Scratching the surface and digging deeper: exploring ecological theories in urban soils

Assessment of Soil Heavy Metal Pollution and Health Risks in Different Functional Areas on the Northern Slope of the Eastern Tianshan Mountains in Xinjiang, NW China

In typical semi-arid areas, the timely and effective monitoring and evaluation of soil heavy metal pollution are of critical importance to prevent soil deterioration and achieve the sustainable use of soil resources. To further understand the degree of soil heavy metal pollution in different functional areas, we studied the soil heavy metal pollution on the northern slope of the eastern Tianshan Mountains in Xinjiang. We collected 104 surface soil samples from typical commercial (A), industrial (B), and agricultural (C) areas with different land-use patterns. The contents of Zn, Cu, Cr, Pb, As, and Hg in the soil of different functional areas were evaluated using the geo-accumulation index, the single-factor pollution index, and potential ecological risk. The results showed that the contents of Pb, As, and Hg in soils of different functional areas exceeded 4.47, 8.03, and 1.5 times the background values of Xinjiang soil, respectively. The average contents of Zn, Cu, and Cr were lower than the background values of Xinjiang soil. Except for As in different functional areas, the contents of the other elements in the different functional areas reached the level of soil environmental quality standards in China (GB15618-2018). The geo-accumulation index of heavy metals in different functional areas was in the order of Area C > Area A > Area B, indicating that Area C was the most polluted. The results of the single-factor pollution index showed that the pollution levels of Pb, As, and Hg were higher, and the pollution levels of Cr, Cu, and Zn were lower. The results of the potential ecological risk index showed that the northwest of Area A was higher, the southeast of Area B was more polluted, and the central and eastern parts of Area C were more polluted. From the perspective of spatial distribution, the spatial distribution characteristics of Zn and Cr elements in different functional areas are consistent, but the spatial distribution characteristics of Cu, Pb, As, and Hg in different functional areas are quite different. The high values of these four elements are mainly distributed in residential areas, factories, and metal smelters. It is necessary to divide the functional areas based on different land-use patterns, and the prevention of soil single-element and heavy metal pollution in different functional areas is reasonable for land resources and provides a scientific basis for the effective planning of quality assurance.

Distribution, risk assessment, and source apportionment of polycyclic aromatic hydrocarbons (PAHs) using positive matrix factorization (PMF) in urban soils of East India

This study investigated 16 United States environmental protection agency priority PAHs profiles and their sources in 40 urban soils collected from two industrialised cities, Jamshedpur and Bokaro, in east India and assessed their health risk to humans. The results showed the predominance of high molecular weight (HMW) PAHs (4-5 rings). The total PAHs concentration in surface soils ranged from 2223 to 11,266 ng/g and 729 to 5359 ng/g (dw), respectively, for Jamshedpur and Bokaro. Higher concentrations of PAHs were recorded at the selected industrial areas and heavy traffic zones of both cities. In JSR city 4-ring PAHs contributed 43% of total PAHs trailed by 5-ring PAHs 27.2%. Similarly, in BKR city 4-ring PAHs contributed 34% of the total PAHs, followed by 3-ring PAHs 28.9% and 5-ring PAHs 22.9%. Total organic carbon in surface soils exhibited moderate correlation with the low molecular weight (ΣLMW) PAHs (R² = 0.69) and a comparatively strong correlation with the ΣHMW PAHs (R² = 0.89), suggesting strong adsorption of HMW PAHs to urban soils. The Diagnostic and PMF modelling analysis indicated that the major sources of PAHs contamination in soils were petroleum combustion, vehicular emissions, biomass, and coal combustion. The health risk assessment shows that the cumulative probability of carcinogenic risks was under the acceptable limits of 10^-4 to 10^-6. At some sampling areas in both cities, the maximum value of total exposure cancer risk slightly exceeded the acceptable limits indicating some carcinogenic risk for adults.

Spatial cover and carbon fluxes of urbanized Sonoran Desert biological soil crusts

Biological soil crusts (BSC) are important contributors to nutrient cycling in arid environments such as the Sonoran Desert. BSC at an urban (University Indian Ruins) and at a non-urban site (Santa Rita Experimental Range) were compared to determine if their structure or function was influenced by proximity to an urban environment. The Step Point method was used in the field to determine ground cover; which was found to be similar between sites. However, the spatial distribution of the BSCs was significantly different, such that more BSCs were found under plants at the non-urban site (P < 0.05). Relative gross photosynthesis was measured in the lab by addition of a watering event. Gross photosynthesis was found to be higher in the non-urban BSCs (P < 0.001), indicating lowered productivity in urban BSCs due to effects caused by proximity to urban environments. This study provides evidence that BSCs at urbanized sites are affected functionally, and therefore may be contributing differently to carbon and nitrogen cycling in these ecosystems.