A multi-faceted, environmental forensic characterization of a paradigmatic brownfield polluted by hazardous waste containing Hg, As, PAHs and dioxins

Brownfield-related studies in the context of climate change: A comprehensive review and future prospects

The global climate change events are expected to augment the vulnerability of persistent organic pollutants within the global brownfield areas to a certain extent, consequently heightening the risk crises faced by these brownfields amidst the backdrop of global environmental changes. However, studies addressing brownfield risks from the perspective of climate change have received limited attention. Nonetheless, the detrimental consequences of brownfield risks are intrinsically linked to strategies for mitigating and adapting to sustainable urban development, emphasizing the critical importance of their far-reaching implications. This relevance extends to concerns about environmental quality, safety, health risks, and the efficacy of chosen regeneration strategies, including potential secondary pollution risks. This comprehensive review systematically surveys pertinent articles published between 1998 and 2023. A selective analysis was conducted on 133 articles chosen for their thematic relevance. The findings reveal that: (1) Under the backdrop of the climate change process, brownfield restoration is necessitated to provide scientific and precise guidance. The integration of brownfield considerations with the dynamics of climate change has progressively evolved into a unified framework, gradually shaping a research paradigm characterized by "comprehensive + multi-scale + quantitative" methodologies; (2) Research themes coalesce into five prominent clusters: "Aggregation of Brownfield Problem Analysis", "Precision Enhancement of Brownfield Identification through Information Technology", "Diversification of Brownfield Reutilization Assessment", "Process-Oriented Approaches to Brownfield Restoration Strategies", and "Expansion of Ecological Service Functions in Brownfield Contexts"; (3) Application methodologies encompass five key facets: "Temporal and Spatial Distribution Patterns of Pollutants", "Mechanisms and Correlations of Pollution Effects", "Evaluation of Pollution Risks", "Assessment of Brownfield Restoration Strategies", and "Integration of Brownfield Regeneration with Spatial Planning". Future brownfield research from the climate change perspective is poised to reflect characteristics such as "High-Precision Prediction, Comprehensive Dimensionality, Full-Cycle Evaluation, Low-Risk Exposure, and Commitment to Sustainable Development".

PAH levels in sediments from a coastal area heavily subjected to anthropogenic pressure (Asturias, north of Spain)

Ninety-two sediment samples collected along the Asturias coastline (north of Spain), were studied based on their concentrations of 16PAHs. Concentrations of Σ16PAH showed an average of 12.650 mg kg-1 d.w., which is higher than most other studies conducted around the world. The origins of PAHs present in the sediments are mainly from fuel combustion in industrial processes. The main source of PAH to the coastal system seems to be the Nalón River, which played a significant past role related to different industrial activities, highlighting thermal power stations located in the basin. On the other hand, the Avilés Estuary, hotspot of the regional heavy metallurgical industry was the area with the highest concentrations of Σ16PAH, with an average of 5 to 6 times higher than the rest studied. The risk assessment of Σ16PAH concentrations in the study area showed a high potential risk of contamination transfer to other environmental compartments.

Hg and As pollution in the soil-plant system evaluated by combining multispectral UAV-RS, geochemical survey and machine learning

The combination of a low-density geochemical survey, multispectral data obtained with Unmanned Aerial Vehicle-Remote Sensing (UAV-RS), and a machine learning technique was tested in the search for a statistically robust prediction of contaminant distribution in soil and vegetation, for zones with a highly variable pollutant load. To this end, a novel methodology was devised by means of a limited geochemical study of topsoil and vegetation combined with multispectral data obtained by UAV-RS. The methodology was verified in an area affected by Hg and As contamination that typifies abandoned mining-metallurgy sites in recent decades. A broad selection of spectral indices were calculated to evaluate soil-plant system response, and four machine learning techniques (Multiple Linear Regression, Random Forest, Generalized Boosted Models, and Multivariate Adaptive Regression Spline) were tested to obtain robust statistical models. Random Forest (RF) provided the best non-biased models for As and Hg concentration in soil and vegetation, with R2 and rRMSE (%) ranging from 0.501 to 0.630 and from 180.72 to 46.31, respectively, and with acceptable values for RPD and RPIQ statistics. The prediction and mapping of contaminant content and distribution in the study area were well enough adjusted to the geochemical data and revealed superior accuracy for As than Hg, and for vegetation than topsoil. The results were more precise than those obtained in comparable studies that applied satellite or spectrometry data. In conclusion, the methodology presented emerges as a powerful tool for studies addressing soil and vegetation pollution and an alternative approach to classical geochemical studies, which are time-consuming and expensive.

Magnetic separation for arsenic and metal recovery from polluted sediments within a circular economy

Several metals and metalloids (e.g., As, Cd, Cu, Pb, Zn) are toxic at low concentrations, thus their presence in sediments can raise environmental concern. However, these elements can be of economic interest, and several techniques have been used for their recovery and some of them have been widely applied to mining or to industrial soils, but not to sediments. In this work, wet high-intensity magnetic separation (WHIMS) was applied for As, Cd, Cu, Pb and Zn recovery from polluted sediments. A composite sample of 50 kg was taken in the Avilés estuary (Asturias, North Spain) with element concentrations above the legislation limits. Element distribution was assessed using wet-sieving and ICP-MS analysis, revealing that the 125-500 μm grain-size fraction accounts for the 62 w% of the material and that element concentration in this fraction is lower than in the other grain size fractions. Subsequently, WHIMS was applied at three different voltage intensities for the 125-500 μm and <125 μm fractions, revealing excellent recovery ratios, especially for the coarser material. Furthermore, magnetic property measurements coupled to microscopy analysis revealed that the success of the technique derives from concentrating metal-enriched iron oxides particles (ferro- and para-magnetic material) in a mixture of quartz and other minerals (diamagnetic particles). These results indicate the feasibility of the magnetic separation for metal and metalloid recovery from polluted sediments, and thus offer a double benefit of coastal area restoration and valuable material recovery in the context of a circular economy.

Iron nanoparticles to recover a co-contaminated soil with Cr and PCBs

Little attention has been given to the development of remediation strategies for soils polluted with mixture of pollution (metal(loid)s and organic compounds). The present study evaluates the effectiveness of different types of commercial iron nanoparticles (nanoscale zero valent iron (nZVI), bimetallic nZVI-Pd, and nano-magnetite (nFe₃O₄)), for the remediation of an industrial soil co-contaminated with Cr and PCBs. Soil samples were mixed with nZVI, nZVI-Pd, or nFe₃O₄ at doses selected according to their reactivity with PCBs, homogenized, saturated with water and incubated at controlled conditions for 15, 45 and 70 days. For each sampling time, PCBs and chromium were analyzed in aqueous and soil fractions. Cr(VI) and Cr leachability (TCLP test) were determined in the soil samples. The treatment with the three types of iron nanoparticles showed significant reduction in Cr concentration in aqueous extracts at the three sampling times (> 98%), compared to the control samples. The leachability of Cr in treated soil samples also decreased and was stable throughout the experiment. Results suggested that nZVI and nZVI-Pd immobilized Cr through adsorption of Cr(VI) on the shell and reduction to Cr(III). The mechanism of interaction of nFe₃O₄ and Cr(VI) included adsorption and reduction although its reducing character was lower than those of ZVI nanoparticles. PCBs significantly decreased in soil samples (up to 68%), after 15 days of treatment with the three types of nanoparticles. However, nFe₃O₄ evidenced reversible adsorption of PCBs after 45 days. In general, nZVI-Pd reduced PCB concentration in soil faster than nZVI. Control soils showed a similar reduction in PCBs concentration as those obtained with nZVI and nZVI-Pd after a longer time (45 days). This is likely due to natural bioremediation, although it was not effective for Cr remediation. Results suggest that the addition of nZVI or nZVI-Pd and pseudo-anaerobic conditions could be used for the recovery of soil co-contaminated with Cr and PCBs.

Analysis of the airborne mercury and particulate arsenic levels close to an abandoned waste dump and buildings of a mercury mine and the potential risk of atmospheric pollution

Abstract

The project SUBproducts4LIFE is a research project financed by the European Union within the framework of the LIFE programme which proposes to demonstrate innovative circular economy concepts by the reuse of industrial subproducts/waste (coal ash and gypsum from coal power plants, blast furnace slag and steelmaking slag from steel factories) for the remediation at a real scale of contaminated soils and brownfield areas related to Hg mining. The area it is developing includes the waste dumps and demolition waste of the metallurgical plant of the abandoned mercury mine La Soterraña in Asturias, Northern Spain. Before this restoration research project takes place, this paper aims to evaluate airborne mercury and arsenic levels in land strongly contaminated with arsenic and mercury. The goal is to evaluate the air quality and compare it with international literature under reference levels. The study sampled gaseous mercury with a high-resolution direct reading device (LUMEX RA-915) and arsenic and mercury particulates with an IOM sampler, Casella personal pump, analyzed in the laboratory, to ensure the Health and Safety of workers, visitors and pedestrians walking near the mine and near the villages. The study concludes that As and Hg levels in the air are below 1 μg/m3 for the general public and villages near the mine. For works in the rubble area in the mine, it is recommended that workers use personal protective equipment and control measures are used to keep arsenic and mercury levels as low as technically possible.

Article Highlights

Multiple pollution sources unravelled by environmental forensics techniques and multivariate statistics

Industrial sites affected by anthropogenic contamination, both past and present-day, commonly have intricate pollutant patterns, and source discrimination can be thus highly challenging. To this goal, this paper presents a novel approach combining multivariate statistics and environmental forensic techniques. The efficiency of this methodology was exemplified in a severely polluted estuarine area (Avilés, Spain), where factor analysis and clustering were performed to identify sub-areas with distinct geochemical behaviour. Once six clusters were defined and a pollution index applied, forensic tools revealed that the As speciation, Pb isotopes, and PAHs molecular ratios were useful to categorise the cluster groups on the basis of distinct pollution sources: Zn-smelting, coaly particles and waste disposal. Overall, this methodology offers valuable insight into pollution sources identification, which can be extended to comparable scenarios of complexly polluted environmental compartments. The information gathered using this approach is also important for the planning of risk assessment procedures and potential remediation strategies.

Status, fuzzy integrated risk assessment, and hierarchical risk management of soil heavy metals across China: A systematic review

Many reviewers have applied bibliometric analysis to conduct research on heavy metals (HMs) in Chinese soil and found that risk management decisions were biased to a certain extent due to case distribution difference and uncertainty. The previous methodologies were optimized integrating further uncertainty control and case identification in this study. A solid database was built, which included 779 cases published from 2009 to 2020. Based on the data features, the weight method was used to objectively shield extreme cases and normalize the concentrations. We conducted fuzzy eco- and health risk models via a triangular fuzzy number, and identified the risks from Pb, Cd, As, and Hg as the priority control metals. However, the national HMs risk had complex spatial heterogeneity and significant uncertainty. Thus, an "integrated risk grade criterion (IRGC)" was coupled with the risk threshold concentrations for the eco- and health risks to classify the each case. The cases above the moderate IRGC grade for Cd or Hg accounted for approximately 50%, and were mainly in the west and north of China, respectively. The high-grade areas were mostly in the south of China, including the Xijiang-Pearl River Basin and the Yangtze River Basin. It was demonstrated that warning health risks were likely a local question and that the ecological risks from Hg and Cd were considerable across China. By reviewing and summarizing the text information, high grades of soil Cd, Pb, and As were frequently reported in the villages associated with the mining industry, and certain soil Cd near suburban industrial complexes also caused warning health risks. Finally, this study proposed priority control objects for hierarchical risk management, including the identified heavy metals, areas, and pilot cities from multi-spatial scales.

Constructed Technosols: A Strategy toward a Circular Economy

Soil is a non-renewable natural resource. However, the current rates of soil usage and degradation have led to a loss of soil for agriculture, habitats, biodiversity, and to ecosystems problems. Urban and former industrial areas suffer particularly of these problems, and compensation measures to restore environmental quality include the renaturation of dismissed areas, de-sealing of surfaces, or the building of green infrastructures. In this framework, the development of methodologies for the creation of soils designed to mimic natural soil and suitable for vegetation growth, known as constructed soils or technosols, are here reviewed. The possible design choices and the starting materials have been described, using a circular economy approach, i.e., preferring non-contaminated wastes to non-renewable resources. Technosols appear to be a good solution to the problems of land degradation and urban green if using recycled wastes or by-products, as they can be an alternative to the remediation of contaminated sites and to importing fertile agricultural soil. Nevertheless, waste use requires analysis to ensure the salubrity of the starting materials. Moreover, materials produced on site or nearby minimize the cost and the environmental impact of transport, thus the involvement of local stakeholders in the urban land management must be encouraged.

Selecting efficient methodologies for estimation of As and Hg availability in a brownfield

The determination of soil metal(loid) availability presents controversy and there is no consensus or uniformity on used analytical methods. In this study nine single extraction methods (H₂O, CaCl₂, NaNO₃, NH₄NO₃, DTPA, EDTA, HCl, LMWOA, TCLP) and four sequential extraction procedures (Tessier, BCR, Wenzel and Fernández-Martínez) have been compared to estimate the availability of As and Hg in two soils from a highly polluted brownfield, especially with As. The metal(loid) concentrations were also determined in three native plant species (Lotus corniculatus, Betula celtiberica and Dactylis glomerata) collected in the habitat under study. Each single extractant showed a particular capacity of As/Hg extraction because they do not extract the same forms of each element. The availability of As and Hg depended on the element characteristics, soil properties, type of extractant and degree of pollution, thus the use of a single extraction procedure provides limited information of metal(loid) availability and to reach general conclusions is difficult. Regarding the sequential extractions, each procedure showed a specific pattern for As and Hg regardless of the soil. Thus, the choice of one or other method depends on the environmental conditions, metal(loid) and soil properties. In risk assessment studies it would be recommendable to select one of the more aggressive extractants, so as not to underestimate the environmental risk. In this regard, the sequential extraction procedures render more detailed information about metal(loid) potential availability in relation to soil properties. The analysis of native plant species showed higher metal(loid) concentrations in roots than in aerial parts and differences were observed depending on the metal(loid) and the species. In general, plants showed a higher BCFs for Hg than As even though the total and available As concentrations were higher than those found for Hg, which highlights the influence of plant species on the metal(loid) uptake.

Correlation between Geochemical and Multispectral Patterns in an Area Severely Contaminated by Former Hg-As Mining

In the context of soil pollution, plants suffer stress when exposed to extreme concentrations of potentially toxic elements (PTEs). The alterations to the plants caused by such stressors can be monitored by multispectral imagery in the form of vegetation indices, which can inform pollution management strategies. Here we combined geochemistry and remote sensing techniques to offer a preliminary soil pollution assessment of a vast abandoned spoil heap in the surroundings of La Soterraña mining site (Asturias, Spain). To study the soil distribution of the PTEs over time, twenty-seven soil samples were randomly collected downstream of and around the main spoil heap. Furthermore, the area was covered by an unmanned aerial vehicle (UAV) carrying a high-resolution multispectral camera with four bands (red, green, red-edge and near infrared). Multielement analysis revealed mercury and arsenic as principal pollutants. Two indices (from a database containing up to 55 indices) offered a proper correlation with the concentration of PTEs. These were: CARI2, presenting a Pearson Coefficient (PC) of 0.89 for concentrations >200 mg/kg of As; and NDVIg, PC of −0.67 for >40 mg/kg of Hg. The combined approach helps prediction of those areas susceptible to greatest pollution, thus reducing the costs of geochemical campaigns.