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 nich es: Escherichia coli HB101 pUCD607 and Pseudomonas fluorescens 10586 pUCD60 7. 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 fr om addition of individual toxicities). Significant synergistic interactions were also observed between the toxicities of Cd and Cu combinations and th e response of P. fluorescens. A longer exposure time was shown to significa ntly increase the sensitivity of E. coli to the metal pollutants. P. fluore scens was observed to significantly decrease in its sensitivity toward Zn a nd Cd with a longer exposure time. It was shown that the toxicity of combin ations of metals could not be modeled on the basis that their toxic action was independent of each other. The application of different models to descr ibe interactions between combinations of metals is discussed. The importanc e of considering the test species and the exposure period selected for toxi city assessment was highlighted, as was the need to further investigate the toxicity of combinations of pollutants.