Polymer leachates emulate naturally derived fluorescent dissolved organic matter: Understanding and managing sample...

Fluorescence spectroscopy has become a fundamental tool for the qualitative and quantitative fingerprinting of dissolved organic matter. Due to the inherent sensitivity of the technique, a strict sampling protocol should be followed to ensure sample integrity. A literature survey conducted as part of this research determined that 27% of fluorescence sampling has been conducted in polymeric containers, while 52% did not report. Given the potential for fluorescence leachates to arise from plastics commonly used in sampling bottles, a systematic laboratory investigation was undertaken to assess the likelihood of leachate contamination and consequent interferences. It was observed that characteristic fluorescent dissolved organic matter (FDOM) leachates from standard polypropylene sampling containers were produced at environmentally relevant peaks, Peak T (λ_Ex/λ_Em: 250/349 nm) and B (λ_Ex/λ_Em: 250/306 nm), commonly attributed to tryptophan-like and tyrosine-like molecular origins. Leachate fluorescence and concentration generally increased with elevated storage temperatures (>4 °C), sample acidification, container steam sterilisation and in new containers, with variability across different manufactured batches. For example, at ambient storage temperatures, the highest observed leachate intensity could contribute an error equivalent to as much as 98% (Peak T) and 2062% (Peak B) for highly treated water or 28% (Peak T) and 398% (Peak B) for surface water. For leachates formed under typical conditions, i.e., 3-day fridge storage, this reduced to 9% (Peak T) and 15% (Peak B) or 3% (Peak T/B) for the same water samples. In addition, PP was found to be typically unsuitable for DOC measurements, except under strict conditions (well-aged containers in short term cold storage). Consequently, we demonstrate the need for container material reporting, refrigerated storage, steam sterilisation avoidance, and the importance of glass usage for low FDOM samples. Future research should investigate the potential for polymer-based pollution as a potential origin of environmentally sampled FDOM.