Environmental monitoring using bioassays

Scientific knowledge regarding the effects of toxic compounds in aquatic ecosystems has increased over recent years. But still there is a need to establish relevant monitoring tools in order to generate an early warning signal of environmental conditions. In the aquatic ecosystems microalgae are the first step in the ecological food chain and as they are very sensitive to toxic elements they can be used as an early warning system when monitoring pollution. The most common parameters when using microalgae in bioassays are photosynthetic parameters and growth. However, there is an increasing need for monitoring tools that are fast and sensitive to a broad range of toxicants. As a complement to more common methods, swimming behavior of microalgae is a promising tool in order to get accurate and rapid analyses. Bioassay methods based on the response of living microorganisms could therefore provide important information concerning the ecological status of aquatic environments. The ECOTOX bioassay calculates the number of motile cells, percentage of cells moving upwards (gravitaxis), the mean velocity, the compactness (form factor) and the precision of orientation (r-value) (cf. Chapter 10: Ecotox, this volume). Studies testing the effects of wastewater and heavy metals on the flagellate Euglena gracilis using the ECOTOX system demonstrate that upward swimming and precision of gravitactic orientation are the most sensitive parameters. The effects show differences between short- and long-term tests but the effects from herbicides showed pronounced effects on velocity and upward swimming of E. gracilis already after 30 and 60 s. ECOTOX measurements from Egyptian lakes which are polluted by industrial and domestic wastewaters showed strong inhibition on upward swimming and r-value of E. gracilis. Samples taken from the wastewater treatment plant west of Alexandria showed that the toxicity is not reduced by the treatment. The results from studies using the ECOTOX system indicate that this bioassay could be very useful in the future for short- and long-term risk assessments