Assessment of Pb and Ni and potential health risks associated with the consumption of vegetables grown on the roadside soils in District Swat, Khyber Pakhtunkhwa, Pakistan

Vegetables cultivated near roads absorb toxic metals from polluted soil, which enter the human body through the food chain and cause serious health problems to humans. The present study investigated the concentration of lead (Pb) and nickel (Ni) in soils and vegetables grown along the roadside of District Swat, Pakistan, and the health risks associated with the consumption of the tested vegetables. In results, Pb concentration was higher in plants located at the distance between 0-10 m away from the roadside than the WHO permissible limit. In such plants, Pb concentration was higher than Ni. Rumex dentatus contained the highest concentration of Pb (75.63 mg kg^-1 DW) among the tested vegetables while Ni concentration (27.57 mg kg^-1 DW) was highest in Trachyspermum ammi as compared to other plants. Concentration and accumulation of both the metals decreased in soil and plants with increasing distance from the road. Similarly, target hazard quotient values noted for Pb (up to 3.37) were greater than unity, which shows that there is a potential risk associated with the consumption of tested vegetables near the road. Moreover, the values of target cancer risk (up to 0.8413) were greater than 0.0001, which shows that there is a risk of cancer with the consumption of tested vegetables. In conclusion, the consumption of tested vegetables was very dangerous as it may lead to higher risks of cancer. Strict regulatory control is recommended on the cultivation of these vegetables along the roadside to avoid any contamination due to roadside exhaust.

Accumulation, environmental risk characteristics and associated driving mechanisms of potential toxicity elements in roadside soils across China

Roadside soils may be affected by potential toxicity elements (TPEs) from vehicles; however, pollution status, ecological and health risks of PTEs in roadside soils were rarely reported on national scale. In this study, a dataset of PTEs in roadside soils was compiled based on the literatures published in 2000-2021, and then pollution level, ecological and health risks of PTEs were evaluated using geochemical accumulation index (I_geo), potential ecological risk index (ER), and human risk assessment coupled with Monte Carlo simulation. Driving factors of PTE accumulation in soils were determined by Geo-detector method. Results indicated that Cd exhibited moderate pollution and considerable ecological risk with the highest I_geo of 1.25 and ER of 100.1, respectively. Vehicle ownership (VP) and precipitation (PP) significantly affected accumulation of PTEs, with q values of 0.209 and 0.191 (P < 0.05), respectively. VP paired with PP enhanced nonlinearly PTE accumulation (q = 0.77). Only 6.89% and 1.54% of non-carcinogenic risks for children and adolescent exceeded the threshold of 1, respectively, whereas 93.11%, 95.67%, 58.80% and 58.14% of carcinogenic risks for senior, adults, adolescent, and children surpassed 1E-06, respectively. The results of this study provided valuable implication for managers to design effective strategies for pollution prevent and risk control.

Abundance and fate of glass microspheres in river sediments and roadside soils: Lessons from the Świętokrzyskie region case study (south-central Poland)

Traffic-related glass microspheres in fluvial and roadside soil settings were used as an indicator for the occurrence and extent of road dust as a source of emissions. Microspheres were found in sediments of two rivers, at a distance of approximately 25 km of the city of Kielce (south-central Poland). Their highest contents in sediments were recorded near street stormwater drains into the Silnica River flowing through the city. The study also showed no influence of local bridges on the spatial distribution of glass microspheres in the river deposits. In contrast, soils adjacent to a two-lane highway revealed the presence of microspheres as far as 60 m of the roadway. As opposed to other road dust components, which have commonly been applied in traffic contamination studies, glass microspheres were a good indicator for road dust contamination. Most microspheres showed diverse concentrations of all minor and trace metal(loid)s. The mean contents of As, Pb and Sb (n = 601) were: 0.003 wt%, 0.014 wt% and 0.010 wt%, respectively, and only in some microspherules these elements exceeded EU current/expected regulatory standard levels (0.02%/0.015% for each). Although generally considered to be non-toxic, silica rich microbeads might be the best proxy for non-exhaust particle matter discharged from the road traffic into the environment.

The source apportionment, pollution characteristic and mobility of Sb in roadside soils affected by traffic and industrial activities

Antimony (Sb), as an emerging pollutant, has aroused people's concerns for its wide usage in industrial production. In this study, we identify and quantify the traffic-derived Sb and investigate its mobility in roadside soils affected by traffic and industrial activities. 73 surface roadside soils and 5 transects in three areas nearby different industries (smelting, power and refining, and waste incineration) were collected and analyzed. Results showed that the Sb concentration ranged between 0.54 and 9.32 mg/kg, and the mean EF_s value was 4.63, which indicated moderate to significant Sb enrichment. Significantly high concentrations of Sb occurred at locations with heavy traffic and frequent braking process, with an average concentration of 4.13 mg/kg, compared to the control sites (2.01 mg/kg). Moreover, Sb diffused exponentially with increasing distance from road edges. These results suggested that traffic activities were the main source of Sb in roadside soils. According to the quantitative calculation, the average contributions from traffic, industrial activities and soil parent material to Sb accumulation in roadside soils were 50.73%, 21.38% and 27.88%, respectively. Even though Sb was slightly mobile, roadside soils was a persistent source of potentially mobile Sb which may release into water and cause long-term environmental risk.

The input of trace elements from the motor transport into urban soils of Wrocław, Poland

The pH and the EC of soil solutions display a typical character of urban soils, and the concentration of some metal content in the selected locations indicate a strong influence of the motor transport on the Wrocław's congested roads. Sampling stands were located at the busiest road junctions. Pollution of soils with Zn, Cu, Pb, Ni, Cr and Cd along the more important traffic roads of Wrocław within the borders of the city has been measured. The internal ring road (encircling the central districts of the city) and the external ring road (the Eastern Ring Road) of the city of Wrocław along with busy exit roads on the border of city were compared. Zinc concentration in soils was exceeded locally relative to standard for soils of group I, according to the Polish Ministry of Environment Regulation from September 1st, 2016. The pollution indexes compared to the geochemical background in the uncontaminated soils of Poland showed an enrichment of Wrocław's soils with trace elements in many locations. Mean values of indexes for all samples display the dominant influence of zinc, copper and nickel on the soil contamination in Wrocław. The results of the studies did not confirm the correlation between the decrease of all metals concentration with the distance from the city center. The Pearson's correlation coefficients between pairs of Zn-Cu, Zn-Pb and Cu-Pb show significantly correlated linear relationships of metals in soils. The frequency histograms of trace elements in soils reveal large deviations from the Gaussian curve due to a significant diversification of metal concentrations between different locations.

Traffic-related distribution of antimony in roadside soils

Vehicular emissions have become one of the main source of pollution of urban soils; this highlights the need for more detailed research on various traffic-related emissions and related distribution patterns. Since the banning of asbestos in the European Union, its substitution with antimony (Sb) in brake linings has led to increased inputs of this toxic metalloid to environmental compartments. The objective of this study was to provide detailed information about the spatial distribution patterns of Sb and to assess its mobility and bioavailability. Roadside soils along an arterial road (approx. 9000 vehicles per day) in Cologne (Germany) were studied along five transects, at four soil depths and at seven sampling points set at varying distances from the road (n = 140). For all samples, comprehensive soil characterization was performed and inverse aqua regia-extractable trace metal content was determined being pseudo-total contents. Furthermore, for one transect, also total Sb and a chemical sequential extraction procedure was applied (n = 28). Pseudo-total Sb for all transects decreased significantly with soil depth and distance from the road, reflecting a distribution pattern similar to that of other trace metals associated with brake lining emissions. Conversely, metals associated with exhaust emissions showed a convex distribution. The geochemical fractionation of Sb revealed the following trends: i) non-specifically sorbed Sb was <5%; ii) specifically sorbed Sb was only detected within 1 m distance from the road and decreased with depth; iii) Sb associated with poorly-crystalline Fe oxides decreased with distance from the road; and iv) content of Sb bounded to well-crystalline Fe oxides, and Sb present in the residual fraction remained relatively constant at each depth. Consequently, roadside soils appear to inhibit brake lining-related Sb contamination, with significant but rather low ecotoxicological potential for input into surface and groundwater.

Heavy metal enrichment in roadside soils in the eastern Tibetan Plateau

The effects of human activities on heavy metal pollution in soil have been less investigated on the Tibetan Plateau. The present study was designed to assess the effects of highway traffic on Cu, Zn, Pb, and Cd enrichments in the 0-60-cm soil profile in the eastern Tibetan Plateau. Soils were sampled at four transects (with an altitude range of 2643-2911 m) across the G212 highway and five transects (3163-3563 m) across the G213 highway. Background concentrations of Cu, Zn, Pb, and Cd to the 60-cm soil depth (measured at each transect 400 m away from highways) varied greatly among transects and between highways. However, this spatial variation in the heavy metal concentrations was not related to the altitude of the investigated areas. On each the left and right sides of G212 or G213, Cu, Zn, and Pb concentrations to the 60-cm depth, at 5, 10, 20, and 50 m away from the highway, were all generally greater than the respective metal background concentrations. Cd concentrations to the 20 cm on G212 or 60-cm soil depth on G213 increased prominently within a distance of 20 m away from the highways, compared to background values in different depths. From the curb to 400 m away from highways, concentrations of Cu, Zn, Pb, and Cd were generally higher in the upper than in the lower soil layers. This may suggest that other factors such as atmospheric deposition were also contributable to the accumulation of heavy metals in soil. The contamination factor (C _f ) calculation showed that roadside soils to the 60-cm depth, within a distance of 50 m from the curbs of both G212 and G213, were moderately (1 ≤ C _f  < 3) contaminated with Cu, Zn, and Pb. The contamination from Cd mainly occurred (1 ≤ C _f  < 8) in the top 20 cm soil with a closer distance from the highways. Our results indicated that traffic effects in enriching heavy metals reached 60-cm depth in roadside soils on the eastern Tibetan Plateau. For assessment of heavy metal pollutions in soil in mountainous areas, it is necessary to in situ identify the background values.

Insights into the chemical partitioning of trace metals in roadside and off-road agricultural soils along two major highways in Attica's region, Greece

We report in this study the magnetic properties and partitioning patterns of selected trace metals (Pb, Zn, Cu, Cd, Ni) in roadside and off-road (>200m distance from the road edge) agricultural soils collected along two major highways in Greece. Sequential extractions revealed that the examined trace metals for the entire data set were predominantly found in the residual fraction, averaging 37% for Cd up to 80% for Cu. Due to the strong influence of lithogenic factors, trace metal pseudototal contents of the roadside soils did not differ significantly to those of the off-road soils. Magnetic susceptibility and frequency dependent magnetic susceptibility determinations showed a magnetic enhancement of soils; however, it was primarily related to geogenic factors and not to traffic-derived magnetic particles. These results highlight that in areas characterized by strong geogenic backgrounds, neither pseudototal trace metal contents nor magnetic properties determinations effectively capture traffic-related contamination of topsoils. The vehicular emission signal was traced by the increased acid-soluble and reducible trace metal contents of the roadside soils compared to their off-road counterparts. In the case of Cu and Zn, changes in the partitioning patterns were also observed between the roadside and off-road soils. Environmental risks associated with agricultural lands extending at the margins of the studied highways may arise from the elevated Ni contents (both pseudototal and potentially mobile), and future studies should investigate Ni levels in the edible parts of plants grown on these agricultural soils.

Traffic-related heavy metals uptake by wild plants grow along two main highways in Hunan Province, China: effects of soil factors, accumulation ability, and biological indication potential

This study was performed to investigate pollution of traffic-related heavy metals (HMs-Zn, Pb, Cu, Cr, and Cd) in roadside soils and their uptake by wild plants growing along highways in Hunan Province, China. For this, we analyzed the concentration and chemical fractionation of HMs in soils and plants. Soil samples were collected with different depths in the profile and different distances from highway edge. And leaves and barks of six high-frequency plants were collected. Results of the modified European Community Bureau of Reference (BCR) showed that the mobile fraction of these HMs was in the order of Cd > Pb > Zn > Cu > Cr. A high percentage of the mobile fraction indicates Cd, Pb, and Zn were labile and available for uptake by wild plants. The total concentration and values of risk assessment code (RAC) showed that Cd was the main risk factor, which were in the range high to very high risk. The accumulation ability of HMs in plants was evaluated by the biological accumulation factor (BAF) and the metal accumulation index (MAI), and the results showed that all those plant species have good phyto-extraction ability, while accumulation capacity for most HMs plants tissues was bark > leaf. The highest MAI value (5.99) in Cinnamomum camphora (L) Presl indicates the potential for bio-monitoring and a good choice for planting along highways where there is contamination with HMs.

Metals in European roadside soils and soil solution--a review

This review provides a summary of studies analysing metal concentrations in soils and soil solution at European roadsides. The data collected during 27 studies covering a total of 64 sites across a number of European countries were summarised. Highest median values of Cr, Cu, Ni, Pb, and Zn were determined in the top soil layer at the first 5 m beside the road. Generally, the influence of traffic on soil contamination decreased with increasing soil depth and distance to the road. The concentration patterns of metals in soil solution were independent from concentrations in the soil matrix. At 10-m distance, elevated soil metal concentrations, low pH, and low percolation rates led to high solute concentrations. Directly beside the road, high percolation rates lead to high annual loadings although solute concentrations are comparatively low. These loadings might be problematic, especially in regions with acidic sandy soils and a high groundwater table.