Synthetic DNA fragments as ultra-high-resolution multitracers to quantify transport behavior of micro- and nanoplastics in plant systems.

Although plant uptake of micro- and nanoplastics (MNPs) has been well documented, accurately identifying MNP sources and tracking their transport within plants remain major challenges, primarily due to the lack of effective multisource tracing technologies. To fill this gap, we established an ultra-high-resolution multisource tracing approach by encapsulating sequence-specific synthetic DNA fragments into MNPs, followed by quantification of their transport using quantitative real-time PCR (qPCR) in controlled lettuce cultivation experiments. This approach enables the quantification of source-specific MNP contributions in plants, while providing quantitative evidence for size-dependent transport behavior and the involvement of transpiration in MNP uptake. High transpiration (VPD = 2.12 kPa) resulted in 10-fold and 20-fold elevations in the MNP bioconcentration factor (BCF) and translocation factor (TF) of lettuce, respectively, compared with low transpiration (VPD = 0.34 kPa). Size-dependent accumulation of MNPs was observed: 200 nm particles exhibited higher BCF and greater TF than 700 nm particles. Smaller particles were preferentially translocated to shoots, while larger ones were retained in roots. Irrigation represented the predominant pathway of MNP uptake (BCF = 1.5 × 10-2), showing higher accumulation than both the atmosphere (BCF = 2.2 × 10-3) and the substrate (BCF = 4.9 × 10-4). The observed patterns also support that atmospherically deposited MNPs penetrate plant tissues through leaf stomata. The findings validate the effectiveness of the synthetic DNA-based labeling approach, providing critical quantitative data to advance our understanding of interaction mechanisms between MNPs and plants.