Distribution and sequential extraction of some heavy metals in urban soils of Guiyang City, China

Heavy metals in the sediments of urban sinkholes in Cancun, Quintana Roo

Soils in urban areas can accumulate heavy metals as a result of anthropogenic inputs. This research focuses on a young coastal tourist city that has been urbanized over the last 52 years and shows accelerated demographic growth and urban development. Deposition of heavy metals in soils is caused by human economic activities, which has significant implications for the environment. We evaluated heavy metal concentrations in urban sinkholes, which are sites for the natural accumulation of water and sediments. These locations also receive rainfall runoff or have been used as unregulated dumps. By performing a multistage extraction to address availability and risk, we found that Zn, Fe and Al were the predominant metals; Cu, Pb and Ni were only detected in some sinkholes. The contamination factor was high for Zn and moderate for Pb. The geoaccumulation index showed that Zn is the most abundant and available metal in urban sinkholes and the metal with the highest potential ecological risk. Between 12 and 50% of the total concentration of all metals was extracted from the organic matter phase. Correlations were found between the degree of urbanization of the city and the degree of pollution, and the trends were stronger in older sections of the city. Zn is the most prevalent element and has high concentrations. The metal concentrations in the sediments can be used as warning signs for their potential risk to environmental and human health, and these results can be compared with those of other tourist cities in karstic environments around the world.

Potentially Toxic Elements in Urban Soils from Public-Access Areas in the Rapidly Growing Megacity of Lagos, Nigeria

Rapid urbanization can lead to significant environmental contamination with potentially toxic elements (PTEs). This is of concern because PTEs are accumulative, persistent, and can have detrimental effects on human health. Urban soil samples were obtained from parks, ornamental gardens, roadsides, railway terminals and locations close to industrial estates and dumpsites within the Lagos metropolis. Chromium, Cu, Fe, Mn, Ni, Pb and Zn concentrations were determined using inductively coupled plasma mass spectrometry following sample digestion with aqua regia and application of the BCR sequential extraction procedure. A wide range of analyte concentrations was found—Cr, 19−1830 mg/kg; Cu, 8−11,700 mg/kg; Fe, 7460−166,000 mg/kg; Mn, 135−6100 mg/kg; Ni, 4−1050 mg/kg; Pb, 10−4340 mg/kg; and Zn, 61−5620 mg/kg—with high levels in areas close to industrial plants and dumpsites. The proportions of analytes released in the first three steps of the sequential extraction were Fe (16%) < Cr (30%) < Ni (46%) < Mn (63%) < Cu (78%) < Zn (80%) < Pb (84%), indicating that there is considerable scope for PTE (re)mobilization. Human health risk assessment indicated non-carcinogenic risk for children and carcinogenic risk for both children and adults. Further monitoring of PTE in the Lagos urban environment is therefore recommended.

Assessment of heavy metals contamination and water quality characterization in the Nanming River, Guizhou Province

The analysis to assess the water quality and potential ecological risks in sediments was carried out by means of the distribution characteristics of nutrient properties and heavy metals in water, and heavy metals in sediments from the Nanming River. The results from nutrient properties demonstrated that the majority of TN and TP exceeded the permissible limit and concentrated within the study area. The concentrations of heavy metal in water were lower than the permissible limits but may pose potential threat to aquatic ecosystems. Based on the potential ecological risk results of heavy metals in sediments, Cd posed risk to ecological environment, and the serious contaminations mainly existed in the center of Guiyang City. The multivariate statistical analyses were used to support the idea that the Upstream Area and Midstream Area were significantly dominated by NH₄⁺, TP, TN and COD_Mn in water. Furthermore, landscape characteristics and hydrology condition better explained the certain trend of water quality. Finally, identifying relationship between nutrient properties and heavy metals that are key ecological components of ecosystem can potentially aid the advances for restoration of geochemical transformations and give rise to river restoration efforts.

Characterization and origin of organic and inorganic pollution in urban soils in Pisa (Tuscany, Italy)

We assessed the quality of 31 urban soils in Pisa by analyzing total petroleum hydrocarbons (TPHs), Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn, and the platinum group elements (PGEs). The risk was evaluated by the geological accumulation index (I _geo) and the enrichment factor (EF). Results were compared with those obtained from a non-urban site and with the quantitative limits fixed by Italian legislation. In nearly all the monitored sites, the legal limit for TPH of 60 mg/kg in residential areas was exceeded, indicating widespread and intense pollution throughout the entire city area. The I _geo indicated no Cd, Cu, Mn, Ni, and Zn pollution and minimal Pb and Cr pollution due to anthropogenic enrichment. Legal Hg and Zn limits of 1 and 150 mg/kg, respectively, were exceeded in about 20% of sites; Cd (2 mg/kg), Cr (150 mg/kg), and Cu (120 mg/kg) in only one site; and the Ni legal limit of 120 mg/kg was never exceeded. Some urban soils showed a higher Hg level than the more restrictive legal limit of 5 mg/kg concerning areas for industrial use. Based on the soluble, exchangeable, and carbonate-bound fractions, Mn and Zn showed the highest mobility, suggesting a more potential risk of soil contamination than the other metals. The TPH and both Cr and Hg amounts were not correlated with any of the other monitored metals. The total contents of Cd, Pb, Zn, and Cu in soils were positively correlated with each other, suggesting a common origin from vehicular traffic. The PGE values (Pt and Pd) were below the detection limits in 75%-90% of the monitored areas, suggesting that their accumulation is at an early stage.

Soil quality assessment using GIS-based chemometric approach and pollution indices: Nakhlak mining district, Central Iran

This paper is a comprehensive assessment of the quality of soil in the Nakhlak mining district in Central Iran with special reference to potentially toxic metals. In this regard, an integrated approach involving geostatistical, correlation matrix, pollution indices, and chemical fractionation measurement is used to evaluate selected potentially toxic metals in soil samples. The fractionation of metals indicated a relatively high variability. Some metals (Mo, Ag, and Pb) showed important enrichment in the bioavailable fractions (i.e., exchangeable and carbonate), whereas the residual fraction mostly comprised Sb and Cr. The Cd, Zn, Co, Ni, Mo, Cu, and As were retained in Fe-Mn oxide and oxidizable fractions, suggesting that they may be released to the environment by changes in physicochemical conditions. The spatial variability patterns of 11 soil heavy metals (Ag, As, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sb, and Zn) were identified and mapped. The results demonstrated that Ag, As, Cd, Mo, Cu, Pb, Sb, and Zn pollution are associated with mineralized veins and mining operations in this area. Further environmental monitoring and remedial actions are required for management of soil heavy metals in the study area. The present study not only enhanced our knowledge regarding soil pollution in the study area but also introduced a better technique to analyze pollution indices by multivariate geostatistical methods.

Elemental contamination in urban parks of Rawalpindi/Islamabad--a source identification and pollution level assessment study

The soil quality of urban parks is of vital importance as the children playing in the parks get themselves easily contaminated. A study was conducted to assess the level of elemental pollution caused by constant urbanization and industrialization, in various parks of Islamabad and Rawalpindi. The soil samples, collected from 14 urban parks of Islamabad and Rawalpindi areas, were analysed for their elemental concentrations. In each sample, 32 elements were quantified using semi-absolute k (0)-instrumental neutron activation analysis and flame atomic absorption spectrophotometry. The quality of analysis was assured by analysing the International Atomic Energy Agency (IAEA) reference material IAEA-S7 (soil). The pollution level was assessed by enrichment factor, pollution load index and our suggested indicator called "average toxic element concentration". The elemental concentrations measured in the parks of two cities were compared by t test. Four sources of different elements in the soils were identified by employing principal component analysis and cluster analysis. The results of multivariate techniques grouped all parks into four classes. The use of enrichment factor indicated the presence of Ni at slightly higher level in all parks while the pollution load index revealed that the parks of Rawalpindi were relatively more polluted as compared to that of Islamabad. The hot spot areas of elemental concentration were closely related to high traffic conditions.