Chemical and Optical Profiling of Textile Effluents and Associated Heavy Metal Risks in Bangladesh

Textile wet-processing generates wastewater containing salts, dyes, organic pollutants, and heavy metals. This study evaluated treated textile effluents using a combined approach based on physicochemical parameters, heavy metal concentrations, pollution indices, and dissolved organic matter (DOM) optical characteristics. Eleven final-effluent samples were collected from textile factories in major industrial areas of Bangladesh. The average pH (7.60 ± 0.37), dissolved oxygen (6.95 ± 1.29 mg/L), and biochemical oxygen demand (19.09 ± 4.74 mg/L) were generally within permissible limits. In contrast, total dissolved solids (1553.27 ± 1042.17 mg/L), chemical oxygen demand (207.90 ± 348.20 mg/L), and conductivity (2318 ± 1554.97 μS/cm) exceeded several national and international discharge standards. Heavy metals followed the order Fe > Ag > Mn > Cu > Cr > Ni > Li. Pollution indices identified F-05, F-06, and F-11 as important contamination hotspots, while F-06 and F-11 showed the highest metal-related risk. DOM fluorescence also showed clear differences among factories, reflecting variations in treatment conditions and industrial inputs. The combined analysis helped distinguish salt-rich, metal-rich, and DOM-dominated residual effluent profiles. Spearman correlation analysis showed strong positive relationships among TDS, conductivity, and salinity (ρ ≥ 0.998, q < 0.001), while HIX and BIX were strongly negatively correlated (ρ = −0.918, q = 0.002). These patterns show that residual pollution was not controlled by a single water-quality parameter alone. The results show that textile effluent quality varied considerably among factories, highlighting the need for site-specific ETP improvement, better monitoring, and targeted control of salts, organic matter, and metals.