Environmental Engineering Reference
In-Depth Information
Derivation of species-specifi c dose-response curves for northern bobwhite and
red-winged blackbird. This approach makes better use of the available toxicity
data than does use of a benchmark based on the most sensitive response observed
in birds. In the risk analyses, the dose-response curves enabled a determination
of the fate of each bird (i.e., dead or alive) in the simulation. The use of the SSD
approach permitted exploration of risks for untested bird species by assuming a
range of sensitivities to CPY.
7.4
Uncertainties in the Refi ned Risk Assessment
for Granular CPY
The refi ned risk assessment of granular CPY to birds contains uncertainties. In this
assessment, conservative point estimates were used when the available data were inad-
equate to defi ne an input distribution (e.g., daily grit retention). Thus, the assessment
erred on the side of conservatism (i.e., over-estimating risk).
The following sources of uncertainty were identifi ed in the refi ned risk assessment
for granular CPY (Table 9 ):
• The refi ned risk assessment considered exposure of birds to granular CPY via inad-
vertent ingestion of grit. Exposure to granular CPY by dermal contact, inhalation or
consumption of CPY in water, insects, and plant material were not the focus of the
assessment. CPY from granular formulations is not expected to occur at elevated
concentrations in the atmosphere, nor is it expected to accumulate or persist in the
fi eld environment (Solomon et al. 2001 ). Given that granular CPY is formulated on
clay particles, birds are unlikely to mistake pesticide granules for seeds.
• 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 species of birds
found in regions where granular CPY is used. Thus, there is little uncertainty
associated with overlooking bird species at risk.
• GranPARAM has a number of sources of uncertainty. Where possible, these
sources were quantifi ed and incorporated in the exposure analyses (e.g., varia-
tion in availability of natural grit particles, grit counts in bird gizzards).
Thus, these sources of uncertainty have been explicitly accounted for in the risk
estimates described here. Other sources of uncertainty, however, could not be
accounted for in GranPARAM, generally because data were too scarce. Examples
include: granule:grit preference factor, daily grit retention in bird gizzards, and
use of the fi eld margin. The general approach for input variables with high uncer-
tainty was to use conservative point estimates. The model evaluation exercise
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