Bypass of Booming Inputs of Urban and Sludge-Derived Microplastics in a Large Nordic Lake

Abstract

Microplastic research, initially focusing on marine environments, left freshwater ecosystems largely unexplored. Freshwaters are also vulnerable to microplastics and are likely the largest microplastic supplier to the ocean. However, microplastic sources, transport pathways, and fluxes at the catchment level remain to be quantified, compromising efficient actions toward mitigation and remediation. Here we show that 70–90% of microplastics reaching Norway’s largest lake, originating primarily from urban waste mismanagement and sludge application on crops, continue their journey toward the ocean without being buried. Indeed, our microplastic budget for the catchment shows that out of the 35.9 tons (7.4–119.4 t) of microplastics annually released into the lake, only 3.5 tons (1.3–8.8 t) are settling to the lake bottom. The spatial and vertical microplastic distribution and diversity in lake sediments, the socio-economic modeling of plastic fluxes and spatial information on land use and potential plastic sources all point toward urban and agricultural areas as emission hotspots of increasing importance. We conclude that the degree to which lake sediments represent a net microplastic sink is likely influenced by the nature of microplastics the lake receives, and ultimately on their origin.

Sources and Fate of Microplastics in Urban Systems

“…Current data indicate that microplastic deposition in the oceans mimics the deposition of fine matter (Claessens et al 2011;Vianello et al 2013;Haave et al 2019;Maes et al 2017). Published data also indicate that a higher proportion of the dense polymers will be represented in such sediments, and that lightweight particles are more likely to remain in circulation and/or distribute in surface waters further from the sources and that considerable amounts may this way be released to the ocean without settling (Clayer et al 2021;Liu et al 2019a).…”

“…In summary, the existing data indicate that we will find the highest concentrations of microplastics in nature close to the source, and that downstream deposition can be expected in deep basins or benthic sediments, mudflats, or at the low-tide marks in sheltered beaches, where currents and energies are low. In contrast, high energy in estuaries, rivers, and inlets may cause microplastics to be transported out of the system (Clayer et al 2021;Scherer et al 2020;Haave et al 2019;Liu et al 2019b). Current data indicate that microplastic deposition in the oceans mimics the deposition of fine matter (Claessens et al 2011;Vianello et al 2013;Haave et al 2019;Maes et al 2017).…”

“…Published data also indicate that a higher proportion of the dense polymers will be represented in such sediments, and that lightweight particles are more likely to remain in circulation and/or distribute in surface waters further from the sources, and that considerable amounts may this way be released to the ocean without settling (Clayer et al 2021;Liu et al 2019a).…”

“…Microplastic-contaminated sludge thus reintroduces microplastics to terrestrial ecosystems, potentially leading to build up in soils (Nizzetto et al 2016). The potential for redistribution from soil to waterways, groundwater, and air is also present when microplastic-polluted sewage sludge is applied as fertilizer on land (Clayer et al 2021) (Fig. 1).…”

The power of multi-matrix monitoring in the Pan-Arctic region: plastics in water and sediment

“…Grab sampling can be appropriate at sites of high sedimentation or at heavily bioturbated sites if the sediment surface is clearly distinguishable. In areas of very low sedimentation, surficial sediment may capture the total history of microplastic deposition at a site (Martin et al, 2017;Clayer et al, 2021). Routine monitoring for other pollutants (i.e., organic contaminants and metals) has been successfully carried out for recent marine sediment deposits.…”