Benzalkonium chlorides (BACs) have been of environmental concern because of their widespread use and potential harm to ecological and human health. Since the registration of the first product containing BACs in the US in 1947, the BACs production has risen for a broad range of applications, including biocides, antiseptics, disinfectants, personal care products, cosmetics, pharmaceuticals, and medical/building materials. Particularly, the ban of triclosan and triclocarban in antibacterial soaps by the US Food and Drug Administration (FDA) in 2016 and the global pandemic of COVID-19 beginning in 2020 have further promoted the use of BACs. BACs are one of the most common groups of cationic surfactants, characterized by a positively charged quaternary ammonium nitrogen atom bonded with a benzyl group and an alkyl chain (C6-C18). Their amphiphilic properties enable them to adhere to solid phases that are predominantly negatively charged such as sediment, soil, sewage sludge, and laboratory glassware. Literature studies have extensively reported the detection of BACs in the aquatic environment, which are primarily composed of BAC homologs with alkyl chain lengths of 12-18 carbons. Surface water concentrations of BACs were typically in the µg/L range; e.g., Taiwanese rivers from 2.5 to 65 µg/L 9 , U.S. stream water from 1.22 to 3.28 µg/L 10 , river water in Spain > 0.1 µg/L 11 and Polish surface water from 72.8 to 331 µg/L. Because of the strong sorption properties, sediment and sewage sludge concentrations can be high, reportedly up to 21 and 191 mg/kg, respectively. Previous studies have documented the toxicity of BACs to aquatic organisms such as fish, crustaceans, 8, 17-19 algae, and bacteria. Despite the findings raising concerns about the potential threat of BACs to the ecological system, the existing database on the toxicity of BACs to aquatic organisms remains unsatisfactory.