An alternative approach to estimate mismanaged plastic waste at the sub-national scale

Plastic debris in the ocean is widely recognized as a significant environmental issue. As several local strategies are needed to prevent plastic releases into the environment, sub-national estimates are essential, but they are still underexplored. Traditional approaches to determine mismanaged plastic waste (MPW) are based on estimating the proportion of plastics in waste that are not adequately managed, an approach that has limitations on a sub-national scale. Understanding that MPW significantly impacts plastic emission estimations, the present study identifies current limitations and develops an alternative approach to estimate MPW at the sub-national scale. This was based on mass balance, in which the total plastic production of a country is distributed among sub-national areas based on the number of inhabitants and their consumption patterns. Subsequently, regional MPW is estimated by excluding properly managed waste based on local solid waste management data. The method was applied to determine MPW in Brazil, which allowed comparisons with previous research. Results show that between 3.12 and 3.77 million metric tons of plastic leaked into the environment in 2019, consistent with earlier estimates. However, at sub-national scales, differences in estimates are higher than 50 % in 3491 of the 5570 municipalities of Brazil. Although the approach still provides an order of magnitude estimate, a path was established to overcome the main limitations in this research area: accounting for local plastic apparent consumption, uncollected waste, informal recycling practices, and plastic losses unrelated to waste management.