The quantification of microplastics along a primary Puget Sound river A study from headwaters to estuary

The world’s reliance on plastic is a contemporary dependence as its malleable function, low production cost, and increasing abundance has been universally favored over all other products. Created with the intention of short-term and one-time use, the global production of plastic reached 299 million tonnes in 2013, with 10-20 million tonnes ending up in the oceans annually. This study explores the contribution of microplastics to the marine environment from river systems, and quantifies the microplastic load within a stream as it passes from rural to urban environments. The sampled river is fed by a remote, glacially fed lake in the Cascadia Mountain Range, flowing into the upper Skykomish River, the Snohomish River, and eventually to the Puget Sound. Samples were collected by towing a 335 μm mesh manta trawl during an ebb tide and analyzed, after a wet peroxide oxidation and density separation, to quantify the concentration of microplastics present in the stream. From the 16 samples analyzed, a trend has been found between the quantity of plastics in the stream and the streams proximity to the headwaters. This trend implies that the growing quantity of microplastics within the stream, as it flows from rural to urban environments, is supplied through anthropogenic influences. This study has found 0.12 tonnes of microplastics are transported every year by this river system, equating to 1.2 x 109 pieces of microplastics. Following this study, microplastic pollution can no longer be thought of as a coastal and marine issue, but rather a problem that starts much further inland.