Stir bar contamination: a method to establish and maintain constant water concentrations of poorly water-soluble chemicals in bioconcentration experiments.

A novel experimental system to establish and maintain constant dissolved concentrations of poorly water-soluble compounds for bioconcentration experiments with algae was developed. Although still recommended in the literature as a "non-adsorptive" material, a commercially available Teflon stir bar that was preloaded with polychlorinated biphenyls (PCBs) proved to be an effective donor for partitioning controlled delivery. When placed in a bioconcentration test chamber, the PCB concentrations in water and in the headspace remained constant for up to 8 days. Henry's law constants determined in experiments using water only were in good accordance with values found in the literature, indicating that the chemical was truly dissolved. When algae (Emiliana huxleyi, class prymnesiophyceae) were added to the chamber, the water and air concentrations varied initially but stabilised within several hours, and smooth uptake curves were obtained for the algae. This indicates that the contamination system compensates for chemical loss from the water column. In addition, the Henry's law constants and the headspace measurements were used to estimate what fraction of the PCB in filtered water was associated with dissolved organic carbon, opening the opportunity to constrain one of the major artefacts in bioconcentration experiments.