Refined Avian Risk Assessment for Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 208

Table 9 Sources of uncertainty in avian risk assessment for granular chlorpyrifos
Area Source of uncertainty Action and infl uence on risk estimates

Exposure
scenarios

Not possible to assess all
scenarios. Potential to miss
high risk scenarios.

Most highly-used crops were assessed at
maximum application rates. Exposure
scenarios included upper bound risk
posed by granular CPY to birds.

Routes of
exposure

Focus of assessment was on
inadvertent ingestion of
CPY granules for grit by
birds. There could be other
important routes of
exposure.

Clay formulation and short half-life of
granules in treated fi elds suggest that
potential exposure routes such as
inhalation, dermal exposure and
ingestion for food are of minor
importance.

Risk to non-focal
bird species

The refi ned risk assessment
considered exposure to fi ve
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 grit and agricultural
areas. This group of species is more
likely to be exposed to granular 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
granular CPY is used. Thus, there is a
low degree of uncertainty associated with
overlooking bird species at risk.

Proportion time
birds on fi elds

See Table 7 . See Table 7 .

Granule:Grit
preference
factor (GGPF)

Only one study quantifi ed
GGPF for CPY.

GGPF of 0.078 from study on controlled
study on house sparrows ( Passer
domesticus ). The uncertainty arising
from the limited available information on
GGPF could lead to under- or over-
estimation of risk.

Other variables in
GranPARAM

Several variables (e.g., spill
concentration factor, size
of spills) were diffi cult to
parameterize because of
limited data.

Sensitivity analyses involving one-at-a-time
manipulations of uncertain variables
indicated they had little infl uence on
predicted CPY exposure within
parameter ranges that could be reasonably
expected to occur in CPY-treated fi elds.
Comparison of model predictions to
results of fi eld studies also indicated that
GranPARAM performed well, though the
database for this comparison was
limited.

Quality and
quantity of
toxicity studies

See Table 7 . See Table 7 .

indicated that model predictions reasonably replicated numbers of pesticide
granules ingested in by birds in fi eld studies, although this dataset is limited.
Overall, it appears that the GranPARAM performs well, despite uncertainties
regarding some input variables.