A Comparison of the Aquatic Toxicity of Fenitrothion Flowable and Fenitrothion Liquid Technical Formulations

Abstract

Fenitrothion, a popular spruce budworm (Choristoneura fumiferarna) insecticide, has recently been produced as a “flowable” formulation which consists of finely milled particles of the active ingredient in suspension. In order to determine if such a formulation change could alter the chemical’s toxicity and bioconcentration potential to non-target aquatic fauna, a series of bioassays was undertaken. In acute (48- and 96-h LC50s) tests using rainbow trout (Oncorhynchus mykiss), threespine stickleback (Gasterosteus aculeatus), freshwater clams (Anodonta spp.), blue mussels (Mytilus edulis) and the water flea (Daphnia magna), the toxicity of conventional fenitrothion (liquid technical) formulations was not substantially different from that of the “flowable” (particulate) formulation. The exception was that the flowable formulation was less toxic than the liquid technical formulation to the freshwater clam by a factor of 1/3 to 1/5. Bioconcentration factors to blue mussels for the flowable formulation (15 to 36) were approximately 1/8 to 1/2 the blue mussel bioconcentration factors previously reported for the liquid technical formulations. The results indicate that the flowable formulation does not represent an increased hazard to the aquatic organisms tested, compared with the conventional liquid technical formulations.