Microplastics Depth-Dependent Distribution, Color Variability and Shape Composition in Dar es Salaam Beach Sediments

Microplastics (MPs) are persistent and accumulate in marine sediments, while burial in beach sediments remains poorly understood, particularly in East Africa. . This study examined the vertical distribution of MPs in beach sediments of Dar es Salaam, Tanzania, at depth 10, 20, 30, and 40 cmfrom beaches: Kunduchi (KD), Kijichi (KJ), Selander Bridge (SL), and Coco Beach (CB) with varying anthropogenic activity. MPs (0.05-2 mm) were extracted using ZnCl2 (1.5 g cm−3) and charecterized visually by shape and colour. Pooled particles were screened by Fourier-transform infrared (FTIR) spectroscopy. Results indicated that MP concentrations were higher at KD from 10 to 30 cm (333 to 893 particles/kg) and differed significantly among sites (p < .05), but were comparable at 40 cm (p > .05). MP concentrations decreased moderately with depth (r = −0.445, p < .001). Blue and black MPs dominated across sites and depths (6 to 40%), with fibers (45 to 82%) and fragments (18 to 71%) the most persistent shapes. The pollution load index was higher at KD (2.15), followed by SL (1.37), KJ (1.34), and CB (0.93). Collectively, the results indicate that MPs are buried within the sediment profile highlighting ecological and remobilization concerns. Future work should include individual-particle polymer identification, organic matter digestion, and sediment dating.