Characterizing pollution and identifying heavy metal sources in surface sediments: a PMF-based assessment of environmental risks from produced water discharges during hydraulic fracturing

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Abstract
This study highlights the critical environmental and human health risks posed by heavy metal contamination in oil and gas drilling regions. Heavy metal contamination in surface sediments resulting from oil and gas drilling activities presents a significant environmental and human health concern. This research critically examines the impacts of hydraulic fracturing wastewater on surface sediment quality, focusing on environmental consequences. For the first time in the region, sediment samples were analysed to identify heavy metals associated with oil and gas operations. A combination of pollution indices, positive matrix factorization (PMF), and health risk assessment (HRA) was applied to comprehensively assess sediment quality, contamination sources, and health risks. To evaluate contamination levels, various pollution indices were employed, including Geoaccumulation Index (Igeo), enrichment factor (EF), contamination factor (CF), pollution load index (PLI), potential ecological risk index (PERI), toxic risk index (TRI), and modified hazard quotient (mHQ). Source apportionment was conducted using PMF and multivariate statistical techniques to identify the potential origins of heavy metals in surface sediments. The results of the pollution indices indicate moderate to severe contamination, with As, Cr, and Pb showing elevated levels beyond sediment quality guidelines. The PERI and TRI values confirmed high ecological risk, with arsenic and chromium contributing the most to environmental toxicity. PMF analysis identified five major contamination sources, including geogenic weathering, petroleum drilling waste, industrial effluents, aquaculture inputs, and agricultural runoff. The HRA results demonstrated that children are at greater non-carcinogenic risk (HI > 1), particularly due to As, Cr, and Pb exposure via ingestion. The carcinogenic risks for As and Cr exceeded the USEPA threshold (1 × 10−4), suggesting long-term health concerns for populations residing near contaminated sites. The integration of pollution indices, PMF source apportionment, and HRA provides a scientific framework for assessing contamination severity and health risks. These findings underscore the urgency of implementing proactive environmental monitoring, stricter regulatory controls, and effective remediation strategies to safeguard ecosystem and human health in hydrocarbon-extraction areas. Graphical abstract

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