Altitude governs the air pollution tolerance and heavy metal accumulation in plants

Plant response to changing air pollution is a function of various factors including meteorology, type of pollutants, plant species, soil chemistry, and geography. However, the impact of altitude on plant behavior has received little attention to date. A study was therefore conducted to evaluate the impact of altitude on the air pollution tolerance index (APTI), heavy metal accumulation, and deposition in plant species. The results favor the hypothesis of a definite impact of altitude on biochemical and heavy metal accumulation in plants. While a significant decline (p < 0.05) in the relative water content (RWC), APTI, and heavy metal accumulation with increasing altitude was evident in the studied plant species, the behavior of ascorbic acid, leaf extract pH, chlorophyll content, and the particle heavy metal deposition was erratic and did not display any statistically significant differences. The metal accumulation index was in the following order: Ni > Zn > Cu > Pb > Cd > Co. Similarly, the particle heavy metal deposition on the leaf surface (µg/cm2) displayed significant species variability (p < 0.05) and was in the order: Cu (0.303) > Pb (0.301) > Ni (0.269) > Zn (0.241) > Cd (0.044) > Co (0.025). The accumulated heavy metal and RWC showcased a significant positive correlation with the APTI, suggesting the dominant role of RWC in the plant's tolerance against air pollution in an altitudinal gradient. Future studies on the role of micrometeorological conditions in altering APTI may be fruitful in ascertaining these postulations.

Pollution resistance assessment of plants around chromite mine based on anticipated performance index, dust capturing capacity and metal accumulation index

Plant species sustaining under a polluted environment for a long time are considered as potentially resistant species. Those plant species can be considered as an eco-sustainable tool used to bio-monitor and mitigate pollution. This study was carried out on a total of ten commonly available plant species to assess their anticipated performance index (API), dust capturing capacity (DCC), and metal accumulation index (MAI) in chromite mine and control areas. According to the anticipated performance index (API), Macaranga peltata (Roxb.) Müll.Arg., Holarrhena pubescens Wall. ex G.Don and Ficus hispida Roxb. ex Wall. are highly tolerant species while Terminalia arjuna (Roxb. ex DC.) Wight & Arn. and Trema orientalis (L.) Blume are intermediate tolerant species. F. hispida was also shown to have the highest dust capturing capacity (5.94 ± 0.43 mg/cm²) whereas that of Woodfordia fruticosa Kurz (1.03 ± 0.11 mg/cm²) was found to be lowest. The metal accumulation index ranged from 17.29 to 4.5 and 6.38 to 1.94 at the mine and control areas, respectively. Two-way ANOVA analysis revealed area-wise significant differences between biochemical and physiological parameters. Also, results showed that the pollution level and heavy metal affected different biochemical and physiological parameters of plant species at the mining area. The plant species with the highest API, DCC, and MAI value could be recommended for greenbelt development in different polluted areas.

Potentially toxic elements contamination and its removal by aquatic weeds in the riverine system: A comparative approach

Thamirabarani river acquires large untreated sewage effluents from the Tirunelveli and Thoothukudi districts of South Tamil Nadu. This study examined the concentration of trace elements in water, sediment, and phytoaccumulation potential of aquatic weeds viz., A. cristata, E. crassipes, S. natans, and P. stratiotes, growing along Srivaikundam dam of Thamirabarani river. The Pb, As, Hg, Cd, and Ni concentrations in water were slightly higher than the US Food and Drug Administration (USFDA) drinking water guidelines; however, their accumulation in sediment was below WHO's sediment quality guideline. This study concludes that the phytoaccumulation factor (PAF) and translocation factor (TF) was >1 in E. crassipes and A. cristata, representing them as hyperaccumulators, suitable for phytoremediation in polluted localities. E. crassipes, A. cristata, and S. natans accumulated (100-500 fold) higher trace elements concentrations than that present in the water. Also, the concentrations of trace elements found in the aquatic weeds were below the recommended levels for the critical plant range (CRP). These selected aquatic weeds are more suitable for plant hybridization to be modified as superbug plants.

Assessing the uptake and accumulation of heavy metals and particulate matter from ambient air by some tree species in Isfahan Metropolis, Iran

The main scope of this study is to evaluate the uptake and accumulation potential of heavy metals in unwashed and washed leaves and particulate matter (PM) in leaf surfaces plus waxes of different tree species in Isfahan city. The highest mean concentrations of Cd, Cr, and Ni in unwashed and washed leaves were detected in M. nigra, Zn and Cu in P. fraxinifolia, and Pb was related to P. orientalis. The highest and lowest mean total depositions of total particulate matter (sum of PM₁₀, PM_2.5, and PM_0.2) were found in the leaf of M. nigra (190.23 ± 23.5) and S. alba (11.9 ± 4.42 μg/cm²), respectively. The maximum bio-concentration factor (BCF) of Cd, Pb, and Ni was observed in Morus nigra; Cu and Zn in Pterocarya fraxinifolia, with the BCF of Cr found in Acer negundo. Comprehensive bio-concentration index (CBCI) and metal accumulation index (MAI) were applied for comparing different tree species in HMs accumulation from soil and ambient air. The highest CBCI was measured for M. nigra (0.86), so this tree has the potential to remediate metals from the polluted soil. Higher MAI values in washed and unwashed leaves were found in S. alba (6.77 and 6.98) and M. nigra (5.93 and 5.62), demonstrating the high capability of these trees for controlling air born-metal pollution. Based on the AOM factor, M. nigra, P. fraxinifolia, U. umbraculifera, P. fraxinifolia, A. altissima, and M. alba trees had the highest ability to capture Cd, Zn, Cu, Ni, Pb, and Cr from air. So, planting these trees would be beneficial in sensitive and critical zones such as industrial and urban areas with such atmospheric pollutants.

Bioaccumulation potential of indigenous plants for heavy metal phytoremediation in rural areas of Shaheed Bhagat Singh Nagar, Punjab (India)

The present study was planned to explore the bioaccumulation potential of 23 plant species via bioaccumulation factor (BAf), metal accumulation index (MAI), translocation potential (Tf), and comprehensive bioconcentration index (CBCI) for seven heavy metals (cadmium, chromium, cobalt, copper, iron, manganese, and zinc). The studied plants, in the vicinity of ponds at Sahlon: site 1, Chahal Khurd: site 2, and Karnana: site 3 in Shaheed Bhagat Singh Nagar, Punjab (India), were Ageratum conyzoides (L.) L., Amaranthus spinosus L., Amaranthus viridis L., Brassica napus L., Cannabis sativa L., Dalbergia sissoo DC., Duranta repens L., Dysphania ambrosioides (L.) Mosyakin & Clemants, Ficus infectoria Roxb., Ficus palmata Forssk., Ficus religiosa L., Ipomoea carnea Jacq., Medicago polymorpha L., Melia azedarach L., Morus indica L., Malva rotundifolia L., Panicum virgatum L., Parthenium hysterophorus L., Dolichos lablab L., Ricinus communis L., Rumex dentatus L., Senna occidentalis (L.) Link, and Solanum nigrum L. BAf and Tf values showed high inter-site deviations for studied metals. MAI values were found to be more substantial in shoots as compared with that of roots of plants. Maximum CBCI values were observed for M. azedarach (0.626), M. indica (0.572), D. sissoo (0.497), and R. communis (0.474) for site 1; F. infectoria (0.629), R. communis (0.541), D. sissoo (0.483), F. palmata (0.457), and D. repens (0.448) for site 2; D. sissoo (0.681), F. religiosa (0.447), and R. communis (0.429) for site 3. Although, high bioaccumulation of individual metals was observed in herbs like C. sativa, M. polymorpha, and Amaranthus spp., cumulatively, trees were found to be the better bioaccumulators of heavy metals.

Potential of trees leaf/ bark to control atmospheric metals in a gas and petrochemical zone

Leaf and bark of trees are tools for assessing the effects of the heavy metals pollution and monitoring the environmental air quality. The aim of this study was to evaluate the presence of Ni, Pb, V, and Co metals in four tree/shrub species (Conocarpus erectus, Nerium oleander, Bougainvillea spectabilis willd, and Hibiscus rosa-sinensis) in the heavily industrial zone of Asaloyeh, Iran. Two industrial zones (sites 1 and 2), two urban areas (sites 3 and 4), and two rural areas (sites 5 and 6) in the Asaloyeh industrial zone and an uncontaminated area as a control were selected. Sampling from leaf and bark of trees was carried out in spring 2016. The metals content in the washed and unwashed leaf and bark was investigated. The results showed that four studied metals in N. oleander, C. erectus, and B. spectabilis willd in all case sites were significantly higher than that of in the control site (p < 0.05). The highest concentration of metals was found in sites 3, 4, and 6; this was due to dispersion of the pollutants from industrial environments by dominant winds. The highest comprehensive bio-concentration index (CBCI) was found in leaf (0.37) and bark (0.12) of N. oleander. The maximum metal accumulation index (MAI) in the samples was found in leaf of N. oleander (1.58) and in bark of H. rosa-sinensis (1.95). The maximum bio-concentration factor (BCF) was seen for cobalt metal in the N. oleander leaf (0.89). The nickel concentration in washed-leaf samples of C. erectus was measured to be 49.64% of unwashed one. In general, the N. oleander and C. erectus species were found to have the highest absorption rate from the atmosphere and soil than other studied species, and are very suitable tools for managing air pollution in highly industrialized areas.

Bioaccumulation of heavy metals in plant leaves from Yan׳an city of the Loess Plateau, China

Urban plants are capable of reducing environmental pollutions through bioaccumulation contaminants in their tissues. The accumulation of heavy metals (Pb, Cu, Cd, Cr, and Zn) in leaves of nine tree species and five shrub species from Yan׳an city of China were investigated, and total metal accumulation capacities of different plants were evaluated using the metal accumulation index (MAI). The results indicated that plants in polluted environments are enriched in heavy metals relative to those in pristine environments, this is mainly caused by traffic emissions and coal combustion. Species with the highest accumulation of a single metal did not have the highest total metal accumulation capacity, the MAI should be an important indicator for tree species selection in phytoextraction and urban greening. Considering total accumulation capacities, Sabina chinensis, Juniperus formosana, Ailanthus altissima and Salix matsudana var. matsudana could be widely used in the Loess Plateau.

Trace element contamination in the estuarine sediments along Tuticorin coast--Gulf of Mannar, southeast coast of India

Sediment samples were collected from Kallar, Korampallam creek and Punnakayal estuaries of Tuticorin coast for assessing the level of contamination by trace elements in these estuarine sediments. The trace element concentration, calcium carbonate, organic carbon and mercury level were analyzed by Inductively Coupled Plasma Atomic Emission Spectrophotometer, Titrimetric method and SnCl2 reduction method. The results reveals that the enrichment factor, metal pollution index and geo-accumulation index of these estuarine sediments were predominantly polluted by Cd, As, Zn, Hg and Pb. The factor analysis revealed the source of trace element accumulation in the estuarine sediments particularly Mn and Fe are from riverine inputs and As and Hg from untreated industrial effluents. Among the selected estuaries, Korampallam creek was found to be highly contaminated by trace elements due to the discharge of effluents from thermal power plant, Tuticorin alkali chemicals, copper smelting, Petrochemical industries and shipping activities.