Urban Soils Research Articles

Impact of different irrigation & trace metals treatments on onion (Allium cepa L.) plant growth cultivated in rural and urban soils

AbstractThe present research attempts to evaluate the response of Allium cepa L. to different irrigation treatments and to indicate the optimum scheme along with plant growth, throughout a pot experiment during Spring 2021. The experimental procedure consisted of two different soil types, three treatments of irrigation and two levels of Cu and Zn (low and high), in four replications each. Irrigation events started when the lower allowable limit (LAL) reached a defined percentage of filed capacity (FC): 40% FC, 60% FC, and 75% FC and an irrigation event occurred with irrigation doses (Dn) equal to 60% FC, 40% FC, and 25% FC, respectively, to reach the value of FC. According to the results, the minimum yield was achieved by both soil types when Cu and Zn solution concentration and water stress were at their highest levels, although light texture soil (loamy sand—LS) allowed for superior growth. The optimum scheme was: the lower concentration of Cu and Zn solution along with LAL equal to 60% FC at the loamy sand soil. The outcomes suggest that frequent short irrigation doses at light-texture soils can result in yield response indicators when planted in pots. Furthermore, the influence of Cu and Zn cations at low concentrations can be advantageous for onions because Cu cations provide protection against fungal diseases, while Zn cations serve as nutrient support reducing the risk of metals deficiency.

Compositional-geochemical characterization of lead (Pb) anomalies and Pb-induced human health risk in urban topsoil.

Urban areas are characterized by a constant anthropogenic input, which is manifested in the chemical composition of the surface layer of urban soil. The consequence is the formation of intense anomalies of chemical elements, including lead (Pb), that are atypical for this landscape. Therefore, this study aims to explore the compositional-geochemical characteristics of soil Pb anomalies in the urban areas of Yerevan, Gyumri, and Vanadzor, and to identify the geochemical associations of Pb that emerge under prevalent anthropogenic influences in these urban areas. The results obtained through the combined use of compositional data analysis and geospatial mapping showed that the investigated Pb anomalies in different cities form source-specific geochemical associations influenced by historical and ongoing activities, as well as the natural geochemical behavior of chemical elements occurring in these areas. Specifically, in Yerevan, Pb was closely linked with Cu and Zn, forming a group of persistent anthropogenic tracers of urban areas. In contrast, in Gyumri and Vanadzor, Pb was linked with Ca, suggesting that over decades, complexation of Pb by Ca carbonates occurred. These patterns of compositional-geochemical characteristics of Pb anomalies are directly linked to the socio-economic development of cities and the various emission sources present in their environments during different periods. The human health risk assessment showed that children are under the Pb-induced non-carcinogenic risk by a certainty of 63.59% in Yerevan and 50% both in Gyumri and Vanadzor.

Potentially toxic elements in urban soils of the coastal city of the Sea of Azov: levels, sources, pollution and risk assessment

Potentially toxic elements in urban soils of the coastal city of the Sea of Azov: levels, sources, pollution and risk assessment

Microbial perspective on restoration of degraded urban soil using ornamental plants

The urban soil where abandoned buildings are demolished is barren and structurally poor, and this degraded soil requires restoration. Ornamental plants enhance the urban environment, increase biodiversity, and affect soil physicochemical properties, microbial diversity; however, their effects remain unclear. Thus, in this study, a mixed-planting meadow consisting of 14 perennial ornamental flower species, including Iris tectorum, Iris lacteal, and Patrinia scabiosaefolia, etc. Was planted at a demolition site with sewage-contaminated soil in Beijing. Simultaneously, a single-planting lawn of I. tectorum was established in a nearby park. We aimed to examine soil physicochemical properties, sequence soil bacterial 16S rRNA and fungal ITS amplicons, and analyze soil microbial diversity and community structure at both sites at five time points in the year after planting, To explore the effect of herbaceous ornamental plants on degraded urban soil, we used FAPROTAX and FUNGuild to predict bacterial and fungal functions, the bin-based null model to evaluate the soil microbial community, and random matrix theory to construct soil microbial molecular networks. The mixed-planting meadow produced a visually appealing landscape and dynamic seasonal enrichment, significantly increasing soil total nitrogen (TN) and organic matter (SOM) contents by 1.99 and 1.21 times, respectively. TN had a positive correlation with soil microbial α diversity and community structure. Dominant phyla at both sites included Proteobacteria, Actinobacteria, and Ascomycota. Although soil microorganisms were primarily influenced by stochastic processes, stochasticity was notably higher in the mixed-planting meadow than in the single-planting lawn. The mixed-planting meadow significantly increased the relative abundance of beneficial microorganisms, improving nitrification and aerobic ammonium oxidation of soil bacteria, as well as symbiotroph of fungi. No significant changes were observed in the single-planting lawn. The mixed-planting meadow established a complex soil microbial molecular network, enhancing the correlation between bacteria and fungi and increasing the number of key microorganisms. Our findings suggest the potential of mixed-planting meadow in restoring degraded urban soils by influencing the soil microbial community and enhancing the ecological service function. Our study provides theoretical support for applying mixed-planting meadow communities to improve the soil environment of urban green spaces.

Accumulation of Mn, Cu, and Zn in Flowers and Leaves of Catalpa bignonioides in an Urban Area Under Climate Change Conditions

Abstract Green areas are an important part of the urban landscape. Trees produce oxygen, provide shade, maintain soil moisture, and reduce the amounts of toxic gases and dust in the air. Due to the changing climate, species characteristic of other climatic zones, e.g. Catalpa bignonioides, are planted in urban parks in Poland, mainly due to the attractive appearance of the leaves and flowers. The aim of the study was to assess the content of Mn, Cu, and Zn in flowers and leaves of C. bignonioides in the urban park and to determine the value of bioconcentration coefficients (BCF) of these metals. The obtained results indicate that the flowers and leaves of C. bignonioides accumulate lesser amounts of manganese, copper, and zinc. It is a consequence of the limited bioavailability of these components in soils, due to too high pH values resulting from alkalinization of urban soils. The values of bioconcentration coefficients (BCF <1) confirm the low accumulation of Mn, Cu, and Zn in both leaves and flowers of C. bignonioides, due to the limited mobility of manganese, copper, and zinc compounds in the soils of the urban park and the low impact of falling dusts, which are the carriers of the analyzed components.

RARE-EARTH elements in the topsoils of a Russian industrial city: Sources and human health risk assessment

Research on rare-earth elements (REEs) in urban soils of Russian industrial cities is extremely limited. This study investigates the potential sources and human health risks of REEs contained in the topsoils of the industrial Russian city of Chelyabinsk. The study also takes into account natural sources of REE as the city is located on the border of granites (Urals) and sedimentary rocks (Western Siberia). We analyzed the concentration and distribution of REEs in the soils of four types of locations: residential courtyards, city parks, roadsides, and industrial locations. The total REE concentrations ranged from 44 to 255 mg/kg, with average concentrations of 140, 124, 113 and 89 mg/kg in the courtyards, roadsides, industrial location and city parks, respectively. The REE content in courtyard soils could be influenced by poor cleaning of fallen leaves. The ratios of light REE (LREE) to heavy REE (HREE) ranged from 9.5 to 10.1, revealing an obvious fractionation between them. The fractionation of LREE and HREE, and the REE/ES (European Shale) pattern showed that REE accumulation in Chelyabinsk soils has been disturbed by human activities. It was shown that the dust from industrial emissions was the main anthropogenic source of REE accumulation in urban soil. The largest amounts of REEs are emitted from an electrometallurgical plant and zinc production plant. Fortunately, the estimated daily intakes of REE from soils for children and adults were well below the safety thresholds. At the same time, in order to prevent social tension and reduce the anthropogenic load on the urban area, it is recommended to use phytoremediation technologies, smart landscaping of industrial and residential areas, more thorough cleaning of fallen leaves and road dust. It is also recommended to move the most dangerous production processes outside the urban area.

Soil source, not the degree of urbanization determines soil physicochemical properties and bacterial composition in Ningbo urban green spaces

Urban green spaces provide multiple ecosystem services and have great influences on human health. However, the compositions and properties of urban soil are not well understood yet. In this study, soil samples were collected from 45 parks in Ningbo to investigate the relationships among soil physicochemical properties, heavy metals and bacterial communities. The results showed that soil dissolved organic matter (DOM) was of high molecular weight, high aromaticity, and low degree of humification. The contents of heavy metals were all below the China's national standard safety limit (GB 3660–2018). The bioavailability of heavy metals highly correlated with soil pH, the content of DOC, the fluorescent component, the degree of humification and the source of DOM. The most abundant genera were Gemmatimonadaceae_uncultured, Xanthobacteraceae_uncultured, and Acidothermus in all samples, which were related to nitrogen cycle and bioavailability of heavy metals. Soil pH, bioavailability of Zn, Cd, and Pb (CaCl2 extracted) were the main edaphic factors influencing bacterial community composition. It should be noted that there was no significant impact of urbanization on soil physicochemical properties and bacterial composition, but they were determined by the source of soil in urban green spaces. However, with the passage of time, the effect of urbanization on urban green spaces cannot be ignored. Overall, this study provided new insight for understanding the linkage among soil physicochemical properties, heavy metals, and bacterial communities in urban green spaces.

Reducing the imperviousness of urban soils to enhance the quality of surface water: obstacles and levers to implementing ecological runoff management in the south of France

Urban pavements, which help to maintain clean and secure streets, generate large amounts of runoff that aggravate flooding and degrade the quality of surface water. In the context of ecological and climatic crisis, they also contribute to the creation of heat islands in cities, as well as hindering biodiversity. So greening cities must be encouraged.Our article highlights the case of Montpellier – Mediterranean Metropolis (Montpellier 3M, Southern France), which is undergoing one of the highest rates of demographic and urban growth in France. It asks questions around the impact of increased construction on the quality of water in small and fragile coastal catchment areas by the Mediterranean. It also examines local collective action in an attempt to identify the brakes and levers on greening initiatives for the effective management of runoff water, encouraged by legislation: de-paving, setting up rain gardens and returning to permeable urban soils.We use empirical material collected during sociological research in addition to hydrological and chemical measurements. Our aim was to elucidate the perspectives of a wide range of stakeholders, since an understanding of these is crucial in adapting blue-green infrastructure to the local context so that it is both efficient and accepted as a legitimate solution. Our examination suggests ways to think democratically about the dismantling of bitumen road paving to slow down urban water flows and thus improve the habitability of Southern European cities in a context of climatic and ecological crisis.

You are what you eat: urban soil lead predicts American robin (Turdus migratorius) blood lead in Flint, MI

You are what you eat: urban soil lead predicts American robin (Turdus migratorius) blood lead in Flint, MI

Impact of trace elements on invasive plants: Attenuated competitiveness yet sustained dominance over native counterparts

Trace element pollution has emerged as an increasingly severe environmental challenge owing to human activities, particularly in urban ecosystems. In farmlands, invasive species commonly outcompete native species when subjected to trace element treatments, as demonstrated in experiments with individual invader-native pairs. However, it is uncertain if these findings apply to a wider range of species in urban soils with trace elements. Thus, we designed a greenhouse experiment to simulate the current copper and zinc levels in urban soils (102.29 mg kg−1 and 148.32 mg kg−1, respectively). The experiment involved four pairs of invasive alien species and their natural co-existing native species to investigate the effects of essential trace elements in urban soil on the growth and functional traits of invasive and native species, as well as their interspecific relationship. The results showed that adding trace elements weakened the competitiveness of invasive species. Nonetheless, trace element additions did not change the outcome of competition, consistently favoring invasion successfully. Under trace element addition treatments, invasive species and native species still maintained functional differentiation trend. Furthermore, the crown area, average leaf area and leaf area per plant of invasive species were higher than those of native species by 157 %, 177 % and 178 % under copper treatment, and 194 %, 169 % and 188 % under zinc treatment, respectively. Additionally, interspecific competition enhanced the root growth of invasive species by 21 % with copper treatment and 14 % with zinc treatment. The ability of invasive species to obtain light energy and absorb water and nutrients might be the key to their successful invasion.

Microbial response to Nature-Based Solutions in urban soils: A comprehensive analysis using Biolog® EcoPlates™

The study presents a comprehensive examination of changes in soil microbial functional diversity (hereafter called microbial activity) following the implementation of Nature-Based Solutions (NBS) in urban areas. Utilizing the Biolog® EcoPlates™ technique, the study explored variations in microbial diversity in urban soil under NBSs implementation across timespan of two years.Significant differences in microbial activity were observed between control location and those with NBS implementations, with seasonal variations playing a crucial role. NBS positively impacted soil microbial activity especially at two locations: infiltration basin and wild flower meadow showing the most substantial increase after NBS implementation. The study links rainfall levels to microbial functional diversity, highlighting the influence of climatic conditions on soil microbiome. The research investigates also the utilization of different carbon sources by soil microorganisms, shedding light on the specificity of substrate utilization across seasons and locations. The results demonstrate that NBSs implementations lead to changes in substrate utilization patterns, emphasizing the positive influence of NBS on soil microbial communities. Likewise, biodiversity indices, such as Shannon-Weaver diversity (H′), Shannon Evenness Index (E), and substrate richness index (S), exhibit significant variations in response to NBS. Notably, NBS implementation positively impacted H′ and E indexes, especially in infiltration basin and wild flower meadow, underlining the benefits of NBS for enhancing microbial diversity.The obtained results demonstrated valuable insight into the dynamic interactions between NBS implementation and soil microbial activity. The findings underscore the potential of NBS to positively influence soil microbial diversity in urban environments, contributing to urban sustainability and soil health. The study emphasizes the importance of monitoring soil microbial activity to assess the effectiveness of NBS interventions and guides sustainable urban development practices.

Biochar application for enhancing water and nitrogen use efficiency of understory acacia species in a suburban native forest subjected to nitrogen deposition in Southeast Queensland

Abstract Purpose The fuel reduction prescribed burning and biochar application can have significant impacts on water and nitrogen (N) use efficiency of understory acacia species as well as soil carbon (C) and N pools in a suburban native forest subject to N deposition in Southeast Queensland, Australia. Methods We evaluated the impact of biochar application rates (0, 5.0 and 10.0 t biochar per hectare) and prescribed burning on soil-plant interactions in carbon (C) and N cycling in a suburban native forest in the first two years of biochar application or three and half years of the recently prescribed burning. Results Anthropogenic N deposition not only enhanced N losses caused by N leaching and denitrification, but also inhibited biological N fixation (BNF) by increasing N availability in forest systems. The Acacia leiocalyx with higher water use efficiency was more inclined to utilize easily available N resources (from N deposition), compared with A. disparismma. In this study, biochar application could indeed reduce N loss in forest soil and improve soil fertility by improving plant water and N use efficiency. Meanwhile, soil moisture content affected by biochar application also influenced soil N transformations by affecting soil microbial activity. Conclusion For urban forest soils, the high N availability caused by N deposition could inhibit the BNF in a suburban native forest ecosystem. The high-porosity physical structure of biochar applied increased the soil water content and soil N retention capacity.

Nitrogen enrichment does not adversely affect exchangeable bases in rainfed urban arable soils of Kumasi, a tropical West African city

Urbanisation induces nitrogen (N) enrichment in tropical soils. This enhances soil acidification, leading in turn to a decrease in effective cation exchange capacity (CECe) and base saturation (BSe). Here, we investigated if and how these effects of urbanisation-induced N inputs affect the soils of tropical urban agroecosystems. Our aim was to quantify the impact of urbanisation intensity (UI) on total N (TN) contents and stocks, and to detect possible adverse N effects on soil pH, CECe, and exchangeable bases in rainfed urban arable soils of Kumasi, a tropical city in Ghana, West Africa. We analysed 618 topsoil samples (0–10 cm) from arable fields within the urban perimeter, categorised into four classes forming a gradient from low to high UI. For baseline comparison, 9 samples each from both rural arable fields and an urban forest were included. Urban arable soils generally had higher TN levels than their rural counterparts. Among the urban arable soils however, TN levels decreased with increasing UI, possibly as crop production and related N export through harvest intensified. Conversely, increasing UI correlated with increased levels of exchangeable Ca2+, K+, and Na+. No adverse N effect on soil pH, CECe, and BSe was detected. This could be explained with the strong TN-SOC relationship (R2 ≥ 0.9), and an increasingly strong relationship between exchangeable bases and TN and SOC (R2 = 0.5–0.8) with increasing UI. These relationships suggested a major common source of TN, SOC, and exchangeable bases. As the soils are neither chemically fertilised nor limed, these findings supported earlier studies that this source is provided by dumped biodegradable household waste, charred matter, ash, and construction materials. We concluded that soil N enrichment through these materials in Kumasi is accompanied by abundant bases in the same materials, which overcompensate any theoretic acidification. Our findings imply that not only can the fertility of tropical urban arable soils in cities like Kumasi be maintained, but also that the crops and ground water may not be at risk from the mobilisation of trace elements and heavy metals due to the hindered soil acidification.

Sources, accumulation levels and environmental hazard of heavy metals and metalloids in soils and PM10 fractions of Severobaykalsk

Relevance. The need to study the ecological state of the soil cover of industrial cities, which is the main depositing environment for technogenic emissions of heavy metals and metalloids, to identify the geochemical characteristics of the region and assess the impact on public health. Aim. To assess the sources and accumulation of heavy metals and metalloids in soils and their fraction PM10 in Severobaikalsk and to assess the risks associated with them for public health. Methods. Total content of Zn, As, Cd, Pb, Cr, Co, Ni, Cu, Sb, Mo, V, W, Sr, Bi in soil, coal and ash samples was determined by mass spectral and atomic emission methods with inductive-coupled plasma. Geochemical (KK, Kc, Zc), sanitary and hygienic (Ko) indicators were used. Health risks for adults and children were assessed. Principal component analysis  was used. Results. In Severobaikalsk, the priority soil pollutants are Sb, Cu, Pb, Mo, Cr. The soils and their PM10 fraction in the transport zone, where Sb, Cu, Pb, Co, V, W, Ni are accumulated, are the most polluted. The greatest influence on the chemical composition of urban soils and PM10 particles is exerted by emissions from railway infrastructure and coal combustion at the Central Thermal Power Plant (22% for soils in general and 48% for the PM10 fraction). The average total level of contamination of urban soils and PM10 fraction corresponds to a low, non-hazardous level (Zc=6). The total non-carcinogenic risk of soil particles contaminated with heavy metals and metalloids. entering the body of children, exceeded the safe level 1 (from 1.60 in a residential one-story zone to 1.81 in a transport zone). For the adult population, HI values were below the acceptable threshold value. For adult health, there is no carcinogenic risk associated with ingestion or skin contact of As, Cr and Pb. For children, a dangerous risk (ILCRingest 5.56*10–4) of ingestion of carcinogenic heavy metals and metalloids was identified. 

Social prescribing of urban agriculture: The importance of minimizing risks from soil contamination

The value of Green Social Prescribing (GSP) of Urban Agriculture (UA) is well proven, with many cities witnessing a rise in such activities. However, with burgeoning interest, there comes an increased need to understand the potential risks associated with these practices. City officials, from planners to policy makers, are keen to scale-up the concept, particularly through supporting a wide range of urban farms and community gardens to contribute within the built environment. Our opinion piece highlights potential barriers associated with a legacy of heavy metal enriched urban soils which underpin many UA activities in post-industrial regions, signposting the need for greater awareness of their use and management. In doing so, we provide a series of recommendations for increasing knowledge exchange around urban soils and risk in the context of GSP.

GRANULOMETRIC COMPOSITION OF SOIL IN ASTANA CITY

Urban soil is one of the most polluted components of the environment. An increase in anthropogenic load on urban soils, as well as pollution by various wastes, the accumulation and compaction of particularly dangerous non-recyclable substances, covering the soil surface with a waterproof layer during construction provoke a violation of the structure and a change in the physical and chemical composition of the soil.
 Soil serves as a natural filter that absorbs and neutralizes toxic substances released by anthropogenic influences. This activity occurs at different levels depending on the mechanical and granulometric characteristics of the soil. Therefore, when studying the state of pollution of urban soils, it is necessary to pay attention to the species composition of soils.
 This article provides an assessment of the granulometric characteristics of soils in Astana. In the city of Astana, soil samples were analyzed from the microdistricts of Saryarka, Baikonur, Almaty, Yesil, Nura (60 points in total). The soils of the territory of the city of Astana are represented by the following types: dark chestnut soils and their varieties, meadow-chestnut soils and their varieties, solonchaks and urbanozems; according to the granulometric composition of the soil, they are represented by heavy, medium and light loams.

Lead bioaccessibility and commonly measured soil characteristics in Detroit, Michigan

Historical and contemporary use of lead (Pb) in gasoline, paints, and industry have led to its concentration in urban soils, presenting a human health risk, with disproportionate impacts on children living in urban areas. Contaminated soil is one of the major contributors to child Pb exposure. While many residents practicing urban agriculture have their soil tested to determine the amount of soil total Pb present, this measure does not provide a direct indicator of soil Pb bioaccessibility (used to predict bioavailability). Because bioavailability is ultimately necessary to determine the exposure risk, we aimed to gain a more refined understanding of Pb risk using measurements commonly performed as part of typical agricultural soil tests. Accordingly, we sampled soils from 142 residential parcels located in Detroit, MI. Soils were evaluated for: pH, organic matter content, cation exchange capacity, phosphorus, sulfur, calcium, potassium, magnesium, and sodium and total and in-vitro bioaccessible (IVBA) Pb. Detroit soil IVBA Pb ranged from 4.5% to 81%, with a mean of 39%. Total Pb, organic matter (OM) content and soil pH were found to be the most important predictors of Pb bioaccessibility. Soils typically had a relatively low OM content (mean of 5%) however, samples with higher OM content had lower IVBA (e.g., the IVBA was 15.2% smaller in soils with 7.5% OM). Soils were typically slightly basic (mean of 7.8); however, samples with pH closer to neutral had lower IVBA (e.g., the IVBA was 11.6% smaller in soils with a pH of 7.3). The proximity of soil sampling locations to former smelter locations was also found to influence Pb bioaccessibility, with samples closer to former Pb smelter sites having a somewhat higher average IVBA. Results suggest increasing soil OM content in urban soils will reduce Pb bioaccessibility. Building soil OM would therefore improve both soil fertility and decrease soil Pb bioaccessibility, imparting a predicted decrease in exposure risks.

Thermal conductivity of urban and artificial soils: methodological aspects and mathematical modeling

There are various methods for experimental determination of the thermal conductivity dependence on soil moisture and substrates. The influence of the sample structure (monolith, bulk sample), sample temperature, the method of installing the probe into the sample on the obtained readings of the TEMPOS device was studied and methodological recommendations were proposed. The dependence of thermal conductivity of soils bulk samples and substrates on moisture is shown. The spread of thermal conductivity values in the moisture range from hygroscopic to full moisture capacity for soddy-podzolic soil is 0.229–1.430 W/(m*K), for peat – 0.250–0.521 W/(m*K), for sand – 0.280–2.605 W/(m*K), for a mixture – 0.234–1.568 W/(m*K). ). The influence of properties such as density, particle size distribution, specific surface area, organic matter content, salinity affected thermal properties to a lesser extent. The established patterns can be used to calculate the temperature regime of soils in solving a number of applied problems related to the construction of special soil objects, for example, when creating urban soil structures. For this, it is necessary either to determine the thermal conductivity experimentally, or to calculate it, using the physical parameters of soils and substrates. The first method is labor-consuming, the second is less accurate. As an example, the equations available for work in the HYDRUS-1D (Chang–Horton and Campbell) model are used. These equations either overestimate the thermal conductivity in the area of high substrate humidity, or underestimate the thermal conductivity in the area of low substrate humidity (sand, loam, peat and a mixture based on them).

Integrated application of multiple indicators and geographic information system-based approaches for comprehensive assessment of environmental impacts of toxic metals-contaminated agricultural soils and vegetables

Conventional monitoring and mapping approaches are laborious, expensive, and time-consuming because they need a large number of data and consequently extensive sampling and experimental operations. Therefore, due to the growing concern about the potential of contamination of soils and agricultural products with heavy metals (HMs), a field experiment was conducted on 77 farm lands in an area of 2300 ha in the southeast of Shiraz (Iran) to investigate the source of metal contamination in the soils and vegetables and to model spatial distribution of HMs (iron, Fe; manganese, Mn; copper, Cu; zinc, Zn; cadmium, Cd; nickel, Ni, and lead, Pb) over the region using geographic information system (GIS) and geostatistical (Ordinary Kriging, OK) approaches and compare the results with deterministic approaches (Inverse Distance Weighting, IDW with different weighting power). Furthermore, some ecological and health risks indices including Pollution index (PI), Nemerow integrated pollution index (NIPI), pollution load index (PLI), degree of contamination (Cdeg), modified contamination degree (mCd), PIaverage and PIvector for soil quality, multi-element contamination (MEC), the probability of toxicity (MERMQ), the potential ecological index (RI), total hazard index (THI) and total carcinogenic risk index (TCR) based on ingestion, inhalation, and dermal exposure pathways for adults and children respectively for analyzing the noncarcinogenic and carcinogenic risks were calculated. Experimental semivariogram of the mentioned HMs were calculated and theoretical models (i.e., exponential, spherical, Gaussian, and linear models) were fitted in order to model their spatial structures and to investigate the most representative models. Moreover, principal component analysis (PCA) and cluster analysis (CA) were used to identify sources of HMs in the soils. Results showed that IDW method was more efficient than the OK approach to estimate the properties and HMs contents in the soils and plants. The estimated daily intake of metals (DIM) values of Pb and Ni exceeded their safe limits. In addition, Cd was the main element responsible for ecological risk. The PIave and PIvector indices showed that soil quality in the study area is not suitable. According to mCd values, the soils classified as ultra-high contaminated for Cu and Cd, extremely high for Zn and Pb, very high, high, and very low degree of contamination for Ni, Mn, and Fe, respectively. 36, 60, and 4 % of the sampling sites had high, medium, and low risk levels with 49, 21, and 9 % probability of toxicity, respectively. The maximum health risk index (HRI) value of 20.42 with extremely high risk for children was obtained for Ni and the HI for adults and children were 0.22 and 1.55, respectively. The THI values of Pb and Cd were the highest compared to the other HMs studied, revealing a possible non-cancer risk in children associated with exposure to these metals. The routes of exposure with the greatest influence on the THI and TCR indices were in the order of ingestion > inhalation > dermal. Therefore, ingestion, as the main route of exposure, is the route of greatest contribution to health risks. PCA analysis revealed that Fe, Mn, Cu, and Ni may originate from natural sources, while Fe was appeared to be controlled by fertilizer, and Cu primarily coming from pesticide, while Cd and Pb were mainly associated with the anthropogenic contamination, atmospheric depositions, and terrific in the urban soils. While, Zn mainly originated from fertilization. Findings are vital for developing remediation approaches for controlling the contaminants distribution as well as for monitoring and mapping the quality and health of soil resources.

A long-term perspective on coal combustion solid waste interacting with urban soil

Diverse wastes are produced during coal combustion and part of it is recycled worldwide in construction, agriculture, and other industries. As the waste becomes part of the environment, both intentionally and unintentionally, it is important to understand its long-term impact on surrounding soils. In this study, we characterized the situation where such waste, composed of mixed slag, fly ash, gangue, and coke material, was deposited 10–15 years ago as a layer within the urban soil. Two types of soil profiles were identified characterized by a different emplacement of the waste, which either occurred as a 10-cm thick layer or thin seams. Combined chemical and mineralogical analyses of the buried waste showed that slag fragments were affected by the dissolution of primary phases and precipitation of secondary carbonates, Fe-(hydr)oxides, and silica. The impact of the waste was detected in the underlying soils using ratios of trace elements enriched in the waste versus the uppermost soils (e.g., Ni/Pb, V/Zn, Ba/Pb) showing that it might be possible to recognize areas affected by similar deposited waste products. Combined leaching and mineralogical observations showed that V was released, but most probably as particles of unreactive V-rich sulfides, and Ba was preferentially leached from Ba-rich slag glass. Moreover, a combination of mineralogical observations, trace element ratios, and Pb isotopes showed that the thick layer of the waste may have acted not only as a source of potentially toxic elements but also as a trap (insulator) that stopped contamination coming from other sources (e.g., atmosphere).