What effect will the changes have on the SGV values being produced?
We have made some further changes to the CLEA model and the supporting technical documentation and software in response to the evaluation period. In particular, these changes affect the assessment of exposure via the indoor inhalation pathways and in all cases decrease the level of exposure predicted. The overall impact on the output assessment criteria is in most cases likely to be small. The most significant changes to our approach were made previously and were set out in the technical package published in August 2008. These revisions were based on our review of the science and our desire to make our guidance documents clearer and easier to use. Every chemical is different and so the impacts of all these changes in how we derive HCV and calculate SGV will vary substantially between substances. In general, the greatest changes will be seen for chemicals in situations when; • for contaminants producing threshold toxicity, background exposure to non-soil sources is greater than fifty pe
