Microplastics

Background

One of the most prevalent environmental issues the East River faces is microplastic pollution. A study on waterways surrounding New York City found that the East River to have a concentration of 556,000 particles per square kilometer, over double to average of 256,000 particles. The high amount of plastic pollution poses various risks to the wide variety of life that lives in the river along with the New Yorkers who use the river as a source of fish. Microplastics accumulate mostly in the gills and digestive tract of fish, through feeding or water passing over the gills during respiration. 

The main function of a fish's gills is to take in dissolved oxygen from the water and release carbon dioxide. A combination of mouth and gill movements pump water through the mouth and over the gills. Gills are made up of comb like filaments called lamellae, which absorb oxygen. Lamellae contain capillaries which transport oxygen and CO2 to and from various parts of the fish. Another important function of the gills is osmoregulation, the process in which salt and water levels are balanced within an organism. Salt water fish want to remain hypotonic, meaning their internal salt levels are lower than the water around them. Chloride cells, located in the gills, allow fish to remain hypotonic by removing excess salts while retaining water. The gills of a fish are very susceptible to being contaminated with microplastics as water is constantly moving over them. When a fish pumps water over its gills, microplastics that are in the water are pumped over the gills as well. This can lead to an accumulation of plastics within the gills over time. 

The gastrointestinal tract or GI tract is the tube or passageway from a fish's mouth to its anus. The function of the GI tract is to break down food and absorb nutrients. The GI tracts of most fish are composed the mouth, esophagus, stomach and intestine. It is essential for survival as it allows fish to break down food, gain energy and nutrients and excrete waste. There are several ways in which microplastics can enter the GI tract of a fish. Microplastics may be mistaken for food or unintentionally ingested while feeding. Another possibility is that plastics are transferred through trophic tranfer. This is the process in which energy, nutrients or even plastics are transferred from from one organism to another as they are consumed across different trophic levels. 

Methodology 

A Cunner (Tautogolabrus adspersus) was collected from Pier 5 to be used as a specimen. It was promptly dispatched and dissected, with both the gills and stomach being collected. The gills and stomach were then soaked in Nile Red1 for several days. After soaking, the samples were rinsed with acetone and dried. Finally, the samples were placed under around 450 nm of blue light, causing any stained plastics to fluoresce yellow or orange. 

1. A type of stain that binds to plastics and lipids, which are then fluorescent under a certain wavelength of blue light.

Photos courtesy of Leo Zell

Results and Discussion

Gills under blue light (small bright yellow or orange particles or flecks are likely plastics):

Stomach contents under blue light (small bright yellow or orange particles or flecks are likely plastics):

Upon observation, some microplastics were found within the gills. The presence of these plastics shows the impact plastic pollution has on fish in the East River. The accumulation of these plastics can damage the filaments that make up a fish's gills, hindering its ability to respirate. While unclear in the data, it is possible that the chloride cells within the gills were also damaged by the plastics. Damage to the chloride cells would reduce a fish's ability to excrete salts and other ions, leading to a buildup of salt within the fish over time. This build up of salt could then cause dehydration, leading to lethargy, loss of appetite and increased respiration rate. In severe cases, dehydration can damage organs or lead to death. Finally, it may be possible that toxins and other chemicals enter the bloodstream of the fish via the gills. Considering the structure of the gill filaments, plastics could bind to said filaments, releasing chemicals through the capillaries within the gills. However, it is important to note that further research is needed to support this hypothesis. 

High levels of microplastics were found within the stomach contents of the fish. Most plastics were too small to identity, however one large fiber was found. These plastics can cause extensive damage to both the GI tract and overall health of the fish. Plastic particles can cause blockages within the GI tract, hindering digestion or stopping it completely. This can lead to reduced nutrient absorption, impaired digestion and death. These microplastics may also damage certain important processes such as growth, reproduction and immune response. This can then lead to health risks such as oxidative stress1, reproductive toxicity2 and inflammatory responses. 

Overall, the presence of microplastics in both the gills and stomach of the specimen reflects the severity and range of consequences plastic pollution has on organisms living in the East River. These plastics can have significant impacts on various processes fish use in order to survive. Further research is needed to understand how the presence of these plastics affect each process individually and how that might affect life in the river.

1. An imbalance of free radicals and anti oxidants in organisms which can lead to cell and tissue damage.

2. The risk from a chemical, physical or biological agent to adversely harm fertility.