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.
Up until 2022, Pyrethroids were measured at all 90 SPoT sites and trends were calculated for individual compounds, the sum of pyrethroids, and the sum of toxic units. Sum pyrethroids were calculated by adding concentrations of bifenthrin, cyfluthrin, lambda cyhalothrin, cypermethrin, esfenvalerate/fenvalerate, fenpropathrin and permethrin. Statewide, concentrations of deltamethrin were significantly increasing. 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. Due to the high percentage of sites with no trends and correlations with urban land use in the first 15 years of the program, pyrethroid monitoring efforts were focused on 40 tier II urban sites in 2023. Trend analysis at these sites between 2010 and 2023 revealed that bifenthrin was increasing/probably increasing at about 35% and deltamethrin was increasing/probably increasing at 25% of the sites. This focused approach also showed decreasing trends in cypermethrin and permethrin at 36% of sites we all as no trends for several pyrethroids at most sites.
Statewide, concentrations of bifenthrin, cypermethrin and permethrin are likely decreasing at these 40 urban sites with no significant relationships with land use. This approach will be continued for next several years to track changes in trends over time at the historically contaminated sites.
Up until 2022, Pyrethroids were measured at all 90 SPoT sites and trends were calculated for individual compounds, the sum of pyrethroids, and the sum of toxic units. Sum pyrethroids were calculated by adding concentrations of bifenthrin, cyfluthrin, lambda cyhalothrin, cypermethrin, esfenvalerate/fenvalerate, fenpropathrin and permethrin. Statewide, concentrations of deltamethrin were significantly increasing. 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. Due to the high percentage of sites with no trends and correlations with urban land use in the first 15 years of the program, pyrethroid monitoring efforts were focused on 40 tier II urban sites in 2023. Trend analysis at these sites between 2010 and 2023 revealed that bifenthrin was increasing/probably increasing at about 35% and deltamethrin was increasing/probably increasing at 25% of the sites. This focused approach also showed decreasing trends in cypermethrin and permethrin at 36% of sites we all as no trends for several pyrethroids at most sites.
Statewide, concentrations of bifenthrin, cypermethrin and permethrin are likely decreasing at these 40 urban sites with no significant relationships with land use. This approach will be continued for next several years to track changes in trends over time at the historically contaminated sites.
