Refined Avian Risk Assessment for Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 172

within a fi eld, but can be quite variable among fi elds within a broad region of the
United States. Thus, for each fi eld, LiquidPARAM randomly chooses an initial
concentration for each dietary item and then these concentrations decline in the
fi eld over time according to the degradation rate for that dietary item. When the
model proceeds to the next fi eld, new initial concentrations are randomly selected.
The process is repeated for 1,000 fi elds.
TIM assumes that bands occupy 17% of each fi eld and furrows 5% of each fi eld.
However, these factors vary among crops. LiquidPARAM has been customized to
have crop-specifi c row widths and spacing.
TIM uses older allometric equations provided by Nagy ( 1987 ) to estimate free
metabolic rate. LiquidPARAM uses the more up-to-date allometric equations from
Nagy et al. ( 1999 ). LiquidPARAM also accounts for uncertainty in estimates of free
metabolic rate arising from error due to lack of model fi t, while TIM does not.
TIM also does not account for the avoidance behavior that has been observed by
birds following initial exposure to CPY (Bennett 1989 ; Wildlife International 1978 ).
LiquidPARAM accounts for this behavior. Further, TIM only simulates acute
exposure following a single pesticide application. LiquidPARAM can simulate both
acute and chronic exposures following multiple pesticide applications.
Exposure assessment—Lorsban 15G . Previously, a simulation model was developed
that estimated exposure and risk for various bird species that are potentially exposed
to the granular formulation of aldicarb (Moore et al. 2010b , c ). That model, referred
to as the Granular Pesticide Avian Risk Assessment Model (GranPARAM), includes
input variables such as: proportion time in the fi eld, rates of ingestion of grit, attrac-
tiveness of pesticide granules compared to natural grit, and proportion of soil
particles in the grit size range preferred by birds. For input variables that are uncer-
tain, variable, or both, frequency distributions are used rather than point estimates.
Monte Carlo analysis is then performed to propagate input variable uncertainties
through the exposure model. Similar to LiquidPARAM, GranPARAM determines the
fate of 20 randomly chosen birds on each of 1,000 randomly selected fi elds for the
use pattern and region of interest. GranPARAM was revised to be specifi c to CPY
for this refi ned avian risk assessment (see Sect. 4 and SI Appendix 3, Sect. 2).
Effects assessment . Effects data can be characterized and summarized in a variety of
ways, ranging from benchmarks designed to be protective of most or all species to
dose-response curves for the focal species of interest. When toxicity data are lacking
for a focal bird species, a species sensitivity distribution (SSD) can be used to give
an indication of the risk range by varying the dose-response curve from that of a
sensitive species to that of a tolerant species. This approach was used by EPA
(USEPA 2005 ) in their avian risk assessment for carbofuran. The SSD approach
was also used in this assessment, except when toxicity data were available for the
focal species of interest (see Sect. 5 ).
Effects associated with survival of juveniles or adults were the preferred measure
of acute effect because this endpoint was judged to be the most appropriate based
on the mode of toxic action of CPY. Gavage studies were used in preference to
dietary studies because of problems in estimating dose when avoidance of treated