Estimating pyrethroid bioavailability in sediment with negligible depletion extraction

Pyrethroid insecticides are used widely for pest control. Their high acute toxicity to non-target aquatic organisms has caused concern about the ecotoxicological effects of environmental contamination in sediments of surface water systems. The purpose of this research was to investigate the effectiveness of negligible depletion extraction to estimate the bioavailability of pyrethroids in sediments. The bioavailability of pyrethroids is important to understand since it is a factor influencing the exposure to biota. The current state of knowledge governing bioavailability of hydrophobic contaminants, such as pyrethroids, is reviewed. Experiments using disposable solid phase microextraction (SPME) fibers coated with polydimethylsiloxane (PDMS) were conducted to evaluate the effectiveness of this negligible extraction technique to estimate pyrethroid bioavailability in sediments. Twenty-four hour bioaccumulation assays with Chironomus tentans and 14C-labeled permethrin, showed that disposable PDMS fibers correlated significantly with biota body residues in two sediments modified with sand (r2 = 0.86, p < 0.0001; and r 2 = 0.38, p = 0.002). Disposable PDMS fiber permethrin concentrations also correlated well with biota across four different sediment types (r2 = 0.91, p < 0.0001). This correlation was better than that for the organic carbon normalized approach (r2 = 0.76, p < 0.0001). A method was developed using disposable 30mum thick PDMS fibers to measure environmentally relevant concentrations of seven non-labeled pyrethroids freely dissolved in sediment pore water. When agitated, fibers reached equilibrium for all pyrethroids, except bifenthrin, in < 5 d. Tests with field-contaminated sediments showed that the developed method was sufficiently sensitive to detect ng/L levels of freely dissolved pyrethroids in pore water. Comparison of fibers with different coating thicknesses (7, 30, and 35 mum) showed that the fiber to water partition ratios (KPDMS) for eight pyrethroids were dependent on coating thickness. The sediment LC50 values based on fiber measured freely dissolved permethrin were generally similar to each other in sediment modified with sand and black carbon, differing at most by a factor of 2.5. Overall, the results from this research indicate that negligible depletion SPME fibers may be useful tools in evaluating the bioavailability and potential risk of pyrethroids in sediments.