I have some issues with the EA CLEA team over how CLEA 1.04 is presenting
pathway contribution information at ‘Step 5: Results’ for SAC calculations.
I think it is misleading and can lead to users misunderstanding the model
output. The Agency CLEA Team disagree and say what is presented is ‘right’.
See what you think in this simple example for BaP:
Active Pathways: Residential Soil Ingestion & Indoor Dust Inhalation
STEP 5 RESULTS OUTPUT
Ingestion Output: 2.70 mg/kg
Inhalation Output: 2.98 mg/kg
Combined SAC: 1.41 mg/kg
Ratio of ADE to HCV
Oral: 0.52 (i.e. 52%)
Inhalation: 0.48 (i.e. 48%)
Pathway Contributions:
Direct Soil Ingestion: 99.68%
Inhalation Indoor Dust: 0.32%
See the apparent discrepancy? It is obvious in this simple example, but it
would be really difficult to unpack the actual significance of each pathway
when more than two pathways are selected. This can lead to a very wrong
impression of what pathways are actually the most significant in terms of
exposure - which after all the most important thing we want to know!
The ‘pathway contribution’ percentage is calculated from the actual physical
intake of BaP (hidden away on Page 6 of 11 of the report as average daily
exposure) irrespective of its relation to the oral & inhalation HCV:
Page 6 of 11 Report output:
Ingestion: 0.0000105 mg/kg-bw/day (99.68% of total)
Inhalation: 0.0000000333 mg/kg-bw/day (0.32 % of total)
So although inhalation only provides 0.32% of total chemical intake into the
body, it actually provides 48% of the safe level of exposure. This would be
become lost for multiple pathways in the way CLEA is currently presenting
outputs and you would need to calculate this understanding by hand.
In my mind, we should want the CLEA model to tell us on a pathway by
pathway basis the ADE ratios. I’m no really that interested as a risk assessor
in the physical amount going into the receptor: sure its interesting to know,
but it doesn’t shed light on how the model is giving rise to the outputs:
COMPLEX example for BaP (All pathways Active):
STEP 5 RESULTS OUTPUT
Ingestion Output: 1.21 mg/kg
Inhalation Output: 2.62 mg/kg
Combined SAC: 0.826 mg/kg
Ratio of ADE to HCV
Oral: 0.68 (i.e. 68%)
Inhalation: 0.32 (i.e. 32%)
CLEA 1.04 ‘Pathway Contributions’:
Soil Ingestion: 44.65%
Veg Consumption: 25.37%
Dermal Indoor: 1.09%
Dermal Outdoors: 28.73%
Dust Indoors: 0.14%
Dust Outdoors: 0%
Vapour Indoors: 0.02%
Vapour Outdoors: 0%
TOTAL ORAL: 99.84%
TOTAL INHALATION: 0.16%
Whereas the actual ADE ratios for each pathway are as follows:
Soil Ingestion: 31%
Veg Consumption: 17%
Dermal Indoor: 1%
Dermal Outdoors: 20%
Dust Indoors: 29%
Dust Outdoors: 0%
Vapour Indoors: 3%
Vapour Outdoors: 0%
TOTAL ORAL: 68%
TOTAL INHALATION: 32%
Which gives an entirely different picture of the significance of each pathway.
If you think that CLEA 1.04 is giving the wrong impression and you want it
presented in a different way, then send an email to the CLEA Team via the
national enquires email ([log in to unmask]) as they don’t
seem interested in listening to just me.
Chris Dainton
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