Introduction
Since World War II, plastics have been manufactured at an exponential rate and have surpassed most other man-made materials (Geyer 2017). This rate can be attributed to plastic’s ability to be very durable and stable (Rhodes 2018). While this may seem like an advantage in application, it negatively impacts the environment because of its inability to biodegrade (Rhodes 2018). It was estimated that 8300 million metric tons (Mt) of virgin plastics have been produced to 2017 with the largest market in single use plastics. Since most plastics are not biodegradable, they accumulate in landfills or the natural environment (Geyer 2017). Plastic can fragment from sun exposure and weathering creating fragments millimeters small called microplastics (Geyer 2017). Other microplastics such as microbeads and glitter are manufactured for cosmetic products (Fackelmann 2019, Hylton 2017, Wong 2020).
The goal for this project is to gain a better understanding of the impact of microplastics in terrestrial and freshwater environments, the implications it has in Bloomington, IN, and to discuss potential solutions to mitigate the possible risk. In addition to a literature review, Bloomington utilities specialists were interviewed to discuss the relationship between microplastics and city water ways, and ways to prevent future plastic pollution to the environment.
Methods
This project takes a journalistic approach by including an extensive literature review and interviews from City of Bloomington Utilities specialists. This was decided to compromise with the limitations of collecting and analyzing water samples further described in the discussion section. More specifically, interviews were conducted with the MS4 Coordinator, Kelsey Thetonia, and the Utilities Director, Vic Kelson. These interviews were formatted in a conversational manner and aimed to clarify some aspects of the city waterways and draw any conclusions on the presence of microplastics within the community. Notes from each interview were taken during and after the interview. Further clarifications were exchanged over email.
Background and Results
Microplastics are Ubiquitous in the Environment
Plastics that are less than 5 mm in size are called microplastics and can be categorized into primary and secondary microplastics. Primary microplastics are manufactured at microscopic sizes like microfibers and microbeads in textiles and cosmetics products; Secondary microplastics come from the weathering of plastics present in the environment (Wong 2020, Hylton 2017). Additionally, other primary microplastics plastics include those microscopic in size for industrial and agriculture use, like air-blasting to remove rust and paint from machinery and low-grade fertilizers from digested and dewatered sludge (Hylton 2017, Wong 2020). Microplastics can enter the freshwater system from agriculture runoffs or directly from poor waste management (Rhodes 2018, Wong 2020). A significant point source recognized by Wong 2020 for microplastics in water ways are agricultural runoffs or direct disposals, as well as wastewater and sewage treatment plants (Wong 2020). While wastewater treatment plants filter the water, not all the microplastics are filtered out, particularly synthetic fibers from laundering clothes, which end up in the final effluent and sewage sludge (Fackelmann 2019, Hylton 2017). Rivers are the likely to be the source of transportation of microplastics, which end up flowing out into the ocean (Hylton 2017, Wong 2020). A study measuring microplastics in tributaries to the Great Lakes found microplastics in all 107 samples, 98 percent of them being microplastics, most frequently fibers from textiles (Baldwin 2016). Similarly, at Ball State University, a study took samples in three areas (Muncie, Yorktown, and Indianapolis) along the West Fork of the Indiana White River and reported presence of microplastics, fibers being the most prevalent (Hylton 2017). High population densities or proximity to urban centers were places where microplastics were more likely to be found showing the link between the frequency of microplastics and anthropogenic activities (Wong 2020). Additionally, microplastics have been researched in atmospheric fallout, showing significant amounts of synthetic fibers in urban areas that are possibly sourced from synthetic fibers from clothes and houses, poor waste management in plastic waste, incinerators and landfills, and fragmentation of macroplastics (Wong 2020). Airborne microplastics vary in areas with seasonal and climate change (Wong 2020). These fibers can be transported by wind all around the world and into terrestrial systems and enter humans and other species though inhalation (Wong 2020). Plastic pollution has contaminated almost all parts of the world, proposing the 1950s as the start of the Anthropocene era (Fackelmann 2019).
Impact of Microplastics
Microplastics have been found all over the Earth, as well as in different species (Fackelmann 2019, Rhodes 2018, Qiao 2019, Wong 2020). Much of the focus on microplastics has been in marine environments because of the amount of plastic that has ended up in the oceans, but this focus has begun to widen to freshwater and terrestrial species because of environmental health concerns for humans and terrestrial species (Wong 2020). Due to their small size, microplastics end up in the ocean from water flows and have been detected in gastrointestinal tracts of zebrafish and other fishes, lugworms and crustaceans (Jabeen 2017, Qiao 2019, Wong 2020). Ingestion of microplastics by zebrafish can lead to inflammation of their gut and alteration of their gut microbiome (Qiao 2020, Fackelmann 2019). In the study, zebrafish were exposed to microplastics that were 5 micrometers (μm) in diameter for 21 days and then their intestine were dissected and tested using histological, biochemical, metabolomic, microbiome, and statistical analyses. Their results show in comparison to the control group who showed no histological changes, the zebrafish who ingested microplastics showed thinning bowel walls, congestive inflammation, and villi damage with the majority of the group with significant intestinal damage (Qiao 2019). In addition to visible damage, metagenomic analysis suggested that exposure to microplastics decreased the gut microbiome diversity and the increase of an important intracellular antioxidant (glutathione) in fish gut tissues indicated that oxidative stress was caused by microplastic exposure (Qiao 2019). Another study showed that microplastics can cause oxidative stress in mice (Deng 2017).
Additionally, microplastics may have the possibility of being a pathogen vector and endocrine disruptors (Fackelmann 2018, Viršek et al. 2017). Microplastics have the possibility to serve as a vector and reservoir because these synthetic materials are not easily broken down, so microorganisms rapidly colonize them (Kirstein 2016). A study aimed to verify or falsify the presence of a potentially pathogenic bacteria (Vibrio) in microplastics found in coastal waters since some species are known to cause coral bleaching, and human infections from polluted water (Kirstein 2016). After collecting samples from the North and Baltic Sea, they detected different species of Vibrio on microplastics and suggested that the seawater may serve as a source for Vibrio colonization on microplastics. However, although they detected pathogenic species of Vibrio, the study was unable to identify a geographical origin because they were unsuccessful in assigning specific ecotypes. A similar study sequenced the microbial communities formed on microplastics in the North Adriatic Sea, and identified the bacterial fish pathogen species Aeromonas salmonicida (Virsek et al. 2017). In addition, there have been some studies researching the impacts of microplastics absorbing heavy metals like copper and zinc (Brenneck et al, 2016). The potential for microplastics to serve as a reservoir or vector for pathogens and heavy metals raises the importance of further research in freshwater systems to determine risks in humans and animals.
Studies have found that the intake of microplastics by organisms is affected by their feeding behaviors and concentration of microplastics in the surface water and sediments (Wong 2020, Fackelmann 2019). Bottom feeders in aquatic systems are more likely to ingest microplastics since they are typically filter feeders. Microplastics ingested by small species could transfer to the next trophic level, bioaccumulating in large filter feeders like whales (Fackelmann 2019). However, there is limited research of the exo-toxicological impacts of microplastics; It potentially stems from one of three pathways including, ingestion of microplastics, leakages of additives in plastics, and concentration and transfer of organic pollutants (Wong 2020). Humans can be potentially exposed to microplastics or the associated contaminates through consuming freshwater organisms (Wong 2020). Novel results of the exposure from microplastics in marine environments can give insight on potential effects humans and terrestrial species could experience. More research is needed in freshwater environments in order to determine the extent of microplastics in the freshwater system since most of the attention has been on marine environments.
In regard to human health, little research has been done to conclude any major health risks to humans. According to the WHO, microplastics in drinking water does not seem to be a human health risk due to the quality water management systems, however, they urge more research is needed to draw further conclusions (Marsden 2019). Additionally, there have been some studies in which microplastics have been biopsied from human lungs, which suggests that microplastics in the air may have negative health effects for those who are susceptible such as children or immunocompromised individuals (Prata 2018). Lastly, plastic particles are known to contain monomers and chemicals known to be endocrine disrupting (Wong 2020, Prata 2018, Fackelmann 2019, Qiao 2019). These chemicals could leach from the microplastics into tissues; however, more research is needed to understand the toxicological effects on humans (Wong 2020, Geyer 2017, Prata 2018, Fackelmann 2019, Qiao 2019).
City of Bloomington Utilities
The water that people living in Bloomington drink, bathe, and cook with comes from the Monroe Reservoir, or Lake Monroe (Fig 1a), which is the largest manmade lake in Indiana that was built in 1964 (Bloomington Utilities). Before the water is filtered and sent across the city to be used, materials are added to the water from the lake such as aluminum added to cause sediments and particles to cluster and coagulate to the bottom. Then the water is treated and filtered using a conventional rapid sand filtration at the Monroe Treatment facility. From Bloomington homes depending on the North or South side of town, wastewater (influent) is sent to Blucher Poole Wastewater Plant or Dillman Road Wastewater Plant (Fig 1b). Blucher Poole Wastewater Plant was built in 1968, treats the northern part of Bloomington and discharges effluent into Bean Blossom Creek (Bloomington Utilities). Conversely, the Dillman Road Wastewater Plant was built in 1983, treats the southern part of Bloomington, and discharges effluent into Clear Creek (Bloomington Utilities). The wastewater plants operate using different methods since they were built years apart. The new plant, Dillman Road, involves tertiary filtration unlike Blucher Poole which relies on different sludge mitigation methods (Bloomington Utilities). Materials filtered out of the water are dewatered, condensed and sent to Dillman Road Landfill or Terre Haute. On the contrary, stormwater from Bloomington is treated as a point source and several programs are implemented in order to prevent contaminants and pollution from entering the storm drains (Bloomington Utilities). From my interviews, I was told the city of Bloomington keeps within the guidelines set by the EPA and therefore does not regularly test for microplastics and does not filter or treat stormwater. However, in light of the WHO releasing an article about microplastics in drinking water, in October 2019 the City of Bloomington decided to test drinking water and the influent and effluent from both wastewater treatment plants. The data is summarized below in Table 1. The data includes influent and effluent samples taken from the Monroe County Water Treatment Plant, Blucher Poole Wastewater Treatment Plant, and Dillman Road Wastewater Treatment Plant. The lowest amounts of microplastics per liter came from the effluent of the county water treatment plant and the highest amounts came from the effluent of the Blucher Poole Wastewater Treatment Plant.
Discussion and Conclusion
The conversational interviews lasted approximately 20 minutes each and involved asking for some clarifications about the City of Bloomington Utilities and knowledge of microplastics. During my conversation with the Utilities Director, he pointed out some of the differences between the samples taken. The rate of the microplastics obtained from each wastewater plant differs drastically. The highest amounts of microplastics per liter come from the Blucher Poole Wastewater Treatment Plant because unlike the Dillman Road plant, Blucher Poole lacks a tertiary filtration system. The tertiary filtration system seems to be an essential step to filter out most of the plastic fragments and fibers, however, it does not filter all the particles as the effluent from Dillman wastewater facility contained 24 microplastic particles per liter. Additionally, taking a closer look at the samples from the Monroe Water Treatment Plant, less than 1 particle per liter was identified. This evidence shows that microplastics in Bloomington drinking water is not an issue and at this time does not seem to invoke any potential risks to human health. In order to prevent more microplastics from getting into our local environments, more filtration systems could be put into place to better filter microplastics that are still passing through.
With this project came many limitations and future directions for research. Although I was able to have two interviews with Bloomington utilities specialists, I had hoped to talk with a researcher involved with microplastics in freshwater environments, yet, all that I came into contact with were too busy to meet but would answer any specific questions I had in regard to their research. While I was able to answer the ultimate question of are there microplastics in Bloomington, IN from microplastic data from the city, the ideal project would have been taking water samples from Lake Monroe and various rivers and creeks to get an idea of the occurrence of microplastics in the Bloomington area, however, money, time, and methodology of analyzing microplastics prevented me from doing so. Collecting samples to analyze the number of particles involves using a small woven net to capture debris from the water, removing organic matter, then manually confirming particles as a microplastic and counting them. Additionally, in regard to the microplastic data from the City of Bloomington, it was not specified of their methodology or limitations in their data collection. Collecting and analyzing samples from Bloomington and other parts of the world would get a better understanding of occurrence and rate of microplastics in freshwater environments. The WWF outlines a list of calls to action in an article discussing the ingestion of plastics in nature and people and suggests all governments to agree to an international treaty to stop plastic pollution from leaking into the oceans to address plastic pollution on a global level, establish national targets for plastic reduction, recycling, and management, and invest in ecologically-sound waste management systems, to name a few (WWF 2019). With more knowledge of overall presence of microplastics, more research can be done in concern to the toxicological effects and potential uptake in the GI tract in freshwater and terrestrial species to better help understand potential human health risks.
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Shelly Keith
Very well written, interesting and informative!