Abundance, characteristics, and risk assessment of microplastics in echinoderms along the Western Cape coastline, South Africa

Microplastics (MPs) are prevalent in coastal environments of South Africa but there is a lack of knowledge about the prevalence and risks of MPs in coastal invertebrates. This study aimed to determine the prevalence, characteristics and ecological risks of MPs ingested by various echinoderm feeding groups. Sampling was conducted during low tide in the summer of 2020 at 14 rocky shores in the Western Cape of South Africa. By sampling various echinoderm feeding types, the abundance and characteristics of MPs (shape, colour, size by using microscopy and polymer type by using a Fourier-transform infrared spectroscopy (FTIR-ATR)) were measured. Potential ecological risks posed by MPs were assessed using hazards of respective polymer types. Mean abundance of MPs from all echinoderms was 9.32 (± 0.76 Standard Error of the Mean (SEM)) MPs/Individual, or based on weight, 1.11 (± 0.09 MPs/g soft tissue wet weight). The abundance of MPs was highest in echinoderms sampled from Kalk Bay (56.41 ± 4.37 MPs/I), with storm water outfall pipes and human activities identified as primary source of MP contamination. Filter-feeding sea cucumbers had the highest MP abundance (21.06 ± 3.03 MPs/I), suggesting that non-selective feeding echinoderms have higher MP uptake rates than other feeding strategy echinoderms. The MPs in echinoderms were mainly black/grey (45%) polyethylene terephthalate (PET) (50%) fibres (93%) that ranged from 1000 to 2000 μm (35%) in size. The potential ecological risk of MPs was highest at Kalk Bay (site 9) due to the prevalence low abundances of Polyvinyl chloride (PVC). This is the first study on MPs in coastal echinoderms of the Western Cape in South Africa and provides a baseline for MPs in echinoderms. The findings are significant because they offer the first indication that MP abundance may differ between echinoderm feeding groups.