(Micro) plastic fluxes and stocks in Lake Geneva basin

Abstract

Large amounts of macro-and micro-plastic have been reported in rivers, lakes and oceans. However, links between the observed pollution and their sources remain unclear. This study aims to clarify these links in the Lake Geneva basin by analysing each step of the watershed's plastic life cycle.Two distinct approaches are compared: (i) a top-down approach based on modelling socio-economic activities, plastic losses and releases into the lake, and, (ii) a bottomup approach based on the extrapolation of plastic flows into the lake from field measurements across 6 different pathways.The two approaches yield results with similar orders of magnitude: 49 tons.year -1 (range 8-193 tons.year -1 ) for the top-down approach, and 59 tons.year -1 (range 34-83 tons.year -1 ) for the bottom-up approach. From this, we estimate plastic flows from land to Lake Geneva -approximately 55 tons.year -1 .Field measurements (bottom-up) showed significant contribution of water run-off as a pathway for plastics, mainly through rivers in wet periods and road-runoff. The samples analysed contained mainly plastic waste from packaging and plastic from the construction industry. The modelling approach (top-down) indicated that abrasion of car tyres could be a major contributor to plastic pollution (one order of magnitude higher than all other sources), as well as textile fibres to a lesser extent. As these particles have not been traced in the environment, further studies are needed to validate these theoretical findings.Preliminary mass balance of plastic in Lake Geneva indicates that 20% of plastic may be deposited on shores, 10% flows in the emissary towards the sea and the rest being deposited in the sediments. We take from these findings that Lake Geneva acts as a sink for plastic pollution, with close to 600 tons accumulation of plastic in lake sediments (i.e. 3 order of magnitude more than the expected surface floating plastic). These findings bring a novel insight into the role of big and deep lakes as a filter for plastic (no flushing through flooding period), thus preventing more plastic from reaching the oceans. This research allows for the first time the combination of bottom-up and top-down modelling approaches as well as plastic stock assessment. In spite of the high uncertainties embedded in such approaches, and the fact that contemporary methods are not suitable for the detection of very small particles or particles maintaining certain characteristics, it provides a comprehensive model of plastic leakage into waterways. We believe such approaches should be replicated in other areas by refining the analytical approaches.

Transport and Behavior of Microplastics Emissions From Urban Sources in the Baltic Sea

“…Microplastic is found in types of sediments and highest concentrations are observed near populated areas and near emission sources, especially in semi-and enclosed systems (Claessens et al, 2011;Vianello et al, 2013;Gray et al, 2018). Some authors consider the sediments even as major sink for microplastics (Boucher et al, 2019) and suggest that microplastics and fine sediments show similar sinking and accumulation behavior (Vianello et al, 2013). This questioned by other authors.…”

Microplastics in freshwater fishes: Occurrence, impacts and future perspectives

“…The foraging habitats of freshwater fish should also impact MP encounter rates, given MP distributions and loadings differ, with typically higher loadings in sediments compared to overlaying surface waters (Bondelind et al, 2020; Boucher et al, 2019; Li, Geng, et al, 2019). Consequently, within a given location, pelagic species ought to encounter fewer floating MPs (e.g.…”

The Way of Macroplastic through the Environment

“…Six lakes in Switzerland were investigated by Faure et al (2015) [135], and an average of 1800 MaP items/km 2 was detected on the water surface. In addition to the samples, an input of 55 t of plastics/a was modelled for Lake Geneva [136].…”