There is an urgent need for a rapid assay of potential toxicity of wastewaters and/or individual process streams to the active biomass in biological wastewater treatment plants (WTP). This can be provided by a whole cell biosensor system called CellSense which has been developed by Euroclone Limited, based upon an original R & D programme undertaken by a consortium incorporating the University of Luton, WRc plc, AstraZeneca , and the Environment Agency.