Determination of Toxicokinetic Parameters for Bioconcentration of Water-Soluble Fraction of Petroleum Hydrocarbon Associated with No. 0 Diesel in Changjiang Estuary and Jiaozhou Bay: Model Versus Mesocosm Experiments

Abstract

A method is proposed for determination of toxicokinetic parameters for bioconcentration by phytoplankton of the water-soluble fraction (WSF) of petroleum hydrocarbon (PH) associated with No. 0 diesel, in which WSF-PH concentration in phytoplankton cells, C_A(d), is estimated by subtracting concentration in water (S-bottle) containing a phytoplankton sample from that in a C-bottle without phytoplankton. It was demonstrated that C_A(d) agrees well with the concentration found by direct ultrasonication extraction of collected cells, C_A(ind) (r = 0.88, p < 0.0001), and its uncertainty was about 17.6%. Mesocosms in 25-m³ ethylene vinyl acetate or 4-m³ polyethylene bags were performed at two sites in China: Changjiang Estuary in spring/summer 1998 and Jiaozhou Bay in autumn 1999 and spring/summer 2000. The experiments were designed to determine toxicokinetic parameters, including specific rates of uptake and elimination, and bioconcentration factor (BCF), for bioconcentration of WSF-PH by phytoplankton. A modified kinetic two-compartment model for bioconcentration of WSF-PH by phytoplankton was developed to estimate the toxicokinetic parameters. In the model, the influence of phytoplankton growth on bioconcentration and WSF-PH decline due to biotic and abiotic processes other than bioconcentration, such as volatilization, microbial degradation, phytolysis, and sorption expressed as an exponential-decay equation, are taken into account. Size-dependent BCF was observed in the laboratory experiment. BCFs were 1.0 × 10⁴ in summer in Changjiang Estuary, 1.6 × 10⁴ in summer, and 1.1 × 10⁴ in autumn in Jiaozhou Bay. The difference in BCF may be interpreted by its size dependence.