Pyrethroid insecticides are commonly used in agricultural crops, nursery operations, commercial urban applications, and consumer residential products. They are effective against a broad range of pests, have low mammalian and avian toxicity, low potential to contaminate ground water and low application rate because of their elevated toxicity. Pyrethroid insecticides are present in concentrations that are toxic to invertebrates in California sediments.
Trends were calculated for individual compounds, the sum of pyrethroids, and the sum of toxic units (TU) using data from 2010 to 2021. Sum pyrethroids were calculated by adding concentrations of bifenthrin, cyfluthrin, lambda cyhalothrin, cypermethrin, esfenvalerate/fenvalerate, fenpropathrin and permethrin. Pyrethroid toxic units were calculated by dividing the organic carbon-corrected concentrations by the published organic carbon-corrected LC50. Sum TUs were calculated by adding together individual TU values for each pyrethroid compound. Samples with no detected pyrethroids were assigned a TU value of zero.
Statewide, concentrations of bifenthrin and deltamethrin were significantly increasing, as were the Sum TUs. Concentrations of other pyrethroids were stable or exhibited no trend. Concentrations of most pyrethroid compounds were significantly correlated with the percent of urban land use in the watershed. Bifenthrin concentrations were significantly increasing at 23% of the sites. Most other pyrethroid compounds showed significant decreases at individual sites. Sum pyrethroids had significant increases at 11% of the sites and significant decreases at 10% of the sites.
Trends were calculated for individual compounds, the sum of pyrethroids, and the sum of toxic units (TU) using data from 2010 to 2021. Sum pyrethroids were calculated by adding concentrations of bifenthrin, cyfluthrin, lambda cyhalothrin, cypermethrin, esfenvalerate/fenvalerate, fenpropathrin and permethrin. Pyrethroid toxic units were calculated by dividing the organic carbon-corrected concentrations by the published organic carbon-corrected LC50. Sum TUs were calculated by adding together individual TU values for each pyrethroid compound. Samples with no detected pyrethroids were assigned a TU value of zero.
Statewide, concentrations of bifenthrin and deltamethrin were significantly increasing, as were the Sum TUs. Concentrations of other pyrethroids were stable or exhibited no trend. Concentrations of most pyrethroid compounds were significantly correlated with the percent of urban land use in the watershed. Bifenthrin concentrations were significantly increasing at 23% of the sites. Most other pyrethroid compounds showed significant decreases at individual sites. Sum pyrethroids had significant increases at 11% of the sites and significant decreases at 10% of the sites.
