Bioconcentration factors for hydrocarbons and petrochemicals: Understanding processes, uncertainty and predictive model performance.

Fish bioconcentration factors (BCFs) are often used to assess substance-specific bioaccumulation. However, reliable BCF data are limited given the practical challenges of conducting such tests. The objectives of this paper are to describe nine rainbow trout studies performed in our lab using tailored dosing and test designs for obtaining empirical BCFs for 21 test substances; gain insights into the structural features and processes determining the magnitude and uncertainty in observed BCFs; and assess performance of six quantitative structure property relationships (QSPRs) for correctly categorizing bioaccumulation given current regulatory triggers. Resulting mean steady-state BCFs, adjusted to a 5% lipid content, ranged from 12 Lkg-1 for isodecanol to 15,448 Lkg-1 for hexachlorobenzene which served as a positive control. BCFs for hydrocarbons depended on aromatic and saturated ring configurations and position. Uptake clearances appeared to be modulated by gill metabolism and substance bioavailability, while elimination rates were likely influenced by somatic biotransformation. Current approaches for quantifying uncertainty in experimental BCFs, which take into account only variability in measured fish concentrations, were found to underestimate the true uncertainty in this endpoint with important implications for decision-making. The Vega (KNN/Read-Across) QSPR and Arnot-Gobas model yielded the best model performance when compared to measured BCFs generated in this study.

Assessing the aquatic hazard of commercial hydrocarbon resins.

Hydrocarbon resins are used to modify polymer products to achieve desired functional properties for a diverse range of products. These complex hydrocarbon-based mixtures are typically poorly soluble in water. However, resins may leach lower-molecular-weight monomers or impurities upon contact with water, thus posing a potential hazard to the aquatic environment. The bioavailability and toxicity of leachable constituents of four solid and three liquid resins were evaluated by analyzing water-accommodated fractions prepared with each resin, using biomimetic solid phase microextraction (SPME) techniques. Liquid resins exhibited concentrations of bioavailable constituents that were sufficiently elevated to cause acute toxicity to the aquatic organism Daphnia magna. All solid resins exhibited lower bioavailable concentrations of leachable constituents that were unlikely to pose an aquatic toxicity concern. Since observed toxicity of both resin types was generally consistent with bioavailable concentrations determined using SPME fiber measurements, it is concluded that this approach provides a convenient in vitro screening tool that can help reduce the use of animal testing in environmental hazard assessment of complex hydrocarbon-based substances.