Contamination often occurs as a result of metals and organic chemicals from industrial processes being deposited on land and in water. Quantification of contamination has traditionally involved measuring the concentration of chemicals present. However, this does not necessarily assess toxicity due to chemical interactions or assess that portion that is “bioavailable”. The work presented in this thesis uses the naturally bioluminescent bacterium Vibrio fischeri as the biosensor in bioassays to assess such toxicity. The growth of the bacterium was characterised and the methodology developed for preservation by freeze-drying. Quality control procedures were established. The response of rehydrated cells was investigated under different conditions, and the toxicity of a range of organic compounds and metals was measured under ideal conditions before progressing to environmental samples. This baseline testing was also used to determine the suitability of methanol as a solvent for biosensor testing and chemical analyses. A site where metal amended sludge cake had been added during a long-term field trial was assessed using the bioassay. Toxicity was shown to be attributable to pH and not metal concentrations. Samples from a contaminated foreshore were assessed with the bioassay and by chemical analysis using methanol as an extraction solvent. The V. fischeri bioassay was shown to be a robust procedure for toxicity assessments, vials of the freeze-dried cells were shown to have a 1 year shelf-life and offered a cost effective alternative to Microtox®. The developed bioassay should be specified in legislation for toxicity assessment particularly if future work demonstrates that it is a surrogate for higher organisms.