Microplastics in the food web

What are microplastics?

Anthropogenic materials infiltrate our environment at an alarming rate, including in some of the most remote locations on earth; from diets of freshwater fish in the Amazon to waters of the Arctic region. Microplastics, which are particles less than 5 mm in size, have been a focus in recent environmental pollution research. Microplastics come in many colors and shapes, sometimes originating from degrading plastic debris. Concerns of rapid accumulation, atmospheric transportation, and harmful health implications associated with microplastics have led to an increase in research of this phenomenon. Microplastics pose a major risk to the environment, with bioaccumulation in aquatic ecosystems that has been shown to transfer among trophic levels. Exposure to microplastics has been shown to negatively affect physiology, feeding behavior, and fitness in aquatic organisms.

Research on microplastic distribution and threats to freshwater environments have increased in recent years. The abundance and prevalence of microplastics can vary based on land use and population density and have been documented even in remote catchments. The small size of microplastics allows for ingestion by organisms of many different trophic levels, from invertebrates to piscivores. Few studies have looked at remote freshwater systems; even fewer studies have investigated microplastic presence in freshwater fish or invertebrate diets.

Why Yellowstone Lake?

Located in Yellowstone National Park, Wyoming, USA, Yellowstone Lake is considered to be a pristine environment situated within the most remote watershed in the contiguous United States. Yellowstone Lake contains the largest nonhybridized population of Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri), a keystone species for the Greater Yellowstone Ecosystem. Identifying and understanding potential threats to Yellowstone Lake, including climate change, non-native species, and other anthropogenic impacts, is critical to the long-term functioning and management of this notable ecosystem.

With the prevalence of microplastics in freshwater systems elsewhere and documented threats to organism health, we aimed to determine whether microplastics were present in the Yellowstone Lake food web. This study addressed the following questions in Yellowstone Lake: (1) are microplastics present in the water, (2) are microplastics present in diets of amphipods and fishes, and (3) if microplastics are present, what are the material types?

What did we find?

Each sample type (water, amphipod, Yellowstone Cutthroat Trout, Lake Trout) had at least one non-organic particle present. All surface water tows had at least three non-organic particles, and three of four vertical water tows had at least two non-organic particles present. The number of particles in water samples was greater than the number of particles in biota samples; surface water samples had a higher number of particles than the vertical water samples. Of the 32 amphipods sampled, only one contained an identifiable non-organic particle. Two lake trout diets had three particles in total, and one Yellowstone cutthroat trout diet contained three particles. Of the 50 samples among sample type and locations, 22% of samples contained non-organic particles.

Where did they come from?

A point source of microplastic deposition is likely not identifiable in Yellowstone National Park, as atmospheric transport and deposition can occur, contributing to microplastic accumulation at remote locations. However, it is highly plausible that some of the plastic observed in this study is a byproduct from the 4 million people who visit Yellowstone National Park annually.

How can you learn more?

Read some recent peer-reviewed publications regarding microplastics in our environment: https://science.sciencemag.org/content/368/6496/1257 , or about microplastics in fish: https://onlinelibrary.wiley.com/doi/full/10.1111/faf.12528. You can read our peer-reviewed article about microplastics in Yellowstone Lake, including our methods, here:https://www.mdpi.com/2073-4441/13/3/264/htm .