Fate and Occurrence of Quaternary Ammonium Compounds in Aquatic Environments: From Photochemical Transformation of Ionic Liquid Cations to Suspect Screening in Lake Sediments

Quaternary ammonium compounds (QACs) are a diverse grou p of organic chemicals with molecular masses ranging from 100 to 600 g/mol and alkyl sidechains of 2 to 22 C atoms. Long-chain QACs are high production volume chemicals that are mainly used as surfactants and biocides in cleaning and personal-care products. Short-chain QACs are used as cations in ionic liquids, an emerging group of
nonvolatile solvents with various potential applications in the chemical industry. The fate and occurrence of QACs in aquatic environments is challenging to study because, especially long-chain QACs, are difficult to quantify reliably with standard mass spectrometry methods. Furthermore, the fate of ionic liquid cations, which potentially deviates from long-chain QACs, has received little attention. To improve the assessment of both long- and short-chain QACs, we have (1) developed a high-resolution mass spectrometry method for target and suspect screening of a wide range of QACs, (2) screened wastewater effluent and lake sediment samples for the presence of long- and short-chain QACs, and (3) quantified the photochemical transformation rates of ionic liquid cations in sunlit surface waters. 13 long-chain QACs could be semi-quantitatively determined in both wastewater effluent and surface sediment samples with average total concentrations of 3 g/L and 3 g/g, respectively. Short-chain QACs were only detected in wastewater effluent samples with three compounds amounting to an average total concentration of 0.3
g/L. Comparison of different wastewater treatment trains suggest that the short-chain QACs are less biodegradable than the long-chain QACs. In addition, our laboratory experiments with ionic liquid cations indicate half-lives of 1-4 months for photochemical transformation in sunlit surface waters. Overall, the transformation of short-chain QACs is expected to be even slower than the transformation of long-chain
QACs in aquatic environments. Combined with the fact that short-chain QACs were not found in surface sediment samples suggest that these small compounds are also not removed efficiently by sedimentation resulting in a potential for their accumulation in surface and groundwater.