Microplastic Pollution Along the Kenya Coast in the Western Indian Ocean (Wio), Region

Abstract

Plastics enter the ocean inform of either large debris or microplastics that are a product of breakdown from the large debris or are primarily microplastics such as beads used in beauty products. Plastic pollution impacts in oceans are remarkable world over. Microplastics (MPs) are tiny plastic particles measuring between 0.1μm and 5000 μm, make an important part of plastic pollution and form a pathway to the aquatic food web including humans. Consuming contaminated fish may transfer MPs additives into humans and being endocrine disruptors, the additives can cause cancers, brain tumours and many developmental disorders. And although this is a global problem, there are limited studies along the Kenyan Coast in the Western Indian Ocean (WIO). This study looked at MPs in the surface waters, sediments and fish within three sites (Tudor, Port Reitz and Mida Creeks) that were sampled in January/February and September 2018. Microplastic samples from surface water were collected by towing neuston nets of 500 μm (large) and 250 μm (medium) mesh sizes and sieving 50 litres of seawater through a 20 μm net (small) size. Sediment samples were collected from the intertidal zone using a 3.6 cm diameter corer up to 10 cm deep. Fish were obtained from fishermen on site and local landing beaches. Samples were digested in 10 % Potassium Hydroxide and, microplastics extracted by Thompson’s improved density separation protocol using super saturated Sodium Chloride (NaCl) solution (1.2g cm-3) pre-filtered over 0.8 μm membrane. Total concentrations of MPs in both water and sediments, was highest in Tudor Creek followed by Port-Reitz and finally Mida. In the water column the smallest MPs (20-250μm) recorded the highest concentration while in the sediments, MPs of the large size (500-4999 μm) were the most abundant. In fish, MPs concentration was highest in demersal fish followed by pelagic fish and in both types, omnivores recorded highest MPs concentrations followed by carnivores and finally grazers. Polyethylene (PE) polymers were the most abundant (63.9 %), followed by polypropylene (PP) (27%), while 9.1 % were unknown. Based on the results, it can be concluded that the marine surface water, sediments and fish along the Kenya coast are polluted with MPs. Although fish are economically important as human food, there is a high risk of transferring MPs in their tissues into humans where MPs additives may cause endocrine disruption, cancers, reproductive and growth and development disorders. The results demonstrate the extent of exposure to the MPs of the region’s ecosystems and provides the impetus for policy development regarding the management and disposal of plastic waste to protect and save oceans rich in biodiversity for sustainable development. Fish gutting and removal of gills regardless of size during preparation is recommended in order to reduce the possible consumption of MPs from fish guts and gills. Bulky sampling of all the three MPs sizes to increase estimation accuracy is recommended for future monitoring programs.