Microplastics in Namibian river sediments – a first evaluation

The African continent is rarely the focus of microplastics research, although the ubiquity of microplastics in the environment is undisputed and still increasing. Due to the high production and use of plastic products and the partial lack of recycling systems in many parts of the African continent, it can be assumed that microplastic particles are already present in limnic and terrestrial ecosystems. Few studies, mainly from South Africa and the Northern African region, show a contamination with microplastics, especially in marine environments. This study aims to explore the presence and composition of microplastics in fluvial sediments of the major catchments in Namibia with a regional focus on the Iishana system in Northern Namibia, as one of the most densely populated areas in the country. In March 2019 and March 2021, at the end of the rainy seasons, sediments from the Iishana system and of the largest river catchments were sampled. Extraction was performed by density separation using the Microplastic Sediment Separator (MPSS) with the separation solution sodium chloride (density of 1.20 g/cm3). The particle size was determined by filtration and fractionation, and the polymer type by measurement with ATR-FTIR spectroscopy (minimum particle size 0.3 mm). Microplastics were found in the sediments of each river system, most of the particles in the Iishana system (average of 13.2 particles/kg dry weight). The perennial, the ephemeral rivers, and the Iishana system are similar concerning polymer type and particle size. Polyethylene and polypropylene were the dominant polymer types. Most of the particles were found in the size fractions 0.3 – 0.5 mm and 0.5 – 1.0 mm. The particles were found mainly as fragments and films, the majority transparent and brown

Evaluating the effectiveness of the MicroPlastic Sediment Separator (MPSS)

Abstract Effective laboratory methods are a requirement to obtain accurate data on the contamination of the environment with microplastics. However, current methods often lack specification and validation of performance. The aim of this work was to provide the first evaluation of the effectiveness of the commercially available MicroPlastic Sediment Separator (MPSS) operated with sodium chloride. We performed density separation experiments with pristine plastic particles spiked into both commercial sand (experiment I) and natural river sediments (experiment II) and with environmental microplastics contained in natural river sediments (experiment III). The natural sediments were taken from the Lahn River in Germany, a medium-scale central European tributary. The pristine test particles were ground polypropylene fragments, sieved in three different size classes: larger than 1 mm, 0.5–1 mm, and 0.3–0.5 mm. In experiment I, the mean recovery rate was 97 % for particles of the largest size class (standard deviation $$s=6~\%$$ s = 6 % ; $$n=30$$ n = 30 per size class), but dropped to 75.33 % ( $$s=21.29~\%$$ s = 21.29 % ) in the medium and to 54 % ( $$s=25~\%$$ s = 25 % ) in the smallest size class. After density separation, 87 % of all unsuccessfully separated test particles were found at the inner walls of the MPSS. In experiment II, the recovery rate was not correlated with the particle size distribution of the natural river sediments. In experiment III, a subsequent second density separation step contributed on average 38 % ( $$s=18~\%$$ s = 18 % ; $$n=5$$ n = 5 ) to the total number of extracted environmental microplastics. This study illuminates central aspects of a density separation and aims to contribute to quality improvements of recovery rate experiments and field studies for the generation of reliable data on microplastics in the environment

Characterizing Ferroelectricity with an Atomic Force Microscopy: An All-Around Technique

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