posted on 2006-04-01, 00:00authored byJon A. Arnot, Don Mackay, Eva Webster, Jeanette M. Southwood
A screening level risk assessment model is developed
and described to assess and prioritize chemicals by estimating
environmental fate and transport, bioaccumulation, and
exposure to humans and wildlife for a unit emission rate.
The most sensitive risk endpoint is identified and a
critical emission rate is then calculated as a result of that
endpoint being reached. Finally, this estimated critical
emission rate is compared with the estimated actual emission
rate as a risk assessment factor. This “back-tracking”
process avoids the use of highly uncertain emission rate
data as model input. The application of the model is
demonstrated in detail for three diverse chemicals and in
less detail for a group of 70 chemicals drawn from the
Canadian Domestic Substances List. The simple Level II and
the more complex Level III fate calculations are used to
“bin” substances into categories of similar probable risk. The
essential role of the model is to synthesize information
on chemical and environmental properties within a consistent
mass balance framework to yield an overall estimate of
screening level risk with respect to the defined endpoint.
The approach may be useful to identify and prioritize
those chemicals of commerce that are of greatest potential
concern and require more comprehensive modeling and
monitoring evaluations in actual regional environments and
food webs.