Two-compartment thermodynamic model for bioconcentration of hydrophobic organic chemicals by alga: Quantitative relationshiop between bioconcentration factor and surface area of marine algae or octanol/water partition coefficient

A two-compartment thermodynamic model for bioconcentration of hydrophobic organic chemicals (HOCs) by algae was proposed. In the model, it was assumed that 1) the bioconcentration is comparable to physicochemical liquid-liquid partitioning, and is predominantly the result of interfacial processes of alga cells as well as HOC; 2) the surface excess quantity of HOC with respect to water phase can be expressed by Gibbs equation, and increases with increasing HOC concentration in alga cells; 3) the hydrophobic nature of alga cells, wherein only dispersion interaction contributes to their surface tension, remain almost unchanged after adsorption of HOC. From the model it was concluded that bioconcentration factor (log BCF) has linear relation with specific surface area (log S) of alga cells, n-octanol/water partition coefficient (log Kow) of HOC, and HOC concentration in the water (log Cw) respectively. The model was tested by the bioconcentration of monochlorobenzene, 1,2-dichlorobenzene, 1,2,3,4-tetrachlorobenzene, and pentachlorobenzene by marine algae including Chlorella marine, Nannochloropsis oculata, Pyramidomonas sp., Platymonas subcordiformis, and Phaeodactylum tricornutum. BCF values were obtained not only with the bioconcentration model, but also with the combined bioconcentration and probability model. It was found that the bioconcentration factors of a chemical was increaseing with the specific surface area (S) of different marine algae.