Export of macro plastics over a tidal cycle by through small urban rivers in the Amazon

Abstract

Plastic pollution in rivers has increased over the years and contributes to the pollution of the oceans. But knowledge of macroplastic flows in small, tidal-influenced urban rivers in the Amazon is still unclear, mainly due to a lack of understanding of the processes that control transport in rivers. Here, we provide the first estimate of the floating macroplastic flows in two tidally influenced urban rivers, based on continuous observations over a 12-h period. This period includes a tidal cycle (high and low tide), and the observation took place from a fixed bridge located on both rivers. A total of 8682 items of solid waste were observed in urban rivers, of which 80% were plastic. We found a bidirectional transport of waste throughout the tidal cycle, with maximum amounts of -198.5 items.hour-1 during high tide and 498.6 items.hour-1 during low tide. The largest quantities (1046.89) of items occurred during the ebb tide. These rivers in an Amazonian metropolis can contribute around 25.84kg of macroplastic items per day. The results demonstrate the importance of tidal dynamics in the transport of waste in Amazonian rivers and indicate that urban rivers act as plastic exporters in the region.