Metal solubility and transport at a contaminated landfill site - From the source zone into the groundwater

Pollution characteristics and source apportionment of heavy metal(loid)s in soil and groundwater of a retired industrial park

Heavy metal(loid)s (HMs) pollution has become a common and complex problem in industrial parks due to rapid industrialization and urbanization. Here, soil and groundwater were sampled from a retired industrial park to investigate the pollution characteristics of HMs. Results show that Ni, Pb, Cr, Zn, Cd, and Cu were the typical HMs in the soil. Source analysis with the positive matrix factorization model indicates that HMs in the topsoil stemmed from industrial activities, traffic emission, and natural source, and the groundwater HMs originated from industrial activities, groundwater-soil interaction, groundwater-rock interaction, and atmosphere deposition. The sequential extraction of soil HMs reveals that As and Hg were mainly distributed in the residue fraction, while Ni, Pb, Cr, Zn, Cd, and Cu mainly existed in the mobile fraction. Most HMs either in the total concentration or in the bioavailable fraction preferred to retain in soil as indicated by their high soil-water partitioning coefficients (Kd), and the Kd values were correlated with soil pH, groundwater redox potential, and dissolved oxygen. The relative stable soil-groundwater circumstance and the low active fraction contents limited the vertical migration of soil HMs and their release to groundwater. These findings increase our knowledge about HMs pollution characteristics of traditional industrial parks and provide a protocol for HMs pollution scrutinizing in large zones.

A prospective ecological risk assessment of high-efficiency III-V/silicon tandem solar cells

III-V/Silicon tandem solar cells offer one of the most promising avenues for high-efficiency, high-stability photovoltaics. However, a key concern is the potential environmental release of group III-V elements, especially arsenic. To inform long-term policies on the energy transition and energy security, we develop and implement a framework that fully integrates future PV demand scenarios with dynamic stock, emission, and fate models in a probabilistic ecological risk assessment. We examine three geographical scales: local (including a floating utility-scale PV and waste treatment), regional (city-wide), and continental (Europe). Our probabilistic assessment considers a wide range of possible values for over one hundred uncertain technical, environmental, and regulatory parameters. We find that III-V/silicon PV integration in energy grids at all scales presents low-to-negligible risks to soil and freshwater organisms. Risks are further abated if recycling of III-V materials is considered at the panels' end-of-life.

A comprehensive assessment of leachate contamination at a non-operational open dumpsite: mycoflora screening, metal soil pollution indices, and ecotoxicological risks

The final disposal of municipal solid waste (MSW) in dumpsites is still a reality worldwide, especially in low- and middle-income countries, leading to leachate-contaminated zones. Therefore, the aim of this study was to carry out soil and leachate physicochemical, microbiological, and toxicological characterizations from a non-operational dumpsite. The L-01 pond samples presented the highest physicochemical parameters, especially chloride (Cl; 4101 ± 44.8 mg L^-1), electrical conductivity (EC; 10,452 ± 0.1 mS cm^-1), and chemical oxygen demand (COD; 760 ± 6.6 mg L^-1) indicating the presence of leachate, explained by its close proximity to the landfill cell. Pond L-03 presented higher parameters compared to pond L-02, except for N-ammoniacal and phosphorus levels, explained by the local geological configuration, configured as a slope from the landfill cell towards L-03. Seven filamentous and/or yeast fungi genera were identified, including the opportunistic pathogenic fungi Candida krusei (4 CFU) in an outcrop sample. Regarding soil samples, Br, Se, and I were present at high concentrations leading to high soil contamination (CF ≤ 6). Pond L-02 presented the highest CF for Br (18.14 ± 18.41 mg kg^-1) and I (10.63 ± 3.66 mg kg^-1), while pond L-03 presented the highest CF for Se (7.60 ± 1.33 mg kg^-1). The most severe lethal effect for Artemia salina was observed for L-03 samples (LC₅₀: 79.91%), while only samples from L-01 were toxic to Danio rerio (LC₅₀: 32.99%). The highest lethality for Eisenia andrei was observed for L-02 samples (LC₅₀: 50.30%). The applied risk characterization indicates high risk of all proposed scenarios for both aquatic (RQ 375-909) and terrestrial environments (RQ > 1.4 × 10⁵). These findings indicate that the investigated dumpsite is contaminated by both leachate and metals, high risks to living organisms and adjacent water resources, also potentially affecting human health.

Stimulated leaching of metalloids along 3D-printed fractured rock vadose zone

Fractured rock aquifers are susceptible to contamination, with metal(loid)s rapidly migrating from poorly developed overburden to the fractured rock vadose zone and thus into groundwater. Compared to typical porous aquifers, retention effects within the rock matrix are small, and rapid advection along fractures leads to a higher risk of groundwater contamination. However, the highly complex anisotropic pathways of natural fractures hinder research in this field. To construct reproducible fractures, this study used 3D printing following Computed X-ray Microtomography (μCT) scans of a fractured rock collected in a natural limestone aquifer. Stimulated metalloid release was observed in the fractured rock during column leaching, and the leachate concentrations of arsenic (As) and antimony (Sb) increased by up to 17.5 and 36.4 times, respectively, compared with the porous vadose zone. Fluctuations in fracture metalloid release patterns in dissolved and adsorbed phases were attributed to retention and filtration effects induced by soil particles within fractures. Geophysical properties of the porous overburden, especially the aggregation characteristics, greatly affected the non-equilibrium leaching behavior of As, but had a limited effect on the near-equilibrium leaching of Sb, which was explored by modifying the surficial soil layer with either montmorillonite clay or charcoal. The results of this study provide a novel method and useful information for modeling and risk assessment of fractured rock aquifers.

Environmental damage caused by coal combustion residue disposal: A critical review of risk assessment methodologies

Coal combustion generates almost 40% of world's electricity. However, it also produces 1.1 billion tons of coal combustion residues (CCR) annually, half of which end up in landfills. Although current regulations require proper lining and monitoring programs, the ubiquitous old, abandoned landfills are often not lined nor included in these programs. In addition, the total number of coal ash disposal sites and their status in the world is unknown. Therefore, this article reviews the environmental damage caused by CCR and three commonly used risk assessment methodologies: leaching assessment, groundwater assessment, and toxicity testing. Leaching methods are usually the first step in coal ash risk assessment, however, a large number of methods with different parameters make a comparison of data difficult. Groundwater pollution is commonly detected near coal ash disposal sites, but other anthropogenic activities may also exist nearby. Therefore, multivariate statistical methods and isotope traces should be used to differentiate between different sources of pollution. So far, both stable (δ¹⁸O, δD, δ¹¹B, δ³⁴S, δ⁷Li) and radiogenic (⁸⁷Sr/⁸⁶Sr, ²⁰⁶Pb/²⁰⁷Pb) isotopes have been successfully used as coal ash pollution tracers. Coal ash also negatively affects biota, reduces the diversity of organisms, affects children's health, and increases the risk for developing various diseases. Toxicity studies are great for early screening of coal ash safety; however, they provide no insights into mechanisms causing the adverse effects. Future directions are also proposed, such as the development of new 'low-level' detection methods for coal ash pollution and sustainable and selective method for recovery of critical elements.

Heavy metal transport driven by seawater-freshwater interface dynamics: The role of colloid mobilization and aquifer pore structure change

Co-transport of colloidal substances and pollutants is a pivotal link that significantly affects the environment of coastal groundwater. The effect of colloid mobilization and aquifer pore structure change on heavy metal transport driven by seawater-freshwater interface dynamics is not fully understood. In this study, packed column experiments were conducted to model the seawater intrusion (SWI) and freshwater replenishment (FWR) processes using a sampled medium from a coastal sandy aquifer. Hydrodynamic, hydrochemical variables, and heavy metal (Pb, Cu, Cd) transport during the propagation of the seawater-freshwater interface were tested and analyzed. During the SWI stage, cation exchange induced heavy metal liberations, and it developed peak concentrations synchronized with the seawater-freshwater interface at the pore volume of 1.00. The colloid-facilitated transport for heavy metals was the predominant mechanism in the FWR stage, characterized by a peak release lagging the interface propagation by approximately 0.5 pore volumes. Because the colloidal fraction was mobilized during aquifer desalination, it lagged behind the decline of the salinity gradient. Furthermore, Derjaguin-Landau-Verwey-Overbeek (DLVO) calculations explained that the replenishment decreased the depth of the secondary energy minimum of the colloids; meanwhile, the thickness of the electrical double layer increased from 0.63 nm to 10.14 nm, resulting in a repulsive energy barrier up to 3,213 kT. The transport of colloids led to a reduction in porosity from 18.16% to 2.28% of the total immobile domain. At these times, the dimension of the transported colloids evolved, showing a size-selective transport and therefore regulating the total emission fluxes of the heavy metals. These mechanisms were proposed to be incorporated in colloid filtration theory for targeting the coastal scenario.

Assessment of natural radionuclide transfer factors and partition coefficients in some Syrian soils

Transfer factors of radium 226(²²⁶Ra), lead 210(²¹⁰Pb), polonium 210 (²¹⁰Po), uranium 238 (²³⁸U) and thorium 234(²³⁴Th) from five different agricultural soils in Syria to coriander, parsley and mint were investigated in a pot culture experiment. Geometric means of transfer factors (TF)were²²⁶Ra (0.13),²¹⁰Pb(0.03), ²¹⁰Po (0.02) and ²³⁸U (1.76) were within worldwide values, while TF values for ²³⁴Th (1.35) were higher than those recorded globally. The available transfer factor (ATF) values ranged between 0.03 and 1.45, 0.33 and 3.2, 0.10 and 3.36, 1.30 and 16.2 and 1.0 and 6.95 for²²⁶Ra,²¹⁰Pb,²¹⁰Po, ²³⁸U and ²³⁴Th, respectively. However, it is worth mentioning that the data from pot experiments may not represent field conditions. Liquid/solid partition coefficients (K_d)of ²²⁶Ra, U, ²¹⁰Pb and ²¹⁰Po for55 soils representing the dominant types of soils in Syria were also determined. Geometric means of K_d values ranged from 280 to1200, 750 to1600, 350to 4800 and 100-120 L kg^-1 for ²²⁶Ra, ²³⁸U, ²¹⁰Pb and ²¹⁰Po, respectively at pH = 4.0, and from 200 to 6700, 670 to 2400, 150 to 2100 and 100 to 160Lkg^-1at pH = 5.5, and from 370 to 790, 130 to 550, 60 to 330 and370 to 920Lkg^-1at pH = 7.0. The effects of soil mineral content, CEC, ECE, pH and soluble ions on the K_d values were investigated. In general, there were logarithmic relationships between the activity concentrations in soil and the K_d values (R² ranged from 0.59 to 1.00 at pH 4.0). There were no relationships between the K_d values and soil pH.

Failure of generic risk assessment model framework to predict groundwater pollution risk at hundreds of metal contaminated sites: Implications for research needs

Soil pollution constitutes one of the major threats to public health, where spreading to groundwater is one of several critical aspects. In most internationally adopted frameworks for routine risk assessments of contaminated land, generic models and soil guideline values are cornerstones. In order to protect the groundwater at contaminated sites, a common practice worldwide today is to depart from health risk-based limit concentrations for groundwater, and use generic soil-to-groundwater spreading models to back-calculate corresponding equilibrium levels (concentration limits) in soil, which must not be exceeded at the site. This study presents an extensive survey of how actual soil and groundwater concentrations, compiled for all high-priority contaminated sites in Sweden, relate to the national model for risk management of contaminated sites, with focus on As, Cu, Pb and Zn. Results show that soil metal concentrations, as well as total amounts, constitute a poor basis for assessing groundwater contamination status. The evaluated model was essentially incapable of predicting groundwater contamination (i.e. concentrations above limit values) based on soil data, and erred on the "unsafe side" in a significant number of cases, with modelled correlations not being conservative enough. Further, the risk of groundwater contamination was almost entirely independent of industry type. In essence, since neither soil contaminant loads nor industry type is conclusive, there is a need for a supportive framework for assessing metal spreading to groundwater accounting for site-specific, geochemical conditions.

Impact of the landfill of ashes from the smelter on the soil environment: case study from the South Poland, Europe

The following research describes the influence of a metallurgical ash dump on both the soil environment and the atmosphere. Soil samples were collected along a line positioned on an unprotected, hazardous ash dump and extended into the adjacent, arable land. Three soil depths were sampled at 0-20-, 20-40- and 40-60-cm depth intervals, and in each sample, pseudo-total concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb, Ti, Zn, Li, Sr and V were analyzed. Additionally, emissions of CH₄ and CO₂ were measured at each sampling site. All emission measurements were taken in the same day, and the duration of gas measurements in each place was six minutes. The results demonstrate elevated concentrations of Cu, Cr, Pb and Zn on dump surface and along its margins, where the maximum concentrations of these elements are, respectively, 82, 23, 1144 and 8349 mg kg^-1. Obtained results exceed several times both the natural background values and the values typical of local soils in the southern Poland. Moreover, natural background values for Fe, Mn, Ni, Li, Sr and V were exceeded, as well. Along the sampling line, no methane emission was detected, whereas the carbon dioxide flux varied from 7 to 42 g m^-2 d^-1. The reconnaissance study of the ash dump revealed a high contamination level of soils with heavy metals, which, together with the changes of soil environment, may cause migration of pollutants into the adjacent areas and, consequently, may generate hazard to the environment and, particularly, to the living organisms. Hence, further studies are necessary in order to evaluate the soil quality and the leaching of heavy metals from the dump.

Geophysical investigation of glass 'hotspots' in glass dumps as potential secondary raw material sources

This study investigates the potential for Electrical Resistivity Tomography (ERT) to detect buried glass 'hotspots' in a glass waste dump based on results from an open glass dump investigated initially. This detection potential is vital for excavation and later use of buried materials as secondary resources. After ERT, test pits (TPs) were excavated around suspected glass hotspots and physico-chemical characterisation of the materials was done. Hotspots were successfully identified as regions of high resistivity (>8000 Ωm) and were thus confirmed by TPs which indicated mean glass composition of 87.2% among samples (up to 99% in some). However, high discrepancies in material resistivities increased the risk for introduction of artefacts, thus increasing the degree of uncertainty with depth, whereas similarities in resistivity between granite bedrock and crystal glass presented data misinterpretation risks. Nevertheless, suitable survey design, careful field procedures and caution exercised by basing data interpretations primarily on TP excavation observations generated good results particularly for near-surface materials, which is useful since glass waste dumps are inherently shallow. Thus, ERT could be a useful technique for obtaining more homogeneous excavated glass and other materials for use as secondary resources in metal extraction and other waste recycling techniques while eliminating complicated and often costly waste sorting needs.

Impact assessment of metals on soils from Machu Picchu archaeological site

Machu Picchu is an archaeological Inca sanctuary from the 15th century, located 2430 m above the sea level in the Cusco Region, Peru. In 1983, it was declared World Heritage Site by UNESCO. The surroundings and soils from the entire archaeological site are carefully preserved together with its grass parks. Due to the importance of the archaeological city and its surroundings, the Decentralized Culture Directorate of Cusco-PAN Machu Picchu decided to carry out a careful monitoring study in order to determine the ecological status of the soils. In this work, elemental and molecular characterization of 17 soils collected along the entire park was performed by means of X-ray Diffraction (XRD) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) after acidic digestion assisted by microwave energy. Thanks to the combination of these analytical techniques, it was possible to obtain the mineral composition and metal concentrations of all soils from these 17 sampling points. Finally, different statistical treatments were carried out in order to confirm the ecological status of the different sampling points from Machu Picchu archaeological site concluding that soils are not impacted.

Radiometrical and physico-chemical characterisation of contaminated glass waste from a glass dump in Sweden

Around former glass factories in south eastern Sweden, there are dozens of dumps whose radioactivity and physico-chemical properties were not investigated previously. Thus, radiometric and physico-chemical characteristics of waste at Madesjö glass dump were studied to evaluate pre-recycling storage requirements and potential radiological and environmental risks. The material was sieved, hand-sorted, leached and scanned with X-Ray Fluorescence (XRF). External dose rates and activity concentrations of Naturally Occurring Radioactive Materials from ²³⁸U, ²³²Th series and ⁴⁰K were also measured coupled with a radiological risk assessment. Results showed that the waste was 95% glass and dominated by fine fractions (<11.3 mm) at 43.6%. The fine fraction had pH 7.8, 2.6% moisture content, 123 mg kg^-1 Total Dissolved Solids, 37.2 mg kg^-1 Dissolved Organic Carbon and 10.5 mg kg^-1 fluorides. Compared with Swedish EPA guidelines, the elements As, Cd, Pb and Zn were in hazardous concentrations while Pb leached more than the limits for inert and non-hazardous wastes. With ⁴⁰K activity concentration up to 3000 Bq kg^-1, enhanced external dose rates of ⁴⁰K were established (0.20 μSv h^-1) although no radiological risk was found since both External Hazard Index (H_ex) and Gamma Index (I_γ) were <1. The glass dump needs remediation and storage of the waste materials under a safe hazardous waste class 'Bank Account' storage cell as a secondary resource for potential future recycling.

A new method for determination of heavy metal adsorption parameters in compacted clay by batch tests

Evaluation of adsorption properties of pollutants on artificial or natural clay strata is normally considered in investigations of soil and groundwater pollution. Batch adsorption tests can be used to obtain the adsorption parameters of clay particles; however, the results from these tests are usually very different from the adsorption of actual clay strata. If the adsorption parameters obtained by batch tests are used to directly evaluate the properties of adsorption of pollutants onto compacted clay, the predicted groundwater and soil pollution will be unsafe. Although the column diffusion tests are closer to the actual situation, they may require much more time, and diffusion and adsorption occur simultaneously in tests, making it difficult to accurately determine the adsorption parameters. To solve this problem, batch adsorption and column diffusion tests were conducted using three kinds of clay materials to investigate the mechanism of the differences in adsorption properties of heavy metal on clay particles and in compacted clay. The amount of adsorption per unit particle surface area of clay particles was found to be equal to that per unit pore surface area of compacted clay. A new simplified method was proposed to determine the adsorption parameters in compacted clay. It is easy to use and provide a reference for prediction and evaluation of soil and groundwater pollution.

A Pilot Survey of Potentially Hazardous Trace Elements in the Aquatic Environment Near a Coastal Coal-Fired Power Plant in Taiwan

BACKGROUND

A limited number of potentially hazardous trace elements were quantified in the aquatic environment near the world's second largest coal-fired power plant (CFPP) and the coal combustion residual (CCR) disposition sites in Central Taiwan. We postulated that contamination from specific trace elements would be present in the abovementioned aquatic environments.

METHODS

Cross-sectional sampling of trace elements was first performed between September 24, 2017 and October 3, 2017 outside the CFPP, in the effluent sampled from Changhua, a county south of metropolitan Taichung, and at the historical CCR disposal sites, using the intertidal zone surface seawater and the seawater in an oyster farm as controls. Aqueous samples were collected from 12 locations for analysis of 13 trace elements (Al, As, B, Cd, total Cr, Co, Fe, Pb, Mn, Se, Sr, Tl, and V). We used inductively coupled plasma (ICP) optical emission spectrometry to determine B and Fe levels, and ICP mass spectrometry for all other trace elements. The Spearman rank correlation coefficient (Rho) was calculated to examine the pairwise relation among the trace elements.

RESULTS

Al (50% of all samples), B (66.7%), Fe (25%), Mn (50%), Sr (8.3%), and V (25%) were identified as being above the Environmental Protection Agency (EPA) regulation limit. The oyster farm seawater had no concerns. Mn (96.4 μg/L) in the CFPP drainage effluent was 1.9-fold above the regulation limit. Fe, Mn, and V were detected from the cooling channel at 4379, 625, and 11.3 μg/L, respectively. The effluent and water from the areas surrounding the 2 CCR dump sites revealed similar magnitudes of trace element contamination. B is highly correlated with Sr (Rho = 0.94, 95% confidence interval [CI], 0.80-0.98). Meanwhile, Fe is highly correlated with Al (Rho = 0.77), Pb (Rho = 0.71), Co (Rho = 0.75), and V (Rho = 0.84).

CONCLUSIONS

The EPA must set an explicit regulation limit for aluminum, boron, iron, and strontium in the aquatic environment. This exploratory research will inform policymaking regarding certain trace elements that could potentially have an adverse impact on public health and wildlife.