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

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
to adverse affects to non-target species, but they are usually characterized in the published
literature in only a general manner limiting their value in the risk assessment process.
• It is assumed that aquatic species exclusively and permanently occupy the water body being
assessed. Actual habitat requirements of aquatic species are not considered. With the possible
exception of scenarios where pesticides are directly applied to water, it is assumed that no habitat
use considerations specific for any species would place the organisms in closer proximity to
pesticide use sites. This assumption produces a maximum estimate of exposure or risk
characterization. It would likely be realistic for many aquatic species that may be found in
aquatic habitats within or in close proximity to treated terrestrial habitats. However, the spatial
distribution of wildlife is usually not random because wildlife distributions are often related to
habitat requirements of species. Clumped distributions of wildlife may result in an under- or
over-estimation of risk depending upon where the initial pesticide concentration occurs relative
to the species or species habitat.
• For species found in the water column, it would be assumed that the greatest bioavailable fraction
of the pesticide active ingredient in surface waters is freely dissolved in the water column.
Additional chemical exposure from materials associated with suspended solids or food items is
not considered because partitioning onto sediments likely is minimal. Adsorption and
bioconcentration occurs at lower levels for many newer pesticides compared with older more
persistent bioaccumulative compounds. Pesticides with RQs close to the listed species level of
concern, the potential for additional exposure from these routes may be a limitation of risk
assessments, where potential pesticide exposure or risk may be underestimated.
• Mass transport losses of pesticide from a water body (except for losses by volatilization,
degradation and sediment partitioning) would not be considered for ecological risk assessment.
The water body would be assumed to capture all pesticide active ingredients entering as runoff,
drift, and adsorbed to eroded soil particles. It would also be assumed that pesticide active
ingredient is not lost from the water body by overtopping or flow-through, nor is concentration
reduced by dilution. In total, these assumptions would lead to a near maximum possible waterborne
concentration. However, this assumption would not account for potential to concentrate
pesticide through the evaporative loss. This limitation may have the greatest impact on water
bodies with high surface-to-volume ratios such as ephemeral wetlands, where evaporative losses
are accentuated and applied pesticides have low rates of degradation and volatilization.
• For acute risk assessments, there would be no averaging time for exposure. An instantaneous
peak concentration would be assumed, where instantaneous exposure is sufficient in duration to
elicit acute effects comparable to those observed over more protracted exposure periods
(typically 48 to 96 hours) tested in the laboratory. In the absence of data regarding time-to-toxic
event, analyses and latent responses to instantaneous exposure, risk would likely be
overestimated.
• For chronic exposure risk assessments, the averaging times considered for exposure are
commensurate with the duration of invertebrate life-cycle or fish-early life stage tests (e.g., 21-28
days and 56-60 days, respectively). Response profiles (time to effect and latency of effect) to
pesticides likely vary widely with mode of action and species and should be evaluated on a caseby-case
basis as available data allow. Nevertheless, because the USEPA relies on chronic
exposure toxicity endpoints based on a finding of no observed effect, the potential for any latent
toxicity effects or averaging time assumptions to alter the results of an acceptable chronic risk
assessment prediction is limited. The extent to which duration of exposure from water-borne
concentrations overestimate or underestimate actual exposure depends on several factors. These
include the following: localized meteorological conditions, runoff characteristics of the
G-28 Appendix G. Integrated Pest Management