A refined aquatic ecological risk assessment for a pyrethroid insecticide used for adult mosquito management

Abstract

Abstract-The use of pyrethroid insecticides has increased substantially throughout the world over the past few decades as the use of organophorous, carbamate, and organochlorine insecticides is being phased out. Pyrethroids are the most common class of insecticides for ultralow-volume (ULV) aerosol applications used to manage high densities of adult mosquitoes. Pyrethroids are highly toxic to nontarget organisms such as certain aquatic organisms, and there have been concerns about the effect of applications of ULV insecticides on these organisms. To address the uncertainties associated with the risks of ULV applications and the contradictory findings of other ecological risk assessments, the authors performed a probabilistic aquatic ecological risk assessment for permethrin using actual environmental deposition on surfaces to estimate permethrin concentrations in water. The present study is the first ecological risk assessment for pyrethroids to quantitatively integrate the reduction in bioavailability resulting from the presence of dissolved organic matter. As part of the risk assessment, the authors incorporated a species sensitivity distribution to take into account the differences in toxicity for different species. The 95th percentile estimated concentration would result in less than 0.0001% of the potentially affected fraction of species reaching the lethal concentration that kills 50% of a population. The results of the present study are supported by the weight of evidence that pyrethroids applied by ground-based ULV equipment will not result in deleterious effects on aquatic organisms. Environ. Toxicol. Chem. 2013;32:948-953. # 2013 SETAC

Pyrethroid effects on freshwater invertebrates: A meta-analysis of pulse exposures

“…Yang et al, 2006;You et al, 2008;Cui et al, 2010), and for these reasons, several authors have argued that pyrethroid contamination in freshwater systems is relevant mostly for sediment-dwelling organisms (e.g. Hill, 1989;Schleier and Peterson, 2013). Nevertheless, there is also evidence that very short pulses (few hours) of pyrethroids in the aqueous phase are capable of producing both acute and long term effects in stream macroinvertebrates (Liess and Schulz, 1996;Schulz and Liess, 2001;Rasmussen et al, 2008;Nørum et al, 2010).…”

To the editor

“…In contrast to the limited influence of DOM on bioavailability and toxicity observed in the Yang et al empirical study, Schleier and Peterson report differences in modeled total water concentrations and freely dissolved concentrations of permethrin of approximately 5 orders of magnitude. Some of their modeling results (50th and 95th percentile estimated C w ) are presented in Table .…”

“…Schleier and Peterson present a refined aquatic ecological risk assessment for permethrin, a pyrethroid insecticide used for adult mosquito management. The modeling approach is transparently described and assumes, among other things, instantaneous mixing of the chemical into the water column and no inflow/outflow (stagnant pond).…”

“…Recognizing the potential role of dissolved organic carbon (DOC) in reducing the bioavailability of chemicals present in the water column , Schleier and Peterson go on to estimate the freely dissolved concentration from the total water concentration using a commonly utilized equation where C w is the estimated freely dissolved concentration of the chemical in the water column (µg/L), C t is the total water concentration (µg/L), f fd is the freely dissolved fraction (unitless), K DOC is the dissolved organic carbon–water partition coefficient of the chemical, and [DOC] is the concentration of DOC in the water column. Note that whereas [DOC] is typically reported in units of mg/L, K DOC is most frequently reported in units of L/kg.…”

“…To parameterize Equation 1 for permethrin, Schleier and Peterson use the empirically derived K DOC values (16 000–79 000 L/kg) and range of dissolved organic matter (DOM) concentrations reported in Yang et al . The main objective of Yang et al was to assess the role of DOM in reducing bioavailability and the manifestation of adverse effects in 96‐h aquatic exposures to cyfluthrin and permethrin using 2 freshwater invertebrates, Ceriodaphnia dubia and Daphnia magna .…”