Riverine anthropogenic litter load to the Mediterranean Sea near the metropolitan area of Barcelona, Spain

Highlights

• Large urban areas substantially contribute to marine pollution through rivers.

• 51% and 68% of the total floating litter in Llobregat and Besòs Rivers are plastic.

• Top plastic items were bags, bottles, EPS items and cover/packaging.

• ~0.4–0.6 tonnes/year of plastic were loaded into the Mediterranean Sea by Catalan Rivers.

Abstract

Every year >4 million tonnes of plastic are estimated to enter the oceans and much of it comes from land-based sources through rivers and estuaries. To fill the lack of information related to plastic inputs from rivers, a harmonized approach based on visual observations for monitoring floating macro litter was followed in this work. We provide the results of one-year monitoring (October 2016–September 2017) in the Llobregat and El Besòs rivers, which are flowing through an industrialized and populated area nearby the city of Barcelona (Catalonia, NE Spain). Floating litter items categories were influenced by urban centres located along the rivers. Overall, similar litter composition was observed in both rivers with a prevalence of plastics, mainly related to the food and beverage sectors. Seasonal variability showed significant correlations with natural factors such as wind and rainfall. Approximately 0.4–0.6 tonnes of plastic per year were estimated to be loaded into the sea by these two Catalan rivers. This study contributes to enlarge our knowledge on anthropogenic riverine litter entering the NW Mediterranean Sea, providing a starting point for the development of further mitigation strategies.

Introduction

In the past decades, new technologies were based on the use of efficient and cheap alternative materials according to industrial interest. As a result, a lot of common commercial products are currently made of synthetic polymers such as plastic. A part of the plastic products is leaking from the production and use processes, e.g. by littering of single use plastics, or through waste mismanagement. The input of this litter into the environment by human activity contributes to increasing the amount of waste in coastal waters, estuaries and oceans (Vikas and Dwarakish, 2015). It represents not only an aesthetic problem but also potential damage to littoral areas, marine wildlife and the socio-economic activities linked to these regions (Rochman et al., 2016). In consequence, international organizations recognize marine litter as a severe environmental problem. In fact, several public policies have introduced different initiatives, e.g. at EU level: the Marine Strategy Framework Directive (MSFD, 2008/56/EC) (Commision, E., 2008) and the European Strategy for Plastics in a Circular Economy (COM/2018/028 final) (Commission, E, 2018a), in order to prevent and limit plastic contamination (Martin, 2013; Galgani et al., 2013; Commission, E., 2018b). However, these efforts are recent, while plastic residues are already abundant in the marine environment and have travelled long distances reaching remote areas (Cózar et al., 2017; Lavers and Bond, 2017) due to their chemical persistence and buoyancy properties. Further, plastic items in the environment are subject to fragmentation processes generating smaller pieces known as microplastics (<5 mm), which interact directly with marine organisms (Harrison et al., 2011) and may also act as vectors of emerging chemical contaminants (Bakir et al., 2014). Until recently, researchers have been mainly focused on litter already present in the marine enviroment (Ruiz-Orejón et al., 2016; Duhec et al., 2015; Martins and Sobral, 2011; Kako et al., 2018; Blettler et al., 2018), especially on the study of coastal waters adjacent to urban areas (Santos et al., 2009; Ramirez-Llodra et al., 2013). Every year between 4.8 and 12.7 million tonnes of plastic enter in the oceans (Jambeck et al., 2015). Some studies suggest that riverine litter can contribute up to 90% to all marine litter input (Öko-Institut, 2011) having an important impact on litter abundances in the marine environment (Schmidt et al., 2017; González et al., 2016) including coastal beaches (Lee et al., 2013; Veerasingam et al., 2016). Although a large share of litter entering the marine environment is assumed to come from land-based sources, these inputs have not been quantified (González-Fernández and Hanke, 2017). Rivers could transport plastic litter over long distances to downstream lakes and coastal environments, where they can interact with biota and the water ecosystem (Desforges et al., 2015; Wesch et al., 2016). The riverine transport is influenced by the morphologic and hydrologic characteristics of the catchment, which can affect the amount of waste emitted from rivers to the sea (González et al., 2016). The human population densities and urban development in the catchment area are among the factors determining the amount of mismanaged waste which could directly (or indirectly) end up in the rivers (Schmidt et al., 2017; Lebreton et al., 2017). Natural events connected to climatic and meteorological conditions (e.g. strong wind, rain or floods) play also an important role regarding the litter transport within the catchment area (Nizzetto et al., 2016; Browne et al., 2010; Yonkos et al., 2014). Therefore, the attribution of riverine litter input from mismanaged waste requires a complex previous study of the riverine area considering hotspots and possible sources, such as urban centres and wastewater treatment plants (WWTPs) (McCormick et al., 2014; Mintenig et al., 2017). In order to fill information gaps about plastic waste input from land to ocean (Jambeck et al., 2015; Schmidt et al., 2017; Lebreton et al., 2017), some initiatives have focused on riverine litter (Van der Wal et al., 2015; Surfrider Foundation Europe, 2014; Hohenblum et al., 2015). Based on needs identified within the MSFD context, the RIMMEL - Riverine and Marine floating macro litter Monitoring and Modelling of Environmental Loading - project (RIMMEL project, 2015) applied a harmonized approach for the monitoring of the litter transported from different European rivers into the marine environment. The objective of our work, within the RIMMEL project, was to estimate the riverine anthropogenic litter flux from Llobregat and Besòs River basins, which are flowing through an industrialized and populated area nearby the city of Barcelona (Catalonia, NE Spain) into the Mediterranean Sea.