Benefits from hazards, benefits from nothing, and benefits from benefits: the combined effects of five quaternary ammonium compounds to Vibrio qinghaiensis Q67

Background Co-exposure of multiple quaternary ammonium compounds (QACs) is widely present in the aquatic environment. The knowledge about their toxicities to microorganism at low concentration is lacking. This study aims to test the toxic response of Vibrio qinghaiensis Q 67 (12-h exposure) to individual and mixtures of QACs by the long-term microplate toxicity analysis method (L-MTA). Results Hormetic effects were observed for five individual QACs at 12-h exposure of Vibrio qinghaiensis Q 67. The maximum stimulation effect of − 339.66% was present in the 0.00561 mol/L tetraethylammonium bromide solution. A stimulation effect (− 23.55%) was detected when each of QACs in the five-component mixture was present at 50% effect concentration (“benefits from hazards”). In addition, significant stimulation effects (− 96.28%) were observed for five QACs combined at the zero-effect point concentration (“benefits from nothing”). Further, a significant stimulation effect (− 406.16%) was observed when each of QACs was co-exposed at its maximum stimulation effect concentration. This phenomenon was termed “benefits from benefits”. Conclusions The results suggest that both single and mixture of QACs presented hormetic effects. Benefits from hazards, benefits from nothing, and benefits from benefits were observed for the QACs mixtures.