Pyrethroid sorption to Sacramento River suspended solids and bed sediments

Area of Science:

• Environmental Chemistry
• Aquatic Toxicology
• Soil Science

Background:

• Pyrethroid insecticides are hydrophobic and their environmental fate is dominated by sorption to solids.
• Understanding sorption behavior is crucial for assessing pyrethroid transport in aquatic ecosystems.

Purpose of the Study:

• To compare the sorption of bifenthrin and λ-cyhalothrin to suspended material and bed sediment from the Sacramento River.
• To investigate the role of differential sorption in pyrethroid environmental transport.
• To determine sorption characteristics under environmentally relevant conditions.

Main Methods:

• Batch reactor isotherm experiments were conducted with bifenthrin and λ-cyhalothrin.
• Low spiking concentrations and a 28-day equilibration time were used.
• Sorption data were fitted to the Freundlich isotherm model.

Main Results:

• Sorption to suspended material was greater than to bed sediment.
• Suspended material exhibited higher specific surface area and organic carbon content.
• Freundlich exponents indicated both nonlinear and linear sorption depending on conditions.
• Organic carbon-normalized distribution coefficients were approximately one order of magnitude higher than previously reported.

Conclusions:

• Sorption to suspended solids significantly influences pyrethroid fate and transport.
• Higher than expected sorption may be attributed to interactions with black carbon and mineral surfaces.
• Differential sorption between suspended and bed materials plays a key role in pyrethroid distribution.