Risks to Aquatic Organisms from Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 142

This pattern, observed in studies conducted 20 yr and 2,000 km apart, implies that
(a) D. pallidus is less sensitive than cyclopoids to CPY, and (b) D. pallidus com-
petes with cyclopoids for food, and therefore benefi ts from reductions in cyclopoid
abundance. It has been reported that “the survival and reproduction of D. pallidus
were substantially enhanced by the addition of rotifers to a threshold algal diet”
(Williamson and Butler 1986 ).The increase in D. pallidus at 3 g L −1 may therefore

have been partly a result of the increase in abundance of rotifers (see below).
The cladocerans were slightly less abundant at 0.3

μ

μ g L −1 than in controls, but

only on d-43. Pronounced effects occurred at 1 μ g L −1 (recovery by d-57) and

3 g L −1 (recovery by d-43). No effects on total numbers of cladocerans were

observed at 0.1

μ

g L −1 . The most abundant cladocerans were Chydorus sphaericus
and Alona sp. C. sphaericus was most sensitive to CPY, while Alona was less
sensitive and appeared to benefi t from changes that occurred at the greater
concentrations.
There were no signifi cant differences in abundance of rotifers among CPY treat-
ment levels on any sample event. The total numbers of the two major rotifer groups,
Ploima and Flosculariaceae, were also unaffected by treatment with CPY. Total
numbers of zooplankton were not signifi cantly reduced at any concentration on any
sample event. The observed reductions in copepods and sensitive cladocerans were
offset by increases in rotifers and more tolerant cladocerans.
Benthic insect communities in the cosms were dominated by Diptera and
Ephemeroptera. Abundance of Diptera was signifi cantly reduced at 0.3 and 1

μ

μ g L −1

on d-15 only, and at 3 g L −1 from d-1 through d-29 (recovery by d-42). Treatment-

related reductions in numbers of Ephemeroptera were found at 0.3

μ

μ g L −1 (d-1

only), 1 and 3 g L −1 (d-1 and -15). There were no signifi cant differences after

d-15. Signifi cant differences in total numbers of benthic insects occurred on d-1
and -15 at 0.3 and 1

μ

g L −1 (recovery by
d-42). No effects on Diptera, Ephemeroptera, or total benthic insects were observed
at 0.1

μ g L −1 , and from d-1 through d-29 at 3 μ

g L −1 . In terms of invertebrate community structure (based on Principal
Response Curve (PRC) analysis) (Giddings 2011 ) and abundance of sensitive pop-
ulations within the community, no ecologically relevant effects occurred at
0.1

μ

μ g L −1 .

Australian stream cosms . Two studies in Australia reported effects of CPY on inver-
tebrate communities in large outdoor experimental streams (Pusey et al. 1994 ; Ward
et al. 1995 ). In the fi rst study, 6-h pulses of CPY were applied at 0.1 and 5 g L −1

and invertebrate community responses were monitored for 80 d. There were no
effects at 0.1

μ

g L −1 . The abundance of chironomids, but not other invertebrate
groups, was reduced at 5

μ

g L −1 . Invertebrate abundance recovered by the end of the
study. In the second study, the same concentrations of CPY were applied continu-
ously for 21 d. Abundance and diversity of invertebrates were slightly reduced at
0.1

μ

μ g L −1 and more severely reduced at 5 μ g L −1 . Abundances of invertebrates at

5 g L −1 recovered between 42 and 70 d after the fi rst treatment. Snails became more

abundant in the treated streams.

μ