Comprehensive monitoring of the spatiotemporal variation of water quality and its associated human health risks in Luvuvhu river catchment, Vhembe biosphere reserve, South Africa

This study investigates the spatiotemporal variations in water quality and assesses the associated human health risks in the Luvuvhu River Catchment (LRC), South Africa. Water quality parameters such as pH, total dissolved solids (TDS), turbidity, temperature, dissolved oxygen (DO), salinity, biological oxygen demand (BOD), chemical oxygen demand (COD), electrical conductivity (EC), nitrate (NO₃⁻), chloride (Cl-), sulphate (SO₄²-), and phosphate (PO₄³⁻) and potentially toxic elements (PTEs) (arsenic, lead, iron, zinc, aluminium, chromium, manganese, cadmium, barium, cobalt, copper, molybdenum, mercury, nickel) were measured across multiple sites during both wet and dry seasons. Seasonal variations using Mann-Whitney U test showed higher pollution levels during the wet season, attributed to increased runoff carrying fertilizers, pesticides, and waste into the river system. Samples were analysed for trace metals levels using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometer" (ICP-MS). The spatial distribution analysis using Inverse Distance Weighting (IDW) technique and temporal analysis highlights the cumulative impact of anthropogenic activities on water quality in the LRC. The Water Quality Index (WQI) was employed to synthesize these data into a single value representing overall water quality, revealing significant degradation downstream (387.48-1357.86) due to domestic discharge, agricultural runoff, and semi-industrial pollution. A human health risk assessment was conducted focusing on two primary exposure pathways: ingestion and dermal absorption. Results indicated that ingestion posed a greater non-carcinogenic risk than dermal exposure, especially for adults (2.43 × 10^-9 - 3.41 × 10^-5) who consume more water daily than children (7.26 × 10^-9 - 1.02 × 10^-5). On the other hand, ingestion exposure for cancer risks ranged from 2.26 × 10⁻¹¹ to 1.12 × 10⁻⁸ for adults and 4.78 × 10⁻¹⁴ to 1.18 × 10⁻¹² for children, with arsenic contributing the highest risk. PTEs like manganese (30.26-169.32 µg/L), molybdenum (0.08-0.43 µg/L), and iron (0.64-2.48 mg/L) exhibited the highest Chronic Daily Intake (CDI) values, raising concerns for long-term exposure. Lead (0.30-1.84 µg/L) and arsenic (0.11-0.43 µg/L), both known neurotoxicants and potential carcinogens, were also detected, highlighting risks particularly in vulnerable populations despite concentrations being below some regulatory thresholds. These findings emphasize the need for improved water management strategies and pollution control measures in the LRC to safeguard both human health and the aquatic environment. Future studies should prioritize the integration of advanced computational approaches, such as machine learning (ML) and artificial intelligence (AI), to enhance predictive modeling and real-time monitoring of water quality in the Luvuvhu River Catchment.