Risks to Aquatic Organisms from Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 145

Fig. 6 Comparison of SSDs for 96-h toxicity values for chlorpyrifos and the NOAEC eco from
cosm studies to greatest annual 95th centiles of concentrations reported by the US Geological
Survey from surface waters samples collected before and after 2001. For a more detailed descrip-
tion of the data, see Williams et al. ( 2014 )

linesterase (AChE) inhibitors, Amphipoda, Cladocera, Copepoda, Trichoptera,
Ephemeroptera, and Diptera are the most sensitive taxa in cosms, with effects
observed at 0.1- to 1-times the LC 50 of the most sensitive standard test species.
Effects on mollusks, annelids, and plants are observed at concentrations 10-100
times greater than the LC 50 of the most sensitive species. Most rotifers are unaf-
fected at even greater concentrations.
• The ecosystem-level NOAEC (NOAEC eco ) is the concentration in which “no, or
hardly any, effects on the structure and functioning of the studied (model) eco-
system are observed” (Fig. 6 , van Wijngaarden et al. 2005b ). For CPY, the
NOAEC eco for a single exposure is 0.1

g L −1 . Effects are generally more severe
with repeated or chronic exposure, but such exposure patterns are not typical for
CPY (Williams et al. 2014 ). The NOAEC eco falls at the 23rd centile of the SSD
for crustaceans, the most sensitive taxon for which data are available (Fig. 6 ).
This implies that use of the HC5 in the risk characterization errs on the side of
protection.
• For inhibitors of AChE and other insecticides, sensitive crustaceans and insects
in static systems usually recover within 8 wk of a single pulsed exposure below
the LC 50 of the most sensitive species. For multiple applications, recovery occurs
within 8 wk of the last application less than 0.1× the LC 50 (van Wijngaarden et al.
2005b ). The extent and rate of recovery in cosms is determined by exposure
concentration, life cycle, and ecological factors such as the degree of isolation of
the test system from sources of recolonization.

μ