he input of solid waste from terrestrial sources to the world's oceans has become a major environmental threat, positioning marine litter and plastic pollution as priority issues in the international agenda [1][2][3][4] . If no effective measures are taken, the prospects for future growth in the production and use of plastics foresee an unsustainable increase in the amount of waste accumulated in terrestrial and aquatic ecosystems around the world 5-7 , with potential impacts on biodiversity and human health 8,9 . Jambeck et al. 10 provided a first approach to modelling mismanaged waste (MW), regarding items as waste if littered or inadequately disposed of on land. Considering the population within a 50-km distance buffer from the coast and assuming a range of conversion rates to marine debris of between 15 and 40% MW, the authors estimated a global annual input of 4.8-12.7 million tonnes (Mt) of plastic to the marine environment. This range of conversion rates of MW to marine debris (15-40%) was based on municipal water quality data gathered in the San Francisco Bay (California) watersheds. Field measurements of plastic input to the oceans are, however, essential for evaluating MW land-ocean transfer rates 6,11,12 , still leaving considerable room for improvement.Rivers act as conduits to the ocean, funnelling the waste dumped into the drainage basins and, as such, they contribute to better understanding the input of litter to the ocean from terrestrial sources. Lebreton et al. 11 and Schmidt et al. 12 estimated the export

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