How much of the plastic we generate in our cities every day ends up in natural water ecosystems? And what are the paths for pollution to enter these systems?
Using a combination of environmental monitoring, laboratory analysis, and computer modelling, a team led by Dr. Mauricio Arias and his Watershed Sustainability lab at the University of South Florida aim to unravel the complex mechanisms responsible for the transport and degradation of plastic once they enter the aquatic environment.
Read the original research: https://doi.org/10.1016/j.envpol.2023.121052
Read more from the team at watershedsustainability.org
Image Source: Pixabay / Michelle Raponi
Hello and welcome to Research Pod. Thank you for listening and joining us today. In this episode, we’re delving into the groundbreaking research led by Dr. Mauricio Arias and his Watershed Sustainability lab at the University of South Florida in the United States. They’ve been on a mission to dissect the intricate dynamics of plastic pollution in aquatic ecosystems.
Their research looks at how urban development and stormwater management affect how much and when pollutants reach aquatic ecosystems such as rivers and lakes. Using a combination of environmental monitoring, laboratory analysis, and computer modelling, they aim to unravel the complex mechanisms responsible for the transport and degradation of plastic once they enter the aquatic environment. All in all, their research seeks to answer the question of how much of the plastic we generate in our cities every day ends up in natural water ecosystems. This research contributes critical scientific information, which can help guide policies for effective waste management and pollution reduction.
As our cities evolved, so did our reliance on plastics—a lightweight and durable material that infiltrates nearly every aspect of modern life. However, this convenience comes at a cost. Plastic waste, particularly microplastics – which are plastic pieces smaller than 5 mm – has left its mark across the globe, from bustling rivers to remote mountain ranges and the depths of our oceans.
Pioneering studies on plastic pollution predominantly focused on marine environments, where microplastics are an ecological hazard across the entire foodweb, from microscopic organisms to large animals. In recent years, attention has gradually shifted toward freshwater systems, such as rivers, lakes, wetlands, etc. As a matter of fact, most microplastics found in the ocean originate from terrestrial sources, including treated wastewater, urban surfaces, and landfills. Freshwater bodies, situated between these sources and the ocean, play a pivotal role in understanding plastic transport processes. Yet, the exploration of microplastics in these ecosystems remains limited.
The Watershed Sustainability lab recognizes the gaps in our knowledge, particularly in stormwater systems. Stormwater runoff—which refers to the water that washes off impervious surfaces like roads and buildings during rainfall—is believed to be a significant source of microplastics in freshwater bodies. However, studies in this area are sparse, with only a handful evaluating microplastic concentrations in stormwater ponds, which are the prevalent infrastructure for managing stormwater flooding and pollution in the US and beyond.
Supported by the City of Tampa and the US National Academy of Sciences Gulf Research Program, a recent study led by Dr. Arias and former student Jenna Brooks aimed to identify the factors influencing the presence and characteristics of microplastics in stormwater ponds. The study involved collecting sediment and water samples from six stormwater ponds in the City of Tampa, Florida, representing diverse residential and commercial catchments.
Three of the ponds were fenced, locked, and receive runoff from residential areas, while the other three were easily accessible, surrounded by public park spaces, and located in catchments with mixed residential/commercial land use.
In the laboratory, the researchers meticulously separated individual plastic pieces from water and sediment, categorizing them by size and weight. Using a Raman microscope, they identified the specific types of plastics present, information that is crucial for distinguishing plastic particles from other materials commonly mistaken for them.
The results of this study exposed the substantial variability in plastic pollution within the urban environment. The number of individual plastic items ranged widely in both water and sediment samples, with microplastics smaller than 1 mm constituting more than half of the plastics detected. Notably, nearly 60% of the identified plastics were polyethylene, a widely used and inexpensive plastic found in everyday items like grocery bags and food containers.
Furthermore, the study shed light on the influence of pond characteristics on plastic pollution. Fenced ponds in exclusively residential catchments exhibited significantly lower and less variable plastic counts than unfenced ponds in mixed catchment areas. Additionally, the proportion of impervious catchment area to the area of the ponds was positively correlated with plastic concentrations in pond sediments. These relationships were found in sediment samples, but not in water samples – potentially indicating that plastic concentrations in sediments are less prone to frequent and extreme fluctuations and therefore may be useful in advancing our understanding of long-term trends.
The study also found that understanding the shape and size of plastic particles in the environment can provide valuable insights into their origin and movement. Shape metrics including area, roundness, and solidity were calculated, and they found variations in particle geometries between sediment and water samples, suggesting that more regularly shaped plastics tend to settle to the bottom of the pond faster. These shapes resembled those observed in the nearby Hillsborough River, indicating that degradation processes influencing plastic behavior may occur before entering stormwater ponds. However, further research is needed to validate this hypothesis and explore the effects of degradation on microplastic geometry.
“These findings could provide valuable information to urban planners and city managers,” says Professor Arias “helping them address plastic pollution in their localities more effectively. Stormwater ponds like the ones investigated in this study are typically designed, constructed, and maintained for flood control, but water quality benefits have been historically overlooked. As awareness and regulations for stormwater pollution continue to increase globally, so will the role of ponds in improving water quality and meeting other benefits in our cities, such as recreation and wildlife habitat.”
Dr Arias adds “Good science is the basis of effective environmental policy. Regulations regarding plastic pollution are virtually absent at all levels in the US and elsewhere, but hopefully it won’t be long before they start appearing. Having a solid idea about where plastic pollution comes from, in what quantities, and how it moves through water is fundamental knowledge that needs to continue to be generated not just for the sake of science, but to ensure a safe environment for all.”
Looking ahead, future studies on microplastics in stormwater and other polluted waters are crucial for detecting, predicting, and preventing plastic pollution in natural waters. These studies could help unravel the sources of plastics in urban areas and optimize the location and management of stormwater ponds so that they can act as effective traps for plastic pollution. Also important, there is a need to harmonize data collection methods across different types of water bodies, including rivers and marine systems, to be able to better track down microplastics through the environment.
In summary, Dr. Arias and the Watershed Sustainability Lab have made significant strides in unraveling the complexities of plastic pollution in stormwater ponds. Their findings emphasize the significance of sediment sample collection, shape characteristics, and land use in understanding and managing microplastic pollution. For a more in-depth look at their work, you can read their article published in 2023 in the journal Environmental Pollution by Brooks, Arias, and their colleagues. To explore more research by Dr. Arias and his team, visit their website at watershedsustainability.org.
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