Critical evaluation of enzymatic extraction for quantification of europium-doped polystyrene nanoplastics in tomato tissues by single particle ICP-MS

This study critically evaluates an analytical approach combining enzymatic extraction and single particle ICP-MS (spICP-MS) for quantifying europium-doped polystyrene nanoplastics (Eu-PS-NPs) bioaccumulated in tomato tissues. Optimization of extraction parameters identified citrate buffer at pH 6.5 and a digestion temperature of 37 °C as the most effective extraction conditions, while maintaining particle stability. Experiments with spiked tomato tissues demonstrated that extraction efficiency is highly tissue-specific, with optimal digestion of 24 h for stem, leaf, and fruit, and 36 h for root tissues, and enzyme concentrations ranging from 10 to 100 mg per sample. Under optimized conditions, good extraction recoveries (85 - 116 %) were achieved for particle number and mass concentrations, particle size and mass, and total Eu mass, with the majority of extracted Eu associated with NPs and around 10 % as ionic Eu. In contrast, analysis of tomato samples exposed to Eu-PS-NPs during their growth revealed substantially lower and tissue-dependent extraction recoveries. Root and stem tissues yielded only 18 - 32 % of total Eu mass concentration, while leaves showed recoveries ≤ 21 % under most extraction conditions. Fruit samples exhibited higher apparent recoveries (66 - 80 % after 24 h digestion), likely due to the acidic environment promoting Eu leaching from NPs. Across all exposed tissues, ionic Eu fraction dominates (reaching up to 97 % in fruits), indicating extensive leaching from Eu-PS-NPs in the tomato plants. These findings underscore the importance of accounting for matrix effects, metal leaching, and the limitation of extrapolating recoveries from spiked controls to exposed samples when interpreting spICP-MS data from plant exposure studies with metal-doped NPs.