Risks to Aquatic Organisms from Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 128

Transparency of data was scored from 1 to 5 (Table 1 ). If critical data were not
provided, a score of 1 was assigned. If full raw data were provided, the score was 5.
If data were provided in tables and graphs, intermediate scores were assigned
depending on the clarity of the data and the description of variance, etc.
Most concentration-response study guidelines require that fi ve concentrations be
used in a toxicity test; therefore, fi ve test concentrations were used to defi ne a maxi-
mum score (5). It was recognized that, in some circumstances, the use of fewer
concentrations could still provide useful data, particularly if the concentration-
response curve was steep. These studies were, however, assigned lesser scores.
The overall evaluation of the strength of the methods was obtained from the
computed average of the scores. Toxicity data for inclusion in the risk assessment
were selected based on the overall score. Guideline and GLP studies with full QA
and QC, and studies with scores of ≥ 4, were preferred. Studies with scores of <4 ≥ 3

were included as qualifi ed values and those with scores <3 were not included.
Additional information was also used to select data for use when multiple results
were available for the same species. For example, fl ow-through exposures were
selected over renewal and renewal over static. However, if only data from static
exposures were available, they were used with caution. Where several stages of the
same species were tested, the more sensitive stage (based on the EC or LC value)
was used. For example, data from larval amphibians were selected over embryos,
which are generally less sensitive (Richards and Kendall 2002 ). The details of toxic-
ity data included and excluded from SSDs are indicated in SI Table 1.
Data for saltwater and freshwater, Palearctic and Nearctic, tropical and temper-
ate organisms were not separated, as differences in sensitivity between these groups
have been shown to be minimal, and their 5th centile concentrations (HC5s) are not
signifi cantly different (Maltby et al. 2005 ). Data from studies that used the formu-
lated product were included as were those with the active ingredient; however, if
data on both formulated and active ingredient were available, only data for the
active ingredient were used. If toxicity values for more than one study were avail-
able for a species and they were of equal quality, the geometric mean of these values
was used to construct the SSD.
For aquatic organisms, the most frequently reported toxicity data were effect
concentrations (ECs) that cause some magnitude of effect. For instance, the EC 50 is
the concentration that causes a 50% change in a measurement endpoint, such as
growth or reproduction. When the effect is mortality, it is expressed as the lethal
concentration that causes 50% mortality in a specifi ed duration of exposure, i.e.,
96-h LC 50 . The HC5, based on acute LC 50 values, has been found to be protective of
responses to CPY at the ecosystem level (Maltby et al. 2005 ).
All durations of exposure from 2 to 5 d were included; durations >5 d were
excluded from the SSDs. Analysis of the exposure profi les (Williams et al. 2014 )
showed that concentrations greater than toxicity values were of short duration
(median = 1 d) and that acute toxicity data were the most appropriate for the assess-
ment. When toxicity values were reported for different periods of exposure, data for
the longest period of exposure up to 5 d were included in the SSDs. Toxicity values
excluded from the data set were LOEL, LOEC, NOEL, NOEC, MATC, unspecifi ed