State of the Planet

News from the Columbia Climate School

Sustainability Science Capstone Workshop Investigates Microplastics in the Hudson River

Imagine this: you are sitting on the beach and 65 garbage trucks begin to line up, side-by-side, and simultaneously dump their respective loads into the ocean. Now picture it happening every day of the year. The result is 88 to 242 million pounds of garbage, which is equivalent to the actual amount of plastic waste that enters the oceans every year. It may not surprise some readers given that plastic products have crept into every aspect of our daily lives, but it did surprise one team of students as they began the Integrative Capstone Workshop of the MS in Sustainability Science Program this past spring.

students with jars of water
Students collecting water samples from the Hudson River. Photo: Benjamin Bostick

The aim of the integrative capstone is to gain practical training on a project that addresses a significant, real-world environmental problem with an organization in the public or nonprofit sector. The students work together to study the science behind a particular sustainability problem, collect and analyze data using scientific tools, and make policy or management recommendations for solving the problem. This year, the team studied microplastics in the Hudson River.

Plastics are mass produced and used around the world in part because they are cheap and can be shaped and molded into a plethora of different products—i.e., grocery bags, take-out containers, water bottles, and single-use utensils. In collaboration with Riverkeeper, the capstone team sought to better understand consumption patterns, how plastic waste impacts our waters, and the ecological and health effects.

While plastic pollution in any form threatens the vitality of terrestrial and marine ecosystems alike, microscopic plastic particles (smaller than the width of a pencil tip), known as microplastics, present a real threat. Apart from their size, microplastics are complex to categorize because they come in different sizes, shapes, and chemical makeups, and can have different levels of additives like BPA or colorants. They typically enter systems either as primary or secondary microplastics. Primary microplastics are pieces of plastic that are designed to be small, like those you might find in cosmetic products, while secondary microplastics are formed when larger plastics chemically and physically break down due to UV light exposure or mechanical action, like waves.

photos of different kinds of microplastics
Examples of microplastics and non-plastic organic material identified in samples from the Hudson River, shown at 200x resolution. Microfibers and microbeads are examples of primary microplastics, while fragments and films are secondary microplastic particles. Algal material (organic) also is abundant in samples that have not been completely processed.

After an initial round of literature reviews, the team discovered that it is often difficult to categorize microplastics and identify the associated dangers. Despite this challenge, it is critical to do so because microplastics have been found in nearly every aquatic environment (including Antarctica) and, more alarmingly, in the tissues of nearly every marine animal species studied. Numerous studies have demonstrated that ingested microplastics can make it difficult for organisms to reproduce and consume food, and they may attract and transport dangerous chemicals like polychlorinated biphenyls (PCBs) and heavy metals. A critical first step in assessing their potential for harm is to quantify and categorize levels of microplastic present. Such studies have been performed regularly in oceanic environments, but in freshwater and estuarine ecosystems, including the Hudson River, much more information is needed.

Throughout the term, the capstone team sought to address these critical data gaps of understanding microplastic prevalence specifically for the Hudson River. They worked with the client to identify potential sources of microplastics and quantify their concentrations in the Hudson. Given how much time analyses can take, this work is just the start of a larger effort that is needed to characterize microplastics throughout the Hudson and New York City. To assist in those future efforts, the team further developed simple and inexpensive methodologies for collecting and analyzing microplastic samples that could be utilized by citizen scientists everywhere.

Students examining water samples under a microscope
A student examines a water sample under a microscope. Photo: Kevin Webb

The team identified New York City’s vast network of combined sewage overflows, or CSOs, as a huge potential source of microplastics in the Hudson River. The city has a combined sewer system, where industrial and domestic wastewater and stormwater are directed through the same pipes to wastewater treatment plants. During heavy precipitation, wastewater treatment capacity becomes overwhelmed and CSOs discharge untreated sewage and stormwater directly into the Hudson River through outfalls. Wastewater can be laden with microplastics introduced from waste, personal care products (i.e., microbeads) or laundered clothing (i.e., microfibers). Meanwhile, stormwater or wind can transport larger plastic products, like plastic bags or city debris, directly into the river, where they can break down to form microplastics.

Though untreated water from storms is a likely vector for microplastics, wastewater that is appropriately diverted to treatment plants can also contain microplastics, and many of these facilities are not designed to filter out microplastics. As such, wastewater treatment plants, which discharge far more water directly into the river than CSOs, are also a likely source of microplastics in the Hudson. Indeed, many studies have confirmed this to be true, finding microplastics in water treatment plants’ discharge at numerous locations. Due to microplastics’ variability in size and density, there is no one-size-fits-all solution to removing them from wastewater treatment plants and CSOs today. Decision makers and municipalities can prioritize technologies and regulations to target the most common or hazardous microplastics with further research on the pathways and dangers of microplastics.

Testing for microplastics demands a method that is both robust and accurate, and cheap and portable enough for the subway without worrying about breakage. Three Manhattan CSOs were sampled during slack tide and one upstream wastewater treatment plant along the Hudson during their study. The team modified several different methods to collect and analyze samples for microplastics from the Hudson River. To make the sampling method approachable for citizen-scientists, a simple collection rig was created using a Ball-Mason jar, a cotton t-shirt, a cotton rope, glue, tape, and a grommet kit (video here). After collection, water was poured through a set of sieves to determine the relative concentrations at three mesh sizes that contain microplastics: 500, 150, and 63 micrometers. Even with limited sample analysis, microplastics were found at each location, with fragments representing the greatest class of microplastic present, with smaller quantities of microfibers and microbeads.

chart showing types of microplastics at two sampling sites
Analysis of microplastic abundance as a function of size on February 24 and 25 in the Hudson River near CSO discharge points in Battery Park and W. 115th Street.

Though COVID-19 closed Columbia’s labs and hindered the team’s ability to complete all of the sample analyses, it made the team rethink the role of science in a world without access to traditional scientific methods. This indeed is the world of many New York City residents, who walk by the river, fish from its docks, and ferry across its shores. For a city so defined by, and dependent on, its water bodies, who better to study and understand this emerging pollutant threat than New Yorkers themselves?

In order to empower citizen scientists and to engage new audiences in continuing this work, the team created a website with more information and instructions on how you can collect data for their microplastic investigations. While the semester may be over, the team is hopeful that additional involvement from citizen scientists can lead to a much richer and detailed record of microplastics in what Riverkeeper lovingly calls “America’s First River.” Your participation is encouraged, so please visit the site to learn more about the project and see how you can get involved.

Happy sampling!

Students sampling the Hudson River at 96th Street.
Students sampling the Hudson River at 96th Street. Photo: Jeffrey Fralick

The Spring 2020 Capstone Team included: Ashley Ziegler, Chandler Precht, Isabela Brown, Kevin Webb, Jeffrey Fralick, and Madeleine Tervet. The team was advised by Benjamin Bostick, Cassie Xu, and Riverkeeper’s staff scientist Bill Wegner. If you would like to contact the team, please email 

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