(340f) Fate and Prevalence of Microplastic in Biotic and Abiotic Ecosystems of Natural Freshwater: A Case Study of Jhapa Lake, Bangladesh

Microplastics (MPs) are a growing concern for human civilization due to the increasing annual production of plastic waste. To date, microplastic research has primarily focused on marine environments, followed by freshwater systems, as the concentration of microplastics (MPs) is significantly higher in these systems. To understand the fate and prevalence of MPs in natural lakes, a comprehensive study was conducted by collecting samples of fish, water, plankton, and sediment. Influencing factors, including seasonal variation, fish habitat, areas prone to human activity, and water depth, were considered in the study. In the study, a total of 34 fish belonging to 11 species were dissected and processed. Twelve sediment samples were collected from three different water depths: (I) 0-2 m, (II) 2-5 m, and (III) greater than 5 m. Ten surface water samples were collected from five different regions of the lake during both the dry and monsoon seasons, taking into account human localization and activities. Zooplankton studies were conducted to investigate the potential transport of microplastics via biotic pathways.

The collected samples were processed using iron-peroxide oxidation to remove organic matter and density separation using NaCl and ZnCl₂ solutions. The size, shape, color, and abundance of MPs in respective samples were determined by digital microscopy and SEM-EDS. Based on the detected MPs, it is found that fiber shape represents 31-50%, transparent represents 32-42%, and particles sized 100-1000 µm represent 59-74% of the MPs in the case of shape, color, and size, respectively. The ATR-FTIR analysis of 50 MPs was conducted to determine the respective plastic types. Polyethylene (66.2%) and Polypropylene (14.3%) are the two dominant plastic types in the lake. However, highly toxic plastics, such as PVC and PPS, were also found among the recovered microplastics. Ecological risk was evaluated using the polymer hazard index (PHI), and the calculated value fell into hazard level IV.

The MPs in surface water, including seasonal variations and collection regions, suggest that stormwater runoff and human activities are two main factors behind MPs transport. The MPs concentration in the sediment, almost double the MPs/Kg was determined in sediments ranging from 0-2 m to greater than 5 m water depth, suggesting that gravity settling and water flow occurring towards higher water depth levels may be the driving force behind the accumulation of MPs. The presence of MPs in plankton and fish emphasized the spread of MP pollution into diverse biotics. The project's findings suggest the severity of MP contamination in a natural lake of a least developed country, such as Bangladesh, and highlight the potential health risk posed to human health through the likely consumption of lake fish.