Risks to Aquatic Organisms from Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 122

Little information has been reported on the effects of CPY or other insecticides on
behaviors of other aquatic vertebrates and, to our knowledge, there have been no
robust extrapolations of effects on behavior to the endpoints of survival, develop-
ment, growth and reproduction. For this reason, we excluded behavioral responses
from this risk assessment, because it is still uncertain as to how one interprets the
data, either for CPY or all other pesticides.
Few studies on aquatic organisms have reported effects on reproduction directly
caused by CPY. Chronic exposure of the guppy ( Poecilia reticulata ) to CPY (com-
mercial formulation) for 14 d at nominal concentrations of 0.002 and 2

g L −1
resulted in concentration-related reductions in the frequency of reproductive behav-
ior (gonopodial thrusts) in males (De Silva and Samayawardhena 2005 ). The num-
ber of young born per female over the 14-d period was reduced from an average of
27 in the controls to 24 in pairs exposed to 0.002

μ

μ g CPY L −1 and 8 in pairs exposed

to 2 g L −1 . Activity of AChE was not reported in this study, so it is diffi cult to relate

these chronic effects to response of AChE in other studies on behavior or to shorter
exposure durations in the fi eld (Williams et al. 2014 ). Another study on tadpoles of
Rana dalmatina (Bernabo et al. 2011 ) reported that exposures to concentrations
of 25 or 50

μ

g CPY L −1 from Gosner stage 25 to 46 (57 d) increased the incidence
of testicular ovarian follicles (TOFs). This observation was reported at environmen-
tally unrealistic concentrations and is the only report of this response for CPY; no
other reports of TOFs in fi sh or amphibians were found in the literature. There
appeared to be no effects of these exposures on mortality or time to metamorphosis.
No measurements of AChE activity were reported and the effects on reproduction
were not characterized. Because of the paucity of data, we excluded the effects of
CPY on reproduction from this assessment. However, we indirectly addressed the
endpoints in some of the cosm studies, where signifi cant changes in reproduction of
invertebrates would likely be encompassed in responses at the population level.

μ

2.2.2 Toxicity of CPY and Temporality of Exposures

Frequency, duration, and intervals between exposures to CPY will infl uence
responses observed in receptor organisms. These differences in response will result
from variations in toxicokinetics and toxicodynamics of CPY in the environment
and in individual organisms. The hydraulics of surface waters and variability of
inputs from uses and precipitation events shape the types of exposures to pesticides
experienced by organisms in fl owing waters (Bogen and Reiss 2012 ). These are
further altered by the individual properties of pesticides, such as rates of degrada-
tion and/or tendency for partitioning into sediments. As illustrated elsewhere in this
volume (Williams et al. 2014 ), most exposures to CPY in fl owing waters are less
than 2 d in duration and are followed by periods of lesser or no exposure. These
episodic exposures are typical of what is observed in fl owing waters for pesticides
in general and are relevant to this risk assessment.
As was pointed out in an earlier risk assessment of CPY (Giesy et al. 1999 ),
exposures via the matrix of the organism (water in this case) are driven by