Compounds with a short butyl or 2-(hydroxyethyl) substituent were "practically nontoxic" (El-Harbawi, 2014) and exhibited ErC50 values exceeding 100 mg dm -3 . Thus, they were less toxic than quinine hydrochloride (10-100 mg dm -3 ). Interestingly, a decrease in the toxicity against C. vulgaris (ErC50 >1000 mg dm -3 ) to a level where the chemical can be considered "relatively harmless" (El-Harbawi, 2014) was noted for 1Asp. Thus, it can be concluded that the introduction of an amino acid anion into the structure of QASs could reduce the toxicity of the quinine structure toward C. vulgaris in some cases, although it had no effect on reducing the adverse effects caused by QASs comprising a quinine-based cation with a longer alkyl substituent.