Distribution of microplastic colour and count in the Crocodile River, South Africa

Sammanfattning: The aim of this paper was to establish sources for microplastic fibres and fragments based on the presence of specific colours (I) within different land use classes and (II) in relation to the location of wastewater treatment plants. Most of the colours did not result in significantly different counts between the land use classes, except for black fragments, which resulted in significantly higher counts in urban environments compared to natural environments. Since sampling was conducted in the rainy season, run-off from roads that introduces tyre wear in the form of black fragments to the river systems can be assumed to be a source for microplastic pollution that has been previously mentioned in papers, but not yet investigated. Other colours showed a similar pattern as black fragments but did not result in significantly different counts between the land use classes, indicating that with more sampling points these patterns could become statistically significant. The location of wastewater treatment plants did not influence colour counts, most likely due to the spatial distribution of sampling points, which were not positioned adequately for this testing. Further research is needed on the influence of river dynamics on the amounts of microplastics sampled on the sides of the river/at the centre of the channel, as well as investigations into emission of microplastics from sewage sludge, which has been applied to agricultural fields.