Risks to Aquatic Organisms from Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 129

measures of effect, responses such as behavior, which are diffi cult to link to survival,
development, and reproduction, and data from strains of insects that had been
selected for resistance to chlorpyrifos. LC values such as LC 5 , LC 10 , LC 90 , and LC 99
were infrequently reported, cannot be combined with LC 50s , and were excluded
from the assessment.

3.2 Species Sensitivity Distributions

As outlined in the Analysis Plan (Sect. 2.5 ), SSDs were used to characterize the
toxicity of CPY to aquatic organisms. Data for different taxa were separated to bet-
ter assess responses in relation to protection goals which might differ between taxa,
for example, invertebrates and fi sh. Using SSDs to characterize toxicity of CPY is
different from using SSDs to develop guidelines and criteria (CCME 2007 , 2008 ).
SSDs were constructed and 5th centiles and their confi dence intervals calculated
with the aid of the SSD Master Version 3.0 software (CCME 2013 ). This software
is a series of macro statements that are executed in Microsoft Excel. Raw data are
entered into a spreadsheet and a cumulative frequency distribution (CFD) is fi tted
using the plotting positions calculated from the Hazen equation and log-transformed
toxicity values to produce an SSD. The data are then fi tted to several models (nor-
mal, logistic, Extreme Value, and Gumbel) and information on goodness of fi t, HC5
and confi dence interval for each model is provided. Graphical displays of the SSDs
are provided and can be inspected to select those that provide best fi t of the data in
the region of interest, such as the lower tail of the SSD.

3.3 Ecotoxicological Profi les by Taxon

Data were evaluated by taxonomic groups, based on the mode of action and likely
sensitivity. These groupings included: plants, crustaceans, insects, fi sh, amphibians,
and other invertebrates. Where insuffi cient data were available to construct a SSD
(

8 species), such as for algae, amphibians, and invertebrates (other than crusta-
ceans and insects), the data are presented in narrative. Results for each taxon are
discussed in the following sections.

≥

Plants . The only data on toxicity of CPY to plants were those generated with
algae. All of the four species assessed (Table 2 ) were saltwater algae. Since there
were <8 data points and only one study met the criterion for inclusion in the analy-
sis, an SSD was not derived. The range of EC 50s for algae was from 138 to 769 g

CPY L −1 , which indicated that algae are relatively tolerant of exposure to chlorpyri-
fos. Given the mode of action and the lack of a critical mechanism of action or
appropriate target site in plants, this is not surprising. Because of this lack of sensi-
tivity, algae were not considered further in the ERA. It is very unlikely that plants

μ