Roadside Soils Research Articles

Heavy metals in roadside soil along an expressway connecting two megacities in China: Accumulation characteristics, sources and influencing factors.

Transportation is widely recognized as a significant contributor to heavy metal (HM) pollution in roadside soils. A better understanding of HM pollution in soils near expressways is crucial, particularly given the rapid expansion of expressway transportation in China in recent years. In this study, 329 roadside topsoil samples were collected along the Beijing-Tianjin Expressway, which connects two megacities in China. Chemical analysis showed that HM concentrations in the soil samples were generally below national limits. The mean pollution index (Pi) values for As, Cr, Cu, Ni, Pb, and Zn ranged from 0.94 to 1.01, while Cd and Hg exhibited slightly higher mean Pi values of 1.19 and 1.13, respectively. The Nemerow integrated pollution index values for all samples ranged from 0.71 to 4.97, with a mean of 1.26. This suggests a slight enrichment of HM above natural background levels, especially for Cd and Hg. Source apportionment using positive matrix factorization revealed that natural sources contributed the most to soil HMs (64.51 %), followed by agricultural sources (19.15 %), traffic sources (9.77 %), and industrial sources (6.57 %). The Shapley additive explanation analysis, based on the random forest model, identified soil organic carbon, deep soil HM content, altitude, total soil K2O, urbanization composite impact index, and total soil P as primary influencing factors. This indicates that the impact of transportation on roadside soils along the Beijing-Tianjin Expressway is currently relatively limited. The prominent influence of soil properties and altitude underscored the importance of "transport" and "receptor" in the soil HMs accumulation process at the local scale. These findings provide critical data and a scientific basis for decision-makers to develop policies for expressway design and roadside soil protection.

Assessing heavy metal contamination in roadside soils as a consequence of motor vehicle emissions

Assessing heavy metal contamination in roadside soils as a consequence of motor vehicle emissions

Salt Tolerance of Phragmites australis and Effect of Combing It with Topsoil Filters on Biofiltration of CaCl2 Contaminated Soil

De-icing salt used for safe winter driving can have negative impacts on local water quality, vegetation, and soils. This study aimed to evaluate the salt tolerance of reeds (Phragmites australis) against calcium chloride (CaCl2) and the biofiltration effect of combining it with topsoil biofilters for desalination in roadside ditches. Two experiments were conducted in a controlled environmental greenhouse over a period of 150 days. For the first experiment, the salt tolerance of P. australis was examined after treating reeds with five different concentrations of de-icing salt: 0, 1, 2, 5, and 10 g·L−1. In a second experiment, the effect of combining two topsoil filters (expanded clay and activated carbon), each planted with and without reeds, was investigated under a high CaCl2 concentration of 10 g·L−1. As the CaCl2 concentration increased, the electrical conductivity (EC) of soil leachate and the level of salt exchangeable cations (K+, Ca2+, Na+, and Mg2+) significantly increased whereas the acidity (pH) significantly decreased (all p ≤ 0.05). No statistical difference was observed in leaf length or width, while plant height, number of leaves, and both fresh and dry weights were significantly increased with increasing CaCl2 concentrations (p ≤ 0.05). Treatments using topsoil filters, particularly those with activated carbon and reeds, showed the greatest reduction in leachate EC and total exchange cations values. These results suggest that combining P. australis with topsoil filters can assist biofiltration effectively, demonstrating its applicability even in roadside soils subject to extreme levels of de-icing salts.

Analysis of lead contamination sources in roadside soil via the isotope tracing method

In addition to industrial contamination sources, road traffic sources are becoming major sources of potentially toxic elements (PTEs) contamination in soil. The PTEs contaminants generated during transport mainly include lead (Pb) and other elements. In this study, to clarify the sources of Pb in the roadside atmosphere and soil and their relative contributions, roadside atmospheric dustfall, sediment and soil samples were collected in industrial and nonindustrial areas, and the Pb isotope values of the samples were determined via inductively coupled plasmamass spectrometry (ICPMS). The sources of Pb in the roadside atmosphere and soil samples were quantified via isotope tracing. The results revealed that vehicle emissions contributed the most to Pb in the roadside atmosphere, followed by road sediment and natural atmospheric dustfall, with contributions ranging from 43.5 % to 48.9 %, 35.3–39.8 %, and 15.8–16.7 %, respectively. Roadside atmospheric dustfall contributed the most to Pb in roadside soil, followed by road sediment. Among these sources, roadside atmospheric dustfall and road sediment contributed 68.3–68.4 % and 31.6–31.7 %, respectively, in nonindustrial areas and 61.2–61.3 % and 38.7–38.8 %, respectively, in industrial areas. The results of this study provide a basis for preventing and controlling Pb pollution in roadside soils.

Assessment of the Heavy Metal Contaminations of Roadside Soil in Aizawl, Mizoram (India): An In-Depth Analysis Utilising Advanced Scientific Methodologies

The study was conducted to evaluate the heavy metal contamination levels in the roadside soil of Aizawl, Mizoram (India). Twelve sites were sampled monthly from August 2020 to July 2021, and concentrations of copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) were analyzed using atomic absorption spectrometer. The concentrations of heavy metals at the twelve studied sites varied widely from 0.43-1.06, 20.54-21.21, 2.69-3.41, 0.25-0.54, 0.31-0.49 and 1.35-1.77 for Cu, Fe, Mn, Ni, Pb, and Zn respectively. Pollution assessment tools such as the pollution load index, geo-accumulation index, and enrichment factor indicated moderate pollution levels. The study also observed fluctuations in the contamination levels due to the monsoon rainfall and the COVID-19 pandemic lockdown. Principal component analysis identified vehicular emissions, industrial activities, and atmospheric deposition as the potential sources of heavy metal contamination, with varying patterns observed at each site. While the observed heavy metal concentrations generally met permissible limits, the elevated levels suggested anthropogenic influences. It is crucial to continuously monitor and manage heavy metal contamination to mitigate potential health risks associated with heavy metal exposure.

The origin of toxic elements, environmental risk and new methods on prediction of weathering processes: case study of roadside soils (highway E75, Vojvodina, Serbia)

The origin of toxic elements, environmental risk and new methods on prediction of weathering processes: case study of roadside soils (highway E75, Vojvodina, Serbia)

Effect of UV exposure and natural aging on the in vitro PAHs bioaccessibility associated with tire wear particles in soil

Tire wear particles (TWP), as an emerging type of microplastics, are a significant source of contaminants in roadside soils due to their high concentration of pollutants, including polycyclic aromatic hydrocarbons (PAHs). This study explored the impact of ultraviolet (UV) exposure and natural aging on the in vitro bioaccessibility of PAHs associated with TWP in soil on a China-wide scale. Our findings suggested that UV exposure amplified the negative charge of TWP by 75 % and increased the hydrophobic groups on the particle surface. The bioaccessibility of 3- and 4-ring PAHs in TWP was significantly (p < 0.05) heightened by UV exposure. After 20 types of soils containing 2 % UV-exposed TWP underwent natural aging, the bioaccessibility of PAHs saw a significant decrease (p < 0.05) to 16–48 %, compared to 28–96 % in the unaged group. Soil pH and electrical conductivity (EC) were the two primary soil properties positively influencing the reduction of in vitro PAHs concentration and PAHs bioaccessibility. According to the prediction results, soils in southern China presented the highest potential region for the release of bioaccessible PAHs from TWP, highlighting the regional specificity of environmental impact. Our study provides valuable insights into the biological impact of PAHs associated with TWP on a regional scale, and offers scientific evidence for targeted soil risk management strategies.

Distribution Characteristics and Ecological Risk Assessment of Heavy Metals in Roadside Soil of Important National Highways on the Qinghai-Xizang Plateau

To clarify the impact of transportation on the sensitive and fragile ecosystems of the Qinghai Tibet Plateau and major ecological safety barrier functions, soil samples within 0-25 m on the roadside were collected from sections of national highways such as G214, G213, G345, G109, G316, and G317, and the contents of six heavy metals were analyzed. Then, the degree of heavy metal pollution and the risk of ecological hazards were evaluated using the single-factor pollution index method （Pi）, Nemero comprehensive index method （PN）, and potential ecological risk index method （RI）. The results showed that the heavy metal contents of As, Cd, Hg, Ni, Pb, and Zn in the soil of important transportation national roads on the Qinghai Tibet Plateau ranged from 5.65 to 176.00, 0.04 to 0.27, 0.01 to 0.14, 9.52 to 113.00, 9.16 to 54.50, and 24.70 to 109.00 mg·kg-1, respectively, showing high variability. In some sections of the soil, the values of the elements As, Cd, and Hg were higher than the local soil background values. The single-factor pollution index of heavy metals in roadside soil was Pi （As） &gt; Pi （Hg） &gt; Pi（Cd） &gt; Pi （Pb） &gt; Pi （Ni） &gt; Pi （Zn）. The Nemero comprehensive pollution index ranged from 0.41 to 9.20, with an average value of 1.53, indicating clean and mild pollution. Some areas showed a moderate or severe pollution. The average potential ecological risk index of the research section was 106.2, and the soil was generally in a state of no pollution and light pollution. Only two road sections had soil heavy metal enrichment reaching moderate and strong ecological hazards. The comprehensive potential risk of the G213a road section indicated moderate to severe ecological risk, mainly contributed by Hg, As, and Cd. The comprehensive pollution risk of the G317 road section indicated mild to moderate ecological risk, mainly contributed by Hg and Cd. The heavy metal content in the soil of the Qinghai Tibet Plateau road area was not significantly correlated with the roadside distance and soil depth but was significantly positively correlated with the annual average temperature （P &lt; 0.05）. In all, there was a trend of heavy metal input into the soil environment in areas with intense human activities and high traffic flow during road construction on the Qinghai Tibet Plateau.

Assessment of Heavy Metal Concentrations in Roadside Soils from Mafraq, Jordan

Assessment of Heavy Metal Concentrations in Roadside Soils from Mafraq, Jordan

Chemical and micronutrients assessment in Himalayan Foothill highway soil surface

This study examines the chemical properties and micronutrient concentrations of roadside soil in the ecologically sensitive Himalayan foothills of Uttarakhand, India. The primary objective is to assess soil contamination levels and their implications for urban ecosystem services. Soil samples from 13 locations were systematically collected, processed, and analyzed using atomic absorption spectrophotometry. Results indicated average concentrations of Zn, Cu, Fe, Mn, and Ni at 9.94, 3.28, 24.32, 17.35, and 0.28 mg/kg, respectively. Significant variations in soil chemical properties and micronutrient levels (p < 0.05) were observed across different sites, excluding phosphate levels. These findings underscore the critical need for targeted environmental management strategies to mitigate soil contamination and preserve vital ecosystem services in urbanized regions. The data provided can guide administrators in developing policies that promote sustainable development and environmental resilience.

A Synoptic Review Of Heavy Metal Accumulation In Soils Along Urban Roadsides

Heavy metal poisoning in roadside soils is a worldwide environmental issue with serious consequences for both ecological health and human well-being. This study provides a detailed summary of the state of heavy metal pollution along roads, spanning multiple locations and centuries

Tree stumps as passive samplers for trace metal dust deposition

Atmospheric dust is contaminated by trace metals in many parts of the world due to human industrial activities. This study evaluates tree stumps as passive samplers of dust deposition and bioindicators of trace metal dust contamination in a mine impacted environment. Tree stumps (n = 230) and adjacent soils from Cu–Zn mining areas in northeastern China were analysed in situ for their trace metal concentrations using portable X-ray fluorescence (pXRF). Arsenic and Zn concentrations in tree stumps and roadside soils of each location all decreased with distance from the road in a power-law relationship, indicating a common pollution source (resuspension and redeposition of road dust). Micro-XRF images of vertical tree stump slices indicate that As and Zn were concentrated on the cut (uppermost) surface of tree stumps. This indicates atmospheric deposition as a primary contributor to elevated As and Zn concentrations in tree stumps. Trace metals in soils may have other sources besides atmospheric deposition (e.g., migration from buried ore-bodies or rock weathering), which may confound distinguishing sources in polluted areas. Here, we show that the analysis of tree stumps are suitable indicators of atmospheric trace metal contamination. Compared to surface soils, tree stumps can better reflect road dust resuspension and redeposition because unlike soils, atmospheric deposition is the primary contributor to their trace metal concentrations.

Data-driven intelligent modeling of unconfined compressive strength of heavy metal-contaminated soil

This study focuses on empirical modeling of the strength characteristics of urban soils contaminated with heavy metals using machine learning tools and their subsequent stabilization with ordinary Portland cement (OPC). For dataset collection, an extensive experimental program was designed to estimate the unconfined compressive strength (Qu) of heavy metal-contaminated soils collected from a wide range of land use pattern, i.e. residential, industrial and roadside soils. Accordingly, a robust comparison of predictive performances of four data-driven models including extreme learning machines (ELMs), gene expression programming (GEP), random forests (RFs), and multiple linear regression (MLR) has been presented. For completeness, a comprehensive experimental database has been established and partitioned into 80% for training and 20% for testing the developed models. Inputs included varying levels of heavy metals like Cd, Cu, Cr, Pb and Zn, along with OPC. The results revealed that the GEP model outperformed its counterparts: explaining approximately 96% of the variability in both training (R2 = 0.964) and testing phases (R2 = 0.961), and thus achieving the lowest RMSE and MAE values. ELM performed commendably but was slightly less accurate than GEP whereas MLR had the lowest performance metrics. GEP also provided the benefit of traceable mathematical equation, enhancing its applicability not just as a predictive but also as an explanatory tool. Despite its insights, the study is limited by its focus on a specific set of heavy metals and urban soil samples of a particular region, which may affect the generalizability of the findings to different contamination profiles or environmental conditions. The study recommends GEP for predicting Qu in heavy metal-contaminated soils, and suggests further research to adapt these models to different environmental conditions.

Preliminary Investigation of Microplastics in Roadside Soils of Port Harcourt and Elele in Rivers State, Nigeria

Preliminary Investigation of Microplastics in Roadside Soils of Port Harcourt and Elele in Rivers State, Nigeria

Road salt applications mobilize trace elements from roadside soil to shallow groundwater

In regions where deicers are applied to roadways, micronutrients and toxic trace elements may be mobilized from soil material into soil porewater. These elements may subsequently migrate with soil porewater to surface waters and groundwaters, potentially leaching the soil of micronutrients or introducing toxins to water resources. Our study thus aims to quantify the timing and extent of trace element releases from soil material to soil porewater and groundwater in response to deicing events. We sampled soil porewater near a road at a rural site for trace elements and compared the results to salt applications and soil porewater Na and Cl levels. We also assessed trace element, Na, and Cl concentrations in a karst spring at the rural site and a karst spring at an urban site to evaluate the role of land use in conveying these contaminants to groundwater. We found that certain trace elements (e.g., As, Ba, Fe, Sr) peaked concomitantly with Na and Cl in soil porewater at the rural site after road deicing events, suggesting their release due to excess salt inputs to the soil. We did not observe increases in trace element concentrations at the rural karst spring following individual road salt applications, likely due to low deicer inputs and trace element levels across its recharge basin. However, at the urban site, we observed that other assemblages of trace elements (e.g., As, Cu, Li) in the karst spring peaked with deicing-related Na and Cl pulses. We also found positive and significant correlations between salt applications to the recharge basin and exports of some trace elements (e.g., As, Cu, Li, Se) at the urban karst spring, indicating deicing events triggered trace element releases to groundwater. Overall, we detected road salt-driven trace element release from soil material to soil porewater and groundwater that was exacerbated by urbanization.

Evaluation of Heavy Metals in Roadside Soil of Tumfure Main Market, Gombe State

Heavy metal pollution has been a problem of concern in soil ecology in recent decades. This study evaluated the physico-chemical characteristics and heavy metal contents in roadside soil samples of Tumfure main market, Gombe, Nigeria. The soil samples were collected from six different sampling points with a control sample each by handpicking, this was followed by oven-drying, ground to fine grain, and then sieved using a 2 mm mesh sieve. The pH, electrical conductivity and bulk density were carried out on the soil samples, sieve and sedimentation method were used to determine the soil texture. The soil samples were weighed and digested using mixture of HCl and HNO3. The contents (mg/kg) of four metals (cadmium, copper, lead and zinc) were estimated using Atomic Absorption Spectrophotometer (AAS). Among the metals analyzed, the contents of Cd, Cu and Pb were not detected while the content of Zn (23.454 - 36.026) was found to be within the desirable permissible limits by the World Health Organization (WHO) and European Regulatory Standards (EURS) whose prevalence is to be considered non-toxic in unpolluted soils.

Assessment of bioremediation potential of Calotropis procera and Nerium oleander for sustainable management of vehicular released metals in roadside soils

Land transportation is a major source of heavy metal contamination along the roadside, posing significant risks to human health through inhalation, oral ingestion, and dermal contact. Therefore, this study has been designed to determine the concentrations of vehicular released heavy metals (Cd, Pb, Ni, and Cu) in roadside soil and leaves of two commonly growing native plant species (Calotropis procera and Nerium oleander).Two busy roads i.e., Lahore-Okara road (N-5) and Okara-Faisalabad roads (OFR) in Punjab, Pakistan, were selected for the study. The data were collected from five sites along each road during four seasons. Control samples were collected ~ 50 m away from road. The metal content i.e. lead (Pb), cadmium (Cd) nickel (Ni) and copper (Cu) were determined in the plant leaves and soil by using Atomic Absorption Spectrophotometer (AAS). Significantly high amount of all studied heavy metals were observed in soil and plant leaves along both roads in contrast to control ones. The mean concentration of metals in soil ranged as Cd (2.20–6.83 mg/kg), Pb (4.53–15.29 mg/kg), Ni (29.78–101.26 mg/kg), and Cu (61.68–138.46 mg/kg) and in plant leaves Cd (0.093–0.53 mg/kg), Pb (4.31–16.34 mg/kg), Ni (4.13–16.34 mg/kg) and Cu (2.98–32.74 mg/kg). Among roads, higher metal contamination was noted along N-5 road. Significant temporal variations were also noted in metal contamination along both roads. The order of metal contamination in soil and plant leaves in different seasons was summer > autumn > spring > winter. Furthermore, the metal accumulation potential of Calotropis procera was higher than that of Nerium oleander. Therefore, for sustainable management of metal contamination, the plantation of Calotropis procera is recommended along roadsides.

Urban roadside greenery as a carbon sink: Systematic assessment considering understory shrubs and soil respiration

Roadside greenery is an efficient strategy for maximizing ecosystem services, including carbon sequestration in urban settings. However, the quantification of carbon sequestration is not comprehensive because understory shrubs and soil respiration have not been thoroughly considered. We developed an integrated methodology that combined field measurements and greenhouse incubation to comprehensively assess carbon sequestration in roadside greenery systems. The system was defined as an 8 m long section comprising a single tree (Zelkova serrata), 79 shrubs (Euonymus japonicus), and soil. Annual carbon uptake by a tree was estimated using an allometric equation derived from an official government report. For shrubs, carbon uptake was measured in the field by monitoring CO2 concentration change in the chamber enclosing the leaves and stems. Annual carbon uptake by shrubs was estimated by using the regression equation among carbon uptake, air temperature, and photosynthetically active radiation. We also estimated shrub root respiration by combining net primary production (NPP) from the greenhouse incubation and measured pruning effect in the field. This enabled us to differentiate heterotrophic respiration from the total soil respiration. The overall methodology accurately assessed net ecosystem production (NEP) from the roadside greenery system, which is 0.528 kg C m−2 yr−1. If this figure is extended to all roads in the target city, it can offset daily carbon emitted from the total registered passenger vehicles in the target city. Considering that shrubs sequester an amount equivalent to 29.3 % of the carbon sequestered by tree species, the current greenhouse gas inventory should include shrubs as an important carbon sink. As we also revealed that roadside soil has high carbon vulnerability, proper soil management is needed to enhance NEP. Our systematic approach evaluating the carbon balance within the roadside greenery system can be applied to other cities, contributing to enhance global understanding of urban carbon cycle.

Re-Interpretation of Metal(Loid) Concentrations in Urban Soils of Two Different Land Uses by Positive Matrix Factorisation

Positive matrix factorisation (PMF) is a receptor model, which is frequently used in environmental geochemistry for metal(loid)s’ source apportionment in various matrices. In this study, concentration data for As, Cu, Co, Cr, Fe, Mn, Ni, Pb, Sb, V and Zn in urban soils of two land uses (playground and roadside soils) from the city of Bratislava (Slovak Republic) were reinterpreted using the PMF model to quantify the contributions of individual sources of metal(loid)s in soils. Brake and tyre abrasion (27.0%), mixed traffic/industrial sources (14.3%), and natural origin (58.7%) were identified for roadside soils, while mixed traffic sources (28.4%), Cu-specific source (24.6%), and natural origin (47.0%) contributed to the metal(loid) concentrations in playground soils. Factor contributions revealed prevailing non-exhaust sources dominated by Cu, Sb and Zn over mixed traffic/industrial sources in roadside soils, following the world trend. Strong negative correlations of the 206Pb/207Pb isotopic ratio with Factor 1 in both groups of soils, representing traffic and industrial sources, are an evidence of the correct assignment of the obtained factor profiles to the actual sources of metal(loid)s in soils. There were significant differences in the proportion of mixed traffic sources in playground soils among the five urban districts, while the largest proportion of this source was identified in the city centre with the longest urbanisation and industrial history. Error estimation methods (displacement, bootstrap, displacement with bootstrap) proved that the data fit the model well and there was a minimal rotational ambiguity and random errors in the base model run.

Human health risk assessment of metal-contaminated soils in Sydney estuary catchment (Australia)

Sydney estuary catchment supports the largest city in Australia and provides essential eco-social and environmental services; however, the region has been influenced by extensive anthropogenic modification. Soil metal concentrations in the catchment had been studied previously; however, the current investigation was designed to determine the risk posed by these contaminants to human health. Soil metal concentrations were higher than observed in most global capitals and increased substantially in the south and south-east of the catchment and close to the central business district. Road-side soils and road dust contained the highest concentration of metals in the catchment. Lead in catchment soils was closely related to traffic density and sourced from the historic use of Pb in petrol. A human health assessment indicated that soil Cd, Ni and Zn posed no non-carcinogenic risk (NCR), or carcinogenic risk (CR) for children, or adults in Sydney estuary catchment and that Cu and Cr may pose minor NCR for children. Vehicle-related Pb raised the greatest human health risk in catchment soils and may pose NCR at 32% and 4.3% of sites for children and adults, respectively. Inconsistent analytical techniques used in CR and NCR evaluations produce incomparable assessments and a consistent` methodology is suggested to improve interpretation. Human health risk may well be higher than commonly calculated due to pollutants present in urban soil not being included in assessments.