Combined toxicity of pesticide mixtures on green algae and photobacteria

• Toxicities of six pesticides and their mixtures to V. qinghaiensis and C. pyrenoidosa were determined.
• Toxicities of three herbicides to C. pyrenoidosa is higher than those to V. qinghaiensis.
• Some binary pesticide mixtures display antagonism to C. pyrenoidosa but synergism to V. qinghaiensis.
• Toxicities of multi-component mixtures are additive to C. pyrenoidosa and V. qinghaiensis.

Different organisms have diverse responses to the same chemicals or mixtures. In this paper, we selected the green algae Chlorella pyrenoidosa (C. pyrenoidosa) and photobacteria Vibrio qinghaiensis sp.-Q67 (V. qinghaiensis) as target organisms and determined the toxicities of six pesticides, including three herbicides (simetryn, bromacil and hexazinone), two fungicides (dodine and metalaxyl) and one insecticide (propoxur), and their mixtures by using the microplate toxicity analysis. The toxicities of three herbicides to C. pyrenoidosa are much higher than those to V. qinghaiensis, and the toxicities of metalaxyl and propoxur to V. qinghaiensis are higher than those to C. pyrenoidosa, while the toxicity of dodine to C. pyrenoidosa is similar to those to V. qinghaiensis. Using the concentration addition as an additive reference model, the binary pesticide mixtures exhibited different toxicity interactions, i.e., displayed antagonism to C. pyrenoidosa but synergism to V. qinghaiensis. However, the toxicities of the multi-component mixtures of more than two components are additive and can be predicted by the concentration addition model.