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 2022. 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 median lethal concentrations (LC50s). Sum of 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, only concentrations deltamethrin were significantly increasing, as were the Sum of pyrethroid 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 24% of the sites. Most other pyrethroid compounds showed significant decreases at individual sites. Sum pyrethroids had significant increases at 12% of the sites and significant decreases at 13% 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 2022. 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 median lethal concentrations (LC50s). Sum of 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, only concentrations deltamethrin were significantly increasing, as were the Sum of pyrethroid 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 24% of the sites. Most other pyrethroid compounds showed significant decreases at individual sites. Sum pyrethroids had significant increases at 12% of the sites and significant decreases at 13% of the sites.
