Fascinatingly, increasing the concentration of 1Asp to sublethal levels (10 mg dm -3 ) did not result in a further increase in toxicity toward D. magna, but instead caused a biostimulatory effect. At the highest concentration of 1Asp tested, the reproductive output increased by 32% compared to the control, and no mortality or signs of stress were observed during the test. This unexpected phenomenon may stem from compensation for the toxic effects of 1-butylquininium cation due to biostimulation induced by elevated concentrations of L-asparagine in the medium.