The Mobility of Plastic Nanoparticles in Aqueous and Soil Environments: A Critical Review

Abstract

Plastic nanoparticles (PNPs) are now widely recognized as a significant, and ever increasing, hazard in aquatic and soil environments. These particles, defined here as plastics <1000 nm across their largest dimension, are released into the environment both as primary products and through the degradation of larger plastic waste. They have the potential to be highly mobile, given their small size, which raises concerns about their global spread. Furthermore, PNPs are capable of adsorbing a variety of other pollutants, including heavy metals, pharmaceuticals, and pesticides, and in doing so may increase the mobility of these harmful materials. Dozens of studies focused on the toxicity of PNPs with and without other adsorbed contaminants for organisms from algae to humans have been published in the past few years. It is also critical to understand the transport of these particles in different environments to fully assess the threat that they pose. In this critical review, we discuss the behavior of suspended PNPs in aqueous systems and water-saturated soil/sediment with a particular emphasis on the processes that may alter their mobility. We describe how PNPs of different sizes and surface functionalities interact with the typical constituents of natural solutions, including metal cations, dissolved and particulate organic matter, and inorganic colloids. These variables all affect PNP aggregation in a range of complex, interrelated ways and can ultimately lead to particle sedimentation and removal from the mobile fluid phase. We also discuss the reactive transport of these PNPs, and PNP aggregates, through soils and sediments, during which PNP mobility can be limited by physical straining and/or attachment to the substrate. Finally, we conclude with some suggested future directions for research within this field, particularly the need for direct measurement of PNP abundances and characteristics in real environmental samples, which to date has been severely limited due to analytical challenges. Plastic nanoparticles do present a serious potential threat to the environment and even to human health, and a thorough understanding of the transport and mobility of these pollutants is critical in assessing these risks.

Toxicity of Tire Rubber Microplastics to Freshwater Sediment Organisms

“…As sediment is the main sink for most types of microplastics (Scherer et al 2020), including tire rubber (Marwood et al 2011), studies that explore their behaviour and toxicity in this environmental matrix are a priority. Similar to what has been observed with other microplastic particles, it is likely that the microrubber particles form homo-and heteroaggregates with other biogenic and inorganic particles and, depending on the density of the particles and of the final aggregate, increase their sinking rates (Brewer et al 2021;Michels et al 2018). These processes are enhanced if the microplastics have been previously covered by biofilm.…”

Effects of Hydrogen Peroxide on Cyanobacterium Microcystis aeruginosa in the Presence of Nanoplastics

“…This discrepancy could be explained by the different strains of M. aeruginosa and/or the different sizes of PS-NH 2 beads used, which may change its toxicity, uptake threshold, and retention time. ,− Indeed, other properties that vary across nanoplastics, including shape, parent material, or surface charge, could alter biological effects, and we recommend these sources of variation be given greater consideration in future research. For example, our particles are likely to have been positively charged, ,, but particles vary in charge in the environment, − with negatively charged particles often having weakened biological effects. ,, Therefore, our results may represent stronger than average effects of nanoplastics on cyanoHAB control.…”

Effects and Impacts of Different Oxidative Digestion Treatments on Virgin and Aged Microplastic Particles

“…Previous studies have already reported a relationship between size and recovery rate highlighting that separation of particles with diameters lower than one mm is more difficult than large MPs [ 27 , 46 , 47 ]. Electrostatic interactions between MPs and other particles depend on the morphology, composition, size, and surface charge of MPs [ 48 ]. Therefore, the presence of the matrix can interfere with the MPs extraction phase from the soil and our study suggests this with the recovery of 100% of PET, in the absence of soil.…”