Transport of microplastics in a stream that receives the discharge of effluents from wastewater treatment plants of a medium-sized city in the southeast of the Buenos Aires province in Argentina.

Understanding how microplastics are transported in rivers and streams is very important since many times the sources of microplastic contamination, such as wastewater treatment plants, are located in such waterways. The transport process involves movement along the waterway and sedimentation and remobilization processes. For this reason, it is important to have data on concentrations of microplastics in both water and sediment. In this work, the concentration of microplastics in water and sediment was studied at different dates at two sites in a stream that receives discharge from treatment plants, finding different behaviors depending on the date. In particular, two dates were analyzed, one in which the concentration of microplastics decreased along the stream and another in which it increased. The influence of water velocity on the variation in concentration of microplastics in the water between the two sampling sites was analyzed, with a greater decrease observed at lower velocities. A spiraling metric was applied to analyze the results, finding that there is mostly no retention in the sediment. The results were discussed within the framework of an advection-dispersion equation considering a remobilization term from the sediment. The experimental results were more adequately described with the remobilization term dependent on the water velocity, this term being different between both dates and depending on the type of sediment. The limitation of considering only effluent discharge as a source of microplastics was analyzed.