Long-term monitoring of heavy metals and physicochemical characteristics in leachate-affected waters of Upper Lake, Bhopal

Rapid urban growth in India has led to a surge in construction and demolition (C&D) waste, much of which is disposed of without regulated management. In Bhopal, Madhya Pradesh, unauthorized dumping near the shoreline of the Upper Lake a primary source of potable water poses a severe risk of leachate contamination. This study investigated the hydro-chemical impact of C&D waste through a year-long monitoring program across georeferenced impact sites. Data were evaluated using descriptive statistics, one-way ANOVA, and Pearson correlation, while Principal Component Analysis (PCA) was employed to identify dominant pollution sources and the "Source-to-Impact" pathway. The results reveal an environment under acute anthropogenic stress, with a singular "C&D Impact Factor" (PC1) explaining over 99% of the total variance in both physicochemical and heavy metal datasets. Critical physicochemical shifts included extreme alkalization (pH: 8.5-11.5; Mean: 10.0), elevated turbidity (100.07-399.93 NTU), and high Total Dissolved Solids (500.17-1199.83 mg/L). High BOD levels (8.01-49.99 mg/L) coincided with a significant decline in Dissolved Oxygen, indicating a shift toward a hypoxic state (r = -0.988). Hazardous heavy metals, including Aluminum (0.5-1.5 mg/L), Lead (0.025-0.045 mg/L), and Chromium (0.050-0.100 mg/L), exhibited perfect synchronization with structural minerals (Ca, Mg), confirming a unified leaching mechanism from cementitious debris. Mechanistic interpretation suggests that hyper-alkaline conditions facilitate the mobilization of amphoteric metals and the degradation of sequestering gels. These findings highlight substantial ecological risks and long-term bioaccumulation threats, emphasizing the urgent need for strict C&D waste regulatory enforcement and sustainable water resource management to preserve the integrity of urban freshwater ecosystems.