Abundance and characteristics of microplastics in major urban lakes of Dhaka, Bangladesh

Abstract

Microplastics (MPs) are prevalent in nature due to the proliferation of plastic in the environment. However, the presence of microplastics in lakes is largely unknown in comparison to other aquatic bodies. This study was performed to evaluate the abundance and characteristics of MPs in water, sediment, and fish from three major urban lakes in Dhaka, Bangladesh, namely Dhanmondi, Gulshan, and Hatir Jheel lake. The highest concentrations of microplastics in surface water (36 items/L), sediment (67 items/kg), fish (17 items/individual), and the gastrointestinal tract (4.88 items/gm) were observed. Highest abundance of microplastic in an individual fish was observed in Oreochromis mossambicus from Dhanmondi Lake. The samples were visually examined using stereomicroscope and SEM, which revealed that films were the most prevalent kind of microplastics in both the water and the sediment samples, whereas pellets and foams predominated in the fish samples. Visual observation also revealed MPs dominated by <100 μm in size and transparent in color. According to the Fourier Transform Infrared (FTIR) analysis, the dominant polymers in the analyzed samples were high-density polyethylene, low-density polyethylene, ethylene vinyl acetate, polyvinyl chloride, polycarbonate, cellulose acetate, and polypropylene. MPs were relatively higher in the water and sediment samples of Gulshan Lake, and fish samples of Dhanmondi Lake. The results of this study indicate that microplastic contamination has occurred not only in the water and sediment but also in the inhabitant fishes of the lakes. However, it is discovered that the microplastic intake of fish was significantly related to body weight and length. The implication of the finding suggests that the presence of MPs in urban lakes has raised concerns about the potential human health impact.

Keywords: FTIR; Freshwater ecosystem; Oreochromis mossambicus; Polymer; Sediment; Water.

Graphical abstract

Fig. 1

Location of sampling areas (Dhanmondi Lake, Gulshan Lake, Hatir Jheel Lake) and different color dots represent sampling sites of each lake.

Fig. 2

Visual identification of microplastic particles under stereomicroscope (40X); grouped into five categories: (a) Fiber (uniform plastic strands); (b) Fiber (fibrous); (c) Fragments (hard); (d) Fragments (jagged-edged); (e) Pellets (hard, rounded particles); (f) Films (2-dimensional plastic films) (g) Foam (Styrofoam material). The black bar on the lower left corner of each picture indicates a 200 μm scale.

Fig. 3

Abundance of detected microplastics in (a) surface water, (b) sediment, (c) fish gut, (d) individual fish samples and (e) distribution by the percentage of microplastics in samples from all sites.

Fig. 4

Size and color composition of detected microplastics in water (a, b), sediment (c, d), and fish (e, f) of urban lakes.

Fig. 5

Microplastic surface morphology under a Scanning Electron Microscope (SEM). SEM images of a) fiber (water) under 5KX magnification, b) fiber (fish) under 1KX magnification, c) fragment (sediment) under 5KX magnification.

Fig. 6

Correlation of MPs abundance with weight and length of fish species.

Fig. 7

IR spectrum of the most prevalent type of MPs found in Urban Lakes. The representative particles showing significant adsorption bands of a) HDPE, b) LDPE, c) PVC, d) PC, e) PP, f) CA, and g) EVA.