Use of sand-living microalgal communities (epipsammon) in ecotoxicological testing

A new ecotoxicological test system employing sand-living microalgal communities is presented. Equipment and procedures were developed for sampling and transportation of epipsammon to the laboratory where they can be kept and prepared for subsequent toxicity testing. The proposed test system make use of small-volume (60 mu d) subsamples in the measurement of metabolic activities in short-term toxicity tests. The replicability is therefore very good and the variance between subsamples was shown to be low. After several hours of storage between sampling and analysis, epipsammon showed only minor changes in metabolic activities and no significant changes in sensitivity to the investigated toxicant tri-n-butyltin (TBT). The use of a community that has been established on a natural, but still homogenous, substratum has several advantages. Similar to other attached communities, but in contrast to phytoplankton, epipsammon represents a certain site and can thus have a known pollution history. The preparation and monitoring of sampling equipment for colonization of periphyton on artificial substrata is avoided. In addition, since epipsammon has been colonizing the sand for a long time, the community is also likely to be more natural than the opportunistic assemblages that are the early colonizers of artificial substrata. Epipsammon from the investigated locality also showed a fairly low spatial variability in most employed structural and functional parameters which indicated that the test system is robust and the actual sampling site not too critical. However, the estimated toxicity of TBT was shown to be lower to epipsammon than to previously investigated phytoplankton and periphyton From indirect evidence, we suggest that this difference is not explained by different bioavailability of the toxicant in the short-term test systems but rather to the adaption of algae to natural environmental conditions in the sediments.