Tiny and Everywhere: Microplastic Density and Distribution in Sediments along the West Coast of Lombok Island, Indonesia

Microplastics have recently received high global attention, as their widespread presence can potentially cause physical and toxicological risks to organisms. The west coast of Lombok Island in Indonesia has a high potential for microplastic accumulation; even so, its presence in this area was not well studied. Therefore, this study aimed to describe the distribution and density of microplastics within the sediments on the west coast of Lombok. Microplastic sampling had been carried out in the northern, middle, and southern portions of the west coast of Lombok based on distinct geographical and vegetational characteristics. Sediment samples were taken within the HTL (High Tide Line) zone based on the excavation depths categories, i.e. A (0–2cm), B (2–4 cm), C (4–6 cm), D (6–8 cm), and D (8–10 cm). The sediment samples were filtered using an aluminum sieve with a mesh size of 4.75 mm, targeting microplastic pieces below that size. A total of 16,685 microplastic debris were found distributed horizontally and vertically throughout the station. There was a significant difference in the microplastic density distributed between stations [F(10,22) = 6.96, p < 0.001] and between sediment depths [F(10,44) = 9.07,p < 0.001]. The order of average microplastic concentration was southern > northern > middle stations group. The highest microplastic number recorded in SMP11 (southern station, open bay, high anthropogenic activity, with river and primary mangrove vegetation) was as many as 2,361 (density, D = 125,920.00 ± 204.33 items/m3), whereas SMP01 (northern station, open bay, low anthropogenic activity, and with river and secondary mangrove vegetation) had the lowest microplastic number of 678 (D = 36,160.00 ± 72.82 items/m3). In general, the majority of microplastics (45.76%) were distributed on the sediment surface (A–B), where there was a repeating pattern in the difference of microplastic density fluctuations of about 3% at every 4cm of sediment depth (B–C and D–E), which is thought to be driven by daily tidal fluctuation.There was no clear pattern that indicated whether the specific type of shoreline or the presence of rivers and mangroves had an influence on the level of microplastic accumulation. However,the southern stations group had a considerably higher average of microplastic accumulation.We suspect that the geographical position towards the main ocean current contributes greatly to the microplastic accumulation at the site.