Original Research
Effects of Polypropylene on Tetrahymena Cell Counts, Swim Speed, and Vacuole Formation Noah Mendoza, Madison Ambrose, Abel Thomas, Rithvik Bartham, Samantha Hodges, Tamarah Adair, Ph.D.
Abstract Nanoplastics, plastic fragments smaller than 1 μm, are prevalent throughout the environment. The effect of nanoplastics on terrestrial ecosystems is largely unknown. Tetrahymena pyriformis is a single-cell model organism frequently used for analyzing toxicity which also represents a major group of predators (ciliates) in the soil ecosystem. The goal of this study is to shed light on the impact of polypropylene (PP) nanoplastics on eukaryotic cells by examining the effects of polypropylene treatments on Tetrahymena pyriformis. To generate potential breakdown products from the polypropylene, treatment solutions were made by shredding and adding heat to polypropylene baling twine in proteose-peptone-tryptone (PPT) media. To test the null hypotheses that polypropylene nanoplastics do not impact reproduction, swim speed, and vacuole formation of Tetrahymena pyriformis, assays were conducted in both the control and the polypropylene treatment cultures after 48 hours. The results disprove the null hypotheses and indicated that polypropylene had a significant impact indicated by an increase in all three variables. These results indicate that nanoplastics do have an effect on single-cell organisms in culture. Further studies will focus on the effect of nanoplastics on terrestrial ecosystems. The soil ecosystem is the foundation for a healthy biotic environment and investing in research within this scope will help determine the system effects of plastics on the overall ecosystem.
Introduction Plastics have found their way into many aspects of our lives, and with an ever-growing population, the presence of plastics and more specifically, nanoplastics, in our lives will continue to grow. The increasing presence of nanoplastics has gained attention over recent decades and is currently gaining the attention of many media outlets, such as the National Geographic article We Depend On Plastic. Now, We’re Drowning in It (Parker, 2018). The term “nanoplastics” refers to particles of plastic that are smaller than 1 μm in diameter. Currently, humans are producing 245 million tons of plastics annually to keep up with the growing population, and this number will only continue to rise (Andrady, 2011). The increase in plastic usage requires an increase in the disposal and recycling of plastics currently consumed. This is problematic because, when not recycled, plastics may take decades or even centuries to fully decompose, leaving an abundance of nanoplastics in the environment. Without an effective way to decompose nanoplastics, this could eventually bring forth negative health effects on humans and organisms in the environment. Nanoplastics are often ingested by organisms in the environment and become embedded in their intestines, leading to digestive blockages and appetite suppression (Galloway & Thompson, 2013). Unfortunately, not all plastics are disposed of properly, resulting in plastics being incorporated into agriculture through mulch and fertilizers. Many fields, however, are being impacted
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by a type of baling twine that is often left behind to be decomposed, resulting in the introduction of nanoplastics directly into the soil and indirectly into agricultural goods. This polypropylene (PP)-based twine is often treated with various chemicals that enhance its ability to withstand weather and UV light. With this being said, limited research has been done regarding the impact of plastics on terrestrial ecosystems and organisms (Rillig, 2012). In order to understand the impact of nanoplastics within ecosystems, Tetrahymena pyriformis was exposed to polypropylene (PP) that was derived from baling twine. In order to study its effects on terrestrial organisms, PP was administered to Tetrahymena pyriformis that was cultured within the lab. Tetrahymena pyriformis was specifically chosen due to its credibility as a model organism in laboratory studies and its presence within various terrestrial ecosystems. The effects of PP on the Tetrahymena pyriformis were examined through asexual reproduction rate (cell counts), swim speed, and food vacuole formation. Tetrahymena pyriformis has been used in countless research studies due to its consistency and easily identifiable developmental traits (Cole et al., 2012; Sauvant et al., 1999). Tetrahymena pyriformis uses phagocytosis to engulf food, in a non-discriminatory manner. This characteristic is observed when feeding on laboratory substances, such as India ink,
