Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

given a percentile value of 50 (i.e., a probability of 0.5), normsinv(50) returns a value of zero.
The plots and regressions were performed using KaleidaGraph 4.03 (Synergy Software).
The decision to use the 10 th percentile rather than the 50 th percentile is consistent with previous
designations by EPA, and is reasonable because of the relative sensitivity of invertebrates that
are most likely consumed by juveniles. In addition, the 10 th percentile is a reasonable threshold
because the data included in the meta-analysis were limited to concentrations that caused
mortality or immobilization within a short period of time (1-4 days). A growing number of
studies on a variety of insecticides have reported that concentrations well below LC50s can cause
delayed mortality or sublethal effects that may scale up to affect populations, especially in
scenarios with multiple exposures and/or other stressors. Evidence for ecologically significant
sublethal or delayed effects includes reduced growth rates (Schulz and Liess 2001b, Forbes and
Cold 2005), altered behavior (Johnson et al. 2008), reduced emergence (Schulz and Liess
2001a), reduced reproduction (Cold and Forbes 2004, Sakamoto et al. 2006), and reduced
predator defenses (Sakamoto et al. 2006, Johnson et al. 2008). Finally, the available toxicity data
– and therefore the data included for these analyzes – are from studies using taxa hearty enough
to survive laboratory conditions. Studies specifically examining salmonid prey that are more
difficult to rear in the laboratory have documented relatively low LC50 or EC50 values when
exposed to current-use pesticides (e.g., Peterson et al. 2001a, Johnson et al. 2008). It is
noteworthy that the most relevant invertebrate study for carbaryl – a study using a diverse group
of seven salmonid prey taxa collected from streams in the Pacific Northwest – reports LC50s for
carbaryl with a geometric mean of 26.28 µg/L (range 11.1 – 61.0) (Peterson et al. 2001a).
The models allow exposures that can include multiple AChE-inhibiting pesticides over various
time pulses. Sigmoidal dose-response relationships, at steady-state, between each single
pesticide exposure and 1) AChE activity and 2) relative prey abundance are modeled using
specific EC50s and EC50s and slopes (Figure 2B and 3B). The timecourse for each exposure
was built into the model as a pulse with a defined start and end during which the exposure
remained constant (Figure 2A and 3A). The timecourse for AChE activity, on the other hand,
was modeled using two single-order exponential functions, one for the time required for the
exposure to reach full effect and the other for time required for complete recovery following the
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