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Despite the lack of data the decision was taken to use route-to-route extrapolation unless there
was evidence to suggest that this was not appropriate. The alternative would have been to not
derive GAC for these compounds. This option was considered less useful than having a set of
GAC for compounds where there remained some uncertainty in the inhalation HCV used to derive
them.
There were two cases where route-to-route extrapolation was considered inappropriate:
1‐methylnaphthalene and 2-methylnaphthalene, both of which have an HCV oral
but no HCV inhal
.
There was evidence to suggest that the toxicity of these compounds via inhalation was likely to
be significantly greater than their toxicity via ingestion and therefore use of the HCV oral
may have
resulted in GAC that were unprotective.
• Where alternative health criteria were available from different authoritative sources then priority
was given to the most recent expert reviews, provided these had considered all available data.
Preference was also given to longer term studies. Where there was no clear case for selection of a
particular HCV, priority was given to the most conservative.
• Three contaminants were considered as non-threshold substances; 1-methylnaphthalene,
bromodichloromethane and carbazole. There were insufficient data to derive an ID for carbazole.
Dose-response data with reported 95 th percentile lower confidence limit benchmark dose
levels (BMDL10) derived from animal experiments involving oral exposure were available for
1‐methylnaphthalene and bromodichloromethane and these were used to derive the ID oral
for each
contaminant in accordance with the methodology given in the Environment Agency of England and
Wales SR2 report.
Methodology
• Reference concentrations (RfC) have been converted to inhalation HCV in accordance with the
Environment Agency of England and Wales SR2 guidance, i.e. by multiplying by 20 m 3 of air inhaled
per day and dividing by 70 kg standard body mass.
3.3
Selection of Mean Daily Intakes
The procedures for collation and choice of mean daily intake (MDI) were in general accordance with the principles
set out in the Environment Agency of England and Wales SR2 document. As with the HCV, all 33 sources listed
in Appendix A of the SR2 report were consulted and relevant data for each contaminant were summarised on the
contaminant proformas. Again, sources that held no data relevant to the substance have been removed from the
proforma to reduce the overall length of Appendix B. Assumptions used in the selection of recommended MDI are
summarised below:
• MDI have been based on available relevant data. Data from near point sources were not considered
relevant and have not been used for the derivation of MDI.
• Preference has been given to data on likely average exposure to the UK population. If no UK
data were available preference was given to average exposure from other countries. Where only
maximum values were reported, but did not relate to point sources, then these were used as a
conservative estimate of MDI.
• Where suitable data were available from more than one information source and there was no
obvious preference for one of these sources then the most conservative (highest) value was chosen
as the basis of the MDI.
• If no data were available and the literature suggests the exposure is likely to be negligible, the MDI
has been set to zero, in line with SR2.
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