ENVIRONMENTAL CONCENTRATIONS OF MICROPLASTICS IN SURFACE WATER, SEDIMENTS AND BIOTA IN EAST AFRICAN MARINE WATERS

Abstract

The prevalence of microplastics (MPs) in East African marine waters was investigated across the abiotic and biotic compartments. Sampling was conducted offshore within Kenya’s exclusive economic zone (EEZ) and nearshore around Zanzibar Island; and a long Kenyan and Tanzania mainland coastlines. A 15L stainless steel bucket and manta net of 300 μm mesh size were used to collect 120 L and three samples per site from EEZ and nearshore surface waters, respectively. Ekman sediment grab was used to collect three nearshore sediment samples per site. Zooplankton groups were collected once per site using a 500-μm mesh size net. The surface waters, sediments and zooplankton samples were preserved in 70%, 96% and 70%, respectively. At least 20 individuals of fish per site were purchased from fishermen and stored in a cool box with ice bags. All surface water samples were sorted directly under a dissecting microscope. MPs in sediments were extracted using density separation, while zooplankton and fish gastrointestinal tracts (GITs) were digested in 1M NaOH and 10% KOH, respectively. The sediment extracts; and zooplankton and GIT digests were vacuum filtered through 0.7 μm GF/C filter papers then sorted under a dissecting microscope. Polymer identifications in the various sample matrices were performed using Attenuated Total Reflectance-Transform Infrared Spectroscopy (ATR-FTIR) and micro (μ)-FTIR. Concentration of MPs in Kenya’s EEZ and the entire East African nearshore surface waters were in the ranges of 33 – 275 particles m–3 and 0 – 6.31 particles m-3, respectively. MPs in nearshore seabed sediments were in the range of 33 to 397 particles kg-1 dry weight (DW). Average concentrations of MPs (individual-1) in the zooplankton groups, L. harak and S. sutor were: 3.98 ± 1.74, 0.99 ± 0.59 and 0.13±0.04, respectively. Filaments/fibers were dominant (76%) in EEZ surface water, while fragments (63%) were common in nearshore surface waters. Sediments, zooplankton and fish species were dominated by fibers/filaments. White coloured MPs were the most common in surface vi waters, while black were dominant in sediments, zooplankton and fish species. Polyethylene (PP) and polypropylenes (PEs) dominated surface waters and zooplankton groups, with naturally occurring polymers dominating in sediments and fish species, respectively.