Refined Avian Risk Assessment for Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 177

• Finally, the SAP (SAP 2001 ) stated that fi eld validation of a model, particularly a
complex model, is critical. This has yet to be done for TIM v1 or v2. An evaluation
of model performance was previously done for LiquidPARAM with fl owable
carbofuran, the results of which are discussed in SI Appendix 3.

It was not possible to incorporate all of the recommendations of the SAP (US
EPA SAP 2001 , 2004 ) because information is still lacking in several areas. For
example, the SAP (SAP 2001 ) expressed concern that TIM equates proportion time
spent in treated fi elds as the proportion of diet obtained from the treated fi elds. The
data required to act on this recommendation are not available for North American
bird species that forage in agroecosystems.
The SAP (SAP 2001 ) also noted that there is considerable uncertainty regarding
how birds obtain drinking water from treated fi elds and other nearby habitats. As in
TIM v1, LiquidPARAM includes three drinking water scenarios (dew, dew plus
puddles on day of application, and dew plus puddles on the day after application).
The Panel (SAP 2001 ) concluded that this approach was reasonable, but recom-
mended that further research be undertaken on: (1) the linkage between time on the
fi eld and amount of water consumed, (2) puddle persistence, (3) concentrations in
dew and puddles, and (4) consumption of dew by different bird species. The SAP
(SAP 2001 ) noted that fi eld telemetry studies combined with laboratory bird behav-
ior studies could provide the needed data. Because such studies have not yet been
conducted, and because drinking water appears to be a minor source of exposure for
fl owable CPY (see the results of the sensitivity analysis in SI Appendix 3, Sect. 1.4),
LiquidPARAM retains the same drinking water scenarios as exist in TIM v1.
A graphical description of the structure of the LiquidPARAM model is illustrated in
Fig. 4 and details of the model are provided in SI Appendix 3

3.2 Description of the Structure of the LiquidPARAM Model

For acute exposure, LiquidPARAM estimates the maximum retained dose that
occurs over a period of 60-d following initial pesticide application in each of 20
birds on each of 1,000 fi elds (Fig. 4 ). The model can accommodate up to three
applications at intervals specifi ed by the user. The model has a 1-h time step. For
each bird, a standard normal Z score is calculated for the maximum retained dose.
This Z score determines how extreme the exposure is relative to the appropriate
LD 50 using a log-probit dose-response relationship. The Z score is then compared to
a randomly selected value from a uniform distribution with a range of 0-1. If the Z
score for exposure exceeds the randomly drawn value from the uniform distribution
the bird dies. Otherwise, it survives (Fig. 4 ).
For species lacking acceptable acute oral toxicity data (all focal species except
the northern bobwhite, C. virginianus , and red-winged blackbird, Agelaius phoeni-
ceus , for CPY), a species sensitivity distribution (SSD) approach is used to generate
the effects metrics. With this approach, a regression analysis is fi rst conducted to