Schoolchildren discover hotspots of floating plastic litter in rivers using a large-scale collaborative approach

Defining plastic pollution hotspots

Plastic pollution in the natural environment poses a growing threat to ecosystems and human health, prompting urgent needs for monitoring, prevention and clean-up measures, and new policies. To effectively prioritize resource allocation and mitigation strategies, it is key to identify and define plastic hotspots. UNEP's draft global agreement on plastic pollution mandates prioritizing hotspots, suggesting a potential need for a defined term. Yet, the delineation of hotspots varies considerably across plastic pollution studies, and a definition is often lacking or inconsistent without a clear purpose and boundaries of the term. In this paper, we applied four common definitions of hotspot locations to plastic pollution datasets ranging from urban areas to a global scale. Our findings reveal that these hotspot definitions encompass between 0.8 % to 93.3 % of the total plastic pollution, covering <0.1 % to 50.3 % of the total locations. Given this wide range of results and the possibility of temporal inconsistency in hotspots, we emphasize the need for fit-for-purpose criteria and a unified approach to defining plastic hotspots. Therefore, we designed a step-wise framework to define hotspots by determining the purpose, units, spatial scale, temporal scale, and threshold values. Incorporating these steps in research and policymaking yields a harmonized definition of hotspots, facilitating the development of effective plastic pollution prevention and reduction measures.

Macrolitter budget and spatial distribution in a groyne field along the Waal river

Current research on riverine macrolitter does not yet provide a theoretic framework on the dynamics behind its accumulation and distribution along riverbanks. In an attempt to better understand these dynamics a detailed field survey of three months was conducted in which location of macrolitter items within a single groyne field along the Waal riverbanks was tracked. The data provided insight into the daily changing patterns of spatial item distribution with respect to the waterline. Furthermore, the rates of item uptake and deposition were monitored and related to hydrologic fluctuations. Uptake was initiated by rising water levels and was generally higher when the water level increased faster. Deposition occurred continuously, despite hydrologic fluctuations. This caused the riverbank macrolitter budget to be positive during stable or dropping water levels and negative during rising water levels. Although the results show clear patterns an extended monitoring duration is required to fully understand the fate of plastic objects.

Exploring the abundance and characteristics of litter in Lithuanian riversides: a citizen science approach

To gain a better understanding of the sources and ecological effects of plastic contamination in Lithuanian rivers, as well as to provide guidance for mitigation, monitoring is necessary. This is a logistically and financially demanding endeavor, particularly in the case of microplastics. Citizen science provides a viable option for sampling sites that are accessible, thus enabling the monitoring of wide areas. In Lithuania, a citizen science approach was employed, with schoolchildren examining litter at riversides and identifying potential sources at 24 sampling sites in Autumn 2022 and 32 in Spring 2023, covering both large and small rivers. The maximum amount of 220 items per location was registered in Autumn 2022, whereas 111 items per location were registered in Spring 2023. The two main types of microlitter discovered were plastic (34-42%) and cigarette butts (17-22%), with glass, paper, and metal also present, which suggests that recreational visitors are the main source of litter. By K-means clustering analysis, all locations were divided into four clusters according to litter composition. To sum up, the findings of this study illustrate the importance of citizen science in providing insight into the contamination of Lithuanian rivers, which can be used to inform the development of conservation strategies.

Citizen scientists study beach litter along 12,000 km of the East Pacific coast: A baseline for the International Plastic Treaty

Anthropogenic Marine Litter (AML) accumulating on beaches causes damage to coastal ecosystems and high costs to local communities. Volunteers sampled AML on 130 beaches along the central and southern East Pacific coasts, with AML densities ranging from 0.46 to 2.26 items m-2 in the different countries. AML composition was dominated by plastics and cigarette butts, the latter especially in Mexico and Chile. The accumulation of AML in the upper zones of the beaches and substantial proportions of cigarette butts, glass and metal pointed mainly to local sources. Statistical modelling of litter sources on continental beaches revealed that tourism, access and related infrastructure (e.g. parking lots) best explained AML densities, while plastic densities were also influenced by the distance from river mouths and national Gross Domestic Product. Large-scale monitoring can be a useful tool to evaluate the effectiveness of public policies that should primarily focus on land sources.

What potential does the EU Single-Use Plastics Directive have for reducing plastic pollution at coastlines and riversides? An evaluation based on citizen science data

To address environmental pollution by plastic litter, the European Union adopted EU Directive 2019/904, the so called "Single-Use Plastics Directive" (SUPD), which bans several single-use plastic products and addresses additional items with measures such as extended producer responsibility and obligatory requirements for product redesign. This study assessed the potential of the SUPD to reduce litter pollution in the environment with three scenarios. The "best case" scenario assumed that all measures of the SUPD completely prevent targeted items from getting into the environment. Another scenario assumed that no measures besides bans were effective. An intermediate scenario assumed partial effectiveness of measures. Data of almost 5,000 sampling events from citizen science protocols (Plastic Pirates, International Coastal Cleanup, Marine Litter Watch) and the OSPAR protocol were used to analyse litter at riversides and coastlines in Germany and the European Union. 44 to 68% of litter items in citizen science protocols consisted of single-use plastics (cigarette butts were the most prominent items). At coastlines sampled by the OSPAR protocol, fishing gear and undefined plastics prevailed. The scenario analysis revealed that substantial litter reductions could be achieved in the "best case" scenario (upwards of 40%), while the intermediate scenario resulted in litter reductions of 13 to 25%. The marginal effect of the "only bans" scenario achieved a reduction of 2-6% in Germany and the European Union, respectively. Thus, depending on implementation and enforcement, the current SUPD can be an important first step, yet further legislative actions are needed to effectively prevent plastic waste pollution.

Amsterdam urban water system as entry point of river plastic pollution

Accumulation of plastic litter in aquatic environments negatively impacts ecosystems and human livelihood. Urban areas are assumed to be the main source of plastic pollution in these environments because of high anthropogenic activity. Yet, the drivers of plastic emissions, abundance, and retention within these systems and subsequent transport to river systems are poorly understood. In this study, we demonstrate that urban water systems function as major contributors to river plastic pollution, and explore the potential driving factors contributing to the transport dynamics. Monthly visual counting of floating litter at six outlets of the Amsterdam water system results in an estimated 2.7 million items entering the closely connected IJ river annually, ranking it among the most polluting systems measured in the Netherlands and Europe. Subsequent analyses of environmental drivers (including rainfall, sunlight, wind speed, and tidal regimes) and litter flux showed very weak and insignificant correlations (r = [Formula: see text]0.19-0.16), implying additional investigation of potential drivers is required. High-frequency observations at various locations within the urban water system and advanced monitoring using novel technologies could be explored to harmonize and automate monitoring. Once litter type and abundance are well-defined with a clear origin, communication of the results with local communities and stakeholders could help co-develop solutions and stimulate behavioral change geared to reduce plastic pollution in urban environments.

Measuring riverine macroplastic: Methods, harmonisation, and quality control

River systems are a key environmental recipient of macroplastic pollution. Understanding the sources of macroplastic to rivers and the mechanisms controlling fate and transport is essential to identify and tailor measures that can effectively reduce global plastic pollution. Several guidelines exist for monitoring macroplastic in rivers; yet, no single method has emerged representing the standard approach. This reflects the substantial variability in river systems globally and the need to adapt methods to the local environmental context and monitoring goals. Here we present a critical review of methods used to measure macroplastic flows in rivers, with a specific focus on opportunities for methods testing, harmonisation, and quality assurance and quality control (QA/QC). Several studies have already revealed important findings; however, there is significant disparity in the reporting of methodologies and data. There is a need to converge methods, and their adaptations, towards greater comparability. This can be achieved through: i) methods testing to better understand what each method effectively measures and how it can be applied in different contexts; ii) incorporating QA/QC procedures during sampling and analysis; and iii) reporting methodological details and data in a more harmonised way to facilitate comparability and the utilisation of data by several end users, including policy makers. Setting this as a priority now will facilitate the collection of rigorous and comparable monitoring data to help frame solutions to limit plastic pollution, including the forthcoming global treaty on plastic pollution.

What can we learn from studying plastic debris in the Sea Scheldt estuary?

The Sea Scheldt estuary has been suggested to be a significant pathway for transfer of plastic debris to the North Sea. We have studied 12,801 plastic items that were collected in the Sea Scheldt estuary (Belgium) during 3 sampling campaigns (in spring, summer, and autumn) using a technique called anchor netting. The investigation results indicated that the abundance of plastic debris in the Scheldt River was on average 1.6 × 10^-3 items per m³ with an average weight of 0.38 × 10^-3 g per m³. Foils were the most abundant form, accounting for >88 % of the samples, followed by fragments for 11 % of the samples and filaments, making up for <1 % of the plastic debris. FTIR spectroscopy of 7 % of the total number of plastic debris items collected in the Sea Scheldt estuary (n = 883) revealed that polypropylene (PP), polyethylene (PE), and polystyrene (PS) originating from disposable packaging materials were the most abundant types of polymers. A limited number of plastic debris items (n = 100) were selected for non-destructive screening of their mineral element composition using micro-X-ray fluorescence spectrometry (μXRF). The corresponding results revealed that S, Ca, Si, P, Al, and Fe were the predominant mineral elements. These elements originate from flame retardants, mineral fillers, and commonly used catalysts for plastic production. Finally, machine learning algorithms were deployed to test a new concept for forensic identification of the different plastic entities based on the most important elements present using a limited subset of PP (n = 36) and PE (n = 35) plastic entities.

Plastic microbiome development in a freshwater ecosystem

To understand biological interactions of plastic litter in freshwater ecosystems, as well the potential effects of plastics on ecosystem processes, studies of the activity and composition of plastic-associated microbial communities are needed. The physical properties and chemical composition of plastic polymers are key components of plastic product design, and may also select for distinct microbial biofilms colonizing plastic litter. We monitored growth and succession of biofilm communities on plastic substrates of common morphotypes (i.e., hard, soft, foam, and film) and a natural surface (i.e., an unglazed ceramic tile) incubated in an urban stream. We measured biofilm biomass, metabolism, extracellular enzyme activity, and bacterial, fungal and algal community composition over four weeks during primary succession. Results demonstrated a general increase in biofilm biomass and enzymatic activity corresponding to carbon, nitrogen and phosphorus metabolism during biofilm development for all substrate types. We observed higher respiration rates and negative net ecosystem productivity on foam and tile surfaces in comparison to hard, soft and film plastic surfaces. Biofilm bacterial, fungal and algal assemblages showed few significant differences in composition among substrates. However, all microbial communities changed significantly in composition over time. While substrate type was not the major factor driving biofilm composition and activity, these data show plastic litter in streams is well colonized by an active and dynamic biofilm community. As plastic litter is increasing across all types of aquatic ecosystems, it should be considered a medium for biologically active organisms that contribute to key ecosystem processes.

Plastic pollution in the surface water in Jakarta, Indonesia

Plastic pollution in the ocean primarily originates from the land-derived mismanaged plastic waste that is transported by rivers. This study aimed to estimate the plastic litter generation in the surface water in Jakarta and Indonesia. A field survey was conducted at six riverine sampling points (upstream to downstream) and three holding facilities of the litter in Jakarta during the rainy season. The Jakarta Open Data database was used to estimate the tonnage of plastic litter. By mass, plastic comprised approximately 74 % of the anthropogenic litter in rivers and 87 % in holding facilities. The riverine plastic proportion slightly increased downstream. Approximately 9.9 g/person/day of plastic litter was discharged into Jakarta's surface water during rainy season and recovered by floating booms. To reduce plastic pollution and its severe impacts on aquatic ecosystems and human health, further field investigation is necessary to design an effective clean-up system and litter-prevention strategy.

Mountain streams flushing litter to the sea - Andean rivers as conduits for plastic pollution

Rivers polluted by anthropogenic litter are major transport routes of litter from inland to the coastal zone and the ocean. However, litter studies have primarily focused on marine environments, and the litter dynamics in rivers are still poorly understood. Herein, we explored the abundances, composition and sources of litter at the riversides and in surface waters of mountain rivers from continental Chile in two different years. Additionally, we evaluated whether different temporal, geographic, topographic, hydrologic or anthropogenic factors influence the abundances of litter. Anthropogenic litter was prevalent in Chilean rivers, both at the riversides and in surface waters. Average abundances of riverside litter, floating macrolitter, and small floating plastics were 1.8 items m^-2, 10.1 items h^-1 and 5.8 items h^-1, respectively, and abundances were generally higher in northern Chile. Plastics dominated in all compartments, comprising 29% of riverside litter and more than 70% of small floating litter, but other litter categories were also present at riversides. Sources of litter in Chilean rivers were mostly local, such as recreational visitors, residents, and illegal dumping, and there were no clear effects of the different tested factors on the abundances of litter. Litter densities in surface waters were low compared to those in lowland slow-flowing rivers in other countries, suggesting that retention of litter is limited in the highly dynamic and rapidly flushing mountain rivers, and thus most litter (primarily plastics) is transported directly to the sea. The results suggest that to adequately address this problem in Chile, prevention measures should be aimed at the identified local sources, by means of education, public policies, legislation, and enforcement.