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

(Detra and Collins 1986; Detra and Collins 1991) and vertebrates including salmonids following
exposures to carbamates and OPs (Beyers and Sikoski 1994, Eder et al. 2007, Grange 2002, Hoy
et al. 1991, Laetz et al. 2009, Li H. X. et al. 2008, Li S. N. and Fan 1996, Liu et al. 2007,
Sandahl J. F. et al. 2004, Sandahl J.F. et al. 2005, Scholz et al. 2006, St. Aubin 2004, Tierney et
al. 2007, Yi et al. 2006, Zinkl et al. 1987).
One highly relevant study measured inhibition of brain AChE, duration of recovery, survival at
24 h, and tissue concentrations in juvenile rainbow trout (O. mykiss) following exposure to
carbaryl at 0, 250, 500, 1,000, 2,000, and 4,000 μg/L (Zinkl, Shea et al. 1987). Rainbow trout
showed dose-dependent AChE inhibition from 61 to 91 % when exposed to 250 – 4,000 μg/L for
24 h. Most trout that died had 85% or greater inhibition. Trout recovered AChE activity
following 24 h in uncontaminated water, indicating that fish recover if given the opportunity
following carbamate exposures (Zinkl, Shea et al. 1987). This study showed that carbaryl is
acutely toxic to rainbow trout in a matter of hours (incidences of death at 1.5 – 4 h) at
concentrations at or above 1,000 μg/L.
pH and toxicity
We located several data sets on toxicity to freshwater fish and aquatic invertebrates exposed to
carbaryl and carbofuran at different pHs (Mayer and Ellersieck 1986). Acute toxicity of carbaryl
and carbofuran increases as pH increased, based on the available freshwater fish assays (Mayer
and Ellersieck 1986). This largely is considered a result of the influence pH has on the creation
of hydrolysis products (Mayer and Ellersieck 1986). However, the persistence of carbaryl and
carbofuran is reduced as pH increases. As noted in the exposure section, degradation half-lives
can vary from hours (in alkaline waters) to weeks (in acidic waters) depending on pH. Within
the Pacific Northwest and California pH varies seasonally and typically may range from 6 – 9.
For methomyl, pH seems to have less of an influence on hydrolysis rates. Due to the influence
of pH on persistence of carbaryl and carbofuran, we evaluated reported toxic effects within the
context of pH if provided and discuss pH in relationship to salmonid habitat utilization.
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