Particle-scale understanding of cypermethrin in sediment: Desorption, bioavailability, and bioaccumulation in benthic invertebrate Lumbriculus variegatus.

Influence of sediment particle size on the desorption, bioavailability, and bioaccumulation potential of cypermethrin was investigated in the present study using two biomimetic techniques (Tenax extraction and solid-phase microextraction (SPME)) and bioaccumulation testing with Lumbriculus variegatus. A field-collected sediment was wet sieved to obtain five particle-size fractions (<20, 20-63, 63-180, 180-500, and >500 μm) and used for cypermethrin spiking. The finest sediment (<20 μm) had the highest rapid desorption fraction (F) and rate (k) when compared to coarser sediments. Elimination rate constants of cypermethrin determined by SPME (k) and L. variegatus (k) for various fractions of sediments followed the same trend, suggesting SPME fiber acts as a good surrogate for benthic organisms considering passive partitioning. Finally, biota-sediment accumulation factors (BSAFs) of cypermethrin in worms were almost the same among the sediments with different particle sizes (0.425 ± 0.07-0.445 ± 0.07 g OC g lipid), suggesting that the differences in desorption and freely dissolved concentrations of cypermethrin did not significantly influence its bioaccumulation potential in worms. Selective ingestion of fine sediment particles may be one of the contributing reasons for no differences in BSAFs observed in the treatments as would have been expected. The different desorption and freely dissolved concentrations of cypermethrin in sediments with different particle sizes observed in this study highlights the need for further work to better understand the influence of particle size on the toxicity of highly toxic insecticides, such as cypermethrin, to sensitive benthic species.