Now that the US EPA has classified
TCE as a carcinogen, and dangerous at levels previously
believed to be safe, what will happen to risk assessments and other
regulatory decision-making in Ontario? Noted risk assessor, Brett Ibbotson, tells me that the new numbers
are two to four times as stringent as the ones just adopted on July
1, 2011, in Ontario:
"The reassessment of TCE by the US EPA includes revising
its toxicity reference values (TRVs). For TCE, the most important
types of health effects are non-threshold effects such as cancer,
so this brief email does not discuss the TRVs for threshold
For exposures via ingestion and dermal contact, the
"new" US TRV is about 3.5 times more stringent than the
TRV used in the revised (July 2011) MOE standards. This means that
if you previously estimated a risk of say 5 x 10-7 that you thought
was acceptable, it will be 3.5 times higher or 1.8 x 10-6 and
therefore not acceptable.
For exposures via inhalation, the "new" US TRV is
about 2 times more stringent than the TRV used in the revised MOE
standards. This means that if you previously estimated a risk of
0.9 x 10-6 that you thought was acceptable, it will be 2 times
higher or 1.8 x 10-6 and therefore not acceptable.
I expect that for a while, the MOE will accept RAs based on the
TRVs in the 2011 Rationale document, but the MOE also says that RAs
should make use of scientific advances and so eventually it will
condone and then expect RAs to use the "new" TRVs from
the US EPA. It is difficult to predict when the MOE will make that
transition. I would say maybe by the spring of 2012.
(BTW – The TRV cited in the MOE Rationale document is
a value recommended by the California EPA in 2005. With numerous
agencies following their separate timelines, it means that there is
almost always some agency out there that has more stringent
information than the others. The others either eventually catch up,
or in some cases chose to disagree with one another's
Thank you so much for this glimpse ahead, Brett!
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