Comparative analysis and human health risk assessment of contamination with heavy metals of Central Asian rivers

Physicochemical Factors Influencing E. coli Contamination in Kathmandu Valley Ponds: Public Health and Environmental Implications

Ponds in Kathmandu Valley reflect its rich history with water resources, but increasing pollution threatens public health and the environment. This study aimed to assess the physicochemical and microbial quality of pond water and further analyze the factors influencing E. coli contamination. In 2023, water samples from 27 out of a total of 35 ponds were examined for physicochemical parameters (temperature, pH, TSS, turbidity, iron (Fe2+), nitrite (NO2 -), phosphate (PO4 3-), ammonia (NH3), DO, BOD, and COD) and microbial parameters (total coliforms and E. coli). Results revealed that all ponds exceeded WHO limits for TSS and turbidity for drinking water. Furthermore 67% surpassed the iron limit, while 96% exceeded USEPA's BOD and COD levels for supporting aquatic life. Coliforms were present in all ponds, with E. coli detected in 67%, indicating the water was unfit for drinking under EU guidelines. Logistic regression revealed a significant association of COD and temperature (P-values 0.001 and 0.023 respectively) with E. coli presence. A 3D visualization of the data further supports the association and illustrates these relationships, COD having a greater impact. These findings underscore public health risks and environmental concerns, urging sewage and runoff management and recommending expanded seasonal studies to establish comprehensive water quality guidelines.

Heavy metal(loid) contamination in forest fire affected soil and surface water: pollution indices and human health risk assessment

Forest fires, whether natural or anthropogenic, release and mobilize heavy metal(loids) (HM). Following intense rainfall events, soil-bound HM are transported from soil to surface water through surface runoff, leading to water quality deterioration. Pollution and ecological risk indices are effective tools for assessing HM contamination. Most forest fire-affected soils and surface water exhibited a degree of contamination greater than 3 and 8 (high and moderate pollution), with associated high and extremely high ecological risks (165 and 2389, respectively). Pollution indices revealed that soils were highly contaminated with Ni, Cu, Cr, and Pb, while Ni, Cu, Hg, Cd, and As posed significant ecological risks. Surface water was heavily contaminated with Pb, Mn, Al, and Fe, with Ni and V contributing to extremely high ecological risks. This study highlights that trace HM also requires substantial removal efforts to make water potable, with removal efficiencies needed for Sb (94.49%), Be (85.83%), Ba (70.75%), V (68.19%), and Se (65.51%). Fire-affected surface water poses an elevated cancer risk to both children (0.18 and 4.5 × 10-3) and adults (0.39 and 1.53 × 10-3) through oral and dermal exposure, respectively. Children are more vulnerable to dermal cancer and noncancer risks compared to adults. Low-cost treatment methods, such as the application of immobilizing agents combined with compost, straw mulching, and seeding, can be implemented to control soil erosion in forest areas, thereby reducing the transport of soil-bound HM to surface water. These findings can aid government agencies in developing new soil and water quality standards and implementing effective treatment measures.

Unveiling mercury's hidden threat: An integrated methodology for soil mercury risk assessment in Syr Darya River Basin, Central Asia

Mercury (Hg) contamination of soil poses a significant threat to ecological and human health. Integrating risk assessment with a comprehensive analysis of the physical and chemical properties of soil enables macroscopic understanding of the potential risks associated with Hg. The integrated risk assessment framework was achieved by applying a projection pursuit clustering (PPC) model that considered ecological and human health risks, soil environmental factors derived from the SHapley Additive Explanation-eXtreme Gradient Boosting (SHAP-XGBoost) model, and exposure risk vulnerability. It was found that the concentrations of Hg in the soils of the Syr Darya River Basin ranged from 3.70 to 40.10 ng/g and Fe2O3, Al2O3, and soil organic carbon (SOC) were important factors in the variation in Hg concentrations. Regions with a high risk of soil Hg were identified using the proposed integrated risk assessment framework, with the geographical distribution concentrated near the cities of Kyzylorda and Kazalinsk. From the perspective of different land use types, shrub soil sampling sites had the largest percentage of high Hg risk values, followed by cropland, bare land, and grassland. These findings confirm that the combined risk values depend not only on Hg concentrations, but also on environmental variables and socioeconomic conditions. Integrated risk assessment of soil Hg is based on machine learning and projection pursuit clustering models, which can provide a novel perspective for potential toxic element pollution evaluation, prevention, and treatment.

Quantifying the sources and health risks of groundwater nitrate via dual NO isotopes and Monte Carlo simulations in a developed planting-breeding area

Nitrate (NO3-) pollution in groundwater is a worldwide environmental issue, particularly in developed planting-breeding areas where there is a substantial presence of nitrogen-related sources. Here, we explored the key sources and potential health risks of NO3- in a typical planting-breeding area in the North China Plain based on dual stable isotopes and Monte Carlo simulations. The analysis results revealed that the NO3- concentration ranged from 0.02 to 44.6 mg/L, with a mean value of 7.54 mg/L, along with a significant spatial variability. Analysis by combining stable isotopes (δ15N-NO3- and δ18O-NO3-) with the Bayesian isotope mixing model (MixSIAR) revealed that soil N (60.3 %) and manure and sewage (35.9 %) contributed the most NO3- in groundwater, followed by chemical N fertilizer (2.9 %) and atmospheric N deposition (0.8 %). However, the contribution of N fertilizer may be underestimated because it has undergone a long-term applied history and have progressively accumulated in the soil, and then promoted the entry of groundwater under frequent rainfall and irrigation practices. From the probabilistic health risk assessment, a relatively low probability of exceeding the threshold (HI=1) was observed (0.2 % for adults and 2.59 % for children); nevertheless, children still face some nonnegligible risk, particularly for the oral ingestion of drinking water at high-pollution sites. Therefore, we highlight the importance of effective management of manure and sewage from breeding plants and reduction of chemical N fertilizer usage are suggested in developed agricultural areas.

Geochemical insights and model optimisation for pilot-scale passive treatment of manganese and zinc in a legacy mine in Japan

Elevated concentrations of manganese (Mn2+) and zinc (Zn2+) in water bodies can disrupt ecosystems and damage aquatic life. However, the mechanisms underlying the removal of Mn2+ and Zn2+ under dynamic conditions and the optimal hydraulic retention time (HRT) for passive treatment plants remain unclear. Here, a pilot-scale passive treatment system for the removal of Mn2+ and Zn2+ from legacy mine drainage in northern Japan is proposed; it was performed at circumneutral pH for 152 days. Comprehensive suspended solid mineralogy analyses and geochemical and numerical modelling were conducted to optimise the passive treatment efficiency. Mn2+ removal (efficiency reaching 98 %) primarily depended on the activity of Mn-oxidising bacteria. Zn2+ removal involved Zn2+ co-precipitation with birnessite combined with adsorption or ion exchange on the birnessite surface. The inverse numerical model successfully determined the Mn2+ oxidation rate constant, Zn mass transfer coefficient, and Zn distribution coefficient. Under dynamic conditions, HRT emerged as a key factor underlying the pilot-scale passive treatment efficiency. An HRT of 0.5 days led to optimal Mn2+ and Zn2+ removal conditions and achieved values lower than the Japanese national effluent limit. The findings provide crucial information for passive treatment strategy development and environmental management, especially when considering real-scale implementation.

Composition, distribution, and risk assessment of heavy metals in large-scale river water on the Tibetan Plateau

Heavy metals present in aquatic ecosystems constitute a significant threat to both the environment and human health. In this study, we analyzed various heavy metals (As, Cr, Co, Ni, Cu, Mo, Cd, Pb and Sb) using extensive surface water samples collected from the Tibetan Plateau in 2021 and 2023. Results showed that downstream water samples exhibited higher content (mean 12.6 μg/L) of heavy metals compared to those from the glacier basins. It is noteworthy that heavy metal content varied significantly both in the glacier basin and downstream (4.6-29.1 μg/L and 7.8-55.2 μg/L, respectively). However, elevated concentrations at certain sites (e.g., Saga County and Dangque Zangbu River) were primarily attributed to the disproportionate contribution of individual heavy metals, possibly stemming from specific human activities or natural conditions. In the glacier basin, only Cr exhibited a decreasing trend in enrich factors (EF) with increasing Sc concentration, whereas, in the downstream areas, most elements displayed a declining trend. Furthermore, apart from a few sampling sites, heavy metal concentrations in the glacier basin remained relatively balanced, suggesting that these metals predominantly originate from natural sources. The values of potential ecological risk for an individual element (Eri) and potential ecological risk index (PER) indicate that the ecological and human risks associated with almost heavy metals (except As) in the aquatic ecosystem are minimal. ENVIRONMENTAL IMPLICATION: Heavy metals in aquatic ecosystems pose a significant threat to ecological and human health. Due to delicate ecological balance of the Tibetan Plateau and its critical role as a water resource, we analyzed various heavy metals (As, Cr, Co, Ni, Cu, Mo, Cd, Pb and Sb) concentrations and EF in land surface river water, to find out the pollution levels and possible sources of heavy metals in the aquatic ecosystems. The results of risk assessment showed that the prevention and management of arsenic in Tibetan Plateau needs attention, but most heavy metals pose no threaten to ecological and human health.

Spatiotemporal variations, health risk assessment, and sources of potentially toxic elements in potamic water of the Anday Stream Basin (Türkiye), Black Sea Region

Monitoring and protecting freshwater habitats are paramount for a sustainable water management perspective. This study investigated potentially toxic elements (PTEs) in the potamic water of the Anday Stream Basin (Türkiye), Black Sea Region, for a hydrological year (from May 2020 to April 2021). Among PTEs, the highest average values were recorded for sodium (Na) at 41.3 mg/L and the lowest for mercury (Hg) at 0.009 μg/L and noted under quality guidelines. The stream was found to be at the level of "Low Heavy Metal Pollution" and "Low Contamination" based on the ecotoxicological risk indices. The highest calculated hazard quotient (HQ) value of 1.21E-02 for Cd was noted in the children via the dermal pathway and the lowest of 6.91E-06 for Fe in adults via the ingestion pathway. Results revealed a higher hazard index (HI) value of 1.50E-02 for Cd to children and the lowest of 1.98E-05 for Fe to adults. As a result of applying agricultural risk indices, the stream showed sodium adsorption ratio values less than 6 and was found to be "Excellent" for agriculture. However, the sodium percentage values were less than 20 and found "Permissible" and the magnesium hazard > 50 and noted as "Unsuitable" for agriculture. Statistical analysis revealed that natural factors mainly attributed to PTE contamination of the Anday Stream Basin.

Fish and Seafood Safety: Human Exposure to Toxic Metals from the Aquatic Environment and Fish in Central Asia

Toxic metals that are released into aquatic environments from natural and anthropogenic sources are absorbed by aquatic organisms and may threaten the health of both aquatic organisms and humans. Despite this, there have been limited studies on the metal concentrations in fish and humans in Central Asia. This study summarizes the presence of the toxic metals arsenic (As), mercury (Hg), cadmium (Cd), and lead (Pb) in aquatic bodies, fish, and seafood products and conducts a risk assessment. While certain areas show a notable increase in fish and seafood consumption, the overall intake in Central Asia remains below recommended levels. However, in regions with high fish consumption, there is a potential for elevated exposure to toxic metals, especially Hg. The risk of exposure to toxic metals in fish and seafood in Central Asia emerges as a significant concern. Comprehensive monitoring, regulation, and remediation efforts are imperative to ensure the safety of water sources and food consumption in the region. Public awareness campaigns and the establishment of dietary guidelines play a crucial role in minimizing the health risks associated with consumption.

Geospatial distribution and machine learning algorithms for assessing water quality in surface water bodies of Morocco

Surface waterbodies being primary source of water for human consumption are being investigated for its quality globally. This study evaluated water quality in three rivers (River Nfifikh, Hassar and El Maleh) of Mohammedia prefecture, Morocco in terms of heavy metals occurrence during two seasons of winter and spring. The heavy metals analyzed were cadmium, iron, copper, zinc, and lead. Heavy metal pollution index was derived to quantify water quality and pollution. Hazard quotient and carcinogenic risk were calculated to determine possible health risk. Modelling and prediction were performed using random forest, support vector machine and artificial neural network. The heavy metal concentration was lower in the winter season than in the spring season. Heavy metal pollution index (H.P.I.) was in the range of 1.5-2 during the winter season and 2-3 during the spring season. In the Nfifikh river, Cd2+ and Fe were the main polluting heavy metal. H.Q. was < 1 in all three rivers, which signified no adverse health effect from exposure to heavy metals. However, carcinogenic risk assessment revealed that 1 in every 100 people was susceptible to cancer during the life span of 70 years. Based on the control point reference, it was found that Mohammedia prefecture as river water was already contaminated before it entered the prefecture boundary. This was again validated with the water lagoon Douar El Marja which is located near the industrial zones of Mohammedia prefecture. Future studies are required to investigate pollution of rivers prior to their entry in Mohammedia prefecture to identify potential source and adopt mitigation measures accordingly.