How suitable is the gold-labelling method for the quantification of nanoplastics in natural water?

Nanoplastics are detected in surface water, yet accurately quantifying their particle number concentrations remains a significant challenge. In this study, we tested the applicabilit y 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 spectrometr y (SP-ICP-MS). We used water samples with various NOM concentrations, with and without the addition of 1 x 107 particles L-1 nanoplastics. Our results indicate that nanoplastics in low NOM samples (,1 mgC L-1) could be successfully quantified. However, in high NOM samples (.15 mgC 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. HIGHLIGHTS center dot Quantification of nanoplastic with gold-labelling using single-particle ICP-MS.center dot Application of nanoplastic labelling in natural waters.center dot Underestimation of nanoplastic due to competing negatively charged NOM.center dot Inefficient digestion to remove NOM.

Automated summary

Nanoplastics in surface water can be accurately quantified using a gold-labelling method, but the presence of natural organic matter (NOM) in high concentration can hinder the quantification process. Further optimization is necessary for effectively applying this method in high NOM water samples.