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Long‐term bioconcentration kinetics of hydrophobic chemicals in Selenastrum capricornutum and Microcystis aeruginosa

The bioconcentration of two chlorobenzenes (CBs) and of seven polychlorobiphenyls (PCBs) to Selenastrum capricornutum and Microcystis aeruginosa was studied with accumulation experiments followed by gas purge elimination experiments. Henry's law constants at 10°C were needed to interpret the gas purge results and were measured in control experiments. For the M. aeruginosa culture, steady‐state uptake was reached within days, whereas uptake by S. capricornutum took several weeks. The relationships between the log bioconcentration factors (BCF) and log octanol–water partition coefficients (Kow) were nonlinear, with relatively low values for the more hydrophobic PCBs. Rate constants for the elimination of CBs and PCBs from the algal cells were shown to be larger than 1 per day when calculated with a one‐compartment model. With such large rate constants, it is unlikely that the curvature observed for these species is caused by slow kinetics or that algal growth affects BCF by dilution of CB or PCB concentrations. The log BCF–log Kow relationships could be described by a simple three‐phase model that accounted for the binding of CBs and PCBs to dissolved organic carbon (DOC). Modeling bioconcentration of hydrophobic chemicals in phytoplankton should account for the binding to DOC.