Jake Peterson, an intern for the Spokane Riverkeeper and student at Gonzaga University, conducted this research in Spring of 2018 on microplastics in the Spokane River. What he found surprised and disturbed us. Microplastics were found in every liter of water he looked at, sometimes in great quantity. This work is continuing through the work of another intern, who was recently featured on KREM 2 news. Read the report below.

Wastewater Microplastics Pollution in the Surface Water of the Spokane River

Jake Peterson

Abstract:  Anthropogenic microplastic pollution is a growing threat in freshwater ecosystems around the world. This has been a long-known threat in the Spokane river watershed with numerous responses undertaken to combat the problems of pollutants. One of the targets has been wastewater effluent, a known point source for pollutants. There is a new emerging anthropogenic pollutant, microplastic, which is being discovered to be pervasive throughout the globe. This study aimed to find if the Spokane Wastewater Treatment plant (WWTP) was a point source for microplastic pollution.


Introduction: Fresh water is essential to life on this planet, and ever increasingly, key freshwater resources face threats from anthropogenic pollution. Anthropogenically produced pollutants are known to cause health problems throughout freshwater ecosystems. Freshwater pollutants are acutely felt by people if they face exposure loads in high enough quantities. The pollutants can have negative health consequences and reducing exposure is important. A common point-source for pollutants in freshwater ecosystems is wastewater treatment effluent (“The Sources and Solutions: Wastewater”).

            An emerging environmental pollutant is anthropogenically produced plastic. It was first reported in surface seawater in 1971 (Buchanan 1971), and since then, it has been found in the environment all over the globe (Fahrenkamp-Uppenbrink 2018). While the exact ecological and health consequences aren’t well understood, initial evidence suggest microplastics could become a large human health problem if high enough levels of exposure occur (Wright et al. 2017). And, it appears that humans are being exposed to microplastics frequently. It has been detected in the air (Prata et al. 2017), in food, and drink, and even tap water (Kosuth et al. 2018). Determining regional sources of microplastic and quantifying the amount of exposure to microplastics by both biota and people will be a key to understanding this threat.

            In the Spokane region, the source for drinking water is the Spokane River and its larger drainage, known as the Spokane Valley-Rathdrum Prairie Aquifer (SVRP).  Freshwater pollution is well documented in the aquatic environments of the Spokane River. The region’s geology makes the SVRP particularly vulnerable to pollution due to high permeability. In 1978, the SVRP aquifer was designated as a “sole source aquifer” by the Environmental Protection Agency in a move that united management of wastewater and stormwater throughout the SVRP to address pollution problems.  However, to this day, the region still suffers from problems with polychlorinated biphenyls (PCB), heavy metals, and other anthropogenic pollutants (“Spokane Valley-Rathdrum Prairie Aquifer | Spokane County, WA.” ). Unfortunately, little research has been done into the emerging microplastic problem on the river. In general, microplastics research has been focused on marine ecosystems and only recently have freshwater ecosystems really come under scrutiny (Eerkes-Medrano et al 2015). Last year, the first microplastics study in the Inland Northwest was conducted on the Spokane River, looking for its presence in fish above and below the Spokane Wastewater Treatment Plant (Caruso 2016).

Through this research, we aimed to develop a method to effectively sample and quantify the presence of microplastic in the Spokane River and other freshwater sources along the SVRP. The projects goals were to first confirm and quantify the presence of microplastics in the river water. Secondly, to determine whether or not the City of Spokane’s Wastewater treatment plant is in fact a point source for microplastic in the Spokane River.



For this project, methods were modified from methods being used at the Florida Microplastics Awareness Project (Florida Microplastic Awareness Project). While methods for marine microplastic sampling is well documented, there are no comprehensive guidelines for sampling microplastics in freshwater ecosystems (Eerkes-Medrano et al 2015). The main goal was to establish a method that could be done without significant lab resources in order to be easily used with the resources available to the Spokane Riverkeeper, with whom the project was developed for.  

We chose sample locations along the river at safe access points with consistent eddies at a wide variety of flow ranges in order to sample as still of water as possible. For looking at the wastewater portion of this study, a site just upstream and a site just downstream were chosen. The area upstream was the Downriver Disc Golf course which had several good eddies at wide flow ranges. Just downstream, the boat access site was chosen. This is a public boat lunch for the lower Spokane River. The wastewater treatment plant effluent is about a half mile upstream from this boat access point. Turbulence causes sediment to sink, and so the idea was to sample areas with eddies where microplastic would be floating on the surface.

Field: Upon arriving at the site and choosing a safe eddy  we used a smartphone to get the global positioning system (GPS) coordinates and flow rate in cubic feet per second (cfs) on the USGS gauge @ Spokane and wrote it down on a Whirl Pak. Furthermore, a visual assessment of the river was taken, noting water color, clarity, and what had been happening in context of flow. For example, a rain on snow run off event was noted to have near the 3/9/18 sampling date, causing the river to become brown and loaded with sediment.

Location of microplastic samples in the Spokane River

Location of microplastic samples in the Spokane River

Once the sample was ready to be taken, A 1-liter surface water sample would then be measured, filtered through a 136-um hand-built filter, and then washed into a Whirl Pak. During every sampling day, six samples would be taken at each of the two sampling sites (Fig 1). On top of these samples, numerous opportunistic samples were taken throughout the Spokane River in order to develop the methods (Fig 2). These opportunistic samples were not included in the final data analysis.

Location of all microplastic samples taken during the study.

Location of all microplastic samples taken during the study.

Lab: Once in the lab, the samples were filtered again onto Whatman 1002-055 Quantitative Filter Paper Circles, 8 Micron, 21 s/100mL/sq. inch Flow Rate, Grade 2, 55mm. During the filtering, the petri dish should be placed just ajar over the funnel in order to prevent any plastics from falling from the air into the sample. Once filtered, the Whirl Pak and funnel rim were rinsed three times with a clean water squirt bottle. The filters were then placed aside to dry. As the samples were filtered, the filtered water was poured into a basin. This water is clean of microplastic as it has been filtered down and would be used to then clean all the equipment down at the end. Any left-over water would be stored in a squirt bottle for next use and to rinse samples as needed.  

Figure 3. Photo of a typical microplastic fiber found in the sampling

Figure 3. Photo of a typical microplastic fiber found in the sampling

Once dry, the filters were looked at under a microscope and microplastics were identified visually using a clear grid overlay to keep track. Plastics that could clearly be observed to be plastics would be marked as knowns, and substances that looked to be plastic but couldn’t be determined beyond a reasonable doubt were marked as unknown. Knowns were identified using the following characteristics “No cellular or organic structures are visible, fibers should be equally thick throughout their entire length, particles must present clear and homogeneous colors” (Hidalgo-Ruz 2012). If fibers were still difficult to view, a durability test would be used. The material would be pressed and rubbed using a bodkin and tweezers. If the material broke, it would not be listed and considered biological material. The most commonly observed were microfibers (Fig 3).

All the information including flow rate, location, GPS coordinates, date, and plastic counts were then recorded into a google spreadsheet. This then allowed the data to be mapped on a google map file that could be potentially used in the future for projects to add data.  

Statistical analysis:

The number of microplastics above and below the wastewater treatment facility were compared using repeated measures ANOVA, where each location was sampled on six dates.


Microplastics were found in every single sample tested throughout the sampling period, including in all of the opportunistic samples. The highest microplastic counts were detected during a high water event. The river spiked and was blown out from a large rain on snow event that added a lot of run off. Several samples were taken on the sample date correlating with this event and were discovered to have more than 40 microplastics per liter (m/l), the highest being 47 m/l during the peak flow of the sample period at 20,200 cfs. The lowest sample recorded 1 m/l microplastic during a slowly rising river regime with lower sediment loads at 9,380 cfs. On average, river samples had 12.1 m/l with the most commonly observed microplastic type being microfibers.

Fig 4: Average microplastic counts by date. Blue: upstream of WWTP sampling site Red: downstream of WWTP sampling site

Fig 4: Average microplastic counts by date. Blue: upstream of WWTP sampling site Red: downstream of WWTP sampling site

We found a difference in the number of microplastics above and below the water treatment facility, such that more microplastics were detected below the wastewater treatment facility (df = 1,8; p = 0.04; Figure 3). In addition, a runoff event resulted in an increased number of microplastics in both locations at one sampling date (4/16/2018;  Figure 4). This suggests the treatment plant is a source of microplastic in the Spokane River.



This research is significant because it's part of a wide body of emerging research showing the extent of plastics pollution in freshwater ecosystems. Typically, this research has been focused on marine environments ever since the first study of its kind was published indicating microfibers in the ocean (Buchanan 1971). There is a broad emerging work on microplastics in freshwater ecosystems around the globe that seems to suggest the pollution shares similar forms to what is being seen in the ocean. There are large quantities and they permeate throughout the ecosystem (Eerkes-Medrana et al 2015).

This research indicates that there are high levels of microplastic present in the water of the Spokane River with an average of 12 m/l. While troubling, this information is not surprising. Numerous other studies looking at the river ecosystem found large amounts of microplastic in the sediment and water, suggesting this level of persistence throughout. (Hurley et al. 2018, Eerkes-Medrano 2015).

Our microplastic study is further supported by the unpublished regional findings of a similar project done on the same section of river. That study found microplastics in the gut of Prosopium williamsoni and indicated the wastewater treatment plant might be a source (Caruso 2016). Considering the migratory patterns of the  P. williamsoni , it's possible that the fish could have moved from somewhere else. However, our data accounts for that potential spatial disparity by looking at water samples in fixed locations. It supports the hypothesis that the wastewater treatment plant is a source for microplastics in the river. WWTP are linked to microplastic effluent in numerous studies (Eerkes-Medrano et al. 2015, Hurley et al 2018, Ziajahromi 2017, Talvitie et al 2017, Murphy et al 2016).

 It's important to contextualize the pollution problem from wastewater treatment. There are several instances in which advanced wastewater treatment plants proved to be beneficial in fighting microplastic pollution and actually remove microplastics (Talvitie et al 2017). Fortunately, the Spokane WWTP is currently constructing an add on to the facility which will include advanced membrane filtering. This could reduce wastewater plastics pollution by 99% (Talvitie et a. 2017). That being said, this study was a relatively small town. Consider the findings of the Murphy study, which reviewed Talvitie among other WWTP microplastic studies. They state “The results of this study show that WWTW [WWTP] can be effective in the removal of microplastic from the municipal effluent. However, even a small amount of microplastic being released per liter can result in significant amounts of microplastics entering the environment due to the large volumes being treated” (Murphy et al 2016). The problem seems to be so persistent that even technological solutions may not drive a fix.

            While we are fortunate to be responding to Spokane’s WWTP pollution problem in a small form unintentionally, these findings are especially disturbing in the broader context. The Spokane River is connected to the larger Spokane Valley-Rathdrum Prairie Aquifer (SVRP), which provides drinking water for the entire region. Opportunistic samples taken during this study in both the lab and feild indicated microplastic in tap water and throughout the Spokane River. Recent findings support this, with one international study finding 81% of tap water samples containing microplastics. North America had the highest concentrations of about 9.8 m/l. This same study indicated microplastics presence in sea salt and beer (Kosuth et al. 2018).  Microplastics have permeated everywhere it seems. They are in the food we eat, the water we drink, even the air we breath (Prata et al 2017, Wrighte et al. 2017). While studies on the direct human impacts of ingested microplastics haven’t occurred yet, there is plenty of parallel evidence supporting microplastics as a harmful pollutant. Case studies in workers have indicated it causing respiratory problems (Eschenbacher et a. 1999). While not in people, there is emerging evidence of numerous toxicological pathways in rats, and plastics are being detected more and more in the human cases according to one literature review. This same study makes an ominous note at the end. This appears to just be the beginning, microplastic loads in people are not well understood due to limitations in finding them in the body, and estimations of loads are likely to increase as the issue becomes better understood (Wright et al 2017).

            Ultimately, larger global forces are going to have to come into play if we hope to significantly reduce the impacts of plastic pollution. Regionally, action can be taken now in order to help solve the problem. Future research in Spokane should look into the three areas where microplastics will likely impact human health the most, in the air, in the drinking water, and in food stuffs. This project in particular was designed with future testing in mind and could easily be expanded to test water samples throughout the SVRP watershed. It was designed to be cheap and relatively simple with minimal lab use. This opens up potential for larger citizen science/student lead testing on a wide variety of sources. Tap water especially should be studied with the procedures as it would incredibly important in informing future management decisions. This would further help us understand if we are likely to see health impacts. Further classification and chemical identification of the types of plastics found in these samples could also help inform sources of microplastic in the region as well.  




Works Cited

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