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

pesticide concentrations in the discharge. Those conditions are not a requirement of the federal
label.
Table 60. Carbofuran Concentrations in CDPR Studies of Rice Effluents (1995-1998)
Statistic All years 1995 1996 1997 1998
Samples in data set 97 22 29 25 21
Quantifiable samples 97 22 29 25 21
% of quantifications in data set 100% 100% 100% 100% 100%
LOQ range (μg/L) 0.1-0.35 0.05-0.35 0.05-0.35 0.05-0.35 0.05-0.35
Minimum concentration (μg/L) 0.0872 0.1240 0.1620 0.1400 0.0872
Maximum concentration (μg/L) 2.97 0.7000 2.97 0.6600 1.35
Arithmetic mean concentration (μg/L) 0.5661 0.3907 0.8995 0.3998 0.4800
Standard deviation (μg/L) 0.5098 0.1465 0.7862 0.1472 0.3276
Median concentration 0.4125 0.3700 0.6100 0.4080 0.3800
Based on these studies, other targeted monitoring studies described in EPA BEs, and open
literature evaluated for the Opinion rendered on chlorpyrifos, diazinon, and malathion (NMFS
2008), and the general state of knowledge regarding field runoff from pesticide applications, we
anticipate the following:
● edge-of-field runoff concentrations will be higher than concentrations measured in
waterbodies with substantial diluting volume,
● low-flow or runoff-dominated systems may contain the highest concentrations
(approaching or exceeding modeled concentrations), and
● measured concentrations are likely to be lower than peak runoff concentrations, as
sampling may not coincide with initial application and/or runoff events.
Monitoring data considerations
Surface water monitoring can provide useful information regarding real-time exposure and the
occurrence of environmental mixtures. A primary consideration in evaluating monitoring data is
whether the study design is sufficient to address exposure in a qualitative, quantitative, or
probabilistic manner. The available monitoring studies were conducted under a variety of
protocols and for varying purposes. None of the datasets discussed above were designed to
capture peak concentrations of exposure for salmon, or define exposure distributions.
Of the monitoring programs discussed, only the studies conducted by the Washington State DOE
were designed to evaluate exposure to listed Pacific salmonid habitats in several Washington
State watersheds. This sampling program was intended to evaluate pesticide occurrence in some
salmonid-bearing streams during the pesticide application seasons (Johnson and Cowles 2003).
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