Characteristics and pollution risks of microplastics in coastal invertebrates adjacent to stormwater outlets of Cape Town

Stormwater runoff in coastal cities are potential sources of microplastics in coastal ecosystems. The abundance and risks of microplastics (MPs) at stormwater pipes in Cape Town is poorly understood. This study aim was to identify if stormwater outlets are sources of microplastics (MPs) to the coast, and if present, whether MPs pose ecological risks to coastal invertebrates. The study compared MPs adjacent to stormwater outlets at Camps Bay, Mouille Point and Three Anchor Bay (Cape Town, South Africa), each with a control site. Microplastics were extracted from biota at intertidal and subtidal sites at each location, counted and categorised based on shape, polymer type, colour and size. Seasonal (wet and dry) abundances of MPs (MPs/individual and MPs/g tissue wet weight) were measured in mussels (Mytilus galloprovincialis), sea urchins (Parechinus angulosus) and whelks (Burnupena sp.) and were higher in the dry season at intertidal impact sites. For all invertebrates, MPs were mainly fibres, dark (black/blue) and 0.5 to 2 mm in length. Polymer type recorded in invertebrates were mainly polyester and cotton blends (fibres). Risk indices (Pollution Load Index, Polymer Risk Index, Pollution Risk Index and Condition Index) were higher (lower for Condition Index) in invertebrates during the dry season at stormwater outlets than during the wet season at control sites. The high prevalence of cotton fibre blends (mixture of cotton and polyester) suggests that stormwater outlets are potential pathways for textile fibres from laundry activities to enter the coastal environment of Cape Town, South Africa. Also see: https://micro2024.sciencesconf.org/546889/document