Application of nd-SPME to determine freely dissolved concentrations in the presence of green algae and algae-water partition coefficients.

Biological tests are essential for toxicity assessment of chemicals to aquatic organisms. Since awareness is increasing that freely dissolved concentrations in test media may change during exposure and deviate significantly from nominal concentrations there is a need for concentration monitoring in biotests. Biotests are increasingly miniaturized with effect amounts of toxicants that are close to or below quantification limits of conventional analytical methods. Thus, the suitability of pre-equilibrium non-depletive (nd) solid phase microextraction (SPME) as an analytical method for small test volumes in the presence of green algae Scenedesmus vacuolatus was investigated. The method was validated for several compounds with different physical-chemical properties and effect concentrations. Limits of quantification were at least about 10 times smaller than the EC(50) of the compounds determined in earlier studies in a cell multiplication inhibition tests with Scenedesmus vacuolatus. Fouling of the fibres due to attached algae cells could be excluded and the method was found to be well suited to measure free concentrations in the algae test. The nd-SPME-method was applied to determine partitioning coefficients between algae and the surrounding aqueous phase and can be used to determine real exposure concentrations in a cell multiplication inhibition test with green algae.