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The microplastic profile of an urban African stream
Summary
Microplastics were detected in water, sediment, and chironomid larvae in the Braamfontein Spruit urban stream in Johannesburg, South Africa, with weirs and areas of reduced flow increasing local accumulation in sediment and invertebrates. The study demonstrates that urban stream features can concentrate microplastics and increase exposure for benthic organisms.
Microplastics are small plastic fragments that have been found around the world, however, research into microplastics in Africa and freshwater systems remains insufficient. In this study, the snapshot microplastic profile of an urban stream was assessed in the Braamfontein Spruit, located in Johannesburg the largest city in South Africa. The abundance of microplastics was determined in water, Chironomus sp. larvae and sediment, while in situ parameters were taken to investigate their relationship to the microplastic profile of the different matrices. Microplastics were detected in water (mean of 705 particles m-), Chironomus sp. larvae (mean of 53.4 particles g- wet weight) and sediment (mean of 166.8 particles kg- dry weight). The study found evidence of how urban stream characteristics such as a weir, stream depth and velocity could affect the abundance and dispersion of microplastics. The results indicate that areas of increased depth and decreased flow allowed microplastics to settle down to the sediment where benthic macroinvertebrates could ingest these fragments. Large obstructions like a weir also increased microplastic counts in sediment and invertebrates above the obstruction, with a decrease of fragments after the obstruction, however, microplastics in surface water were able to flow over the obstruction and increase in abundance downstream. This study concludes that first order urban streams such as the Braamfontein Spruit may be contributing large numbers of microplastics to higher order streams and large rivers in times of increased flow.
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