Background

Photodegradation of manufactured plastics can contribute to the release of artificial toxins; in in terrestrial ecosystems, these compounds can inhibit the efficient metabolic activity of localized microbes, including photosynthetic protists. Microorganisms at the primary trophic level are vital to natural carbon sequestration, but their metabolic activity is impaired by chemical toxins released from degrading microplastics. Thus, the impaired metabolic function of soil-based microbes can act as a bioindicator for the adverse effect of plastic pollution.

The accumulation of plastics in natural environments is posing a serious risk to marine species. According to a study done by the American Society of Microbiology, “Plastics are widely used in the global economy... due to poor recycling and low circular use, millions of tons accumulate annually in terrestrial or marine environments” (“Plastics: Environmental and Biotechnological...”). Because plastics have little response to natural breakdown processes, the most prevalent biogeochemical process able to effect these polymers- at least to some degree- is photodegradation. This demonstrates that the UV-related breakdown of plastics is the most prevalent cause of microplastic fragmentation rather than other processes. While oceanic photodegradation does involve a certain degree of mechanical breakdown via the impact of tidal activity, the primary agent in the breakdown of plastics continues to be sunlight.

As plastics photodegrade, the implicit implications of these tiny particles entering the food supply are evident. However, more evidence is needed to determine the implications of toxins released from plastic breakdown since additives are rampant in plastic production. In the research conducted thus far, Dr. Shiye Zhao notes that, “[there is a] potential that plastics are releasing bio-inhibitory compounds during photodegradation in the ocean [that] could impact microbial community productivity and structure...” (“Simulated Sunlight...”). This is further elucidated in a study published by Communications Biology in which the scientists state that, “plastics may provide some dissolved organic carbon sources for some bacteria to metabolize, but they can also leach organic compounds and metals that negatively impact growth of a variety of microorganisms...” (“How will Marine...”). This evidence suggests that additives in plastic manufacturing could exacerbate the negative effects of microplastic breakdown.

While limited evidence suggests that plastic-based additives could leach toxins that have adverse effects on marine organisms, more concrete research needs to be done on this distinct issue. Multiple scientific publications have declared this need for requisite experimentation, particularly scientists in the American Society of Microbiology, who asserted that, “While many reports describing microbial communities degrading chemical additives have been published, no enzymes acting on the high-molecular-weight polymers are known” (“Plastics: Environmental and Biotechnological...”). It is clear there may be implications beyond the metabolic activity of individual microorganisms. In Figure 1 of an article published on nature.com, an illustration denotes the potential impact of a release of organic/inorganic compounds on bacterial populations in an ecosystem. A proposed impact of this process is that the inhibition of ecological productivity in one microorganism may cause an opposing bacterial species to accelerate its growth; the ecological implications of this disproportionate population bloom have the potential to be detrimental (“How will marine plastic...”). Overall, considering the implications of this phenomenon, research into this subject will be pivotal in elucidating the nuanced effects of plastic breakdown in the ocean.