Recreational activities as a major source of microplastics in aquatic environments

Microplastics (MPs) have been extensively studied in the marine environment in recent years, but their occurrence in recreational waters, and recreational activities as a source of MPs, have been less explored. In this study, we investigate the temporal variation of MPs in the Salt River, a natural surface waterway heavily used for recreation, and in community swimming pools in nearby Tempe, Arizona. Samples were processed using established methodologies and MP shapes and number concentrations were obtained by optical microscopy. The MP concentrations in samples of surface water collected during recreational activity ranged from 27,798 to 222,391 MPs/m3, with the highest concentrations occurring at 16:00 and lowest at 8:00, consistent with recreational activities. Fibers were the dominant shape (≥ 71%) of MPs overall in the Salt River, accounting for as much as 96% of all MPs at peak activity time (16:00). MP concentrations in water samples from apartment community swimming pools ranged from 59,160 to 254,574 MPs/m3. In terms of shape, fibers were again dominant (sometimes as high as 87%) in these water samples. Raman spectroscopic characterization of the MPs revealed the presence of polyethylene (PE), polyvinyl chloride (PVC), polyester (PES), polyamide (PA), and polypropylene (PP), showing a larger variety of polymers in the pool samples, while more MP pieces remained chemically unidentifiable. The prevalence of PES and PA fibers indicates that release from synthetic fabrics such as swimwear is a substantial source of MPs in the environment.