Recovery of synthetic pyrethroids in water samples during storage and extraction

Monitoring for synthetic pyrethroids in surface water at the sub-parts per billion level requires reproducible sampling and analytical methods. We studied the recovery of bifenthrin, permethrin, and deltamethrin in water during storage in glass containers and extraction using solid-phase membranes. In solid-free water, the concentration of all compounds quickly decreased and then remained constant at 58-72% of the initial concentration, likely due to adsorption to the glass surface. The recovery was enhanced in runoff samples that contained suspended solids, which was attributed to the association of pesticides to the suspended solids. However, the greatest loss occurred when runoff samples were not agitated before extraction, and the loss was largely caused by the exclusion of the suspended solids from the aqueous phase. Nearly 100% extraction recoveries were obtained when C(8) or C(18) membranes were used for extracting runoff samples. Adsorption to glass surfaces and suspended solids can result in substantial underestimation of pyrethroid concentrations or biological activity and therefore should be considered when designing monitoring protocols.