Refined Avian Risk Assessment for Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 162

Mammals are far less sensitive than birds to acute exposures of chlorpyrifos
(see review in Solomon et al. 2001 ). In addition, mammals are less exposed to
granular CPY because they do not consume grit to aid digestion as do birds
(Solomon et al. 2001 ). Therefore, risks due to exposure to CPY are likely to be
greater for birds than for mammals. We did not conduct a refi ned risk assessment for
mammals because any mitigations stemming from the avian risk assessment should
also be protective of mammals foraging in treated fi elds.
This assessment builds upon past assessments of CPY, including the most recent
EPA re-registration assessment (USEPA 1999 ) and a refi ned risk assessment to
birds by Solomon et al. ( 2001 ). Using a conservative, screening-level risk assess-
ment approach, the USEPA ( 1999 ) concluded that single and multiple applications of
CPY potentially pose risks to birds. However, a more refi ned assessment of exposure
based on simulations and analyses of fi eld studies and incident reports demonstrated
that the risks of exposure to fl owable and granular CPY were small (Solomon et al.
2001 ). Solomon et al. ( 2001 ) used a probabilistic individual-based model to predict
mortality for eight focal species exposed to fl owable and granular CPY in corn.
The model predicted that the eight focal species would not experience any mortality.
Since the completion of the assessments by USEPA ( 1999 ) and Solomon et al.
( 2001 ), the labels have been amended to require buffer zones, reduce single and
seasonal application rates, reduce the number of applications per season, and
increase the minimum re-treatment intervals (USEPA 2009 ). In addition, EPA is
preparing a new assessment of risk of fl owable and granular formulations of CPY to
birds that will make use of their standard screening-level risk assessment approach
( USEPA 2008a ). An initial draft of the reassessment by EPA was to be released for
public comment in the latter part of 2013 (USEPA 2009 ).
A refi ned assessment of risks posed by labeled uses of CPY in agriculture in the
USA was conducted to refl ect changes made to the label and the availability of new
information and methods for conducting exposure assessments of birds to insecti-
cides. We initiated the preparation of this assessment by carefully formulating the
problem to be addressed. Such problem formulation establishes the scope of the
assessment, including defi ning the routes of exposure to be considered, focal
species of birds and patterns of use. The problem formulation concludes with an
analysis plan. Subsequent sections describe the methods and assumptions for
assessing exposure and effects and characterization of risks. This paper is part of a
series that describes the properties and environmental chemodynamics (Solomon
et al. 2014 ), long-range atmospheric transport (Mackay et al. 2014 ), concentrations
in aquatic environments (Williams et al. 2014 ), risks to aquatic organisms (Giddings
et al. 2013 ), and risks to pollinators (Cutler et al. 2014 ) of CPY.

2 Problem Formulation

The goal of problem formulation is to develop a plan for the analysis that will guide
the assessment of risks to terrestrial birds. To accomplish this task, the following
topics are briefl y reviewed: (1) patterns and amounts of CPY used; (2) formulations;