Refined Avian Risk Assessment for Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 201

for carbofuran, our analyses described herein indicate that LiquidPARAM may be
more substantially over-predicting risk of fl owable CPY. The small number of inci-
dents (2) involving CPY reported since 2002 suggests that the current labels for CPY
are generally protective of birds (SI Appendix 4).

6.6 Uncertainties of the Refi ned Risk Assessment

for Flowable CPY

This refi ned assessment of acute and chronic risks of CPY to birds contains uncer-
tainties. Uncertainties in the problem formulation and assessment of exposure and
effects can infl uence the characterization of risks. It is therefore important to iden-
tify the sources of uncertainty in the assessment, and specify the magnitude and
direction of their infl uence.
The following sources of uncertainty were identifi ed in this refi ned risk assessment
for birds (Table 7 ):

• The refi ned risk assessment considered exposure of birds to CPY via ingestion
of food and water. As discussed in Sect. 2.4 , dermal contact, inhalation and
preening are unlikely to be important exposure routes for birds in fi elds treated
with fl owable CPY. At present, refi ned models are lacking to quantify these
exposure routes in birds.
• The refi ned risk assessment considered exposure to 15 focal species. Thus,
there is a possibility that bird species not considered in this assessment are at
risk on or near CPY-treated fi elds. The focal species were selected because of
their affi nity for agricultural areas and the crops considered in this assessment.
This group of species is more likely to be exposed to fl owable CPY than would
most other bird species. Furthermore, they span a range of sizes and taxonomic
groups, and are representative of bird species found in regions where CPY is
used. However, it is conceivable that there are bird species at greater risk to
fl owable CPY than those included for the 11 crops considered in this
assessment.
• When there was uncertainty, these sources were quantifi ed and incorporated in
the exposure analyses (e.g., free metabolic rate, initial dietary residue levels
following application). Thus, these sources of uncertainty have been explicitly
accounted for in the risk estimates described here. Other sources of uncertainty,
however, could not be fully accounted for in LiquidPARAM, generally because
data were too scarce to reliably parameterize distributions. For example, acute
dose-response curves were unavailable for all focal species except the northern
bobwhite ( C. virginianus ) and red-winged blackbird ( A. phoeniceus ). The general
approach for input variables for which values were uncertain was to use conser-
vative point estimates or rely on surrogate approaches (e.g., the species sensitivity
distribution approach to estimate dose-response curves for species of differing
sensitivities). The model evaluation exercise indicated that model predictions
reasonably replicated patterns of mortality observed in fi eld studies conducted