ABSTRACT We present the first report of plastic biomedia contamination on Brazilian beaches based on evidence collected from 14 beaches of the Paraná state coastline (southern Brazil). Plastic biomedia, also called biocarriers, are small, perforated plastic pieces used worldwide in wastewater treatment plants (WWTP) that apply the Moving Bed Biofilm Reactor (MBBR) process. Accidental release of these particles into the environment adds to Ocean’s long-term plastic pollution problem. A high amount of plastic biomedia presence in the coastal areas of Paraná was first noticed by a community member, who found 411 plastic particles on a beach located in Pontal do Paraná, bringing this issue to our attention. In this study, plastic biomedia was retrieved from drift line alongshore transects (0.3 to 1 km long) and cross-shore transects (5 m wide) from the water line to the backshore zone. A total of 749 items were collected from 11 of the 14 sampled beaches, including the Mel and Superagui Islands nature reserves. The decreasing trend in plastic biomedia abundance with the increase in distance of the PEC southern outlet suggests that these particles probably originate from a WWTP in the Paranaguá Estuarine Complex (PEC). Once in the water, these floating plastic particles that followed the suspended sediment transport pattern were exported to coastal waters and were transported by longshore currents. Highlighting the potential role of the PEC as a substantial vector for marine debris to the Paraná coastline. The most likely source of this novel plastic contaminant to the Brazilian coastline are WWTP with MBBR systems. Therefore, stakeholders need to discuss and establish a reporting system so that plastic biomedia spillovers or losses are reported, and its dispersal in the environment is reduced. Brazil. Brazil . Brazil) biocarriers small (WWTP (MBBR process Oceans Ocean s longterm long term problem member 41 attention study 0.3 03 0 3 (0. crossshore cross shore 5 ( wide zone 74 reserves PEC. (PEC) currents systems Therefore reported reduced 4 0. (0 7 (PEC