Abstract
The aquatic toxicity profiles of synthetic pyrethroid insecticides are remarkably similar, and results for a large number of species can be combined across compounds in Species Sensitivity Distributions (SSDs). Normalizing acute toxicity values (median lethal concentrations, LC50s) for each species and each pyrethroid to the LC50 of the same pyrethroid to the freshwater amphipod Hyalella azteca (the most sensitive species to all pyrethroids tested) enabled expression of LC50s as Hyalella equivalents that can be pooled across pyrethroids. The resulting normalized LC50s (geometric means for each species across pyrethroids) were analyzed using SSDs. Based on tests with measured exposure concentrations, the fifth percentiles (Hazard Concentrations, HC5s) of the SSDs were 4.8 Hyalella equivalents for arthropods (36 species) and 256 Hyalella equivalents for fish (24 species). HC5 values are useful as effects metrics for screening-level risk assessments, and the full SSDs can be integrated with estimated exposure distributions for higher-level risk characterization. The combined pyrethroid SSDs provide a more taxonomically representative and statistically robust basis for risk characterization than data for the most sensitive single species or SSDs based on data for a single pyrethroid alone, and are especially useful for pyrethroids that have been tested with smaller numbers of species.
Highlights
Synthetic pyrethroids are a class of insecticides registered for agricultural, residential, and public health uses for more than 35 years
This paper describes the selection of data for deriving combined pyrethroid Sensitivity Distributions (SSDs), the steps in the data analysis, and the resulting acute SSDs for arthropods and fish
The final sets of mean Hyalella equivalent LC50s are shown in Table 1 and Table 2
Summary
Synthetic pyrethroids are a class of insecticides registered for agricultural, residential, and public health uses for more than 35 years. These compounds are synthetic analogs of pyrethrins, which are naturally occurring esters found in the flower of the pyrethrum plant, Tanacetum cinerariifolium. The Pyrethroid Working Group (PWG), a consortium of pyrethroid registrants, has worked for more than a decade to obtain, evaluate, and compile relevant, reliable data on the toxicity of synthetic pyrethroids to aquatic organisms. The PWG aquatic toxicity database (available for public download at www.pyrethroids.com/aquatictoxicity-database/) contains endpoints and supporting information from more than 1100 open literature publications and registrant-sponsored study reports. The database currently includes more than 5300 records for nine pyrethroids (and their isomer variants and degradates) and nearly 350 species (79 crustaceans, 99 insects, 86 fish, 31 mollusks, and 52 other species)
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