Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

7.2.3 Assumptions for ecological risk assessments
Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
There are a number of assumptions involved with the ecological risk assessment process for
terrestrial and aquatic organisms associated with utilization of the US Environmental Protection
Agency’s (2004) process. These assumptions may be risk neutral or may lead to an over- or underestimation
of risk from pesticide exposure depending upon site-specific conditions. The following
describes these assumptions, their application to the conditions typically encountered, and whether or
not they may lead to recommendations that are risk neutral, underestimate, or overestimate ecological
risk from potential pesticide exposure.
• Indirect effects would not be evaluated by ecological risk assessments. These effects include the
mechanisms of indirect exposure to pesticides: consuming prey items (fish, birds, or small
mammals), reductions in the availability of prey items, and disturbance associated with pesticide
application activities.
• Exposure to a pesticide product can be assessed based upon the active ingredient. However,
exposure to a chemical mixture (pesticide formulation) may result in effects that are similar or
substantially different compared to only the active ingredient. Non-target organisms may be
exposed directly to the pesticide formulation or only various constituents of the formulation as
they dissipate and partition in the environment. If toxicological information for both the active
ingredient and formulated product are available, then data representing the greatest potential
toxicity would be selected for use in the risk assessment process (US Environmental Protection
Agency 2004). As a result, this conservative approach may lead to an overestimation of risk
characterization from pesticide exposure.
• Because toxicity tests with listed or candidate species or closely related species are not available,
data for surrogate species would be most often used for risk assessments. Specifically, bobwhite
quail and mallard duck are the most frequently used surrogates for evaluating potential toxicity to
federally listed avian species. Bluegill sunfish, rainbow trout, and fathead minnow are the most
common surrogates for evaluating toxicity for freshwater fishes. However, sheep’s head minnow
can be an appropriate surrogate marine species for coastal environments. Rats and mice are the
most common surrogates for evaluating toxicity for mammals. Interspecies sensitivity is a major
source of uncertainty in pesticide assessments. As a result of this uncertainty, data is selected for
the most sensitive species tested within a taxonomic group (birds, fish, and mammals) given the
quality of the data is acceptable. If additional toxicity data for more species of organisms in a
particular group are available, the selected data will not be limited to the species previously listed
as common surrogates.
• The Kanaga nomogram outputs maximum EEC values that may be used to calculate an average
daily concentration over a specified interval of time, which is referred to as a time-weightedaverage
(TWA). The maximum EEC would be selected as the exposure input for both acute and
chronic risk assessments in the screening-level evaluations. The initial or maximum EEC
derived from the Kanaga nomogram represents the maximum expected instantaneous or acute
exposure to a pesticide. Acute toxicity endpoints are determined using a single exposure to a
known pesticide concentration typically for 48 to 96 hours. This value is assumed to represent
ecological risk from acute exposure to a pesticide. On the other hand, chronic risk to pesticide
exposure is a function of pesticide concentration and duration of exposure to the pesticide. An
organism’s response to chronic pesticide exposure may result from either the concentration of the
pesticide, length of exposure, or some combination of both factors. Standardized tests for
chronic toxicity typically involve exposing an organism to several different pesticide
concentrations for a specified length of time (days, weeks, months, years or generations). For
G-24 Appendix G. Integrated Pest Management