Microplastics Fingerprinting: Reflections at the Halfway Point – Part B

The Microplastics Fingerprinting project is currently about halfway through its four-year funding period. At this year’s annual meeting, the team took stock of what it has learned so far. Researchers presented their work to one another and then divided into two groups to synthesize results into two 15-minute presentations. Part A summarizes the first presentation that focused on ​identifying biases in environmental sampling and extraction methods and highlighting advances in detection and identification techniques. Part B highlights advancements in understanding the fate, transport, and sources of environmental microplastics (MPs). 

Part B: Fate, Transport, and Sources of Microplastics in the Grand River Watershed and Beyond 

By Lewis Alcott, Erin Griffiths, Peter Huck, Hang Nguyen, Amir Reshadi, Alexander Waldie, and Meredith Watson 

Microplastics in the Grand River Watershed 

To better understand the sources of microplastic (MP) pollution, it is helpful to compare emissions from rural vs urban land uses. To do this, the Grand River Watershed (GRW) offers us a great opportunity. While about 70 per cent of the land in the GRW is used for agricultural purposes, the watershed also has five major urban areas. Master's student Meredith Watson has been investigating long-term trends in MP loads through dated sediment cores from Belwood Lake (with a predominantly agricultural catchment area) and Conestogo Lake (which is a more urban watershed). So far, results indicate that MPs have been present in the Belwood Lake since 1957. However, there is no evidence of an increasing trend in microplastic abundance. Since Belwood Lake is surrounded mostly by agricultural land, the findings suggest that this type of land use is not exacerbating the microplastics problem in the GRW. Next, Watson will analyze the cores from Conestogo Lake, which should provide further insight into the urban-agricultural comparison.  

Microplastics in urban stormwater ponds 

Master’s student Hang Nguyen and PhD candidate, Amir Reshadi are working to better understand MP emissions across different types of urban land uses. They are assessing the accumulation of MPs in sediment cores taken from five stormwater management ponds (SWMPs) in industrial, residential, and commercial catchment areas. The ponds are within the City of Kitchener boundaries, and each have a different composition of land uses. Early findings suggest that SWMPs in industrial areas have the highest microplastics accumulation rate, followed by SWMPs in residential areas. The commercially dominated SWMP had the lowest microplastic accumulation rates. This work suggests that SWMPs are better at removing sediment than MPs, and that because of the way that they are currently designed, they could be releasing MPs to environment.  

 To quantify microplastic pollution in urban areas, Hang and Amir calculated MP emissions from each urban catchment using aerial imagery analysis. They found that industrial sites contributed the highest number of MPs while residential areas contributed significantly less. Surprisingly, parking lots surpassed roads and highways as major sources of MPs. Overall, they found a meaningful relationship between sediment and microplastic production/retention in SWMPs, suggesting there may be a way to improve the ability of ponds to mitigate MP pollution. 

Microplastics in the Great Lakes watershed 

In work led by postdoctoral fellow Lewis Alcott, the project is also working to understand how MPs are transported through the Great Lakes watershed. Lewis developed a large-scale model of microplastic transportation at the Great Lakes scale. This model allows us to estimate microplastic emissions from each of the Great Lakes watersheds, based on relationships between total mismanaged macroplastic waste and measured influents from wastewater treatment plants. In his model, Lewis estimates that approximately 5.7 billion MP particles are coming from the Canadian side of the border each year, whereas the US generates around 30 billion particles. When he considered the fluxes and the impact of wastewater treatment plants, he determined that Lake Michigan had the highest concentration of MPs, followed by lakes Erie, Ontario, Huron, and Superior respectively. 

Microplastic removal in drinking water 

Master’s student Jaita Saha, who is working with Dr. Peter Huck, reviewed the effectiveness of MP removal by drinking water plants. She found that there is much uncertainty in identifying the best methods for removing MP particles from drinking water. Some studies suggest that larger particles are more efficient to remove, whereas other studies find that smaller particles are easier to remove. Similarly, there is quite a range of removal efficiencies reported for each shape and polymer type.  

Fate and degradation of microplastics 

Another question that the project is tackling relates to the degradation of MPs in the environment, with hopes of eventually identifying methods for speeding up the process. Master’s student Erin Griffiths is studying the degradation rate of PET plastic in stormwater ponds as well as in the lab. She has found that warmer temperatures help polymers degrade faster. In the lab, she used an enzyme and an incubation temperature of 55°C to reduce the mass of PET plastic by 80 per cent in 10 days. Environmental degradation, on the other hand, is much slower. The PET in the stormwater ponds has shown little degradation over the last eight months of observation. Erin’s work continues to better understand the timescale for degradation in stormwater ponds. 

By understanding more about the role of enzymes in the degradation of refractory plastics, we hope to identify strategies for accelerating the degradation of plastic in the environment. This is the primary focus of Master’s student Alexander Waldie’s research, who is working under the supervision of Dr. John Honek. He is studying two types of plastics that are commonly found in the environment: polyethylene (PE) and polystyrene (PS). In the first set of experiments, neither the peroxidase nor laccase enzyme systems helped degrade the plastic. However, Alexander has three more enzyme systems to test.    

Figure 1: The role of enzyme systems in the degradation of PE and PS plastics.

In another of Alexander’s projects, he is using affinity peptides to fluorescently label different types of MPs. The hope is that this could allow him to easily identify the composition of plastic, using fluorescent microscopy. The use of peptides could be promising a tool in the future for identifying specific plastic types in environmental samples.  

Research towards to mitigation strategies 

These days, microplastic particles can be found in almost every corner of the environment – in urban and agricultural landscapes, from stormwater ponds through to lake systems, as well as in water from drinking water plants. Understanding the sources of MPs, how they are transported through a watershed, and their degradation potential may provide valuable insights into how managers may be able to reduce the impact of MP pollution on people and the environment in the future.