Willistown Conservation Trust Pilot Report
PolyGone has announced a new collaboration with the Willistown Conservation Trust under the support of the prime award granted by the National Oceanic and Atmospheric Administration (NOAA) Sea Grant, under the PI New York Sea Grant for the purpose of Aquatic Microplastic Filtration Device Research and Pilot Deployment. The Pilot aims to provide educational opportunities to students through a Co-op collaboration as well as promote water monitoring and filtration. The management of the Pilot this year was done by Co-op Daniel Price.
Pilot Site:
Ashbridge Preserve, located in West Chester, Pennsylvania, is a nature reserve managed by the Willistown Conservation Trust, which serves as the partner organization for this study. The preserve encompasses a section of Ridley Creek, a tributary of the Delaware River. A previous deployment of the Plastic Hunter device was conducted in a smaller tributary within the preserve, near the outflow of a local wastewater treatment plant. For this study, the Plastic Hunter was deployed in the main channel of Ridley Creek, into which the previous tributary discharges. Microplastics pose a significant environmental threat in ecosystems such as Ridley Creek, which supports a diverse food web, making it vulnerable to the rapid biomagnification and bioaccumulation of these contaminants.
Plastic Hunter Design with circles denoting the positions of the collected filters.
Project Design:
This iteration of the Plastic Hunter deployed silicone filters arranged in five distinct rows. The silicone material is highly hydrophobic, a property shared with microplastics, facilitating their natural adherence in aquatic environments. Over the course of nine weeks, the filters were periodically retrieved to evaluate the effects of time and environmental conditions on microplastic accumulation. Filters were also collected from various positions on the device to investigate potential correlations between microplastic counts and location. Filter C4, positioned in the center of the device, was collected weekly, while filters from the first, third, and fifth rows (from upstream to downstream) were retrieved every two weeks. In addition to filter collection, grab samples of stream water were taken during each collection event to measure the microplastic concentration in the stream itself, independent of the material gathered on the filters.
Goals:
Collecting the same filter each week to compare microplastic counts to weather patterns.
Sampling from the middle, front, and last columns to compare saturation differences at different time intervals. This will allow us to see how much is collected at the outside columns before and after reaching the middle column.
Collecting grab samples of the stream water to investigate any factors that change microplastic concentration.
Project Deployment:
With the assistance of Willistown Conservation Trust (WCT) staff, the Plastic Hunter was secured to the stream bank and anchored to cinder blocks on the streambed using stainless steel cables. Some slack was left in the tethers to allow the device to rise during rain events, as the water level in this section of Ridley Creek can fluctuate significantly. Although the area is relatively secluded, a notice was posted near the Plastic Hunter to inform the public, as Ashbridge Preserve is accessible to visitors. A game camera was mounted on a nearby tree enclosure to monitor potential vandalism or wildlife interaction with the device. Sample collection took place every Tuesday morning throughout the deployment period. WCT staff provided clean glass jars for sample collection and used dish soap to remove microplastics from the silicone filters. To prevent any soap from contaminating the stream and harming wildlife, filter cleaning was performed over a container, which was then properly disposed of at the WCT laboratory.
Results:
Goal #1 : The results from the weekly collection of Filter C4 indicated that during periods of heavy rainfall and the subsequent increased discharge, the filters captured fewer microplastics compared to periods of low or normal flow during dry conditions.
Goal #2: The biweekly collection of filters demonstrated a steady increase in microplastic accumulation up to six weeks, followed by a significant decline in microplastic counts between weeks six and eight for both Rows A and C. This decrease may not reflect the saturation capacity of the filters, as most rainfall, including a flood event, occurred during this period. Row A collected the highest quantity of microplastics, followed by Rows E and C. This outcome was unexpected, as the initial hypothesis predicted that Row A would accumulate the most microplastics, followed by Row C and then Row E. However, this result is not incomprehensible, considering the dynamic nature of water flow and the various particulates present in a stream environment.
Goal #3: The weekly grab samples did not reveal a significant relationship between microplastic concentration and rainfall. Additionally, temperature did not appear to influence microplastic concentration. There was also no discernible correlation between the microplastic concentrations observed in the weekly grab samples and the microplastic counts from the weekly collection of Filter C4. This lack of correlation is somewhat anticipated, as grab samples provide a snapshot of microplastic levels at specific moments, whereas the filters were exposed to water continuously over a week. This observation could suggest that the local wastewater treatment plant, a known source of microplastics, may not have a consistent discharge schedule, or that multiple factors could influence why the microplastic concentration in stream water did not correlate with flow variations.
In conclusion, some very promising results and lessons came from this deployment. The filters proved to be very effective at collecting microplastics during dry periods. The filters also collected microplastics continually for up to six weeks, regardless of the sediment and biofilm that also coated the filters. We now have a better idea about what a long-term deployment with the Plastic Hunter looks like, and how to better prepare for future implementations. The Plastic Hunter will continue to undergo improvements for future field deployments, with another deployment with WCT scheduled for 2025.
