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

The three insecticides are highly toxic to aquatic macroinvertebrates; and concentrations that are
not expected to kill salmonids are often lethal for their invertebrate prey (e.g., for carbaryl, range
of mean LC50s for salmonids = 250-3,000 μg/L, vs. range of geometric mean EC50s for water
fleas = 3-120 μg/L). In particular, prey items that are preferred by small juvenile salmonids
(including midge larvae, water fleas, mayflies, caddisflies, and stoneflies) are among the most
sensitive aquatic macroinvertebrates. In addition, effects on the prey community can persist for
extended periods of time (weeks, months, years), resulting in effects on fish feeding and growth
long after an exposure has ended (Ward, Arthington et al. 1995; Van den Brink, van
Wijngaarden et al. 1996; Liess and Schulz 1999; Colville, Jones et al. 2008).
Selection of aquatic invertebrate toxicity values to represent salmonid prey items
The model requires for each insecticide an EC50 (defined as a 50% reduction in the biomass of
salmonid prey items) and a corresponding slope (Appendix 1). The term “EC50” will be used in
this section to describe short-term survival data for aquatic invertebrates (death and immobility).
To determine what levels of the three pesticides reduce aquatic invertebrate numbers, we
reviewed the available field and laboratory studies. We found robust data for carbaryl,
carbofuran, and methomyl with respect to laboratory acute toxicity tests that measured survival
at 24-, 48-, 72-, and 96 h with an array of aquatic invertebrates. We did not locate a field study
that measured aquatic community response to a range of concentrations of the three insecticides.
Therefore, we did not select concentration data from field experiments as we did in NMFS’ 2008
Opinion on the registration of chlorpyrifos, diazinon, and malathion (NMFS 2008).
To determine a single effect concentration to use in the model analyses, a search was completed
using the EPA’s ECOTOX database for each pesticide (http://cfpub.epa.gov/ecotox/). Several
criteria were used to determine which reported effect concentrations were included in the final
analysis. The data included were from studies on taxa that are known to be salmonid prey (or are
functionally similar to salmonid prey); these include a diverse group of aquatic insects and
worms and fresh and saltwater crustaceans. Studies with exposures of at least 24 h and not more
than 96 h were included. Studies examining shorter and longer exposure times are known to
affect invertebrates (Peterson, Jepson et al. 2001), but these were excluded so that estimated
EC50s would be comparable. Studies reporting survival EC50s in which mortality or
immobilization was the recorded endpoint were included. Data derived for sublethal endpoints
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