Source: Yujia Xiang, Li Jiang, Yaoyu Zhou, Zirui Luo, Dan Zhi, Jian Yang, Su Shiung Lam, Microplastics and environmental pollutants: Key interaction and toxicology in aquatic and soil environments, Journal of Hazardous Materials, Volume 422, 2022, 126843, ISSN 0304-3894, https://doi.org/10.1016/j.jhazmat.2021.126843. (https://www.sciencedirect.com/science/article/pii/S0304389421018112)
A Breakdown On Plastics
Plastics are incredibly useful materials. They are flexible, strong, and maintain their durability over long periods of time. Unfortunately, the last quality listed is exactly why plastics have become a massive ecological concern. Whereas other materials like metal or wood can be easily broken down and recycled, recycling of the most commonly used plastics only makes use of roughly 5% of the material being recycled. This translates to lots of plastic waste ending up breaking down slowly in landfills or as litter. Because of the durability of plastics, its breakdown over time simply creates smaller and smaller pieces of plastic, resulting in millions of plastic particles smaller than 5 millimeters in size, which easily disperse through diverse ecosystems. Since the discovery of the spread of these plastic particles, coined ‘microplastics’ in 2009, extensive research has been done to estimate the exact scope of the ecosystems affected by microplastics, and the interactions microplastics have as a pollutant on the environments it reaches. To gauge the progress scientists have made in understanding microplastics, researchers from several Chinese and Malaysian universities and research groups summarized findings from 18 studies on the dispersal of microplastics, interactions of microplastics with other pollutants, and health effects of microplastics and associated pollutants.
Taking the World by Storm
In learning to deal with the environmental threat represented by microplastics, we must first know just how much of the world is affected. Unfortunately, the result of most research on the spread of microplastics has determined that wherever we look for them, we are likely to find them. Microplastics have become so widespread that they’ve even reached the abyssal sections of the ocean, where there is no sunlight. How did such small particles travel so far? While microplastics travel through a variety of means, the most common means found by recent research are through human wastewater, natural runoff, and, most of all, being deposited from the atmosphere. Winds can easily carry small particles thousands of miles, and microplastics can easily become airborne through the incineration of trash, the abrasion of tires and roads, and many other means. Certain types of microplastics are especially predisposed to being carried by winds, such as those used in synthetic fibers for clothing. While other means of dispersal, like agricultural tilling, move microplastics on a more local level, the movement via waterways and airways have allowed microplastics to reach the farthest corners of the globe with incredible speed.
While microplastics on their own are concerning as a pollutant, due to the frequent treatment of plastic with reinforcing chemicals such as flame retardants, UV stabilizers, and antioxidants, the combined effect of microplastics and other pollutants is a large consideration on the environmental impact of microplastics. Additionally, due to the chemical structure of many microplastics, there is a tendency for microplastics to absorb other toxic substances, such as heavy metals and a variety of organic chemicals released into wastewater and soil as part of industrial processes. This tendency to absorb other toxic substances can make microplastics more harmful to those exposed to them than either material individually. This phenomenon is especially concerning when accounting for the effects of a known process called bioaccumulation, in which toxic materials eaten by organisms lower on the food chain accumulate to more dangerous concentrations in those higher on the food chain. With these processes working in tandem, even mildly toxic materials have the potential to accumulate to vastly more harmful concentrations. The absorption of other toxic substances also has unique consequences for ocean-dwelling filter-feeders, such as clams, as the amount of water they process puts them at particular risk to water-bound toxic substances, even without the new concern of accumulation via microplastics. Interestingly, not all the studies reviewed found this accumulation of toxic substances in microplastics to have an immediate negative impact. Depending on the variety of microplastic and the toxic substance being absorbed, environmental conditions improved due to the removal of widespread toxic substances, reducing mortality in fish, phytoplankton, and earthworms, as could be seen in three of the studies they covered. However, it is critical to note that these studies are still recent, and the long-term effects of microplastics on these environments are not yet understood and may be just as detrimental to these ecosystems, if not more so.
Whether it be via dust, drinking water, or food, microplastics make their way into the bodies of living organisms all over the world. Once inside the body of a person, microplastics can gather in different tissues, causing potential damage to the digestive system, the respiratory system, and the cardiovascular system. Additionally, the chemical structure of microplastics put cells under increased oxidative stress, which can damage proteins, DNA, and other necessary cellular structures. These health risks are comparable in many other animals, with one notable difference being that, because of the cold temperature of ocean water, chemicals interact differently and microplastics are much less likely to be absorbed into organic tissues in marine animals. In plants, both terrestrial and aquatic, microplastics can block the flow of water and nutrients, damage tissue, and lead to reproductive issues. Aside from the effect on the environment, these health risks also represent large concerns in the quality of livestock and crops for food production. With the incredibly far reach of microplastics, as well as their impactful chemical properties, it is imperative for ourselves and our world that we are more conscious of the types of plastic we use and how we dispose of them.