Studies on the environmental impact of nanoplastics face challenges in plastic analysis and a scarcity of nanoplastic materials necessary for the development of analytical techniques and experiments on biota impact. Here we provide detailed procedures for obtaining nanoparticles suspended in water for the most commonly used polymers: Polypropylene (PP), Polyvinylchloride (PVC), Low- and High-Density Polyethylene (PE-LD, PE-HD), and Polystyrene (PS). We dissolved larger size material to reprecipitate nanoparticles. For all plastic types, we obtained nanoparticles with a size between 50 and 300 nm, and a mainly spherical morphology. We verified that no irreversible agglomeration or coalescence of the particles occurred after 5 days of storage. The concentrations obtained in the final carrier solution were of the order of 10⁹ particles mL⁻¹. To prevent the persistence of reagents in the final carrier solution, a filtration step was implemented at the end of the process. The method proved unsuitable for Polyethylene Terephthalate (PET).

Amazonian podzols store huge amounts of carbon and play a key role in transferring organic matter to the Amazon River. In order to better understand their C dynamics, we modelled the formation of representative Amazonian podzol profiles by constraining both total carbon and radiocarbon. We determined the relationships between total carbon and radiocarbon in organic C pools numerically by setting constant C and ¹⁴C inputs over time. The model was an effective tool for determining the order of magnitude of the carbon fluxes and the time of genesis of the main carbon-containing horizons, i.e. the topsoil and deep Bh. We performed retrocalculations to take into account the bomb carbon in the young topsoil horizons (calculated apparent ¹⁴C age from 62 to 109 years). We modelled four profiles representative of Amazonian podzols, two profiles with an old Bh (calculated apparent ¹⁴C age 6.8 × 10³ and 8.4 × 10³ years) and two profiles with a very old Bh (calculated apparent ¹⁴C age 23.2 × 10³ and 25.1 × 10³ years). The calculated fluxes from the topsoil to the perched water table indicate that the most waterlogged zones of the podzolized areas are the main source of dissolved organic matter found in the river network. It was necessary to consider two Bh carbon pools to accurately represent the carbon fluxes leaving the Bh as observed in previous studies. We found that the genesis time of the studied soils was necessarily longer than 15 × 10³ and 130 × 10³ years for the two younger and two older Bhs, respectively, and that the genesis time calculated considering the more likely settings runs to around 15 × 10³–25 × 10³ and 150 × 10³–250 × 10³ years, respectively.

Advancements in microplastic research are progressing rapidly, yet detecting and identifying nanoplastics remain challenging, especially in natural samples. In this study, we addressed these challenges by employing fluorescent labeling on nanoparticles of six prevalent plastic types (PP, LDPE, HDPE, PS, PET, and PVC) to enable their specific detection via the analysis of 3D fluorescence spectra post-staining. Four fluorescent molecules were tested: cyanine-3 phosphoramidite, rhodamine-6G, fluorescein sodium salt, and Vat Red 15. Our observations indicated that adsorption onto nanoplastic particles resulted in peak shifts in the fluorescence signal, providing sufficient specificity for nanoplastic identification. Among the tested fluorophores, fluorescein was the most effective, successfully discriminating PP, PVC, HDPE, LDPE, and PS. Rhodamine-6G produced shifted signals for HDPE, LDPE, and PS but grouped them together. Cyanine-3 effectively distinguished PVC, PS, and PET, while Vat Red was only able to discriminate PVC.

Transfer of organic carbon from topsoil horizons to deeper horizons and to the water table is still little documented, in particular in equatorial environments, despite the high primary productivity of the evergreen forest. Due to its complexing capacity, organic carbon also plays a key role in the transfer of metals in the soil profile and, therefore, in pedogenesis and for metal mobility. Here we focus on equatorial podzols, which are known to play an important role in carbon cycling. We carried out soil column experiments using soil material and percolating solution sampled in an Amazonian podzol area in order to better constrain the conditions of the transfer of organic carbon at depth. The dissolved organic matter (DOM) produced in the topsoil was not able to percolate through the clayey, kaolinitic material from the deep horizons and was retained in it. When it previously percolated through the Bh material, there was production of fulvic-like, protein-like compounds and small carboxylic acids able to percolate through the clayey material and increase the mobility of Al, Fe and Si. Podzolic processes in the Bh can, therefore, produce a DOM likely to be transferred to the deep water table, playing a role in the carbon balances at the profile scale and, owing to its complexing capacity, playing a role in deep horizon pedogenesis and weathering. The order of magnitude of carbon concentration in the solution percolating at depth was around 1.5–2.5 mg L⁻¹. Our findings reveal a fundamental mechanism that favors the formation of very thick kaolinitic saprolites.