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How suitable is the gold-labelling method for the quantification of nanoplastics in natural water?
Summary
This study tested a gold-labelling method for quantifying nanoplastics in natural water samples and found that the method faces significant challenges from interfering organic matter. Accurately measuring nanoplastic concentrations in real-world water remains technically difficult, limiting risk assessment for this smallest and potentially most harmful plastic size class.
Abstract Nanoplastics are detected in surface water, yet accurately quantifying their particle number concentrations remains a significant challenge. In this study, we tested the applicability of a gold-labelling method to quantify nanoplastics in natural organic matter (NOM) containing water matrices. Gelatin-coated gold nanoparticles (Au-gel NPs) form conjugates with nanoplastics via electrostatic interaction which produces peak signals which can be translated into particle number concentration using single-particle inductively coupled plasma–mass spectrometry (SP-ICP-MS). We used water samples with various NOM concentrations, with and without the addition of 1 × 107 particle–1 nanoplastics. Our results indicate that nanoplastics in low NOM samples (<1 mg·C L−1) could be successfully quantified. However, in high NOM samples (>15 mg·C L−1), only 13–19% of added nanoplastics were successfully quantified. Further digestion to remove NOM yielded only 10% of spiked nanoplastics. This discrepancy in high NOM samples could likely be attributed to the competition between nanoplastics and NOM existing in the water sample to bind with Au-gel NPs. Our study highlights the suitability of the Au-gel labelling method for quantifying nanoplastics in low NOM water samples. Nevertheless, further optimization, including pre-digestion steps, is essential to apply this method for high NOM water samples effectively.