Co-Contamination and Combined Effects of Microplastic and Microbial Load on Water Quality and Public Health Risks in Industrial and Urban Canals of Coastal Bangladesh

Microplastic pollution and microbial contamination are increasingly recognized as interconnected threats to freshwater quality and public health, yet their co-occurrence and interactions in coastal freshwater systems of developing regions remain poorly understood. To address this gap, microplastic characteristics, health risks, and microbial indicators including Escherichia coli , fecal coliforms, and total plate counts were assessed across industrial and urban sectors of a coastal freshwater canal in Bangladesh used for drinking, irrigation, and domestic purposes. Microplastic concentrations ranged from 0.45 to 0.93 items/L, with significantly higher levels in the industrial zone, where fibers (46%) predominated, and over 98% of MPs were <0.5 mm in size, indicating advanced degradation. Microbial loads exceeded WHO limits, with E. coli reaching 3,433 CFU/100 mL and fecal coliforms up to 4,033 CFU/100 mL, classifying the canal water as high-risk. Strong correlations between MP characteristics (type, color, size) and microbial loads, as revealed by correlation and PCA analyses, suggest that MPs serve as substrates for microbial growth. Pollution indices (PLI: 1.78 industrial vs. 1.19 urban) confirmed significant microplastic contamination. These elevated MP concentrations and microbial loads, exceeding WHO thresholds, significantly degrade water quality and pose severe human health risks, underscoring the compounded environmental and public health hazards associated with MP-microbial interactions. The results highlighted the urgent need for integrated wastewater management and pollution mitigation strategies in coastal Bangladesh.