Biosensing the acute toxicity of metal interactions: Are they additive, synergistic, or antagonistic?

The toxicity of Zn, Cu, and Cd, alone or in combination, was assessed using two luminescence-based microbial biosensors from different ecological niches: Escherichia coli HB101 pUCD607 and Pseudomonas fluorescens 10586 pUCD607. Significant synergistic interactions occurred between the toxic effects of the Zn and Cu and Zn and Cd combinations and the response of E. coli (i.e., toxicities of combinations of pollutants were greater than predicted from addition of individual toxicities). Significant synergistic interactions were also observed between the toxicities of Cd and Cu combinations and the response of P. fluorescens. A longer exposure time was shown to significantly increase the sensitivity of E. coli to the metal pollutants. P. fluorescens was observed to significantly decrease in its sensitivity toward Zn and Cd with a longer exposure time. It was shown that the toxicity of combinations of metals could not be modeled on the basis that their toxic action was independent of each other. The application of different models to describe interactions between combinations of metals is discussed. The importance of considering the test species and the exposure period selected for toxicity assessment was highlighted, as was the need to further investigate the toxicity of combinations of pollutants.