MICROPLASTIC POLLUTION IN TRIBUTARIES OF THE MOHAWK RIVER, NEW YORK STATE

The Mohawk River in upstate New York is the largest tributary of the Hudson River and a source of municipal drinking water. The present study follows on our 2016 finding that all of the water and sediment samples we collected in the main channel of the Mohawk River contained microplastic particles. In June-July 2018, we sampled water in 22 tributaries of the Mohawk River and the main stem of the Mohawk River in Rome, NY, for microplastics. The 22 tributaries included the three major tributaries and 19 smaller tributaries. All of the streams were sampled under relatively low-flow conditions; one stream (Hans Groot Kill, HGK) was also sampled at high flow. We used a 3-m neuston net with 335-µm mesh and a detachable mesh cod end attached to a 1-m x 0.5-m aluminum frame. The net was positioned so that the water surface lay within the net opening. Flow velocities ranged from 0.067 m/s to 1.061 m/s, stream width varied between 2.6 m and 81 m, and stream depth ranged from 0.15 m to 0.61 m. Sampling intervals were 15 to 27 minutes for all streams except the high-flow sampling of the HGK, which was sampled for 8 minutes in a downpour. The calculated volume of water passing through the net opening during each sampling event ranged from 14 m³ to 287 m³. Solids captured in the net were washed into the cod end, then transferred to a glass jar. In the lab, samples were decanted onto stacked 4.75-mm and 0.300-mm sieves. Larger organic material was rinsed and removed for drying. Remaining particles were transferred to a 600-ml glass beaker. Residual organic material was dissolved using a modified version of the NOAA protocol for wet peroxide oxidation. With 10 samples completed, preliminary microscope examination indicates that microplastic particles are present in 8 of 9 samples collected in the tributaries and in the sample from the Mohawk River. Preliminary tallies of microplastic particles range from 3-4 to 90-111. The low-flow HGK sample has a preliminary count of 94 microplastic particles. Lab work on the high-flow HGK sample has yet to be completed, but a wealth of macroplastic was removed during initial processing. The stark contrast between the HGK at low flow and high flow suggests that storm events may enable usually tiny streams that receive input from storm sewers to deliver high microplastic loads to the Mohawk River when raised to bankfull by heavy rainfall.