Effects of different pH values on the time-dependent toxic interactions of copper and Amikacin sulfate in Vibrio qinghaiensis sp.-Q67

Pollutants are mixed in various forms or concentrations, and their cumulative toxicity and interaction have potential risks to environmental health under the natural condition. While pH plays a very important role in the toxicity of chemical substances. Using Vibrio qinghaiensis sp.-Q67 (Q67) as the test organism, the cumulative toxicity and interction of mixtures of Amikacin sulfate (AMI) and heavy metal Cu were investigated using the time-dependent microplate toxicity analysis method. The experiments were carried out under four pH conditions of 6.0, 7.0, 8.0 and 9.0, respectively. The representative mixtures with different concentrations and ratios were designed by direct equipartition ray (EquRay). The independent action model (IA) was used as reference to analyze the mixture toxicity interactions. The intensity of toxic interaction between AMI and Cu was evaluated using the modified area-concentration ratio method (MACR) .The results showed that: (1) The toxicity order of Cu to photobaterium Q67 at different pH values was: (pH=9)>(pH=7)>(pH=8)>(pH=6). The toxicity difference of AMI to Q67 at four pH values was relatively small, and the toxicity of AMI was 2-3 orders of magnitude higher than that of Cu. (2) The toxicity of Cu and AMI mixture system was obviously component-dependent. The toxicity of the mixture system increased with the addition of AMI components, and the difference of toxicity was more significant with the extension of exposure time. (3) The mixture system at pH 6 showed the highest toxicity and others had the similar toxicity. (4) There were 20 rays in the mixture system at 4 pH values, and synergistic or additive effects existed; The mixture system at pH 6 showed the lowest MACR values and the synergy effects. The mixture system at pH 7, 8 and 9 had the similar MACR values and toxic interaction intensity.