Hi all
The Environment Agency says that where a contaminant is considered to exhibit non-threshold effects (i.e. a threshold for adverse health effects cannot be presumed) then an Index Dose should be used for the assessment.
A site being redeveloped has used RBCA for the risk assessment so I asked for confirmation that Index Doses have been used instead of slope factors. They responded that:
within the RBCA model, slope factors are used to derive an index dose
(Risk-BAsed Exposure Limit):
Carcinogens: RBEl=TR/(E*SF)
Upon consultation with the Environment Agency, they confirmed that the approach outlined within the CLR package of documents is that Index Doses should be used rather than slope factors. They continued: "when using models such as RBCA and RISC they can be modified to undertake an assessment broadly consistent with the CLEA model and the toxicological approaches set out in CLR9. In particular, we can see no technical reason why the index dose for benzo(a)pyrene cannot be used within RBCA if that is what is required, although the actual process of converting and inputting an index dose into to model needs to be undertaken with some care as it cannot be merely substituted for a slope factor."
But now I still don't know how they would convert the index dose into the model to check it's been done correctly, nor whether their suggestion for the conversion of slope factors is feasible. I've tried asking the EA this and whether there is any information about how we are to audit model outputs for all the necessary model changes (for a non-UK model) if we don't have specific details on what needs to be changed at every step of the way and how it is done. I haven't received a response yet.
Can anyone help with this slope factors issue? It seems to be that the CLEA derived index doses should be used instead of the conversion that the consultant's have done. Can anyone confirm this?
Many thanks, and a happy bank holiday weekend to you all.
Fleur
Pollution Control Officer
Spelthorne Borough Council
Tel: 01784 446 256
Fax: 01784 446 437
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