Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

100
80
n
itio
h
ib
60
in
E
h
C
A
40
%
20
A. B.
Mixture
M 8 5 ug/L
Cn 19 ug/L
Cl 41 ug/L
0
0.0 01 0.01 0 .1 1 10 1 00 1000
Concentration relative to E C50
10 0
80
lity
60
r
ta
o
m
% 40
386
20 Cl 41 ug/L
Cn19 ug/L
M 85 ug/L
Mixture
0
0.0 01 0.01 0 .1 1 10 1 00 100 0
Concentration relative to LC50
Figure 42. Percent AChE inhibition (A.) and percent mortality (B.) for salmonids expected from
exposure to carbaryl (Cl), carbofuran (Cn), and methomyl (M) as separate constituents and as
mixtures (Cl 41 µg/L, Cn 19 µg/L, and M 85 µg/L) 4 .
We used a variety of exposure estimates and monitoring data to evaluate responses to different
mixtures of carbaryl, carbofuran, and methomyl (Table 73). The predicted additive responses
from these mixtures ranged from 16-74% inhibition of AChE and 0.01-74% mortality. The
predicted additive response to AChE inhibition is likely to result in increased behavioral
consequences to salmonids. What is not captured in these responses is the likelihood of exposure
to the various mixture concentrations. The PRZM-EXAMS values were estimates selected from
EPA simulations of western crops. The scenarios were representative of use rates and numbers
of applications on current product labels. Additionally, we used 60 d, time-weighted averages of
exposure rather than predicted peak concentrations as exposure to multiple pesticides would be
expected to occur more frequently over chronic durations. This may underestimate effects as
responses assumed 96 h exposure. Site specific considerations will also have an influence on the
frequency of exposure.
4 EPA's default pesticide slope was used for acute mortality (3.63 or probit slope of 4.5) [EPA 2004]. The slope
used for AChE inhibition was based on pooling data from five cholinesterase-inhibiting insecticides; including
carbofuran, carbaryl, chlorpyrifos, diazinon, and malathion Laetz, C. A., D. H. Baldwin, et al. (2009). "The
synergistic toxicity of pesticide mixtures: Implications for risk assessment and the conservation of endangered
Pacific salmon." Environmental Health Perspectives 117: 348-353..