Tracking Microplastics and Their Associated Chemical Additives in Plant Tissues: A Pyrolysis GC-MS Approach to Identification, Quantification, and Translocation Mechanism

The accumulation and subsequent uptake of micro/nanoplastics (MP, 100 nm-5 mm), along with their associated chemical additives, within edible plant systems pose significant threats. Precisely quantifying MPs remains a considerable analytical challenge, complicated by their propensity to concentrate contaminants and their capacity to translocate from the root system to aerial tissues via as-yet-uncompletely understood mechanisms. Thus, reliable methods are required to identify MPs and chemical additives in plants. This work reports a sample preparation technique for quantifying polystyrene (PS) and related chemical additives in basil (<i>Ocimum basilicum</i>) plants using pyrolysis gas chromatography-mass spectrometry (Py-GC-MS). Employing an acid digestion method, PS MPs were effectively extracted from basil plant samples and analyzed by a multishot Py GC-MS technique. Scanning electron microscopy (SEM) was utilized to meticulously characterize the size and shape of the recovered MPs. Chemical additive identification was facilitated using an Agilent mass spectral library. Calibration curves for MPs quantification were generated using the standard addition method. Polystyrene was reliably detected and quantified via its characteristic pyrolytic indicator peaks of the styrene trimer (<i>m</i>/<i>z</i> 91-312), which matched the National Institute of Standards and Technology (NIST) library. The limits of detection (LODs) for PS, utilizing the styrene trimer (<i>m</i>/<i>z</i> 91-312) as the quantifier ion, were determined to be 0.9, 0.3, and 0.7 μg/g in roots, shoots, and leaves, respectively. Corresponding limits of quantification (LOQs) were established at 3.0, 1.1, and 2.2 μg/g for roots, shoots, and leaves. The percent recovery of MPs across different plant tissues ranged from 64.8 to 96.0%, with relative standard deviations (RSDs) consistently below 6.9%, indicating good method precision. The observed translocation of MPs from roots to shoots was mechanistically attributed to the establishment of a concentration gradient, facilitating passive transport. This study offers novel insights toward the establishment of a standardized operating protocol for accurately quantifying low concentrations of micro/nanoplastics within complex plant matrices.