Refined Avian Risk Assessment for Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 173

food is a factor. Because fl owable CPY may be applied up to four times per growing
season, chronic risk was also estimated for that formulation. For the chronic
assessment, preferred metrics included the most sensitive of the population-relevant
endpoints, viz., survival, growth and reproduction.
The following decision criteria were used in deriving effects metrics for each
focal species: (1) If a toxicity study with fi ve or more treatments was available for
the focal species or a reasonable surrogate, then a dose-response curve was derived
for that species; (2) If multiple toxicity studies that followed a similar protocol
and together had fi ve or more treatments were available for the focal species or a
reasonable surrogate, then a dose-response curve was derived for that species;
(3) For untested focal species, an SSD was derived.
Without toxicity data for a focal species, there is uncertainty regarding the sensi-
tivity of that species to CPY. To deal with this uncertainty, the SSD was used to
bound the risk estimates (i.e., assume 5th and 95th centile sensitivity on the SSD) and
to estimate median risk (i.e., assume 50th centile sensitivity on the SSD) (USEPA
2005 ). Dose-response curves were then derived for low (95th centile), median
(50th centile) and high (5th centile) sensitivity species by using a distribution of the
available LD 50 data and measured dose-response curve slopes. Because insuffi cient
bird species have been tested for chronic exposure, the most sensitive effects metrics
were assumed for all focal species.
Each toxicity study was evaluated, and acceptable studies met the following
criteria: (1) Single contaminant exposure only; (2) Gavage (acute) or dietary
(chronic) route of exposure; (3) Ecologically-signifi cant endpoint (e.g., survival,
reproduction, growth); (4) Adequate statistical design (e.g., fi ve or more treatments
including controls, responses spanning most of the range of 0-100% effect includ-
ing at least one treatment with a partial response) to estimate toxic effect doses; and
(5) Study employed acceptable laboratory practices or was previously accepted by
EPA (USEPA 2009 ). Studies that did not meet the above criteria were not used to
derive effects metrics.

Risk characterization . Three lines of evidence were used to characterize risks of
CPY to birds: (1) Modeling of exposure and effects; (2) Information available from
fi eld studies; and (3) Information available from incident reports.
Risk curves were derived for each exposure scenario and focal bird species by
determining the percentages of fi elds that had

≥ 5% mortality ( ≥ 1/20 dead birds per

fi eld), 3/20 dead

birds per fi eld), … , 100% mortality (20/20 dead birds per fi eld). The result was a
plot of probability of exceedence versus magnitude of effect. Similar approaches
have been used in ecological risk assessments performed for the EPA at the Calcasieu
Estuary, Louisiana, the Housatonic River, Massachusetts (USEPA 2002 , 2004a )
and by others assessing the ecological risk of pesticides (Giddings et al. 2005 ;
Moore et al. 2010a , b , c ; Solomon et al. 2001 ). In this assessment, area under the
risk curve (AUC) was estimated for each combination of focal species and exposure
scenario. AUC is the area under the curve divided by the sum of the AUC and the
area above the curve, with the result multiplied by 100. The AUC was used to

≥ 10% mortality ( ≥ 2/20 dead birds per fi eld), ≥ 15% mortality ( ≥