Measurement of short- and long-term toxicity of polycyclic aromatic hydrocarbons using luminescent bacteria

Growing concern over environmental contamination has stimulated rigorous efforts to establish reliable biological monitoring assays. Methodology was developed for measuring photoinduced short- and long-term toxicity of an important group of contaminants, polycyclic aromatic hydrocarbons (PAHs), using the luminescent bacterium Vibrio fischeri. The toxicity of most PAHs can be greatly enhanced on exposure of a living organism and/or the chemicals to ultraviolet (UV) radiation. There are two major mechanisms involved in photoinduced toxicity of PAHs: photosensitization and photomodification. In the former, production of singlet oxygen leads to cellular damage. In the latter, photooxidation of PAHs results in new compounds (usually oxygenated PAHs) that are often more toxic than their parent PAHs. Microbial toxicity assays were developed to measure short- and long-term photoinduced toxicity of PAHs. The bioassays were based on inhibition of luminescence and growth of V. fischeri. The short-term assay should detect toxicity of chemicals that are taken up rapidly and/or whose photosensitization activity is immediate. The long-term assay should identify chemicals where the rate of assimilation is slow and/or time is required for photoinduced effects to be realized. The assays were tested with 12 different PAHs. The short-term assay did not reveal photoinduced toxicity for any of the test chemicals. However, photoinduced toxicity was apparent in the long-term assay, indicating that short-term assays may be opaque to this key mechanism of PAH toxicity.