Subcellular accumulation of polychlorinated biphenyls in the green alga Chlamydomonas reinhardii

In this study, the subcellular accumulation of 13 polychlorinated biphenyl (PCB) congeners was investigated in the green alga Chlamydomonas reinhardtii. Two main arguments pertaining to the mechanism of bioaccumulation of persistent bioaccumulative toxic chemicals (PBTs) in phytoplankton were evaluated, including the controversy of whether the limitation of uptake of ultra-hydrophobic pollutants is kinetic or due to a physical barrier presented by the membrane that prevents transfer into the internal parts of the cell, and second, the role of surface adsorption for the bioaccumulation process. The first argument was addressed by studying the time-dependent subcellular uptake of PCBs into thylakoids (photosynthetic membranes) as representative internal membranes. The second issue was addressed by investigating the role of the alga] cell wall as a potential extracellular sorbate. Accumulation of PCBs in thylakoids was found to be limited kinetically and slow compared to total accumulation in the alga. Super-hydrophobic PCBs with K-ow > 6 were not restricted from entering the cell. Sorption to the cell wall was found to be less than 10% and insignificant compared to total bioaccumulation in C. reinhardtii. To our knowledge, this is the first study in which the subcellular uptake of a class of PBTs was investigated directly. The results offer a mechanistic framework for improving kinetic modeling of PBT bioaccumulation in phytoplankton.