Contribution of Stormwater Outfalls to Microplastic Pollution in a Subtropical Estuary Using Data Collected with the Assistance of Citizen Scientists

Stormwater outfalls are frequently listed as sources of microplastic (MP) contamination into aquatic systems. To date, few studies have been undertaken to determine if stormwater outfalls are MP hotspots in estuaries. This study compared the surface waters adjacent to and at least one kilometer away from stormwater outfalls of a subtropical estuarine system: the Indian River Lagoon (IRL) on the east coast of Florida, USA. Citizen scientists collected water samples monthly for 12 months from stormwater outfalls (n = 24) and control sites (n = 6). Overall, 958 MPs were identified from 1800 L of water, with the most found in the fall months during hurricane season. Stormwater outfalls (mean: 0.53 MP/L) were found to discharge smaller MPs (GLM: p = 0.0008) in significantly higher amounts compared to control sites (GLM: p = 0.02), documenting stormwater as a point-source pollutant in this system. Two types of stormwater outfalls drained into the IRL-closed culverts and open drainage channels-with no difference in MP abundances between the two (GLM: p = 0.60). Microfibers dominated collections (89%). Using ATR-FTIR for polymer identification, 80% of the materials found were plastic; polypropylene (29%), polyethylene (18%), and polyethylene terephthalate (18%) were the most abundant polymers found.