Microplastic distribution in the surface water and potential fish uptake in an oligotrophic lake (Lake Mainit,...

Analyzing microplastic distribution patterns in freshwater ecosystems provides critical insights into pollution sources and accumulation zones, contributing to ecosystem health and functioning. Here, the surface water of Lake Mainit, an oligotrophic body of water in the Philippines, and the potential ingestion by Glossogobius giuris (15), a local fish species inhabiting the lake, were investigated. The surface water samples collected in ten sampling sites revealed an average microplastic concentration of 313.33 ± 252.11 particles/m³, with elevated levels in the northern part of the lake, likely due to adjacent industrial and agricultural activities. Fibers were the predominant microplastic morphology (58 %), with polyamide (28 %) as the most common polymer found in the surface water, suggesting primary sources from textiles and household waste. Size analysis showed that particles under 100 μm in size were most abundant, posing increased ingestion risks for aquatic organisms. All examined fish samples contained microplastics, averaging 0.7 particles per fish, primarily from the smallest particle class, indicating a potential risk of bioaccumulation. Risk assessment using the Polymer Hazard Index (PHI) and Pollution Load Index (PLI) indicated that polyvinyl chloride (PVC) and polyamide (PA) pose moderate to high pollution risks due to their persistence and toxicity potential. The PERI value for Lake Mainit was 34.63, classifying it as a minor risk. While current contamination levels are low, continued monitoring is essential to prevent future ecological risks. These results highlight the ecological threat of microplastics in Lake Mainit, with implications for biodiversity and human health, as the lake is an important local food source. To mitigate these risks, stricter pollution control, enhanced waste management, and public awareness initiatives are recommended. This study presents foundational data on microplastic pollution in an oligotrophic Philippine lake, emphasizing the need for further research to support protective management strategies.