Anacostia Riverkeeper Finds Microplastics in Anacostia Tributaries

Debris found in a microplastics trawl conducted by ARK and George Mason University in summer 2019.

The Anacostia is one of the most urbanized watersheds in the United States and, by being such, has long suffered the human impacts that come with such a distinction. Trash and litter are continually one of the most abundant sources of pollution in our local waterways. From plastic bags to Styrofoam, many of us have seen trash along the Anacostia and its streams whether when out for a paddle on the river or when on a walk along its many trails. Over the last few decades, a new, and potentially more nefarious, pollutant has  worked its way into every corner of our watershed–microplastics. Microplastics are loosely defined as any plastic particle typically falling between 5mm and 0.01mm in size, around the size of a grain of rice or sand. These plastics can come from a host of sources from beads in cosmetic facewashes and exfoliants to larger plastic bottles or debris breaking down over time due to sunlight and wave motion. Microplastics can have adverse effects on both humans and ecosystems alike, because their small size allows them to easily pass through water filtration systems, introducing unintended contaminants like bacteria and toxins that are attached to the plastic into otherwise clean habitats.

In the fall of 2020 we at Anacostia Riverkeeper, with funding from the Chesapeake Bay Trust, partnered with One Montgomery Green (OMG) to adjust their Clean Headwaters microplastics education program to fit a “virtual” format due to COVID-19, and sample for microplastics in local Anacostia tributaries. Three tributaries in the Anacostia (Sligo Creek, Northwest Branch, and Bel Pre Creek) were selected for monitoring due to their urban geography, heavy presence of localized litter, and lack of readily available microplastic data for those streams. Additionally, OMG expanded their program to include one site along Rock Creek at Meadowbrook Farm.  Surface waters at each site were sampled twice from October to December 2020. Samples were collected in a 250mL glass vessel from the stream’s surface, shipped to SimpleLabs Tap Score, filtered to capture all particles from 5mm to .003mm, and results reported in microplastic particles per liter (MPP/L).

All samples collected throughout the Anacostia watershed tested positive for microplastic contamination, with all samples averaging above 40 MPP/L. Sligo Creek exhibited the lowest average microplastic contamination at 45 MPP/L, while Bel Pre Creek and the NW Branch both exhibited higher averages, including the highest single-sample value, both recording 100 MPP/L during the October sampling event. In comparison, Rock Creek at Meadowbrook Farm averaged 100 MPP/L over the two sampling events. All of these results pale in comparison, however, to results found during an Anacostia Riverkeeper pilot study conducted in May of 2019 where microplastics were found in excess of 450 MPP/L in four samples collected from along the DC portion of the Anacostia. One sample, collected next to Yards Park in Navy Yard, was found to contain over 600 microplastic particles per liter of surface water! In the future, we hope to investigate spatial and seasonal variability of microplastics throughout the watershed.

A majority of microplastics in the Anacostia seem to be secondary microplastics, meaning they originated from larger plastics like straws or plastic bottles that have broken down over time.

Moving into the coming months and years, we at Anacostia Riverkeeper plan to fully incorporate microplastic monitoring into our larger water quality monitoring efforts with the aim to recruit more local volunteers and community scientists to help. We’ll be teaming up with other local organizations to spread awareness about this issue as well as working with local researchers and universities to make sure we stay up-to-date on current science surrounding these particles. But information and data are only as good as the goal in which they’re put to use. In the Anacostia watershed, the next step beyond stream monitoring will be to identify what types of plastics make up the majority of the microplastics in our waters and to advocate for cogent policy aimed at reducing those sources. Whether its synthetic fibers from artificial turf fields, or broken-down plastic bottles or bags, our advocacy and policy push will be backed by science and real, boots on the ground, stream data collected by us and a host of Anacostia watershed stewards. Sign up for our newsletter to stay as current as possible on all our microplastic work in the watershed and to keep up with our other programs. Volunteers can also find a local Anacostia Riverkeeper sponsored cleanup HERE to help us reduce the primary source of microplastics in the watershed, waterborne and streamside litter.


For more information about our microplastic work contact Robbie O’Donnell, Watershed Program Manager (