What the Agency has done is essentially create a new sub-pathway for the
indoor air dust pathway.
Indoor dust now comprises of two elements:
1. A dust element based on the outdoor PEF (i.e. outdoor dust blowing into
the house)
2. A dust element based on an indoor suspended dust concentration created
from indoor dust.
The second element uses an inputted indoor dust concentration in air (default
of 60 ug/m3 for residential and 100 mg/m3 for commercial).
A proportion of this suspended dust is then assumed to be derived from
outdoor soil tracked back into the building. The default position is that 70%
(i.e. the 0.7 factor) of the suspended dust is derived from outdoor soil. This
means that for residential there is 42 ug/m3 of contaminated soil suspended in
the indoor breathing air.
The second element is why we are no seeing indoor dust as the "new killer"
giving rise to much lower criteria for indoor dust compared to the CLR-10
model and the outdoor SR3 output. This is especially pertinent for compounds
with very low inhalation HCV compared with their Oral HCV - e.g. BaP !
These two elements are independent of each other and the intake for each is
summed. This means that a possible double accounting via Element 1 & 2
needs further consideration.
I am 75% of the way through doing a ground up model build of our own
SR2/SR3/SR4 model and have just codified the dust pathway.
For BaP (beta output - model not yet fully QA’d)
For AC-1-6 model give outdoor dust as 3,920 mg/kg
For AC-1-6 model give indoor dust as 1.8 mg/kg
Without the Dust Element 1, for AC-1-6 model gives indoor dust as 177 mg/kg
Without the Dust Element 2, for AC-1-6 model gives indoor dust as 1.8 mg/kg
So the indoor dust killer is down to the new sub-pathway and the combination
of the default dust concentration in air and the assumption of how much of
that dust is derived from outdoor soil.
Quite frankly, it just another example of how poorly thought out the
implementation of SR3 has been to date.
And having now codified most of SR2-4, I am at a loss how the Agency has
made their Excel software such a pain to use. There is no excuse. (For
example, I got all the modelling answers shown above out of our model in
under 10 seconds).
I hope to post some other “things you need to know about New CLEA” in the
coming weeks (have had a long back and forth saga with the EA over the new
surface soil pathway for vapour inhalation, but that’s for another time)
If people are unhappy with the default conceptualisation of the indoor dust
pathway, I suggest emails are sent to CLEA comments.
The last thing we need all need is another stupid pathway to worry about.
Chris Dainton
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