Plastics, Particles and Additives: An abrasive relationship
The fate of plastic waste in the oceans and surface water has garnered much attention, with images of plastic gyres such as the North Pacific Subtropical Gyre. However, there is increasing appreciation that these floating plastic islands represent a small fraction of the plastic present in the world’s oceans and freshwaters. Of the approximately 4.8 to 12.7 million metric tons3 of plastic annually emitted to the ocean, larger plastic materials are likely to fragment into smaller millimeter-sized particles or even smaller colloidal fractions that are not entirely accounted for based on oceanic circulation models1. The plastic pollution on land and in freshwaters5 can be many times greater than the ocean inputs and little is known regarding the levels of colloidal plastics in these environmental compartments. Nanoplastics are the smaller nano-scale fraction of these colloids and are most likely incidentally produced from the fragmentation of larger plastic debris1. Although complete breakdown of larger plastic debris can take up to hundreds of years, it is likely that mechanical wear, heat, UV degradation and, in some cases, biological factors, lead to relatively rapid fragmentation of plastic debris down to micron- and potentially nano-scales.
Plastics often contain a wide variety of chemical additives as well as non-intentionally added substances such as degradation products, reaction by-products and/or impurities. Since these other chemicals are not generally covalently bound to the polymer matrix, they may leach out of the plastic. These leached chemicals include bisphenol A, phthalates, nonylphenols, brominated flame retardants, to name a few. Also, nanomaterials are sometimes incorporated as nanofillers into polymer formulations to enhance existing properties or to add new properties of interest in the products made from these plastic composites. For example, multiwalled carbon nanotubes (MWCNTs) are known for their unique and diverse properties (mechanical, electrical, thermal, electrochemical, optical and hydrophobic properties) and have many applications in the polymer industry, especially in improving a polymer’s mechanical properties when added to the polymer matrix.2 Even though there are many advantages to using MWCNTs in polymers, the potential release of manufactured nanomaterials (MNMs), such as MWCNTs during the product life cycle and resultant probabilities of exposure for manufacturing workers, product users, and the environment, has raised concerns.3-5
Wiesner reviews some recent work examining the release of nanomaterials from plastic composites, methods for evaluating plastic abrasion, calculations of non-nano additive release and possible consequences of plastic fragmentation for human health and the environment.
Mark R. Wiesner holds the James B. Duke Chair in Civil and Environmental Engineering at Duke University. His work has focused on applications of nanomaterials to membrane science and water treatment and an examination of the fate, transport, and effects of nanomaterials in the environment. Dr. Wiesner holds a B.A. in Mathematics and Biology from Coe College, an M.S. in Civil and Environmental Engineering from the University of Iowa, a Ph.D. in Environmental Engineering from the Johns Hopkins University, and did post-doctoral work in Chemical Engineering at ENSIC, Nancy, France. Professor Wiesner was among the first researchers in the US researching low-pressure membranes for water treatment, serving as the founding chair of the American Water Works Association’s (AWWA) membrane research committee, and co-organizing AWWA’s first Membrane Technology Conference. He was managing editor and co-author of the first membrane processes book for environmental engineers, “Water Treatment Membrane Processes” (McGraw-Hill, 1996; translated to Spanish, 1998). He pioneered the area of environmental nanotechnology, organizing the first-ever public forum in 2001 of international scientists on applications and potential health and environmental impacts of nanomaterials and editing/co-authoring the book Environmental Nanotechnology (McGraw Hill, 2007). Wiesner teamed with the late Nobel Laureate Rick Smalley to create the world’s first government- funded effort evaluating the environmental applications and implications of nanotechnology (CBEN) and led the US National Science Foundation -funded Center for the Environmental Implications of NanoTechnology (CEINT). Author of more than 350 peer-reviewed publications, Professor Wiesner is a Fellow of ASCE, AEESP, AAAS and IWA, received the 2004 de Fermat Laureate (France), the 2011 recipient of the Clarke Water Prize and was elected to the U.S. National Academy of Engineering in 2015.
1. Gigault, J.; El Hadri, H.; Nguyen, B.; Grassl, B.; Rowenczyk, L.; Tufenkji, N.; Feng, S.; Wiesner, M., Nanoplastics are neither microplastics nor engineered nanoparticles. 2021, 16 (5), 507.
2. Ma, P.-C.; Siddiqui, N. A.; Marom, G.; Kim, J.-K., Dispersion and functionalization of carbon nanotubes for polymer-based nanocomposites: A review. Composites Part A: Applied Science and Manufacturing 2010, 41 (10), 1345-1367.
3. Nowack, B.; David, R. M.; Fissan, H.; Morris, H.; Shatkin, J. A.; Stintz, M.; Zepp, R.; Brouwer, D., Potential release scenarios for carbon nanotubes used in composites. Environ Int 2013, 59, 1-11.
4. Petersen, E. J.; Zhang, L.; Mattison, N. T.; O'Carroll, D. M.; Whelton, A. J.; Uddin, N.; Nguyen, T.; Huang, Q.; Henry, T. B.; Holbrook, R. D.; Chen, K. L., Potential release pathways, environmental fate, and ecological risks of carbon nanotubes. Environ Sci Technol 2011, 45 (23), 9837-56.
5. Kingston, C.; Zepp, R.; Andrady, A.; Boverhof, D.; Fehir, R.; Hawkins, D.; Roberts, J.; Sayre, P.; Shelton, B.; Sultan, Y.; Vejins, V.; Wohlleben, W., Release characteristics of selected carbon nanotube polymer composites. Carbon 2014, 68, 33-57.