Why Do Microplastics Matter?

Microplastics are everywhere! They can be found in our oceans, rivers, air, and even the food we eat. They are very tiny in size (the tip of your pencil eraser and smaller) and are persistent in the environment, making them a growing concern for our ecosystems and even human health. With the growing use of plastics in agriculture the very industry itself is contaminating its own product. Microplastics have the ability to settle in soils, which lets the plants intake them. Which then leaves humans vulnerable to ingesting the microplastics which may have negative health effects due to the chemical makeup of the plastics. 

The Salton Sea is a highly stressed body of water in the California desert, and is no exception to the impacts of microplastics. Could agricultural runoff be a significant source of microplastics in the region? We wanted to find out to help us understand the global significance that microplastic pollution can have, check out this cool article by Yale University explaining microplastics more in depth and more on their impact on the environment. 

The Hypothesis: Where Will the Microplastics Take Us?

The purpose of our study was to determine if there is microplastic pollution in the Salton Sea region, and to determine if the large agricultural industry in the area was to blame. We hypothesized that the irrigation runoff leaving agricultural fields would carry higher concentrations of microplastics than cleaner water entering these fields due to the amount of plastics used by the industry. Furthermore, we expected the Salton Sea, where all agricultural runoff collects, to have the highest microplastic concentrations. Aiming to shine a light on how the farming practices in the region may contribute to pollution, offering insights into a crucial but surprisingly under-researched problem for the area.

Sampling the Salton Sea and Techniques
Five total sites were tested:

• Managed Marsh Clean (Clean MM) – Clean water before agricultural exposure.
• Managed Marsh Ditch (Drain MM) – Runoff after agricultural use.
• Alamo River Water (AR Water) – One of 3 rivers entering the Salton Sea.
• Alamo River Ditch (AR Ditch) – Agricultural runoff entering the Alamo River.
• Salton Sea Desert Shores (SS DS) – A Salton Sea site far from inputs.

Two bottles were collected for each site to be further investigated in our lab. We also filtered the water to collect the microplastics on a singular filter. Instruments such as Fourier-transform infrared (FTIR) spectroscopy, and Fluorescence Microscopy were used to quantify and identify microplastic particles from these sites respectively. Each step of the way was carefully completed to not further contaminate the samples.

What We Found
Our findings contradicted our expectations of what we thought previously. The highest concentration of microplastics (36,000 particles/filter) was found in Alamo River Water, a river that is exposed to a plethora of agricultural runoff. Surprisingly, the “clean” irrigation water (Clean MM) also had high levels of microplastics (30,000 particles/filter), refuting our hypothesis that agricultural runoff is the primary source of microplastic pollution. The Salton Sea site, far from any inputs and agricultural exposure, had the lowest concentration (7,480 particles/filter), suggesting that the microplastics are settling into sediments rather than circulating throughout the Sea.

The FTIR analysis revealed diverse plastic types are found within the Salton Sea. As polypropylene dominated the test—likely for its common use in agricultural equipment and packaging. However, the unidentified “other plastics” also emerged as another highly dominating composition, highlighting the need for broader standards and further investigation.

What Does This Mean?
Our data went against our hypothesis that agricultural runoff would contain the higher concentrations of microplastics. Instead, we found that clean irrigation water already has high microplastic levels, indicating that there is a more complex pollution problem. These plastics may be settling in soils and being absorbed by plant roots, explaining the reduction of microplastics after water passes through agricultural fields. But could be entering our food supply which may affect our health, not just the environmental ecosystem. 

Unanswered questions remain:

• What are the sources of microplastics in irrigation water?
• How are the plastics impacting soil health and plant uptake?
• What other plastics are prevalent in the Salton Sea region?

Final Notes

Microplastic pollution is not only an environmental issue, but is also a public health and agricultural concern. This should not only concern the people of the region but anyone who consumes produce.  Identifying the unknown plastics and their sources would be crucial  in addressing this problem especially for governmental action to regulate plastic use. Through continued research, we hope to support underprivileged communities in the region and work toward a cleaner, healthier environment for all.

Provided are tables and figures directly from the study:

Image Citation: