Defining Benthic Organism Exposure: Bioavailability and Effects of Non-Polar Organics
Laboratory and field tests were conducted to evaluate the hypothesis that factors such as the total organic carbon (TOC) contents and groundwater-surface water interactions (GSI) in the sediments can affect chemical desorption, bioavailability and benthic organism exposure. Laboratory studies were conducted with the polycyclic aromatic hydrocarbon fluoranthene (FLU) and the herbicide trifluralin (TF). Toxicokinetic parameters were determined for Lumbriculus variegatus and Hyalella azteca in water-only exposures to 0, 5, 20 and 50 µg/L of the compounds and bioaccumulation was measured during exposures to 0, 100 and 200 mg/kg of FLU and TF spiked onto sediments from Lakes Erie and Huron. Mean uptake clearance rates ranged from 150-180 mL/g wet animal/h for FLU and 84-120 mL/g/h for TF, and elimination rates were 0.12-0.18 and 0.067-0.10/h for FLU and TF, respectively. The uptake clearances in sediments (ks) ranged from 0.021 to 0.070 g dry sed/g wet animal/h for FLU and 0.013 to 0.041 g/g/h for TF. The desorption kinetics of FLU and TF from spiked sediments were measured over 34 d by extraction with Tenax®. The rapidly desorbing fraction for FLU and TF ranged from 31.3 to 54.9% of the initial concentrations and rates of the rapidly (krap), slowly (kslow) and very slowly (kvs) desorbing fractions were on the order of 10-1/h, 10-2–3/h and 10-4/h, respectively. The influence of GSI on contaminant bioavailability was demonstrated with in situ exposures of benthic invertebrates to river sediments that were contaminated primarily with chlorobenzenes (CBs). Hydrologic and chemistry data from nested mini-piezometers explained the exposure-effects relationships. Overall, downwelling conditions reduced the in situ exposure of organisms in surficial sediments, and hence, the toxicity and bioaccumulation of CBs. Data from these field and laboratory investigations were combined with literature values of contaminant partitioning (i.e., Koc values), and L. variegatus feeding rates and chemical assimilation efficiencies to parameterize a bioaccumulation model. Simulated tissue concentrations at sites containing contaminated sediments were compared to the body burdens measured in the field. The model predicted field observations within an order of magnitude and indicated that TOC, GSI and organism feeding behavior were sensitive parameters. The bioaccumulation model represents a useful tool that can reduce resource expenditures associated with site assessments and provide more accurate risk characterizations.
School:Wright State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:sediments desorption toxicokinetics bioavailability benthic model groundwater surface water interaction
Date of Publication:01/01/2002