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

(e.g., growth or reproduction) were not included. If specific data were represented more than
once in the ECOTOX output, duplicates were eliminated. Data from recent peer-reviewed
studies that report survival EC50s were also included (Norberg-King, Durhan et al. 1991;
Takahashi and Hanazato 2007). Next, we calculated the geometric mean when more than one
survival EC50 was reported for a species.
Probability distributions of aquatic prey survival toxicity values (EC50s)
We plotted the survival EC50 data for each of the three insecticides using cumulative probability
distributions. We also plotted the data based on all test results for the species without taking the
geometric means. From the distributions of the data, a single effect concentration and slope were
derived to best represent the diverse community of prey available in juvenile salmonid
freshwater and estuarine habitats. The distributions of individual EC50s and the geometric
means of EC50s by taxa were analyzed to estimate the 50 th , 10 th , and 5 th percentiles. Figure 43
shows the distributions of geometric means of EC50s by taxa. Specifically, for each pesticide, a
probability plot was used to graph the EC50 concentrations normalized to a normal probability
distribution. For each plot, the X axis is scaled in probability (between zero and 100%) and
shows the percentage of entire data whose value is less than the data point. The Y axis displays
the range of the data on a log scale. The results of a linear regression of the log-transformed
concentrations are shown and highlight the lognormal distribution of the data (Figure 43). In the
regression equation, the normsinv function returns the inverse of the standard normal cumulative
distribution. The standard normal distribution has a mean of zero and a standard deviation of
one. For example, 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).
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