Algal density dependent bioconcentration factors of hydrophobic chemicals

The bioconcentration factors (BCFs) of anthracene, hexachlorobenzene, 4,4′-dichlorobiphenyl, and 2,2′5,5′-tetrachlorobiphenyl decreased with increasing density of the algae Chlorella vulgaris and Chlorella pyrenoidosa. Concomitant with algal density, the organic carbon concentration as measured by chemical oxygen demand (COD) in the aqueous phase after centrifugation of the algal suspensions, increased. It is argued that the decreased BCFs in the presence of algae is due to the inability of the centrifugation technique to separate organic exudates, which bind hydrophobic organic chemicals, from water. The apparent decrease of the BCFs of the organic chemicals is thus caused by a reduction in bioavailability of the chemicals in the aqueous phase due to binding to exudate.