Hafiz Faiq Bakhat

Arsenic uptake, accumulation and toxicity in rice plants: Possible remedies for its detoxification: A review

Arsenic (As) is a toxic metalloid. Serious concerns have been raised in literature owing to its potential toxicity towards living beings. The metalloid causes various water- and food-borne diseases. Among food crops, rice contains the highest concentrations of As. Consuming As-contaminated rice results in serious health issues. Arsenic concentration in rice is governed by various factors in the rhizosphere such as availability and concentration of various mineral nutrients (iron, phosphate, sulfur and silicon) in soil solution, soil oxidation/reduction status, inter-conversion between organic and inorganic As compounds. Agronomic and civil engineering methods can be adopted to decrease As accumulation in rice. Agronomic methods such as improving soil porosity/aeration by irrigation management or creating the conditions favorable for As-precipitate formation, and decreasing As uptake and translocation by adding a inorganic nutrients that compete with As are easy and cost effective techniques at field scale. This review focuses on the factors regulating and competing As in soil-plant system and As accumulation in rice grains. Therefore, it is suggested that judicious use of water, management of soil, antagonistic effects of various inorganic plant-nutrients to As should be considered in rice cultivated areas to mitigate the building up of As in human food chain and with minimum negative impact to the environment.

Influence of groundwater and wastewater irrigation on lead accumulation in soil and vegetables: Implications for health risk assessment and phytoremediation

ABSTRACT The current study evaluated the effect of groundwater and wastewater irrigation on lead (Pb) accumulation in soil and vegetables, and its associated health implications. A pot experiment was conducted in which spinach (Spinacia oleracea), radish (Raphanus sativus), and cauliflower (Brassica oleracea) were irrigated with groundwater and wastewaters containing varying concentrations of Pb. Lead contents were measured in wastewaters, soils and root and shoot of vegetables. We also measured health risk index (HRI) associated with the use of vegetables irrigated by wastewaters. Results revealed that Pb contents in groundwater and wastewater samples (range: 0.18–0.31 mg/L) were below the permissible limits (0.5 mg/L) set by the Food and Agriculture Organization (FAO). Application of Pb-containing groundwater and wastewater increased Pb concentration in soil and vegetables. Lead concentrations in all soils ranged from 10 to 31 mg/kg and were below the permissible limits of 300 mg/kg set by the European Union. Significant Pb enrichment was observed in the soils whereby all types of vegetables were grown and assessed for Pb risk. Our data showed that Pb contents, in all three vegetables (21–28 mg/kg DW), were higher than the permissible Pb limit of FAO (5 mg/kg Dry Weight (DW)). The HRI values were > 1.0 for radish and cauliflower. It is proposed that Vehari city wastewater/groundwater must be treated prior to its use for irrigation to avoid vegetable contamination by Pb, and as such for reducing Pb-induced human health risk.

Protective Role of Silicon (Si) Against Combined Stress of Salinity and Boron (B) Toxicity by Improving Antioxidant Enzymes Activity in Rice

The beneficial element silicon (Si) is known to enhance plant tolerance against various kinds of biotic and abiotic stresses. However, little is known about its protective role for plants facing multiple stresses such as salinity and boron (B) toxicity. Therefore, the current study was planned in pots to evaluate the beneficial role of exogenous applied Si (150 mg kg-1) nutrition against salinity stress (10 dS m−1), and B toxicity (2.5 mg kg−1) alone or in combinations. Results showed that both salinity and B toxicity reduced plant growth and biomass of rice, with maximum damage under their combined stress due to increased uptake of toxic ions such as sodium (Na+) and B. Contrarily, Si application helped the plants to overcome negative effects of these toxic ions by increasing silica and K+ uptake and decreasing Na+ and B entry in plants that ultimately lead to improvement in plant biomass. High silica uptake ability of rice significantly improved the efficiency of antioxidant mechanism, as indicated by reduced catalase (CAT) activity and improvement in guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) activity by Si application under stress, resulting in reduced oxidative damage. From this study, we conclude that Si fertilization can enhance crop production in salt affected soils by helping plant defenses against salts as well as associated B toxicities; however, field trials should be carried out before setting any recommendations for farmers.

Agroforestry: a sustainable environmental practice for carbon sequestration under the climate change scenarios—a review

Agroforestry is a sustainable land use system with a promising potential to sequester atmospheric carbon into soil. This system of land use distinguishes itself from the other systems, such as sole crop cultivation and afforestation on croplands only through its potential to sequester higher amounts of carbon (in the above- and belowground tree biomass) than the aforementioned two systems. According to Kyoto protocol, agroforestry is recognized as an afforestation activity that, in addition to sequestering carbon dioxide (CO2) to soil, conserves biodiversity, protects cropland, works as a windbreak, and provides food and feed to human and livestock, pollen for honey bees, wood for fuel, and timber for shelters construction. Agroforestry is more attractive as a land use practice for the farming community worldwide instead of cropland and forestland management systems. This practice is a win–win situation for the farming community and for the environmental sustainability. This review presents agroforestry potential to counter the increasing concentration of atmospheric CO2 by sequestering it in above- and belowground biomass. The role of agroforestry in climate change mitigation worldwide might be recognized to its full potential by overcoming various financial, technical, and institutional barriers. Carbon sequestration in soil by various agricultural systems can be simulated by various models but literature lacks reports on validated models to quantify the agroforestry potential for carbon sequestration.

Arsenic Behaviour in Soil-Plant System: Biogeochemical Reactions and Chemical Speciation Influences

Arsenic (As) is classified as a Class A human carcinogen and has gained a substantial attention in recent years owing to its high levels currently observed in the environment and adverse impacts on human health. Several studies have delineated the biogeochemical behaviour of As in soil-plant system in relation to its chemical speciation and bioavailability. This chapter establishes a link between As speciation and biogeochemical behaviour of As in complex soil-plant systems. It gives an overview of different biogeochemical processes that govern environmental behaviour of As in soil-plant system; highlights how the chemical speciation of As affects its biogeochemical behaviour (adsorption/desorption, mobility, bioavailability/phytoavailability) in soil-plant system; and discusses relationship of soil physico-chemical properties (pH, clay contents, biological and microbial conditions, presence of organic and inorganic ligands and competing anions/cations) with chemical speciation of As as well as its biogeochemical behaviour in soil-plant system.

A Review on Synthesis, Characterization and Applications of Copper Nanoparticles Using Green Method

To address accosts of this modern age, the synthesis of metal nanoparticles is more important than ever. Copper has been recognized as a nontoxic, safe inorganic material, cheaper antibacterial/ant...

Effect of water management and silicon on germination, growth, phosphorus and arsenic uptake in rice

Silicon (Si) is the 2nd most abundant element in soil which is known to enhance stress tolerance in wide variety of crops. Arsenic (As), a toxic metalloid enters into the human food chain through contaminated water and food or feed. To alleviate the deleterious effect of As on human health, it is a need of time to find out an effective strategy to reduce the As accumulation in the food chain. The experiments were conducted during September-December 2014, and 2016 to optimize Si concentration for rice (Oryza sativa L.) exposed to As stress. Further experiment were carried out to evaluate the effect of optimum Si on rice seed germination, seedling growth, phosphorus and As uptake in rice plant. During laboratory experiment, rice seeds were exposed to 150 and 300µM As with and without 3mM Si supplementation. Results revealed that As application, decreased the germination up to 40-50% as compared to control treatment. Arsenic stress also significantly (P < 0.05) reduced the seedling length but Si supplementation enhanced the seedlings length. Maximum seedling length (4.94cm) was recorded for 3mM Si treatment while, minimum seedling length (0.60cm) was observed at day7 by the application of 300µM As. Silicon application resulted in 10% higher seedling length than the control treatment. In soil culture experiment, plants were exposed to same concentrations of As and Si under aerobic and anaerobic conditions. Irrigation water management, significantly (P˂0.05) affected the plant growth, Si and As concentrations in the plant. Arsenic uptake was relatively less under aerobic conditions. The maximum As concentration (9.34 and 27.70mgkg DW-1 in shoot and root, respectively) was found in plant treated with 300µM As in absence of Si under anaerobic condition. Similarly, anaerobic condition resulted in higher As uptake in the plants. The study demonstrated that aerobic cultivation is suitable to decrease the As uptake and in rice exogenous Si supply is beneficial to decrease As uptake under both anaerobic and aerobic conditions.

Anaerobic degradation of municipal organic waste among others composting techniques improves N cycling through waste-soil-plant continuum

This study aimed to examine the effect of composting techniques of municipal organic solid waste (MSW) for (i) total carbon (C), nitrogen (N) losses, and changes in its chemical characteristics during composting phase and (ii) value of the composted materials as fertilizer when applied to vegetables. Treatments included: aerobic composting (AC), anaerobic composting (ANC), co-composting (CC) and open dumping (OD) for 4 months. During the composting phase, about 61, 50, 35, and 13% of the initial N was lost from CC, AC, OD, and ANC, respectively. The respective values in case of total C loss were 17, 13, 14 and 11%. After field application, about 41% of the applied organic N was mineralized from ANC material, whereas the respective values for OD, CC and AC were 25-26, 15-16, and 12-19%. Consequently, dry matter (DM) yield and vegetable N uptake from the resultant compost were in the order ANC>OD>CC>AC. Moreover, vegetable apparent N recovery (ANRf) was the highest from ANC (spinach: 36 and carrot: 45%) followed by OD (26 and 34%), CC (18 and 26%) and AC (18 and 24%) material. When composting N losses were taken into account during calculations, about 31-39, 17-22, 9-10, and 7-12% of the N collected from filth depots ended up in plants from ANC, OD, CC and AC, respectively. We concluded that ANC results in least C and N losses during the composting phase and greatest N mineralization in the soil, which enhances vegetable yield, N recovery and thereby the N cycling through waste-soil-plant continuum.

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.

Biosorption potential of natural, pyrolysed and acid-assisted pyrolysed sugarcane bagasse for the removal of lead from contaminated water

Lead (Pb) is a ubiquitous pollutant which poses serious threats to plants, animals and humans once entered into the food chain via contaminated industrial effluents on their discharge into the surface of water bodies and/or geological materials. This study aimed to examine and compare the biosorption potential of natural sugarcane bagasse (NB), pyrolysed sugarcane bagasse (PB) and acid assisted pyrolysed sugarcane bagasse (APB) for the removal of Pb from contaminated water. To explore this objective, a series of batch experiments were conducted at various adsorbent mass (0.25, 0.5, 0.75, 1.0 g per 100 ml contaminated water), initial Pb concentration (7, 15, 30, 60 and 120 ppm), and contact time (7, 15, 30, 60 and 120 min). Results revealed that all the tested bio-sorbents have potential to adsorb and remove Pb ions from the contaminated water. In this regard, APB proved more effective since it removed 98% of Pb from aqueous solution at initial Pb concentration of 7 ppm and mass of 0.25 g per 100 ml of aqueous solution. The respective values in case of NB and PB were 90 and 95%. For a given adsorbent type, Pb adsorption decreased by increasing the mass from 0.25 to 1.0 g per 100 ml of aqueous solution. However, the greatest Pb removal occurred at adsorbent mass of 1.0 g per 100 ml of aqueous solution. Initial Pb concentration had a great impact on Pb adsorption and removal by adsorbent. The former increased and the latter decreased with the increase in initial Pb concentration from seven to 120 ppm. At seven ppm Pb concentration, maximum Pb removal took place irrespective to the adsorbent type. Out of the total Pb adsorption and removal, maximum contribution occurred within 15 min of contact time between the adsorbate and adsorbent, which slightly increased till 30 min, thereafter, it reached to equilibrium. Application of equilibrium isotherm models revealed that our results were better fitted with Freundlich adsorption isotherm model. Overall, and for the reasons detailed above, it is concluded that sugarcane bagasse has capabilities to adsorb and remove Pb ions from contaminated water. Its bio-sorption potential was considerably increased after pyrolysis and acid treatment.