Vertex 70 5 spectrometer

MPs were collected and characterized as described previously in Cormier et al. (2021a) . MPs were sampled from the sand surface of two beaches: Capesterre in Marie-Galante Island (MG), and Petit Bourg (PB) in Guadeloupe Basse-Terre Island, in October 2017. MPs were sampled according to the standardized NOAA protocol (Lippiatt et al., 2013) with slight modification for millimetric plastic debris. In brief, polymer composition was determined using FTIR in ATR mode (Vertex 70 V Bruker spectrometer, MA, USA) and data were analyzed using OPUS software. Then, MPs were cryomilled (SPEX, 6770 Freezer-mill) and powder was sieved for 12 h (100 and 53 μm stain sieves). The particle-size distribution was measured using a Malvern laser diffraction particle size analyzer.
Regarding sample preparation prior to chemical analysis, more information can be found in Cormier et al. (2021a) and are summarized in supplementary materials.

The chemical characterization of water was carried out by measuring pH, NO 2 -, NO 3
-and H 2 O 2 . pH was acquired by means of a pHmeter. Nitrite concentration was measured spectrophotometrically (540 nm) following the reaction with Griess reagent. Nitrate concentration was measured using a Merck Nitrate assay kit (Spectroquant nitrate test 1.09713.0001) based on the photometrical determination (340 nm) of 4-nitro-2,6-dimethylphenol formed following the reaction of ions with 2,6-dimethylphenol (DMP). The method used for the detection of H 2 O 2 was based on the oxidation of iodide (I -) in yellow iodine which can be measured spectrophotometrically (390 nm). The quantification of the analytes is achieved through comparison with a calibration curve.
2.4. Chemical and morphological characterization of seeds 2.4.1. ATR-FTIR absorption spectroscopy ATR-FTIR was carried out on NTS and US treated seeds to identify any chemical changes induced on the seed surface after the ultrasound treatment. ATR spectra (32 scans per analysis, 4 cm -1 resolution) were obtained in transmission mode with a Vertex 70 V Bruker spectrometer. The spectrometer was evacuated to less than 150 Pa for 10 min before each acquisition. Spectra were normalized by the maximum intensity of the CH x stretching band at 2935 cm -1 .