Refined Avian Risk Assessment for Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 176

have taken place that can be used to refi ne components of the model. These studies
address areas not included in TIM, such as avoidance behavior of birds exposed to
CPY (Bennett 1989 ; Wildlife International 1978 ) and measured concentrations
of CPY on dietary items. Thus, one reason for developing LiquidPARAM was to
expand the model structure of TIM to accommodate new information. Changes
to TIM were also required to address the recommendations of the SAPs (SAP 2001 ,
2004 ) that reviewed the TIM model. Where possible, LiquidPARAM incorporated
recommendations of the SAP (SAP 2001 , 2004 ) including, for example:

• Addition of many new focal species and use patterns to ensure better representa-
tion of the bird community that forages in agroecosystems.
• Use of a 1-h time step in LiquidPARAM, instead of the 12-h time step used in
TIM v1. TIM v2 also moved to a 1-h time step. This refi nement was considered
necessary to account for the changes in avian foraging behavior, avoidance
behavior, and clearance of the pesticide that occur throughout the day.
• For each time step in TIM v1 and v2, the model randomly determines whether a
bird is on or off the treated fi eld. The SAP (SAP 2001 ) felt that this approach
misrepresented how birds forage in agroecosystems. LiquidPARAM allows
birds to forage on and off fi elds in each time step. The model also accounts for
between-fi eld differences in foraging behavior of bird populations that have been
observed due to factors affecting the relative attractiveness of treated fi elds to
birds (e.g., type of edge habitat, availability of cover, etc.). Relative attractive-
ness of fi elds to birds can vary dramatically between treated areas.
• The SAP (SAP 2001 ) observed that TIM v1 confused inter- and intra-fi eld varia-
tion by using dietary residue distributions that included both sources of variation.
Residue levels in each fi eld in TIM v1 relied on the same distributions, as is the
case in TIM v2. However, one would expect larger differences in mean concen-
trations of residues between fi elds than within fi elds because of differences in
soil type and topography, operator skill, type of application machinery, etc.
Further, birds spatially and temporally average their dietary exposures within
fi elds because they generally make multiple foraging trips within any given 1-h
time step (see Sect. 1.2 in SI Appendix 3). LiquidPARAM incorporates a model
structure that accounts for the expected variation between fi elds in mean concen-
trations of residues in dietary items.
• LiquidPARAM incorporates an avoidance behavior component that was sug-
gested by the SAP (SAP 2001 ) as being a potentially important factor in reduc-
ing risk (see EFSA 2008 ).
• The SAP (SAP 2001 ) noted that acute oral studies do not account for the effect
of the dietary matrix on adsorption rate of pesticides by birds. LiquidPARAM
can account for the difference in toxicity to birds of fl owable pesticide adminis-
tered in water versus a dietary matrix if such data are available.

• Because fl owable CPY may be applied up to four times per season, there is a

potential for chronic exposure. As a result, LiquidPARAM has been extended to
a 60-d model that can be used to estimate chronic risks potentially arising from
multiple applications.