Freshwater contamination from industrial effluent discharge: heavy metal mobilisation, water quality degradation and probabilistic health risk assessment

Context Marble-processing facilities generate slurry-containing wastewater that may mobilise toxic metals through equipment wear, mineral dissolution and the use of polishing materials. Evidence on the combined pollution burden and probabilistic health risks associated with marble-processing effluent in Pakistan remains limited. Aims This study aimed to characterise heavy-metal contamination in marble-processing wastewater in Faisalabad, Pakistan; evaluate water-quality degradation using complementary pollution indices; estimate deterministic and probabilistic human-health risks; and investigate probable metal sources using correlation analysis and principal component analysis. Methods In total, 90 samples in replicates from 30 sites in Faisalabad, Pakistan, were analysed for arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), copper (Cu), zinc (Zn), calcium (Ca) and magnesium (Mg) by inductively coupled plasma–optical emission spectroscopy (ICP-OES). Pollution was assessed through heavy metal pollution index (HPI), metal index (MI) and contamination factors, and health risks were assessed by hazard quotient and carcinogenic risk calculations. Non-carcinogenic and carcinogenic risks were additionally evaluated using Monte Carlo simulation (10,000 iterations) generating 5th to 95th percentile uncertainty ranges. Key results All toxic metals exceeded WHO standards. Lead showed highest contamination factor (CF = 97.5). Wastewater was critically contaminated (HPI = 2844; MI = 135). Hazard indices were 22.3 (adults) and 53.0 (children). Carcinogenic risks for As, Cr and Cd exceeded the US Environmental Protection Agency threshold by 36 to 189 fold. Principal component analysis linked toxic metals to equipment wear and Ca/Mg to carbonate dissolution. Monte Carlo confirmed these findings; median hazard indices were 19.9 (13.8–29.5) for adults and 47.1 (30.7–74.5) for children, and As, Cr and Cd risks remained above acceptable limits across the 90% uncertainty interval. Conclusions The investigated wastewater was severely contaminated and presented substantial potential non-carcinogenic and carcinogenic health risks, particularly for children. Implications Treatment before discharge, closed-loop water reuse, regulatory monitoring and seasonal surveillance of receiving waters are needed. Multi-season and multimedia studies should be conducted to refine exposure estimates and source apportionment.