Naeem Shahid

Role of metal speciation in lead-induced oxidative stress to Vicia faba roots

Chemical speciation of metals in soil/solution plays an important role in determining their biogeochemical behavior in soil-plant system. The current study evaluated the influence of applied form of Pb (metal speciation) on its toxicity to metal sensitive Vicia faba L. roots. Lead was applied to young V. faba seedlings alone or chelated by organic ligands (citric acid and ethylenediaminetetraacetic acid). Plants were exposed to all treatments for 1, 4, 8, 12, and 24 h in nutrient solution, and contents of H2O2 and thiobarbituric-acid-reactive substances (TBARS) production were analyzed in V. faba roots. The results showed that Pb toxicity to V. faba roots depended on its applied chemical form and duration of exposure. Lead alone caused two burst of lipid peroxidation and H2O2 induction at 1 h and 12 h. Addition of EDTA dose-dependently inhibited Pb-induced H2O2 and TBARS production, indicating a protective role of this chelator against Pb toxicity during the first 24 h. In contrast, citric acid did not show significant effects on Pb-induced H2O2 and TBARS production, but delayed the induction of these effects. This study suggested that Pb toxicity to V. faba roots varies with Pb speciation in growth medium.

Heavy Metal Stress and Crop Productivity

Heavy metal contamination of the environment through anthropogenic activities and/or natural processes is a widespread and serious problem. Heavy metals occur in various forms in soil, which differ greatly with respect to their solubility/bioavailability. The geochemical behavior of heavy metals in soil, their uptake by plants, and effect on crop productivity is affected by various physicochemical properties of soil. Heavy metals mainly accumulate in root cells, due to their blockage by Casparian strips or due to trapping by the cell walls of roots. Excessive heavy metal accumulation in plant tissue impairs either directly or indirectly several biochemical, physiological, and morphological functions in plants and in turns interferes with crop productivity. Heavy metals reduce crop productivity by inducing deleterious effects to various physiological processes in plants including: seed germination, accumulation and remobilization of seed reserves during germination, plant growth, and photosynthesis. At the cellular level, heavy metal toxicity reduces crop productivity by producing reactive oxygen species, disturbing the redox balance and causing oxidative stress. Under heavy metal stress, plants have numerous defense mechanisms to manage heavy metal toxicity and to maintain their productivity, which include reduced heavy metal uptake by plants, sequestration into vacuoles, binding by phytochelatins, and activation of various antioxidants. This chapter presents the effect of heavy metals on physiological reactions in the plants’ crop productivity.

Industrial wastewater treatment in internal circulation bioreactor followed by wetlands containing emergent plants and algae

Wastewater treatment based on ecological principles is a low cost and highly desirable solution for the developing countries like Pakistan. The present study evaluated the effectiveness of biological treatment systems including Internal Circulation (IC) anaerobic bioreactor and constructed wetlands (CWs) containing macrophytes and mixed algal cultures for industrial wastewater treatment. The IC bioreactor reduced COD (52%), turbidity (89%), EC (24%) of the industrial wastewater. However, the effluents of IC bioreactor did not comply with National Environmental Quality Standards (NEQS) of Pakistan. Post-treatment of IC bioreactor effluents was accomplished in CW containing macrophytes (Arundo donax and Eichhornia crassipes) and mixed algal culture. The CWs planted with macrophytes lowered the concentrations of COD (89%) and turbidity (99%). CWs with algal biomass were not effective in further polishing the effluent. Inhibition of algal biomass growth was observed due to physicochemical characteristics of wastewater. The integrated treatment system consisting of IC bioreactor and macrophytes was found more suitable option for industrial wastewater treatment.

The Role of Hydrophobicity in Bio-Accessibilityof Environmental PollutantsAmong Different Organisms

This study concerns the relationship between hydrophobicity and bio-accessibility of environmental pollutants among the protozoan Tetrahymena pyriformis, the water flea Daphnia magna, and the fish Poecilia reticulata. The toxicological data of 55 chemicals in terms of 50% effect concentration was selected toward these three biological objects along with their hydrophobic potential (octanol-water partition coefficients (log Kow)). Overall, a significant correlation was achieved among all test systems, with the highest between Tetrahymena pyriformis and Poecilia reticulata (R = 0.93). The acute toxicity results revealed substantial differences in the sensitivity of the three test systems, but at a certain level of hydrophobicity (log Kow values 0.5 to 2.5), where all environmental pollutants have the utmost ability to reach biological compartments as cytosole and target sites within the membranes, to interfere with normal cell functioning by effecting normal enzymatic activity and directly to biological macromolecules.