Heavy metal pollution in leachates and its impacts on the quality of groundwater resources around Iringa municipal solid waste dumpsite

Evaluation of machine learning models for accurate prediction of heavy metals in coal mining region soils in Bangladesh

Coal mining soils are highly susceptible to heavy metal pollution due to the discharge of mine tailings, overburden dumps, and acid mine drainage. Developing a reliable predictive model for heavy metal concentrations in this region has proven to be a significant challenge. This study employed machine learning (ML) techniques to model heavy metal pollution in soils within this critical ecosystem. A total of 91 standardized soil samples were analyzed to predict the accumulation of eight heavy metals using four distinct ML algorithms. Among them, random forest model outer performed in predicting As (0.79), Cd (0.89), Cr (0.63), Ni (0.56), Cu (0.60), and Zn (0.52), achieving notable R squared values. The feature attribute analysis identified As-K, Pb-K, Cd-S, Zn-Fe2O3, Cr- Fe2O3, Ni-Al2O3, Cu-P, and Mn- Fe2O3 relationships resembled with correlation coefficients among them. The developed models revealed that the contamination factor for metals in soils indicated extremely high levels of Pb contamination (CF ≥ 6). In conclusion, this research offers a robust framework for predicting heavy metal pollution in coal mining soils, highlighting critical areas that require immediate conservation efforts. These findings emphasize the necessity for targeted environmental management and mitigation to reduce heavy metal pollution in mining sites.

Insight into the Specific Adsorption of Cu(II) by a Zinc-Based Metal-Organic Framework Mediated via a Proton-Exchange Mechanism

In the context of scarce metal resources, the one-step separation and recovery of high-value copper metal ions from secondary resources is of significant importance and presents substantial challenges. This study identified a Zn-based triazole MOF (Zn(tr)(OAc)) with accessible and noncoordinated terminal hydroxyl groups within its framework. The Zn(tr)(OAc) surpasses most currently reported Cu-specific MOF adsorbents regarding adsorption capacity and Cu2+ selectivity. Furthermore, in the one-step separation and recovery experiment of Cu2+, the Cu2+ concentration was increased from 79.64% in the simulated secondary copper resource solution to 98.62% in the adsorbed phase. Both experimental and theoretical studies indicated that the high ion selectivity for Cu2+ is primarily due to the specific recognition ability of the terminal hydroxyl (-OH) group, enabling only Cu2+ to undergo proton exchange with the hydrogen. The strong adsorption capacity of the material was attributed not only to proton exchange between the hydroxyl groups in the framework and Cu2+ but also to interactions between the nitrogen (N) and oxygen (O) atoms in the heterocyclic rings and Cu2+. In summary, Zn(tr)(OAc) demonstrates great potential in the separation and recovery of Cu2+ from secondary copper resources and provides additional possibilities for enhancing Cu2+ selectivity in MOF-based adsorbents.

Comprehensive assessment of heavy metal (HMs) contamination and associated health risks in agricultural soils and groundwater proximal to industrial sites

Industrial waste significantly impacts water and soil quality, restricting their suitability for agricultural and domestic use. This study investigates the distribution of heavy metals (HMs) in groundwater and soils across the Shazand plain under different irrigation methods and rainfed farming systems. It evaluates the Total Hazard Quotient (THQ) and Carcinogenic Risk (TCR) associated with HMs for both children and adults, considering exposure through ingestion, dermal contact, and inhalation. A total of 104 samples were collected, comprising water samples from wells and boreholes, and soil samples. Concentrations of Pb, Cd, Cr, Ni, Hg, Zn, and Cu were analyzed using atomic absorption spectrometry, and the data were assessed using descriptive and inferential statistics. The highest average concentrations of HMs in groundwater samples were observed for Cr (19 µg l-1) and Zn (22.8 µg l-1). In soil samples, Cr (35.28 µg g-1) and Zn (216.52 µg g-1) exhibited the highest values. The Total Hazard Index (HI) indicated a high risk across different age groups, ranging from moderate to very high in the study areas. The Soil Pollution Load Index (PLI) was 18.22 in rainfed farming and 71.17 in irrigated farming, indicating severe HM contamination across the site. Carcinogenic health risks from HMs exceeded acceptable levels, with children showing greater vulnerability compared to adults. This research underscores the urgent need for effective environmental management strategies to mitigate HM contamination, safeguard public health, and ensure sustainable agricultural practices in industrialized regions.

Characterization of microplastics in soil, leachate and groundwater at a municipal landfill in Rayong Province, Thailand

Recent years have witnessed a dramatic increase in global plastic production, leading to heightened concerns over microplastics (MPs) contamination as a significant environmental challenge. MP particles are ubiquitously distributed across both continental and marine ecosystems. Given the paucity of research on MPs in Thailand, particularly regarding MPs contamination in terrestrial environments, this study focused on investigating the distribution and characteristics of MPs in a landfill area. We collected 15 soil samples, 2 leachate samples, and 7 groundwater samples from both inside and outside a municipal landfill situated in the urbanized coastal region of Rayong Province. Our findings revealed variability in MPs concentration across different sample types. In soil, the MP count ranged from 240 to 26,100 pieces per kg of dry soil, 58.71 % of all sample sizes are lower than 0.5 mm. Similarly, the size found in the leachate sample, and the average MP in the leachate samples was 139 pieces per liter of MPs. The groundwater samples showed a fluctuation in MPs count from 18 to 94 pieces per liter, and the size of MPs ranged mostly from 0.5 to 1 mm. The predominant forms of MPs identified were sheets, followed by fragments, fibers, and granules. According to μ-FTIR analysis, the majority of the MPs were composed of polyethylene and polypropylene, commonly used in plastic packaging and ropes. The observed high concentrations and extensive distribution of MP contamination underscore the urgency for further studies and effective management strategies to mitigate the adverse impacts of this pollution on various organisms and ecosystems.

Toxic heavy metals in a landfill environment (Vientiane, Laos): Fish species and associated health risk assessment

Leachates from municipal landfills introduce toxic heavy metals into water, causing bioaccumulation. This study assesses metal levels and potential human health risks associated with consuming Anabas testudineus and Channa striata. Inductively coupled plasma mass spectrometry detected Cd, Cu, Cr, Ni, Pb, and Zn in both fish species. Leachate metal concentrations meet international discharge standards, Cd, Cr, and Pb in the fish exceed the international accepted values. Gastrointestinal tract+liver samples show significant variation between species, particularly in Cd and Pb. EDI, THQ/HI, and TR for the both species fall below TDIs, lower than the limit of 1, and within the acceptable range of the US-EPA permissible limit, respectively. Fish consumption appears safe regarding carcinogenic risk, but exceeding metal limits could impact heavy metals accumulation in the local food chain. Raising public awareness is crucial, and governmental agencies and environmental organizations should enhance waste treatment technologies and enact relevant health legislation.

Trace element pollution tracking in the complex multi-aquifer groundwater system of Al-Hassa oasis (Saudi Arabia) using spatial, chemometric and index-based techniques

In a global context, trace element pollution assessment in complex multi-aquifer groundwater systems is important, considering the growing concerns about water resource quality and sustainability worldwide. This research addresses multiple objectives by integrating spatial, chemometric, and indexical study approaches, for assessing trace element pollution in the multi-aquifer groundwater system of the Al-Hassa Oasis, Saudi Arabia. Groundwater sampling and analysis followed standard methods. For this purpose, the research employed internationally recognized protocols for groundwater sampling and analysis, including standardized techniques outlined by regulatory bodies such as the United States Environmental Protection Agency (USEPA) and the World Health Organization (WHO). Average values revealed that Cr (0.041) and Fe (2.312) concentrations surpassed the recommended limits for drinking water quality, posing serious threats to groundwater usability by humans. The trace elemental concentrations were ranked as: Li < Mn < Co < As < Mo < Zn < Al < Ba < Se < V < Ni < Cr < Cu < B < Fe < Sr. Various metal(loid) pollution indices, including degree of contamination, heavy metal evaluation index, heavy metal pollution index, and modified heavy metal index, indicated low levels of groundwater pollution. Similarly, low values of water pollution index and weighted arithmetic water quality index were observed for all groundwater points, signifying excellent groundwater quality for drinking and domestic purposes. Spatial distribution analysis showed diverse groundwater quality across the study area, with the eastern and western parts displaying a less desirable quality, while the northern has the best, making water users in the former more vulnerable to potential pollution effects. Thus, the zonation maps hinted the necessity for groundwater quality enhancement from the western to the northern parts. Chemometric analysis identified both human activities and geogenic factors as contributors to groundwater pollution, with human activities found to have more significant impacts. This research provides the scientific basis and insights for protecting the groundwater system and ensuring efficient water management.

Heavy metals/-metalloids (As) phytoremediation with Landoltia punctata and Lemna sp. (duckweeds): coupling with biorefinery prospects for sustainable phytotechnologies

Heavy metals/-metalloids can result in serious human health hazards. Phytoremediation is green bioresource technology for the remediation of heavy metals and arsenic (As). However, there exists a knowledge gap and systematic information on duckweed-based metal phytoremediation in an eco-sustainable way. Therefore, the present review offers a critical discussion on the effective use of duckweeds (genera Landoltia and Lemna)-based phytoremediation to decontaminate metallic contaminants from wastewater. Phytoextraction and rhizofiltration were the major mechanism in 'duckweed bioreactors' that can be dependent on physico-chemical factors and plant-microbe interactions. The biotechnological advances such as gene manipulations can accelerate the duckweed-based phytoremediation process. High starch and protein contents of the metal-loaded duckweed biomass facilitate their use as feedstock in biorefinery. Biorefinery prospects such as bioenergy production, value-added products, and biofertilizers can augment the circular economy approach. Coupling duckweed-based phytoremediation with biorefinery can help achieve Sustainable Development Goals (SDGs) and human well-being.

An overview of in situ remediation for groundwater co-contaminated with heavy metals and petroleum hydrocarbons

Groundwater is an important component of water resources. Mixed pollutants comprising heavy metals (HMs) and petroleum hydrocarbons (PHs) from industrial activities can contaminate groundwater through such processes as rainfall infiltration, runoff and discharge, which pose direct threats to human health through the food chain or drinking water. In situ remediation of contaminated groundwater is an important way to improve the quality of a water environment, develop water resources and ensure the safety of drinking water. Bioremediation and permeable reactive barriers (PRBs) were discussed in this paper as they were effective and affordable for in situ remediation of complex contaminated groundwater. In addition, media types, technology combinations and factors for the PRBs were highlighted. Finally, insights and outlooks were presented for in situ remediation technologies for complex groundwater contaminated with HMs and PHs. The selection of an in situ remediation technology should be site specific. The remediation of complex contaminated groundwater can be approached from various perspectives, including the development of economical materials, the production of slow-release and encapsulated materials, and a combination of multiple technologies. This review is expected to provide technical guidance and assistance for in situ remediation of complex contaminated groundwater.

Leachate leakage enhances the microbial diversity and richness but decreases Proteobacteria and weakens stable microbial ecosystem in landfill groundwater

Sanitary landfill is the most prevalent and economic method for municipal solid waste disposal, and the resultant groundwater pollution has become an environmental problem due to leachate leakage. The pollution characteristics in groundwater near landfill sites have been extensively investigated, although the succession characteristics and driving mechanisms of microbial communities in leachate-contaminated groundwater and the sensitive microbial indicators for leachate leakage identification remain poorly studied. Herein, results showed that leachate leakage enhanced the microbial diversity and richness and transferred endemic bacteria from landfills into groundwater, producing an average decrease of 17.73% in the relative abundance of Proteobacteria. The key environmental factor driving the evolution of microbial communities in groundwater due to leachate pollution was organic matter, which can explain 16.13% of the changes in microbial community composition. The |βNTI| values of the bacterial communities in all six landfills were <2, and the assembly process of microbial communities was primarily dominated using stochastic processes. Leachate pollution changed the assembly mechanism, transforming the community assembly process from an undominated process to a dispersal limitation process. Leachate pollution reduced the efficiency and stability of microbial communities in groundwater, increasing the vulnerability of the stable microbial ecosystems in groundwater. Notably, microbial indicators are more sensitive to leachate leakage and could accurately identify landfills where leachate leakage occurred and other extraneous pollutants. The phylum Proteobacteria and mcrA could act as appropriate indicators for the identification of leachate leakage. These results provide a novel insight into the monitoring, identification of groundwater pollution and the scientific guidance for appropriate remediation strategies for leachate-contaminated groundwater.

Assessment of potential health risks from heavy metal pollution of surface water for drinking in a multi-industry area in Mali using a multi-indices approach

The Niger River, Bamako's population's primary drinking water source, is threatened by human activities. This study examines the Niger River pollution trend using heavy metals pollution indexes and Bamako's population's non-carcinogenic and carcinogenic related health risks. Parameters were monitored at fifteen sampling locations in low and high flow seasons. pH (7.30-7.50) and fluoride (0.15-0.26 mg/L) were within the normal drinking water range. Among seven heavy metals (copper, zinc, cadmium, nickel, iron, manganese, and lead), the latter three were above the drinking water standard. The degree of contamination was negative, pointing to better water quality. However, the heavy metal evaluation index (HEI) was below the mean (5.88), between the mean and twice the mean, indicating a low and medium degree of pollution. Besides, heavy metal pollution indexes (HPI) were above the standard value (100), explaining a low-medium pollution level. High values of HPI could be explained by the industrial units' intensive activities coupled with the runoff effect. The hazard index (HI) indicated a low and medium non-carcinogenic health risk for adults and children. The probability of cancer risk (PCR) of nickel showed a cancer risk. Therefore, the river was polluted with trace elements and could not be used for drinking water without any treatment.

Heavy Metals in Groundwater of Southern Italy: Occurrence and Potential Adverse Effects on the Environment and Human Health

This study reports the data on the contamination caused by heavy metals in the groundwater of the Campania Plain (CP) in Southern Italy. A total of 1093 groundwater samples were obtained from the following aquifers: coastal plains (GAR, VCP, VES, SAR, and SEL), volcanic districts (PHLE and VES), and carbonate massifs (MAS and LAT). In this study, the investigation depth ranged from 5 m (GAR) to 200 m (PHLE). The sequence of heavy metal content in groundwater samples was B > Fe > Al > Mn > Zn > Ba > Ni > As > Cu > V > Se > Pb > Cd. The heavy metal pollution index (HPI) and heavy metal evaluation (HEI) demonstrated that the study areas in which groundwater samples were sampled are not risk zones. Moreover, health risk assessment shows that hazard index (HI) values for heavy metals were found to be significantly low in groundwater samples. In non-carcinogenic risk evaluation for the adult group, the risk was low, whereas for children and infants, the risk was >1 for arsenic alone. Carcinogenic risk assessment (CR) was found lower for adults, children, and infants. The Jenks optimization method was used to evaluate the distribution of heavy metals in the groundwater of CP, and the principal component analysis technique (PCA) was employed to determine the source of heavy metals, and it was found that mixed sources (natural and anthropogenic) may be responsible for heavy metals presence.