Toxicokinetics and toxicity of sediment‐associated pyrene to lumbriculus variegatus (oligochaeta)

The oligochaete Lumbriculus variegatus has been proposed for whole‐sediment bioassays to assess sediment contamination. Our work examines Lumbriculus variegatus exposure to pyrene‐dosed Lake Michigan sediment at 0.4 ng g −1 and 64, 132, 206, and 269 μg g −1 . Both bioaccumulation and survival were followed to enhance Lumbriculus variegatus development as a bioassay organism. Lumbriculus variegatus accumulated sediment‐associated pyrene rapidly and achieved apparent steady state within 48 to 168 h. The pyrene uptake clearances (k s , g sed g −1 animal h −1 ) ranged from 0.039 to 0.132 and decreased with increasing pyrene concentration. At high pyrene concentrations, the worms avoided the sediment, which reduced accumulation and likely minimized the mortality response. In addition, the effect of organism loading on bioaccumulation was determined at different animal densities, 1:10, 1:50, and 1:100 g dry weight Lumbriculus variegatus:g sediment organic carbon, and a sediment pyrene concentration of 0.4 ng g −1 . Surprisingly, the bioaccumulation declined as organism density decreased. Pyrene elimination was rapid in clean sediment (k e = 0.026 ± 0.002 h −1 ) but was much slower in water (k e = 0.0043 ± 0.0007 h −1 ). Bioavailability apparently declined for exposures in sediment stored 1.5 months, based on the estimate of k e from nonlinear regression compared to direct measures of elimination. The apparent decline was attributed to both a decline in lipid content during the experiment and changes in pyrene bioavailability. Finally, for bioaccumulation studies, gut purging at a set time (e.g., 24 h) may result in an underestimate of contaminant concentration in organisms. An elimination study with extrapolation to the initial body burden can ensure that biases due to incomplete elimination of gut contents and body burden losses during the purging process are minimized.