Dissipation fate of non-phthalate plastic additives in well water using UHPLC-Q-Orbitrap-HRMS and GC-Q-Orbitrap-HRMS: A comparison with pure water

Non-phthalate plastic additives (NPPAs) are increasingly being used as alternatives to phthalates, which are avoided due to health and environmental risks. However, the behaviour and hazards of many NPPAs remain poorly understood. To better characterise their fate in aquatic environments, two representative NPPAs, 1-hydroxycyclohexyl phenyl ketone (HCPK) and acetyl triethyl citrate (ATEC), were selected for dissipation and degradation studies in deionized water under three environmental conditions: exposure to sunlight, darkness, and sunlight in the presence of 10 mg/L of nitrate. Same experiments were carried out in well water. Analyses were performed using ultra high-performance liquid chromatography and gas chromatography, both coupled with quadrupole-Orbitrap high resolution mass spectrometry (UHPLC-Q-Orbitrap-HRMS and GC-Q-Orbitrap-HRMS). HCPK degradation followed a single first-order (SFO) kinetic model in deionized water and a double first-order in parallel (DFOP) model in well water, with a maximum half-time (t_1/2) of 8.66 days in well water, while remaining detectable after 365 days in deionized water. In contrast, ATEC degradation followed a DFOP model, with longer t_1/2, 49.97 days in well water and 95.41 days in deionized water, highlighting the influence of water matrix components, such as amount of salts, and microorganisms among others, on its breakdown. Suspect and non-targeted screening revealed potential transformation products. For HCPK, 17 metabolites were tentatively identified (1 suspect and 16 unknown), and for ATEC, 13 metabolites (1 suspect and 12 unknown). Of these, one HCPK (cyclohexyl phenyl ketone) and two ATEC metabolites (triethyl citrate and 1,2-diethyl citrate) were confirmed with commercial standards revealing complex and diverse degradation pathways.