MICROPLASTICS ALONG THE BOISE RIVER IN URBAN IDAHO

Microplastics are a growing global environmental concern. Particularly in urban environments, microplastics have many pathways to get into surface water and suspended sediment. The Boise River is a tributary of the Snake River in western Idaho. While its head waters are in high, remote areas of the Sawtooth mountains, it is highly human impacted as it flows through the Treasure Valley, the most populated region in Idaho, with several reservoir, hydroelectric, and flood control dams along its length. These dams include the Boise River Dam located just over 10 km from the state capital of Boise, Idaho. Downstream of this dam, on a stretch of the Boise River that passes through urban, suburban, and rural reaches, we took dip samples (˜50 mL each) in the city of Boise, Idaho and further downstream in Caldwell, Idaho. Additionally, a small, highly disturbed Boise River tributary within Caldwell (Indian Creek) was sampled. From these samples, suspended microplastics were analyzed, looking at the distributions of different forms (fibers, films, fragments, and beads) as well as the overall spatial variations. All samples were found to contain microplastics, ranging from 5 to over 40 individual microplastic pieces various samples. In general, fibers were the dominant form contributing over 50% of the counted microplastics. While preliminary results indicate more suspended microplastics within the city of Boise then downstream in the less populous Caldwell, individual variation between locations was found to be large. Similar to the overall pattern of microplastics, films and beads were more common within the City of Boise reaches. Other water quality indicators, such as common nutrient pollutants like nitrates and phosphorous, varied considerably along the Boise River stretches and preliminary analysis does not indicate a strong correlation with the microplastic content.