Nanoplastics Identification in Complex Environmental Matrices: Strategies for Polystyrene and Polypropylene.

Identification of nanoplastics in complex environmental matrices remains a challenge. Despite the increase in nanoplastics studies, there is a lack of studies dedicated to nanoplastics detection, partially explained by their carbon-based structure, their wide variety of composition, and their low environmental concentrations compared to the natural organic matter. Here, pyrolysis coupled to a GCMS instrumental setup provided a relevant analytical response for polypropylene and polystyrene nanoplastic suspensions. Specific pyrolysis markers and their indicative fragment ions were selected and validated. Possible interferences with environmental matrices were explored by spiking nanoplastics in various organic matter suspensions (i.e., algae, soil natural organic matter, and soil humic acid) and analyzing an environmental suspension of nanoplastics. While a rapid polypropylene nanoplastics identification was validated, polystyrene nanoplastics require preliminary treatment. The strategies presented herein open new possibilities for the detection/identification of nanoplastics in environmental matrices such as soil, dust, and biota.

Deposition of environmentally relevant nanoplastic models in sand during transport experiments.

Nanoplastics (NPTs) are defined as colloids that originated from the unintentional degradation of plastic debris. To understand the possible risks caused by NPTs, it is crucial to determine how they are transported and where they may finally accumulate. Unfortunately, although most sources of plastic are land-based, risk assessments concerning NPTs in the terrestrial environmental system (soils, aquifers, freshwater sediments, etc.) have been largely lacking compared to studies concerning NPTs in the marine system. Furthermore, an important limitation of environmental fate studies is that the NPT models used are questionable in terms of their environmental representativeness. This study describes the fate of different NPT models in a porous media under unfavorable (repulsive) conditions, according to their physical and chemical properties: average hydrodynamic diameters (200-460 nm), composition (polystyrene with additives or primary polystyrene) and shape (spherical or polymorphic). NPTs that more closely mimic environmental NPTs present an inhomogeneous shape (i.e., deviating from a sphere) and are more deposited in a sand column by an order of magnitude. This deposition was attributed in part to physical retention, as confirmed by the straining that occurred for the larger size fractions. Additionally, different Derjaguin-Landau-Verwey-Overbeek (DLVO) models -the extended DLVO (XDLVO) and a DLVO modified by surface element integration (SEI) method-suggest that the environmentally relevant NPT models may alter its orientation to diminish repulsion from the sand surface and may find enough kinetic energy to deposit in the primary energetic minimum. These results point to the importance of choosing environmentally relevant NPT models.

Assessing the interactions of metal nanoparticles in soil and sediment matrices - A quantitative analytical multi-technique approach.

The impact and behavior of engineered nanomaterials (ENMs) entering the environment is an important issue due to their growing use in consumer and agricultural products. Their mobility and fate in the environment are heavily impacted by their interactions with natural particle components of saturated sediments and soils. In this study, functionalized gold nanoparticles (AuNPs - used as model ENMs) were spiked into complex solid-containing media (standard soils and estuarine sediment in moderately hard water). AuNPs were characterized in the colloidal extract (< 1 µm) following centrifugal separation of the non-colloidal phase, using different analytical techniques including asymmetric-flow field-flow fractionation and single particle inductively coupled plasma mass spectrometry. Attachment of functionalized AuNPs to the soil particles did not significantly depend on their concentration or surface coating (citrate, bPEI, PVP, PEG). Similarly, UV degradation of coatings did not substantially alter their recovery. Conversely, the presence of natural organic matter (NOM) is a key factor in their adhesion to matrix particles, by decreasing the predicted influence of native surface chemistry and functional coatings. A kinetic experiment performed over 48 h showed that attachment to soil colloids is rapid and that hetero-aggregation is dominant. These results suggest that transport of ENMs away from the point of discharge (or entry) could be limited in soils and sediments, but additional experiments under more realistic and dynamic field conditions would be necessary to confirm this more generally. Transport properties may also differ substantially in matrices where NOM is largely absent or otherwise sequestered or when dissolution of ENMs is an important factor.

Investigation of cloud point extraction for the analysis of metallic nanoparticles in a soil matrix.

The characterization of manufactured nanoparticles (MNPs) in environmental samples is necessary to assess their behavior, fate and potential toxicity. Several techniques are available, but the limit of detection (LOD) is often too high for environmentally relevant concentrations. Therefore, pre-concentration of MNPs is an important component in the sample preparation step, in order to apply analytical tools with a LOD higher than the ng kg-1 level. The objective of this study was to explore cloud point extraction (CPE) as a viable method to pre-concentrate gold nanoparticles (AuNPs), as a model MNP, spiked into a soil extract matrix. To that end, different extraction conditions and surface coatings were evaluated in a simple matrix. The CPE method was then applied to soil extract samples spiked with AuNPs. Total gold, determined by inductively coupled plasma mass spectrometry (ICP-MS) following acid digestion, yielded a recovery greater than 90 %. The first known application of single particle ICP-MS and asymmetric flow field-flow fractionation to evaluate the preservation of the AuNP physical state following CPE extraction is demonstrated.