Identifying environmental pollution recorded in street dust using the magnetic method: a case study from central eastern China

​Quantitative assessment of heavy metal concentrations, pollution levels, and sources apportionment in one of China's top 10 most livable cities

Urban topsoil is not only an essential part of the urban ecosystem, but also a powerful carrier of pollutants in the urban environment. In this paper, 130 topsoil samples from urban area of Xinyang in central-eastern China were selected, the aim is to quantitatively investigate the concentrations, pollution levels, and sources apportionment of 8 heavy metals (HMs, encompassing arsenic (As), cobalt (Co), copper (Cu), chromium (Cr), lead (Pb), nickel (Ni), vanadium (V), and zinc (Zn)) via geochemical method. The main conclusions are as follows. (1) The eight HMs in the topsoil have been artificially enriched to varying degrees, which are lower than the street dust levels sampled in pairs. (2) Cu, Zn, and Pb were significantly contaminated, and As, Co, Ni, Cr, and V were relatively low levels of contamination. Overall, comprehensive pollution levels were particularly severe, with 30.0%, 39.2%, and 30.8% for slight, moderate, and serious pollution, respectively. (3) Co, Ni, V, and Cr predominantly originated from natural sources, the percentage contribution of which is 6.3%; Pb, As, Cu, and Zn were predominantly derived from traffic-derived sources, with a percentage contribution of 93.7%. Thus, the first-order source of HMs in the topsoil originates from traffic-induced activities, similar to the case of street dust. Our findings can be beneficial in providing local governments with a reference to formulate environmental pollution controls, and also provide a case study for environmental pollution control in the other livable cities in China.

High-throughput screening of 222 pesticides in road environments in a megacity of northern China: A new approach to urban population exposure

A large number of pesticides have been widely manufactured and applied, and are released into the environment with negative impact on human health. Pesticides are largely used in densely populated urban environments, in green zones, along roads and on private properties. In order to characterize the potential exposure related health effects of pesticide and their occurrence in the urban environment, 222 pesticides were screened and quantified in 228 road dust and 156 green-belt soil samples in autumn and spring from Harbin, a megacity in China, using GC-MS/MS base quantitative trace analysis. The results showed that a total of 33 pesticides were detected in road dust and green-belt soil, with the total concentrations of 650 and 236 ng/g (dry weight = dw), respectively. The concentrations of pesticides in road dust were significantly higher than that in green-belt soil. Pesticides in the environment were influenced by the seasons, with the highest concentrations of insecticides in autumn and the highest levels of herbicides in spring. In road dust, the concentrations of highways in autumn and spring (with the mean values of 94.1 and 68.2 ng/g dw) were much lower than that of the other road classes (arterial roads, sub-arterial roads and branch ways). Whereas in the green-belt soil, there was no significant difference in the concentration of pesticides between the different road classes. A first risk assessment was conducted to evaluate the potential adverse health effects of the pesticides, the results showed that the highest hazard index (HI) for a single pesticide in dust and soil was 0.12, the hazard index for children was higher than that for adults, with an overall hazard index of less than 1. Our results indicated that pesticide levels do not have a significant health impact on people.

An integrated approach combining magnetic, geochemical and particle-based techniques to assess metal(loid) loadings in urban venues frequented by children

Urban venues frequented by children, such as playgrounds, are potentially important sources of exposure to anthropogenic metal(loids). Environmental quality of outdoor playgrounds is mainly assessed through direct geochemical monitoring, which is time-consuming and expensive. In this study we adapted a multidisciplinary approach combining magnetic measurements, geochemical analyses, particle-based techniques and bioaccessibility data so as to evaluate the applicability of magnetic methods as a low-cost and easy-to-use technology to monitor pollution level in public playgrounds. Playground sands were collected and their magnetic characteristics were studied in detail aiming to gain helpful additional details in relation to the type, concentration and particle-size distribution of the sand-bound magnetic particles. The obtained χ_lf values indicated an enhanced level of sand-bound magnetic components, while the dominant control of SSD grains on the magnetic load of playground-PG sands was revealed. Hysteresis parameters and thermomagnetic curves indicated low-coercivity ferrimagnetic minerals, such as magnetite and/or maghemite, as the predominant magnetic carriers. Ratios of χ_ARM/χ_lf and χ_ARM/SIRM indicated the dominance of coarser anthropogenic magnetic grains in the sampled PG sands compared to other recreational areas. Correlation analysis among magnetic variables and reported metal(loid) contents designated χ_ARM as a more effective indicator for the detection of anthropogenic load in PG sand samples than χ_lf or SIRM. Simultaneously, through geochemical analyses in magnetic extracts separated from PG sands, metal(loid) contents were notably enriched in the magnetic fraction validating their strong affinity with sand-bound magnetic particles. Finally, bioaccessibility tests revealed lower UBM-extracted fractions for the magnetic extracts of PG sands compared to bulk samples. However, arsenic (As) was more bioaccessible in the sand-bound magnetic particles raising serious concerns for the children exposed to playground sands.

Pollution characteristics, spatial distribution, and source identification of heavy metals in road dust in a central eastern city in China: a comprehensive survey

Road dust enriched with heavy metals (HMs) is detrimental to ecosystems and human health in urban environments. In this study, it is to explore the concentrations, spatial distribution, contaminated levels, and source identification of six HMs (lead (Pb), zinc (Zn), copper (Cu), cobalt (Co), chromium (Cr), and nickel (Ni)) based on 130 road dusts in Xinyang urban area. The results indicated that the contents of Pb, Zn, Cu, and Co were higher than the background values in more than 99% of the samples, and their average concentrations were 15.2, 9.2, 8.6, and 6.3 times the background value, respectively. The spatial distribution of high-value areas for Pb, Zn, Cu, Cr, and Ni was more similar, which was associated with traffic density near major roads and population and settlement patterns. Co was relatively different from the five elements, which was distributed in the areas of residence, commerce, and industry. Furthermore, the investigated HMs were clearly polluted, with Pb, Zn, Cu, and Co indicating high levels of contamination, while Cr and Ni were moderately polluted. The comprehensive pollution of the six HMs was mostly moderate to heavy in this study. Moreover, three sources of HMs designated by correlation analysis (CA) and principal component analysis (PCA) were mixed traffic emissions and industrial waste for Cu and Cr; automotive emissions for Pb, Ni, and Zn; and mixed domestic waste and industrial activities for Co, with contributions of 42.3%, 46.4%, and 11.3% via the principal component analysis-multiple linear regression (PCA-MLR) model. The multi-factor index for pollution assessment combined with source identification is extremely effective and practical for providing reliable data support and a theoretical reference for pollution monitoring and governance.

Magnetic monitoring of topsoil and street dust in Xinyang (China) and their environmental implications

The magnetic measurement is an effective tool to identify the source of pollutants and diagnose the urban pollution. In this study, 132 group samples (that topsoil and street dust were sampled at the same location is regarded as a group) were collected from Xinyang, central eastern China. In addition, the background samples (19 topsoils under woodland around the outskirts) were also sampled. Herein, the aim was to investigate and compare the magnetic characteristics of both topsoil and street dust, and further to discuss the source and environmental implications using magnetic and diffuse reflection spectrum methods. The following points are highlighted: (1) the primary magnetic carrier of both materials was magnetite and that of the background sample were magnetite and maghemite. Furthermore, the ferrimagnetic mineral concentration and magnetic domain follow the order: street dust > topsoil > background sample. (2) The source of both materials was mainly from anthropogenic activities (e.g. industrial and traffic vehicles). The difference between them was the contribution related to natural sources (e.g. parent materials), which was negligible in street dust, and played a secondary role in topsoil. (3) Both materials showed that areas with a higher intensity of anthropogenic activities had higher pollution level, whereas areas with a lower anthropogenic intensity had lower pollution level.

Traffic-related pollution history (1994-2014) determined using urban lake sediments from Nanjing, China

With the development of urbanisation and the increasing number of modern vehicles, traffic contamination has become an important source of environmental pollution. Most previous studies have focused on using roadside soil or plants to determine the spatial pattern of traffic pollutants along roads and the factors that influence this pattern, whereas few studies have reconstructed pollution histories caused by traffic using suitable methods. In this study, two gravity cores were obtained from Qianhu Lake, which is in the Zhongshan tourist area of Nanjing City and is distant from industrial areas. An accurate chronological framework covering the period from 1994 to 2014 was established using the correlation between the variation in grain size of the sediment cores and the variation in annual rainfall in Nanjing City. Moreover, magnetic and chemical parameters were also measured, and the results demonstrated that concentration-related magnetic parameters exhibited different correlations with different heavy metal concentrations. These correlations were significantly positive for Zn, Pb, and Co; weakly positive for Ni; absent for Cr; and negative for V. Combined with statistical data on industrial emissions and private cars in Nanjing City since 1994, the observed variations in magnetic susceptibility, anhysteretic remanent magnetisation, saturation isothermal remanent magnetisation, Zn, Pb, and Co, were controlled by traffic activities in the tourist area but not by industry. Therefore, the variations in these parameters record the traffic pollution history of the study area. Combined with the obtained chronological framework, the traffic-related pollution history could be divided into two stages: 1) from 1994 to 2003, when traffic-related pollution became increasingly serious because of the exponential increase in the number of private cars and the prosperity of tourism; 2) from 2003 to 2014, when traffic-related pollution continuously increased but at a much slower rate than in stage 1. This slower rate of increase was probably related to the maximum carrying capacity of the tourist area and technological innovations in automobile manufacturing, as well as improvements in fuels.