Along an urbanization gradient, we explored the soil metal pollution in Vienna, Austria. We analyzed the physical and chemical parameters of topsoil from urban, suburban, and rural areas. The following elements were quantified using ICP-OES technique: Al, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Pb, S, Sr, and Zn. For heavy metals, PI (pollution index) values were used to assess the level of pollution. We found that the concentration of Cu, Pb, Sr, and Zn was higher in the urban and suburban area than in the rural area. The PI values indicated a moderate level of pollution by Cd (1 ≤ PI ≤ 2) along the urbanization gradient. We found a low level of pollution for Cr, Cu, Ni, Pb, and Zn (PI ≤ 1) in studied areas. Our findings demonstrated the presence of anthropogenic contamination, and it is likely that traffic emission may be the major source of metal pollution in Vienna. Our findings also demonstrated that the elemental analysis of soil and the values of PI are adequate indicators of the level of pollution based on soil sample analysis in urban ecosystems.

We used the Air Pollution Tolerance Index (APTI), the amount of PM₅ and PM₁₀, and the elemental analysis of leaves to explore the sensitivity of tree species to air pollution. We assessed the tolerance of Robinia pseudoacacia, Acer saccharinum, Tilia × europaea, Acer platanoides, Fraxinus excelsior, Betula pendula, Celtis occidentalis, and Platanus × acerifolia to the amount of dust, APTI, and the elemental concentration of leaves. Leaves were collected in Debrecen (Hungary), which has a high intensity of vehicular traffic. The highest amount of PM (both PM₁₀ and PM₅) was found on the leaves of A. saccharinum and B. pendula. Our results demonstrated that A. saccharinum was moderately tolerant, while P. acerifolia was intermediate, based on the APTI value. There was a significant difference in the parameters of APTI and the elemental concentration of leaves among species. We found that tree leaves are reliable bioindicators of air pollution in urban areas. Based on the value of APTI, A. saccharinum and P. acerifolia, and based on PM, A. saccharinum and B. pendula are recommended as pollutant-accumulator species, while other studied species with lower APTI values are useful bioindicators of air pollution. The results support landscape engineers and urban developers in finding the best tree species that are tolerant to pollution and in using those as proxies of urban environmental health.

Potentially toxic elements (PTEs) and microplastics (MPs) in the atmosphere raise widespread apprehension due to their association with the ecosystem and public health. The accumulation of airborne MPs and PTEs was analyzed in Polyalthia longifolia leaves, and the Pollution Index (PI) was calculated along an industrial, residential, and rural gradient in Bangladesh. Only polyethylene terephthalate (PET) was found in the highest concentration in industrial areas compared to other areas. In leaves, a significantly higher Cd, Pb, and Zn concentration was found in industrial regions compared to residential and rural areas. For Cd, the PI was observed to be higher than 1 in rural areas, indicating a moderate level of pollution; it was higher than 3 in residential areas, showing considerable pollution; and it was found to be more than 6 in industrial areas. The higher concentration of both MPs and PTEs with increasing urbanization reflects the influence of anthropogenic activities. The findings of the study demonstrate the fascinating potential of P. longifolia tree leaves as a promising bioindicator for air quality biomonitoring.

In this study, we examined over 200-year-old Ginkgo biloba L. specimens under different environmental conditions. The overall aim was to explore which factors influence their vitality and general fitness in urban environments and thus their ability to tolerate stressful habitats. In order to determine this, we used a number of different methods, including histological examinations (stomatal density and size) and physiological measurements (peroxidase enzyme activity), as well as assessing the air pollution tolerance index (APTI). The investigation of the genetic relationships between individuals was performed using flow cytometry and miRNA marker methods. The genetic tests revealed that all individuals are diploid, whereas the lus-miR168 and lus-miR408 markers indicated a kinship relation between them. These results show that the effect of different habitat characteristics can be detected through morphological and physiological responses, thus indicating relatively higher stress values for all studied individuals. A significant correlation can be found between the level of adaptability and the relatedness of the examined individuals. These results suggest that Ginkgo biloba L. is well adapted to an environment with increased stress factors and therefore suitable for use in urban areas.

Soil has the ability to serve as a universal sink, meaning it may absorb contaminants from the environment. Additionally, plant leaves can also be used as indicators of environmental contamination. In our study, the bioaccumulation factor (BAF) was used to assess metal accumulation in the soil and leaves of the neem tree (Azadirachta indica) in Faisalabad, Pakistan. We analyzed the primary physical and chemical characteristics of the surface layer of soil in urban, suburban, and rural areas along an urbanization gradient. The ICP-OES technique was used to analyze the following elements: Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr and Zn. The highest concentration of all elements was found in soil samples from urban areas, with an increasing tendency along with the urbanization gradient. A significant difference was found along the urbanization gradient on the plant leaves except for Cd, Cu, and Zn; a high level of pollution was measured for Ba, Pb, Co, Ni, Cr, and Cd in the urban area. We also calculated the bioaccumulation factor (BAF), but no clear pattern was found. Our findings show that high concentrations in soil do not always turn into higher plant uptake for plants. Our findings suggest that traffic and industrial emissions are likely the main cause of the metals in Faisalabad, because their concentration is higher than their background concentration. Our results also suggest that elemental analysis of soil and plant leaves is an appropriate indicator of environmental contamination.

This study focused on the spatial and temporal changes in photosynthetic pigment concentrations in the leaves of Ginkgo biloba and their integration into a new bioindicator index, the Pigment Integrity-to-Dust Ratio (PIDR), to assess urban air pollution stress on trees in Budapest, Hungary. High levels of chlorophyll and carotenoids in early summer indicated greater pigment integrity at the moderate-traffic site, whereas there were clear indications of reductions in the high-traffic area. The control site represented a low-traffic, pollution-free baseline. Chlorophyll concentrations dropped in the traffic-exposed leaves, and there were increased levels in the formation of pheophytin. It is thought that these reductions were caused by city stress. Responses of pigments were also variable at the moderate site, perhaps due to some form of recovery or adjustment in the study’s time frame. The observed negative relationships between selected pollutants and PIDR suggested that pollutant exposure was associated with pigment degradation and foliar dust deposition, although these associations should be interpreted as exploratory. The Air Pollution Tolerance Index (APTI) was significantly different between the pollution-exposed sites and the control, reflecting physiological tolerance in chronically exposed trees rather than directly measuring pigment damage. Therefore, the APTI and PIDR provide complementary information. Overall, the PIDR appears to be a promising exploratory bioindicator of physiological stress response, based on pigment concentration changes and dust deposition.