Freshwater plastic pollution: Recognizing research biases and identifying knowledge gaps

Abstract

The overwhelming majority of research conducted to date on plastic pollution (all size fractions) has focused on marine ecosystems. In comparison, only a few studies provide evidence for the presence of plastic debris in freshwater environments. However, owing to the numerous differences between freshwater studies (including studied species and habitats, geographical locations, social and economic contexts, the type of data obtained and also the broad range of purposes), they show only fragments of the overall picture of freshwater plastic pollution. This highlights the lack of a holistic vision and evidences several knowledge gaps and data biases. Through a bibliometric analysis we identified such knowledge gaps, inconsistencies and survey trends of plastic pollution research within freshwater ecosystems. We conclude that there is a continued need to increase the field-data bases about plastics (all size fractions) in freshwater environments. This is particularly important to estimate river plastic emissions to the world's oceans. Accordingly, data about macroplastics from most polluted and larger rivers are very scarce, although macroplastics represent a huge input in terms of plastics weight. In addition, submerged macroplastics may play an important role in transporting mismanaged plastic waste, however almost no studies exist. Although many of the most plastic polluted rivers are in Asia, only 14% of the reviewed studies were carried out in this continent (even though the major inland fisheries of the world are located in Asia's rivers). The potential damage caused by macroplastics on a wide range of freshwater fauna is as yet undetermined, even though negative impacts have been well documented in similar marine species. We also noted a clear supremacy of microplastic studies over macroplastic ones, even though there is no reason to assume that freshwater ecosystems remain unaffected by macro-debris. Finally, we recommend focusing monitoring efforts in most polluted rivers worldwide, but particularly in countries with rapid economic development and poor waste management.

Abundance of plastic debris across European and Asian rivers

“…The generation of plastic waste is accelerated by an increasing population, growing economy, and rapid urbanization. Often, waste treatment, recycling, and recovery routes cannot develop at a rate necessary to dispose all the plastic [6]. Of the 6.3 billion tonnes of plastic waste generated until 2015, 79% accumulated in landfills or the natural environment [7].…”

“…These models are generally uncertain due to a lack of data and complexities in the fate and transport of plastics. Model results show that most riverine plastics are emitted in Southeast Asia, but most data driven riverine plastic studies are biased towards European and North American rivers [6] (e.g. the Danube [18], the Thames [19], the Tiber [20], and the Los Angeles basin [21]).…”

“…Another complicating factor is that plastic transport and composition are often not measured consistently over time and space. While riverine macroplastic debris (>5 mm) remains understudied, this makes up most of the observed mass on the ocean and poses direct hazards on marine life [6,8]. Available studies on riverine plastic debris focus mainly on plastic in rivers with large basins, but these basins are not necessarily the largest contributor to the ocean plastic pollution [22].…”

Riverine plastic emission from Jakarta into the ocean

“…In recent years, several studies have quantified plastic pollution in rivers, such as the river Seine (Gasperi et al 2014), the Thames (Morritt et al 2014), rivers in the Los Angeles area (Moore et al 2011) and the Saigon river (Lahens et al 2018, van Emmerik et al 2018. However, most studies tend to be biased towards European and North American rivers, as almost 70% of the riverine plastic studies have been done in highincome countries (Blettler et al 2018). Unfortunately, this does not match the locations where recent modeling efforts predict the largest sources of marine plastic pollution (Lebreton et al 2017, Lebreton andAndrady 2019).…”

Malacological survey in a bottle of water: A comparative study between manual sampling and environmental DNA metabarcoding approaches

“…INTRODUCTION 49 Anthropogenic activities have adverse effects on ecosystems (Parmesan and Yohe, 2003), 50 including a decrease of biodiversity (Waldron et al, 2017), habitat fragmentation (Strayer and 51 Dudgeon, 2010) and pollution (Blettler et al, 2018). Freshwater ecosystems appear to be 52 particularly threatened by human activities leading to local species extinction (Blettler et al, 53 2018).…”