ABSTRACT
Assessing the quality of river and drinking water in relation to consumer health is crucial for informed decision-making regarding its use. This study evaluates the health risks associated with the Karun and Dez rivers, as well as the water treatment plants in Ahvaz city. The research focused on measuring the levels of metals, including Ag, Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Sn, Ti, V, and Zn, in water sources and the urban water distribution network of Ahvaz during the winter of 2022 and summer of 2023. To achieve this, samples were collected from the inflows and outflows of water treatment plants 1, 2, 3, 4, and 5, as well as from six points within the distribution network, selected based on their geographical locations across the city. The concentrations of metals in the samples were determined, and health risks were assessed using the Hazard Index (HI) and Cancer Risk Index (CR). The results revealed that the HI at all sampling points was below 1, indicating that non-carcinogenic risks from metals do not pose a threat to human health at any of the studied locations. Furthermore, the CR for metals such as As, Pb, and Cd, which have a higher potential for carcinogenicity, was estimated to be zero at all sampling stations, suggesting no carcinogenic risk from drinking water metals at these sites. Based on the calculated health risks, there is no threat to consumer health from heavy metals in Ahvaz's drinking water.
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EXTENDED ABSTRACT
Introduction
The availability of freshwater in river basins is essential for agricultural, industrial, and cultural development, with sustainability heavily reliant on a dependable water supply. However, rapid urbanization and industrialization have significantly escalated pollution in river systems, presenting severe environmental challenges. Among various pollutants, heavy metals are particularly concerning due to their persistence, toxicity, and potential for bioaccumulation. These metals, introduced into rivers through industrial discharges, agricultural runoff, and improper waste disposal, profoundly affect aquatic ecosystems and human health. The bioaccumulation and biomagnification of heavy metals in the food chain can result in toxic effects, including damage to the neurological, circulatory, and immune systems. Prolonged exposure to certain heavy metals, such as cadmium and chromium, may also lead to carcinogenic effects. In the Karun-Dez river basin—a critical region for fish farming and drinking water supply in southern Iran—the presence of metal industries, petrochemical plants, and oil activities has heightened concerns about metal pollution. This study assesses the carcinogenic and non-carcinogenic risks associated with heavy metal exposure from drinking water sources in the region, providing crucial insights for decision-makers responsible for managing treatment plants and the rivers that supply them.

Materials and methods
This study investigated the Karun and Dez rivers in Khuzestan Province, which are key water sources for Ahvaz's treatment plants 1 to 5. Sampling was conducted during the wet season (winter 2022) and the dry season (summer 2023) at designated locations. Heavy metal concentrations were analyzed using ICP-OES. Health risks were assessed, focusing on both non-carcinogenic and carcinogenic effects. Non-carcinogenic risks were evaluated using the Hazard Quotient (HQ) and Hazard Index (HI), while carcinogenic risks were calculated based on the Cancer Slope Factor (CSF) for metals such as As, Cd, and Pb. The study identified potential health risks through the evaluation of HI and CR values.

Results and discussion
Our recent report on the analysis of metal concentrations in water samples revealed that they were below the WHO's standard limits. Furthermore, the report indicates that, based on heavy metal pollution indices, the water in the studied areas is not considered polluted. However, water entering the treatment plants during winter lacks suitable quality for drinking before treatment. It was also found necessary to optimize the use of coagulants in the treatment plants to reduce concentrations of aluminum (Al) and iron (Fe) in the outflows. This study assessed the health risks of heavy metals by considering both ingestion and dermal exposure, evaluating non-carcinogenic and carcinogenic effects on adults and children. For this purpose, Hazard Quotient (HQ), Hazard Index (HI), and Cancer Risk (CR) values were calculated based on Average Daily Dose (ADD) and Reference Dose (RfD) for each metal. The results showed that HQ values for both children and adults were below 1 for all measured metals at sampling points, indicating no significant health risk from these metals. Notably, HQ values were higher for children compared to adults, suggesting that children are more vulnerable in the same environment. The HI index was also below 1 at all sampling points, meaning that, according to USEPA standards, the water can be considered safe for consumption for both children and adults. Therefore, non-carcinogenic risks from metals do not pose a threat to human health at any of the studied stations. Additionally, since the concentrations of metals with higher carcinogenic potential, such as arsenic (As), lead (Pb), and cadmium (Cd), were determined to be zero at the sampling stations, the carcinogenic risk (CR) was also evaluated as zero. According to USEPA standards, there is no significant carcinogenic risk from drinking water at these locations.

Conclusion
This study aims to investigate the concentration of heavy metals in the water sources supplying Ahvaz water treatment plants 1 to 5 (Karun and Dez rivers), as well as the drinking water distribution network of Ahvaz city during the winter of 2022 and the summer of 2023. In this study, non-carcinogenic and carcinogenic risks from the metals present in the water samples were assessed. The health risk assessment results indicate that the drinking water of Ahvaz city, in terms of heavy metal content, poses no health hazard to consumers.