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Microplastics in aquaculture ponds of Bangladesh: Source attribution, pollution load, and ecological risk assessment
Summary
A survey of aquaculture ponds in Bangladesh's Jashore district found significant microplastic contamination in both surface water and sediments, with fibers and fragments being the dominant forms and polyethylene the most common polymer. The study identifies aquaculture ponds as underappreciated microplastic sinks that may pose risks to farmed fish and ultimately to people who eat them. Given Bangladesh's heavy reliance on pond aquaculture for food security, the findings raise important concerns about the safety of locally farmed seafood.
Microplastics (MPs) have emerged as a global pollutant of concern due to their persistence and ecological impacts in aquatic environments. Yet, their effects on freshwater aquaculture environments in Bangladesh remain largely uncharted, especially for aquaculture ponds. Therefore, this study explores the occurrence, distribution, characterization, and potential risks of MPs in surface water and sediment samples from aquaculture ponds in Jashore district, Bangladesh. A total of 64 paired water and sediment samples were processed using a standard procedure, including wet peroxide oxidation, density separation, and optical microscopy. Polymer types were confirmed using Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR). The analysis revealed significant MPs concentration averaging 2533.00 ± 311.00 MPs/kg dw in sediments and 219.69 ± 100.27 MPs/L in surface water, with considerable diversity. The dominant features of identified MPs were fibers (water = 85.37%; sediment = 75.97%), size ranges for water: 58.29% of MPs were >0.1 mm; for sediment, 34.85% were in the 0.1-0.5 mm range; and a predominantly black color. Seven polymer types were identified, with polyethene (PE) accounting for the highest proportions-47% in sediments and 41% in water, respectively. Multivariate analysis identified domestic wastewater, aquaculture processes, and feed additives as key sources of pollution. Risk assessments, including the Pollution Load Index (PLI > 1) and Nemerow Pollution Index (NPI), indicated high levels of contamination. Moderate (Grade II) to considerable (Grade III) risks were identified from the polymeric hazard index. In contrast, the MPs-polymer-based ecological risk assessment indicates environmental risks ranging from low (Grade I) to very high (Grade V) for the study area's aquaculture ponds. This study offers critical insights into the prevalence of MPs in Bangladeshi aquaculture systems. It emphasizes the pressing need for targeted mitigation to safeguard freshwater ecosystems and ensure sustainable aquaculture practices.