The annual production of plastic worldwide has increased exponentially from about 2 million tons in 1950 to 460 million tons in 2019, and current levels are expected to triple by 2060.
Plastic contains more than 10,000 chemicals, including carcinogenic substances and endocrine disruptors. Plastic and associated chemicals are responsible for widespread pollution, contaminating aquatic (marine and freshwater), terrestrial, and atmospheric environments globally.
Atmospheric concentrations of plastic particles are on the rise, to the extent that in a remote station in the Eastern Alps in Austria, the contribution of micro- and nanoplastics (MNPs) to organic matter was comparable to data collected at an urban site.
The ocean is the ultimate destination for much of the plastic. All oceans, on the surface and in the depths, contain plastic, which is even found in polar sea ice. Many plastics seem to resist decomposition in the ocean and could persist in the environment for decades. Macro- and microplastic (MP) particles have been identified in hundreds of marine species, including species consumed by humans.
The quantity and fate of MP particles (> 10 µm) and smaller nanoplastics (< 10 µm) in aquatic environments are poorly understood, but what is most concerning is their ability to cross biologic barriers and the potential harm associated with their mobility in biologic systems.
MNP Exposure
MNPs can originate from a wide variety of sources, including food, beverages, and food product packaging. Water bottles represent a significant source of ingestible MNPs for people in their daily lives. Recent estimates, using stimulated Raman scattering imaging, documented a concentration of MNP of approximately 2.4 ± 1.3 × 105 particles per liter of bottled water. Around 90% are nanoplastics, which is two to three orders of magnitude higher than previously reported results for larger MPs.
MNPs enter the body primarily through ingestion or inhalation. For example, MNPs can be ingested by drinking liquids or eating food that has been stored or heated in plastic containers from which they have leaked or by using toothpaste that contains them. Infants are exposed to MPs from artificial milk preparation in polypropylene baby bottles, with higher levels than previously detected and ranging from 14,600 to 4,550,000 particles per capita per day.
MNP and Biologic Systems
The possible formation of hetero-aggregates between nanoplastics and natural organic matter has long been recognized as a potential challenge in the analysis of nanoplastics and can influence toxicologic results in biologic exposure. The direct visualization of such hetero-aggregates in real-world samples supports these concerns, but the analysis of MNPs with traditional techniques remains challenging. Unlike engineered nanoparticles (prepared in the laboratory as model systems), the nanoplastics in the environment are label-free and exhibit significant heterogeneity in chemical composition and morphology.
A systematic analysis of evidence on the toxic effects of MNPs on murine models, however, showed that 52.78% of biologic endpoints (related to glucose metabolism, reproduction, oxidative stress, and lipid metabolism) were significantly affected by MNP exposure.
Between Risk and Toxicity
MNP can enter the body in vivo through the digestive tract, respiratory tract, and skin contact. On average, humans could ingest from 0.1 to 5 g of MNP per week through various exposure routes.