Hina Rizvi

Cadmium stress in rice: toxic effects, tolerance mechanisms, and management: a critical review

Cadmium (Cd) is one of the main pollutants in paddy fields, and its accumulation in rice (Oryza sativa L.) and subsequent transfer to food chain is a global environmental issue. This paper reviews the toxic effects, tolerance mechanisms, and management of Cd in a rice paddy. Cadmium toxicity decreases seed germination, growth, mineral nutrients, photosynthesis, and grain yield. It also causes oxidative stress and genotoxicity in rice. Plant response to Cd toxicity varies with cultivars, growth condition, and duration of Cd exposure. Under Cd stress, stimulation of antioxidant defense system, osmoregulation, ion homeostasis, and over production of signaling molecules are important tolerance mechanisms in rice. Several strategies have been proposed for the management of Cd-contaminated paddy soils. One such approach is the exogenous application of hormones, osmolytes, and signaling molecules. Moreover, Cd uptake and toxicity in rice can be decreased by proper application of essential nutrients such as nitrogen, zinc, iron, and selenium in Cd-contaminated soils. In addition, several inorganic (liming and silicon) and organic (compost and biochar) amendments have been applied in the soils to reduce Cd stress in rice. Selection of low Cd-accumulating rice cultivars, crop rotation, water management, and exogenous application of microbes could be a reasonable approach to alleviate Cd toxicity in rice. To draw a sound conclusion, long-term field trials are still required, including risks and benefit analysis for various management strategies.

Influence of Pseudomonas aeruginosa as PGPR on oxidative stress tolerance in wheat under Zn stress

Plant Growth Promoting Rhizobacteria (PGPR), whose role is still underestimated, plays an important (or perhaps essential) role in improving plant growth. The comprehensive understanding of bacterial plant growth promoting mechanism helps to get sustainable agriculture production under biotic and abiotic stresses. In the present study, plant growth promoting (PGP) bacterial strain Pseudomonas aeruginosa having maximum inhibitory concentration of 1500mg kg(-1) against Zn was isolated from arable land, irrigated with industrial effluent and evaluated to determine it bioremediation potential. The study was mainly focused on plant biomass production, nutrient uptake and oxidative stress tolerance in relation to the activities of antioxidative enzymes and the content of non-enzymatic antioxidants. The oxidative stress tolerance was measured by estimating the MDA accumulation as well as H2O2 production in wheat plants under Zn (1000mg kg(-1)) stress and inoculation of soil with Zn resistant Pseudomonas aeruginosa. Zn in rooting medium reduced the plant growth, leaf photosynthetic pigments as well as uptake of N and P. However, content of MDA and H2O2 increased at higher concentration of Zn. Inoculation of P. aeruginosa improved the uptake of P and N in wheat plants with an increase in leaf chlorophyll, total soluble protein and plant biomass production. Analysis of plant root and shoot disclosed that Zn concentration was significantly lowered in P. aeruginosa inoculated zinc stressed plants as compare to the plants grown under Zn stress only. The amelioration of adverse effects of Zn stress on biomass production due to P. aeruginosa inoculation was related with enhanced antioxidative enzyme activities (SOD, POD and CAT), and the contents of non-enzymatic components such as ascorbic acid and total phenolics (TPC) as compare to Zn-treated plants. The up-gradation in antioxidative defense mechanism, resulted a reduction in H2O2 and MDA content due to the scavenging of ROS by antioxidants. It was concluded that P. aeruginosa is an ideal candidate for bioremediation and wheat growth promotion against Zn-induced oxidative stress by improving the availability of necessary nutrient, eliciting antioxidant defense system as well as by lowering the Zn metal uptake.

Phytomanagement of heavy metals in contaminated soils using sunflower: A review

ABSTRACT Contamination of soils with heavy metals (HMs) is an important issue due to the contamination of agricultural crops, which are further transferred into the food chain. Phytoremediation is an emerging method of remediating metal-contaminated soils. Sunflower has been widely adopted for phytomanagement of HM-contaminated soils owing to its high biomass production and capacity for metal accumulation. Sunflowers can tolerate the toxic effects of certain HMs through different mechanisms, such as enhancements in antioxidant enzyme activities, deposition in nonactive parts of the plant, and stimulation of osmolytes. Stress caused by HMs affected negatively the seed germination, nutritional status, photosynthesis, and growth of sunflower. However, the responses of sunflowers to this stress vary with cultivar/variety, soil type, metal type, dose, and duration of metal exposure. This review critically summarizes the effects of HMs in sunflowers and examines field-relevant approaches to improve the phytoextraction capability of sunflowers. Proper selection of tolerant cultivars along with agronomic practices may be an effective strategy for the phytomanagement of soils contaminated with HMs.

Review of Upflow Anaerobic Sludge Blanket Reactor Technology: Effect of Different Parameters and Developments for Domestic Wastewater Treatment

The upflow anaerobic sludge blanket (UASB) reactor has been recognized as an important wastewater treatment technology among anaerobic treatment methods. The objective of this study was to perform literature review on the treatment of domestic sewage using the UASB reactor as the core component and identifying future areas of research. The merits of anaerobic and aerobic bioreactors are highlighted and other sewage treatment technologies are compared with UASB on the basis of performance, resource recovery potential, and cost. The comparison supports UASB as a suitable option on the basis of performance, green energy generation, minimal space requirement, and low capital, operation, and maintenance costs. The main process parameters such as temperature, hydraulic retention time (HRT), organic loading rate (OLR), pH, granulation, and mixing and their effects on the performance of UASB reactor and hydrogen production are presented for achieving optimal results. Feasible posttreatment steps are also identified for effective discharge and/or reuse of treated water.

Textile Wastewater Treatment Options: A Critical Review

Textile industry is one of the largest water-consuming industries in the world, and its wastewater contains many pollutants such as dyes, degradable organics, detergents, stabilizing agents, desizers, inorganic salts, and heavy metals. In Pakistan, most of the textile industries discharge untreated wastewater into water bodies without any treatment, which percolates into the groundwater posing a threat to the health and socioeconomic life of the people. Pretreatment, dyeing, printing, and finishing are the main steps in dyeing and printing process of textile industries. A large amount of wastewater is being generated by all these processes, which contains many pollutants like reactive dyes, chemicals, high chemical oxygen demand (COD), biological oxygen demand (BOD), and organic compounds. Research has been conducted since long to treat textile wastewater in an economical and efficient way. There are many processes for removal of polluted compounds from water that include physicochemical, biological, combined treatment processes, and other technologies. All over the world, ecological standards are gaining importance in every step of textile unit. Due to the strict implementation of environmental standards, it is important to adopt an eco-friendly model of textile industry that overcomes all flaws from its start to end product. The main challenge is to develop a design that can be considered as cost-effective and to substitute chemicals that are less harmful or can be easily treated. On the basis of wastewater characteristics and literature review, appropriate scheme of treatment processes was proposed.