air pathway: i.e. the pathway only goes up from 0.27 to 0.34 mg/kg. (CLEA uses non-log values in the calculations). So as you decrease the significance of the veg pathway plant uptake (100% down to 10%), the CWAC tends towards the maximum of 0.34 mg/kg given by indoor air pathway at the 5th percentile Koc of 100.
For veg consumption, varying the Kow probabilistically does not change the CWAC outputs much: the Agency SGV uses a Kow of 135, the LQM Kow values range from 36 to 177 (min & max of triangle PDF): so the veg pathway can only vary from 0.11 to 0.16 mg/kg. This means that the biggest variation with regards to veg consumption takes place when LQM progressively decrease the plant uptake to 10%.
I would also disagree with LQM (their conclusions section) that a possible increase in the benzene CWAC from 0.08 mg/kg to 0.24 mg/kg (at 10% plant uptake) would represent a ‘significant increase’ for real world coking sites, especially where GACs are compared against data mean UCLs on redevelopment sites. Three times not a lot is still not a lot. So it’s a moderate improvement at best.
For benzene, it is my view that there has been no advantage of using probabilistic modelling over deterministic modelling and all LQM have done is effectively selected a different deterministic Koc to the EA SGV and qualitatively varied the significance of the veg pathway. This means that the outputs then just tend towards the indoor air pathway output at 0.4 mg/kg, which is based on the 5th percentile Koc value.
For redevelopment schemes, cover layers and vapour protection are typically employed, so the indoor vapour pathway is the driver to assess the level of reliance being placed on the vapour protection measures, so not a lot is changed by the CWAC approach using a revised Koc of 100 (SAC would go from 0.27 to 0.34 mg/kg).
Some of you will remember that before SR7, the widely adopted Koc for benzene was 134. Using this Koc, the SGV at 1% SOM would be 0.10 mg/kg.
BAP
Not a lot has really changed, as acknowledged by LQM. The existing GAC for 1% SOM is 0.83 mg/kg, and the CWAC of 0.9 up to 1.4 mg/kg are all essentially the same number i.e. 1 mg/kg.
As with benzene, I don’t envisage assessors adopting the slightly higher numbers as GACs, though it’s good have the new technical basis used to generate the 0.9 to 1.4 mg/kg range, as any new approach to help screen out some low BaP concentrations is welcomed. However, I really can’t see the cost of site-specific oral BaP bioaccessibility being worthwhile/feasible if all it could do (at best) is raise the CWAC from 0.9 to 1.4 mg/kg.
For BaP at sites impacted by coking works processes in a Redevelopment Scenario, existing site soils are not usually left at surface and redevelopment schemes usually adopt robust intervention measures such as appropriate cover layers and vapour protection. As BaP should (in line with VOCs handbook) be considered insufficiently volatile and not of concern via vapour inhalation, this usually means that BaP is not normally a human health substance of concern for sites appropriately remediated/redeveloped and the BaP CWAC is unlikely to be of much use to an assessor.
For BaP at potential Part IIa type sites (e.g. former coking work process areas now in residential use where any past remediation is undocumented or questionable, or adjacent land etc), the information in CWAC could provide additional mechanisms/information for assessors to generate SAC. However, the published CWAC is unlikely to significantly change an initial assessment compared with using the current GAC.
Although similar discussions could also be had for BaP about the worthiness of a probabilistic approach, versus an informed deterministic approach or detailed parameter/algorithm assessment, the LQM comments in the conclusions section are well considered and could help point the way to a more informed overall approach to the modelling of BaP (and not just on coking sites).
I hope all this starts off an open discussion and look forward to people thoughts.
Might need a break before arsenic.....
Kind regards
Chris Dainton
Peak Environmental Solutions Limited
Unit 10, Aston Ind Estate, Parsons Lane, Hope, Hope Valley, Derbyshire, S33 6RB
Tel: 01433 620030
www.peakenvironmentalsolutions.com
Adam Czarnecki
Director
McAuliffe Environmental
12 Bath Street
Hale
Cheshire
WA14 2HG
Mob: 07960 677677
Tel: 0161 9287740
www.mcauliffegroup.co.uk
Company Registered Office:
McAuliffe House, Northcott Road, Wolverhampton
WV14 0TP
Tel: 01902 354400
Fax: 01902 491455
Before printing this email, please think about the environment
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-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Chris Dainton
Sent: 21 September 2011 16:32
To: [log in to unmask]
Subject: LQM authored CL:AIRE CWAC for Benzene & BaP
CL:AIRE Bulletins on CWAC for Benzene and Benzo(a)pyrene
Many thanks to Paul, the LQM Team and CLA:IRE for publishing these bulletins.
I’ve had a general read through of benzene and BaP, so thought I’d dive in and start a discussion. I know Paul is always up for some robust debate.
RB15 & RB16 for BaP & Benzene
1% versus 6% SOM
Does anybody actually use organic SGV/GACs based on 6% SOM on any site, let alone sites impacted by coking works processes?
Reading between the lines of RB15/16 comments on made ground: as most urban and previously developed sites are likely to include shallow made ground deposits (all likely to be relatively low in SOM), are LQM of the view that a more cautious default 1% SOM is more appropriate for all UK published GAC/SGV?
We would agree with this stance – all our assessments already use GACs/SGVs based on 1% SOM as we do not believe that 6% SOM is justifiable for GACs based on the range of SOMs we typically see.
RESIDUAL PHASE CONTAMINATION
A position we often come across is a very simplistic one – “The modelling outputs are above saturation limits, therefore there might be free product, therefore CLEA/RTM can’t be used”. And this can be on sites with observed site concentrations well above RTM/CLEA sat limits and no separate phase contamination!
How to deal with separate phase contamination (including defining the terms) and the applicability of the CLEA/RTM algorithms is a broad issue that really needs to be dealt with more thoroughly/directly/clearly by the UK risk community (SoBRA?). But that’s for another day.
PATHWAY CONTRIBUTION
This is something that has been brought up JISCMail a number of times, so I’m surprised that LQM has adopted the CLEA 1.06 ‘Distribution by Pathway %’ outputs as a means to discuss the relative significance of each pathway (though there is some discussion about ‘contribution’ to the CWAC for inhalation wrt BaP).
The CLEA Distributions by Pathway are based on pathway intake/uptake (mg/day). However, the best way to understand the actual pathway significance is via %ADE (average daily exposure) contribution to the GAC/SGV/SAC. Unfortunately, the CLEA 1.06 does not give these outputs.
Using %ADE paints a more illuminating/accurate picture for BaP & benzene GACs at 1% SOM:
Bap Distribution by Pathway % in LQM Reports
Ingestion soil/dust: 45%
Home Grown (combined):25%
Outdoor dermal: 29%
Indoor Dermal: 1%
Indoor Dust: 0.14%
Indoor Vapour 0.02%
Bap %ADE by Pathway
Ingestion soil/dust: 30.6%
Home Grown 17%
Home Grown (soil attached): 0.4%
Outdoor dermal: 19.7%
Indoor Dermal: 0.8%
Indoor Dust: 27.7%
Indoor Vapour 3.4%
Outdoor surface 0.4%
And we all know why indoor dust is at 28% ADE for BaP – via the combination of Indoor Air Dust Loading and the Soil to Dust Transport factors.
Benzene Distribution by Pathway % in LQM Reports
Home Grown (combined):35%
Indoor vapour 65%
Bap %ADE by Pathway
Home Grown 70%
Indoor vapour 30%
Ingestion soil/dust: 0.2%
Home Grown (soil attached): 0.0%
From the above, the actual significance of the pathways for benzene are reversed from that alluded to in the LQM report.
INDOOR AIR VAPOUR CORRECTION FACTOR FOR BENZENE
I’m surprised LQM didn’t vary this parameter. Did the LQM team come to any conclusion about the data/research discussed in the CIRIA VOCs handbook?
VOLATILITY ASSESSMENT FOR BAP
Although overall vapour inhalation %ADE for BaP is small at 3.8%, did LQM consider ruling out vapour inhalation pathways for BaP using the Sufficient Volatility/Toxicity tests discussed in the CIRIA VOCs handbook?
PROBABILISTIC MODELLING
In general, it seems a lot of effort has been expended by adopting a probabilistic approach, with no apparent gain in revising the current GACs. Could LQM have seen this as a likely outcome of the exercise or quickly established this with a few test runs, thinking about the algorithms or parameter sensitivity analysis? See specific comments at end with regard to benzene.
I really hope the CL:AIRE RB documents do not mark a return to widespread use of a probabilistic approach in UK human health modelling. The last thing we need is added complexity for no benefit. However, as a technical review exercise, the documents do provide a useful additional resource for assessors to draw upon in generating SAC for materials impacted by coking works processes.
The biggest issue I see from the typical use of probabilistic modelling is that selected PDFs are adopted for specific parameters, 1000s of iterations run, and then 5th percentile adopted as the CWAC, thereby removing all the potential benefits of the probabilistic approach.
As the general approach of the EA SR documents was to adopt average/typical values in the SR CLEA CSMs, did LQM consider a different approach to the outputs from the probabilistic modelling, rather than the 5th percentile adopted in the withdrawn CLR-10/CLEA 2002?
WHAT DO RB15 & RB16 CHANGE FOR IMPACTS FROM COKING WORKS PROCESSES
BENZENE
Not a lot is changed by the CWAC, as acknowledged by LQM.
The existing GAC for 1% SOM is 0.08 mg/kg, with the CWAC 0.1 to 0.24 mg/kg. Essentially the same low concentration. I don’t envisage assessors adopting the higher numbers as GACs, though it’s good to have the 0.1 to 0.25 mg/kg range as a technical basis to possibly screen out lower concentrations as unlikely to be of concern.
The small potential increases in the CWAC should have been obvious to LQM from the start and they could have avoided probabilistic modelling altogether as the change in the CWAC for benzene is driven by indoor air as they decreased plant uptake.
The only parameter varied for indoor air was Koc and then the 5th percentile is taken at the end of the modelling process. The Agency SGV uses a Koc of 68, the LQM 5% percentile (ish) Koc is around 100, so the best you could hope for is a c. 30% increase in the indoor air pathway: i.e. the pathway only goes up from 0.27 to 0.34 mg/kg. (CLEA uses non-log values in the calculations). So as you decrease the significance of the veg pathway plant uptake (100% down to 10%), the CWAC tends towards the maximum of 0.34 mg/kg given by indoor air pathway at the 5th percentile Koc of 100.
For veg consumption, varying the Kow probabilistically does not change the CWAC outputs much: the Agency SGV uses a Kow of 135, the LQM Kow values range from 36 to 177 (min & max of triangle PDF): so the veg pathway can only vary from 0.11 to 0.16 mg/kg. This means that the biggest variation with regards to veg consumption takes place when LQM progressively decrease the plant uptake to 10%.
I would also disagree with LQM (their conclusions section) that a possible increase in the benzene CWAC from 0.08 mg/kg to 0.24 mg/kg (at 10% plant uptake) would represent a ‘significant increase’ for real world coking sites, especially where GACs are compared against data mean UCLs on redevelopment sites. Three times not a lot is still not a lot. So it’s a moderate improvement at best.
For benzene, it is my view that there has been no advantage of using probabilistic modelling over deterministic modelling and all LQM have done is effectively selected a different deterministic Koc to the EA SGV and qualitatively varied the significance of the veg pathway. This means that the outputs then just tend towards the indoor air pathway output at 0.4 mg/kg, which is based on the 5th percentile Koc value.
For redevelopment schemes, cover layers and vapour protection are typically employed, so the indoor vapour pathway is the driver to assess the level of reliance being placed on the vapour protection measures, so not a lot is changed by the CWAC approach using a revised Koc of 100 (SAC would go from 0.27 to 0.34 mg/kg).
Some of you will remember that before SR7, the widely adopted Koc for benzene was 134. Using this Koc, the SGV at 1% SOM would be 0.10 mg/kg.
BAP
Not a lot has really changed, as acknowledged by LQM. The existing GAC for 1% SOM is 0.83 mg/kg, and the CWAC of 0.9 up to 1.4 mg/kg are all essentially the same number i.e. 1 mg/kg.
As with benzene, I don’t envisage assessors adopting the slightly higher numbers as GACs, though it’s good have the new technical basis used to generate the 0.9 to 1.4 mg/kg range, as any new approach to help screen out some low BaP concentrations is welcomed. However, I really can’t see the cost of site-specific oral BaP bioaccessibility being worthwhile/feasible if all it could do (at best) is raise the CWAC from 0.9 to 1.4 mg/kg.
For BaP at sites impacted by coking works processes in a Redevelopment Scenario, existing site soils are not usually left at surface and redevelopment schemes usually adopt robust intervention measures such as appropriate cover layers and vapour protection. As BaP should (in line with VOCs handbook) be considered insufficiently volatile and not of concern via vapour inhalation, this usually means that BaP is not normally a human health substance of concern for sites appropriately remediated/redeveloped and the BaP CWAC is unlikely to be of much use to an assessor.
For BaP at potential Part IIa type sites (e.g. former coking work process areas now in residential use where any past remediation is undocumented or questionable, or adjacent land etc), the information in CWAC could provide additional mechanisms/information for assessors to generate SAC. However, the published CWAC is unlikely to significantly change an initial assessment compared with using the current GAC.
Although similar discussions could also be had for BaP about the worthiness of a probabilistic approach, versus an informed deterministic approach or detailed parameter/algorithm assessment, the LQM comments in the conclusions section are well considered and could help point the way to a more informed overall approach to the modelling of BaP (and not just on coking sites).
I hope all this starts off an open discussion and look forward to people thoughts.
Might need a break before arsenic.....
Kind regards
Chris Dainton
Peak Environmental Solutions Limited
Unit 10, Aston Ind Estate, Parsons Lane, Hope, Hope Valley, Derbyshire, S33 6RB
Tel: 01433 620030
www.peakenvironmentalsolutions.com
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