A Methodology for Measuring Microplastic Transport in Large or Medium Rivers

Abstract

Plastic waste as a persistent contaminant of our environment is a matter of increasing concern due to the largely unknown long-term effects on biota. Although freshwater systems are known to be the transport paths of plastic debris to the ocean, most research has been focused on marine environments. In recent years, freshwater studies have advanced rapidly, but they rarely address the spatial distribution of plastic debris in the water column. A methodology for measuring microplastic transport at various depths that is applicable to medium and large rivers is needed. We present a new methodology offering the possibility of measuring microplastic transport at different depths of verticals that are distributed within a profile. The net-based device is robust and can be applied at high flow velocities and discharges. Nets with different sizes (41 µm, 250 µm, and 500 µm) are exposed in three different depths of the water column. The methodology was tested in the Austrian Danube River, showing a high heterogeneity of microplastic concentrations within one cross section. Due to turbulent mixing, the different densities of the polymers, aggregation, and the growth of biofilms, plastic transport cannot be limited to the surface layer of a river, and must be examined within the whole water column as for suspended sediments. These results imply that multipoint measurements are required for obtaining the spatial distribution of plastic concentration and are therefore a prerequisite for calculating the passing transport. The analysis of filtration efficiency and side-by-side measurements with different mesh sizes showed that 500 µm nets led to optimal results.

Knowledge about Microplastic in Mediterranean Tributary River Ecosystems: Lack of Data and Research Needs on Such a Crucial Marine Pollution Source

“…A thorough examination of scientific literature on abundance, distribution patterns, and characteristics of microplastics in freshwater environments in Mediterranean tributary rivers has shown a substantial lack of information and the need to apply adequate and uniform measurement methods.have shown that MPs are present in different layers of the river-bed and of the water column (e.g. [20] or [21]). Classified according to the annual discharge, the ten largest Mediterranean tributary rivers are the Rhone, Po, Drin-Bojana, Nile, Neretva, Ebro, Tiber, Adige, Seyhan, and Ceyhan.…”

“…have shown that MPs are present in different layers of the river-bed and of the water column (e.g. [20] or [21]).…”

Small Microplastic Sampling in Water: Development of an Encapsulated Filtration Device

“…Costs are denoted as relative estimates ranging from "+" (lowest costs) to "+++" highest costs as actual costs may vary depending on supplier and chosen design specifics. References of method application [10,11], present study [2][3][4][5][6][7][8] [12] * = high density polymers (i.e., denser than water); ** = low density polymers (i.e., lighter than water).…”

“…If a lower sample volume is acceptable or if longer filter cartridges are used and operated separately, the system seems suitable for streamlined sampling of replicates, e.g., in short time intervals or at different positions at the same location. A recent study on MP monitoring underpinned the importance of replicated sampling throughout a river cross-section [5]. This is just one possible modification to adapt the system to specific sampling scenarios and we encourage others to contact us for requests or comments and to replicate or improve upon the suggested design.…”

“…These include, foremost, Manta trawls [1] that skim a film of surface water of constant depth for floating matter and retain the mesh-size-defined particulate filtrate in a cod-end [2][3][4]. Bongo nets, WP-2 nets, as well as special constructions for layered profiling have been applied alike [5][6][7][8]. Single or staggered open sieve constructions, as well as encapsulated flow-through filtration devices are approaches that have been utilised by other studies [9][10][11].…”