Soil Chemical Analysis

Human health effects of air pollution

The aim of this review is to assess the mode of action and role of antioxidants as protection from heavy metal stress in roots, mycorrhizal fungi and mycorrhizae. Based on their chemical and physical properties three different molecular mechanisms of heavy metal toxicity can be distinguished: (a) production of reactive oxygen species by autoxidation and Fenton reaction; this reaction is typical for transition metals such as iron or copper, (b) blocking of essential functional groups in biomolecules, this reaction has mainly been reported for non-redox-reactive heavy metals such as cadmium and mercury, (c) displacement of essential metal ions from biomolecules; the latter reaction occurs with different kinds of heavy metals. Transition metals cause oxidative injury in plant tissue, but a literature survey did not provide evidence that this stress could be alleviated by increased levels of antioxidative systems. The reason may be that transition metals initiate hydroxyl radical production, which can not be controlled by antioxidants. Exposure of plants to non-redox reactive metals also resulted in oxidative stress as indicated by lipid peroxidation, H(2)O(2) accumulation, and an oxidative burst. Cadmium and some other metals caused a transient depletion of GSH and an inhibition of antioxidative enzymes, especially of glutathione reductase. Assessment of antioxidative capacities by metabolic modelling suggested that the reported diminution of antioxidants was sufficient to cause H(2)O(2) accumulation. The depletion of GSH is apparently a critical step in cadmium sensitivity since plants with improved capacities for GSH synthesis displayed higher Cd tolerance. Available data suggest that cadmium, when not detoxified rapidly enough, may trigger, via the disturbance of the redox control of the cell, a sequence of reactions leading to growth inhibition, stimulation of secondary metabolism, lignification, and finally cell death. This view is in contrast to the idea that cadmium results in unspecific necrosis. Plants in certain mycorrhizal associations are less sensitive to cadmium stress than non-mycorrhizal plants. Data about antioxidative systems in mycorrhizal fungi in pure culture and in symbiosis are scarce. The present results indicate that mycorrhization stimulated the phenolic defence system in the Paxillus-Pinus mycorrhizal symbiosis. Cadmium-induced changes in mycorrhizal roots were absent or smaller than those in non-mycorrhizal roots. These observations suggest that although changes in rhizospheric conditions were perceived by the root part of the symbiosis, the typical Cd-induced stress responses of phenolics were buffered. It is not known whether mycorrhization protected roots from Cd-induced injury by preventing access of cadmium to sensitive extra- or intracellular sites, or by excreted or intrinsic metal-chelators, or by other defence systems. It is possible that mycorrhizal fungi provide protection via GSH since higher concentrations of this thiol were found in pure cultures of the fungi than in bare roots. The development of stress-tolerant plant-mycorrhizal associations may be a promising new strategy for phytoremediation and soil amelioration measures.

Plant responses to abiotic stresses: heavy metal‐induced oxidative stress and protection by mycorrhization

Reactive oxygen species (ROS) were initially recognized as toxic by-products of aerobic metabolism. In recent years, it has become apparent that ROS plays an important signaling role in plants, controlling processes such as growth, development and especially response to biotic and abiotic environmental stimuli. The major members of the ROS family include free radicals like O2● −, OH● and non-radicals like H2O2 and 1O2. The ROS production in plants is mainly localized in the chloroplast, mitochondria and peroxisomes. There are secondary sites as well like the endoplasmic reticulum, cell membrane, cell wall and the apoplast. The role of the ROS family is that of a double edged sword; while they act as secondary messengers in various key physiological phenomena, they also induce oxidative damages under several environmental stress conditions like salinity, drought, cold, heavy metals, UV irradiation etc., when the delicate balance between ROS production and elimination, necessary for normal cellular homeostasis, is disturbed. The cellular damages are manifested in the form of degradation of biomolecules like pigments, proteins, lipids, carbohydrates and DNA, which ultimately amalgamate in plant cellular death. To ensure survival, plants have developed efficient antioxidant machinery having two arms, (i) enzymatic components like superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR); (ii) non-enzymatic antioxidants like ascorbic acid (AA), reduced glutathione (GSH), α-tocopherol, carotenoids, flavonoids and the osmolyte proline. These two components work hand in hand to scavenge ROS. In this review, we emphasize on the different types of ROS, their cellular production sites, their targets, and their scavenging mechanism mediated by both the branches of the antioxidant systems, highlighting the potential role of antioxidant

Reactive oxygen species (ROS) and response of antioxidants as ROS-scavengers during environmental stress in plants

Health risks of heavy metals in contaminated soils and food crops irrigated with wastewater in Beijing, China

Tropospheric ozone (O3), a secondary air pollutant, was assessed to evaluate the intra-urban variability of O3, its local and distant sources, and the influence of O3 precursor gases and meteorological variables on seasonal and temporal trends of O3 from 2013 to 2017 in a tropical urban city located in the middle Indo-Gangetic Plains of India. Passive samplers and data from real-time air quality monitoring station were considered. Trajectory statistical models, multivariate statistical methods, and geographic information system were further used to identify spatial-temporal variability and source apportionment. O3 concentrations showed significant intra-urban variability with higher concentrations in suburban or background regions of the city, which were mostly attributed to the transport of O3 at high wind speed from distant and rural areas away from the city, while lower concentrations in traffic and commercial areas were due to titration of O3 by nitric oxide (NO). Variations in meteorological variables (temperature, relative humidity, wind speed) and planetary boundary layer height were responsible for seasonal variations in O3 concentrations. Long-range and regional transport of O3 and its precursors such as volatile organic compounds and NOx from the northwestern and eastern directions of the city significantly influenced O3 variability with distinct seasonal patterns. A negative trend in O3 levels was recorded during the study period which may be due to increase in NOx emission in the city. The observed outcomes suggest significant intra-urban variability of O3 in the city which is influenced by traffic as well as by distant and local sources.

Intra-urban variability of ozone in a tropical city—characterization of local and regional sources and major influencing factors

The growth of population, increasing urbanization and rising standards of human have contributed to increase in both quantity and variety of solid wastes generated by agricultural, domestic and industrial activities. Industrial wastes contributed more than 85 % of solid waste generation globally. Metals are the major component of almost all the industrial activities but their mining, extraction, purification and various manufacturing processes generate mining and metallurgical wastes having enormous environmental and health impacts. This chapter aims to describe the metals in solid wastes from mining and metallurgical industries and their toxicological impacts on plant community. Industrial wastes are composed of a wide range of essential macro- and micronutrients such as Na, K, Ca, Mg, Mn, Fe, Cu, Zn, Ni, Co, and Mo which are required by plants for their growth and development. But the concentrations of micronutrients in plants when they exceed certain thresholds may interfere with plant metabolic activities leading to the reduction in their productivity. Similarly, non-essential metals and metalloids such as Cd, Pb, As, Al, Bi, Cr, Hg, Ti and Si at elevated concentrations in plants cause phytotoxic effects and lead to food chain contamination. These wastes are generated in huge quantities and discarded without any proper pretreatment; therefore, chances of contamination of environmental components are obvious. This chapter also suggests the possible and better management opportunities including site restoration by rehabilitation and phytoremediation of metal-contaminated sites using native and medicinal plant species to reduce food chain contamination and an ultimate risk to human health.

Metals from Mining and Metallurgical Industries and Their Toxicological Impacts on Plants

Abiotic stress, notably high ultraviolet-B (eUV-B), limit growth and productivity of many crop plants, but information on response of forage grasses to eUV-B radiation is rather limited. The present study was therefore conducted to increase our understanding of differential age-related responses on growth, metabolism and fodder quality of Cenchrus ciliaris-3108 (Buffel grass) to elevated UV-B (eUV-B: 7.2 kJ·m-2 ·day-1 ). Plant growth at both growth stages was notably reduced in response to eUV-B, except for the number of nodes and tillers at vegetative and reproductive stages. At anthesis, tillering increased due to the perennial habit of this plant, but leaf senescence reduced the number of leaves per tiller. Unlike ambient UV-B, eUV-B at the vegetative stage resulted in diversion of photosynthate for the formation of secondary metabolites (tannins and phenolics), providing dual protection from photooxidative damage and from herbivory. The forage biomass as well as quality showed a marked decline under eUV-B and relative nutritive value was reduced at both growth stages.

Age‐wise performance of tropical perennial fodder grass, Cenchrus ciliaris L.: Cross‐talk between elevated Ultraviolet‐B radiation and herbivory

A field study was conducted around two coal-fired thermal power plants (TPP) to analyse the impact of their emission on the structure of herbaceous communities in a dry tropical area. Phytosociological studies reflected that Cassia tora, Cynodon dactylon and Dichanthium annulatum dominate at heavily polluted sites. Alsycarpus monilifer, Convolvulus pluricaulis, and Desmodium triflorum are uniformly distributed, whereas Paspalidium flavidum, Phyllanthus simplex, and Rungia repens are dominant at less polluted sites. On the basis of Importance Value Index, the species were classified as sensitive, intermediate and resistant to TPP emissions. Shannon-Wiener Index of species diversity, species richness and evenness were inversely related, whereas concentration of dominance was directly related to the pollution load in the area. Significant negative correlation between ambient SO2 concentration and species diversity suggested selective elimination of sensitive species from the heavily polluted sites.

Madhoolika Agrawal

Papers

Intra-urban variability of ozone in a tropical city—characterization of local and regional sources and major influencing factors

Metals from Mining and Metallurgical Industries and Their Toxicological Impacts on Plants

Age‐wise performance of tropical perennial fodder grass, Cenchrus ciliaris L.: Cross‐talk between elevated Ultraviolet‐B radiation and herbivory

Effect of power plant emissions on plant community structure.

Effects of fumigating rice plants with sulphur dioxide on photosynthetic pigments and nonstructural carbohydrates