Comparison of properties and aquatic arsenic removal potentials of organically modified smectite adsorbents.

Arsenic (As) poses a tremendous threat to human health due to exposure through arsenic-contaminated drinking water and/or food. We aimed to develop organically modified clay adsorbents for the removal of As from aqueous solution. We modified a smectite sample using three organic agents, namely hexadecyl trimethylammonium (HDTMA), chitosan and citric acid, and characterized the products using X-ray diffraction, infrared spectroscopy, and scanning electron microscopy techniques. The characterization techniques suggested successful organic modifications of the smectite sample. The surfactant-modified smectite was the most efficient (66.9%) As removing adsorbent with a maximum adsorption capacity of 473.2 µg g-1. Kinetic study showed that the adsorbents reached As adsorption equilibrium within 3 h, and the data fitted reasonably well to power function and simple Elovich equations (R2 > 0.89). The adsorption data were explained well by the Freundlich and Sips isothermal models. The surfactant-modified and chitosan-grafted organoclays adsorbed As by electrostatic attraction and anion exchange, whereas the citric acid activated smectite followed ligand exchange and simple anion exchange mechanisms. This study thus demonstrated the potential of surfactant-modified clays in removing As from contaminated waters.

Host-Induced Silencing of Two Pharyngeal Gland Genes Conferred Transcriptional Alteration of Cell Wall-Modifying Enzymes of Meloidogyne incognita vis-à-vis Perturbed Nematode Infectivity in Eggplant.

The complex parasitic strategy of Meloidogyne incognita appears to involve simultaneous expression of its pharyngeal gland-specific effector genes in order to colonize the host plants. Research reports related to effector crosstalk in phytonematodes for successful parasitism of the host tissue is yet underexplored. In view of this, we have used in planta effector screening approach to understand the possible interaction of pioneer genes (msp-18 and msp-20, putatively involved in late and early stage of M. incognita parasitism, respectively) with other unrelated effectors such as cell-wall modifying enzymes (CWMEs) in M. incognita. Host-induced gene silencing (HIGS) strategy was used to generate the transgenic eggplants expressing msp-18 and msp-20, independently. Putative transformants were characterized via qRT-PCR and Southern hybridization assay. SiRNAs specific to msp-18 and msp-20 were also detected in the transformants via Northern hybridization assay. Transgenic expression of the RNAi constructs of msp-18 and msp-20 genes resulted in 43.64-69.68% and 41.74-67.30% reduction in M. incognita multiplication encompassing 6 and 10 events, respectively. Additionally, transcriptional oscillation of CWMEs documented in the penetrating and developing nematodes suggested the possible interaction among CWMEs and pioneer genes. The rapid assimilation of plant-derived carbon by invading nematodes was also demonstrated using 14C isotope probing approach. Our data suggests that HIGS of msp-18 and msp-20, improves nematode resistance in eggplant by affecting the steady-state transcription level of CWME genes in invading nematodes, and safeguard the plant against nematode invasion at very early stage because nematodes may become the recipient of bioactive RNA species during the process of penetration into the plant root.

Optimization of isotherm models for pesticide sorption on biopolymer-nanoclay composite by error analysis.

A carboxy methyl cellulose-nano organoclay (nano montmorillonite modified with 35-45 wt % dimethyl dialkyl (C14-C18) amine (DMDA)) composite was prepared by solution intercalation method. The prepared composite was characterized by infrared spectroscopy (FTIR), X-Ray diffraction spectroscopy (XRD) and scanning electron microscopy (SEM). The composite was utilized for its pesticide sorption efficiency for atrazine, imidacloprid and thiamethoxam. The sorption data was fitted into Langmuir and Freundlich isotherms using linear and non linear methods. The linear regression method suggested best fitting of sorption data into Type II Langmuir and Freundlich isotherms. In order to avoid the bias resulting from linearization, seven different error parameters were also analyzed by non linear regression method. The non linear error analysis suggested that the sorption data fitted well into Langmuir model rather than in Freundlich model. The maximum sorption capacity, Q0 (µg/g) was given by imidacloprid (2000) followed by thiamethoxam (1667) and atrazine (1429). The study suggests that the degree of determination of linear regression alone cannot be used for comparing the best fitting of Langmuir and Freundlich models and non-linear error analysis needs to be done to avoid inaccurate results.

Monitoring temperature sensitivity of soil organic carbon decomposition under maize-wheat cropping systems in semi-arid India.

Long-term storage of soil organic carbon (SOC) is essential for sustainability of agricultural ecosystems and maintaining overall environment quality as soils contain a significant part of global carbon stocks. In this study, we attempted to explain the carbon mineralization and temperature sensitivity of SOC in maize-wheat systems, a common cropping system in the semi-arid regions of India. Soil samples(0-0.15 m) from long-term experimental plots laid in split plot design with two tillage systems (conventional tillage and bed planting) and six nutrient management treatments (T 1 = control, T 2 = 120 kg urea-N/ha, T 3 = T2 (25 % N substituted by farmyard manure (FYM)), T 4 = T 2 (25 % N substituted by sewage sludge), T 5 = T 2 + crop residue, T 6 = 100 % recommended doses of N through organic source - 50 % FYM + 25 % biofertilizer + 25 % crop residue) were incubated at different temperatures (25, 30, 35, and 40 °C) to determine the thermal sensitivity parameters associated with carbon mineralization. Earlier reports suggest a selective preservation of C3-derived carbon fractions over C4 in the SOC pool, and this is the first instance where δ (13)C signatures (C4-derived carbon) were used as a qualitative measure to assess thermal sensitivity of SOC pools in the maize-wheat crop rotation systems of semi-arid India. Among the nutrient management treatments, mineral fertilizers were found to add more C4-derived carbon to the SOC pool in both the tillage systems but shows less promise in SOC stability as indicated by their lower activation energies (Ea) (14.25 kJ mol(-1)). Conventional tillage was found to mineralize 18.80 % (T 1-control at 25 °C) to 29.93 % carbon (T 3-mineral fertilizer + FYM at 40 °C) during the 150 days of incubation which was significantly higher than bed planting system (14.90 % in T 1-control at 25 °C and 21.99 % in T 6-100% organic sources at 40 °C). Organic manures, especially FYM (19.11 kJ mol(-1)) and 100 % organics (19.33 kJ mol(-1)) were more effective in enhancing the Ea of SOC than plots with mineral fertilizers alone (14.25 kJ mol(-1)), but had relatively higher Q 10 values thereby corroborating the thermal sensitivity hypothesis of recalcitrant organic compounds in soil. Michaelis-Menten derivatives along with thermal sensitivity indicators such as Ea and Q 10 were found to be efficient parameters for explaining carbon mineralization and CO2 efflux from soils.

Soil carbon fractions under maize-wheat system: effect of tillage and nutrient management.

Soil organic carbon plays a major role in sustaining agroecosystems and maintaining environmental quality as it acts as a major source and sink of atmospheric carbon. The present study aims to assess the impact of agricultural management practices on soil organic carbon pools in a maize-wheat cropping system of Indo-Gangetic Plains, India. Soil samples from a split plot design with two tillage systems (bed planting and conventional tillage) and six nutrient treatments (T1 = control, T2 = 120 kg urea-N ha(-1), T3 = T2 (25 % N substituted by FYM), T4 = T2 (25 % N substituted by sewage sludge), T5 = T2 + crop residue, T6 = 100 % organic source (50 % FYM + 25 % biofertilizer + 25 % crop residue) were used for determining the organic carbon pools. Results show that there was a significant improvement in Walkley and Black carbon in soil under integrated and organic nutrient management treatments. KMnO4-oxidizable carbon content of soil varied from 0.63 to 1.50 g kg(-1) in soils and was found to be a better indicator for monitoring the impact of agricultural management practices on quality of soil organic carbon than microbial biomass carbon. Tillage and its interaction were found to significantly influence only those soil organic carbon fractions closely associated with aggregate stability viz, labile polysaccharides and glomalin. The highest amount of C4-derived carbon was found to be in plots receiving recommended doses of N as urea (29 %) followed by control plots (25 %). The carbon management index ranged between 82 to 195 and was better in integrated nutrient sources than ones receiving recommended doses of nutrients through mineral fertilizers alone.

Simultaneous removal of multiple pesticides from water: effect of organically modified clays as coagulant aid and adsorbent in coagulation-flocculation process.

Contamination of drinking water sources with agrochemical residues became a major concern in the twenty-first century. Coagulation-flocculation is the most widely used water-treatment process, but the efficiency to remove pesticides and other organic pollutants are limited compared to adsorption process. Thus, simultaneous action of adsorption on normal bentonite or organo-modified montmorillonite clays [modified with octadecylamine (ODA-M) and octadecylamine + amino-propyltriethoxysilane (ODAAPS-M)] followed by coagulation-flocculation by alum and poly aluminium chloride has been evaluated for removal of 10 different pesticides, namely atrazine, lindane, metribuzin, aldrin, chlorpyriphos, pendimethalin, alpha-endosulphan, beta-endosulphan, p,p'-DDT, cypermethrin and two of its metabolites, endosulphan sulphate and p,p'-DDE, from water. The coagulation without integration of adsorption was less effective (removal % varies from 12 to 49) than the adsorption-coagulation integrated system (removal % varies from 71 to 100). Further, coagulation integrated with adsorption was more effective when organically modified montmorillonite was used as adsorbent compared to normal bentonite. The removal efficiency of organic clay depends upon the concentration of pesticides, doses of clay minerals, and efficiency was more for ODAAPS-M as compared to ODA-M. The combination of ODAAPS-M-clay with coagulants was also used efficiently for the removal of pesticides from natural and fortified natural water collected and the results exhibit the usefulness of this remediation technique for application in water decontamination and in treatment of industrial and agricultural waste waters.

Kinetics of metribuzin release from bentonite-polymer composites in water.

A series of bentonite polymer-composites (BPCs) loaded with metribuzin were studied for their controlled release in aqueous medium. The release of active ingredient from BPCs was significantly lower as compared to commercial metribuzin formulation. The results revealed that the cumulative metribuzin release was highest (81%) from the BPCs containing 8% clay (commercial bentonite) and 2% metribuzin which correspond to the lowest (14 days) half-life values i.e., time required for 50% release of active ingredient (t1/2). The metribuzin release from the BPCs decreased with increased concentration of clays in polymer matrix and the release was further decreased with BPCs prepared with pure nano-bentonite. BPCs containing 12% clay and 2% metribuzin showed maximum t1/2 values i.e., 25 and 51 days for commercial bentonite and pure nano-bentonite as clay sources, respectively. The differential behaviour in the metribuzin release rates from BPCs was ascribed due to variations in crosslinking of metribuzin in the composites. As metribuzin release was found to be slower in BPCs compared to commercial formulation, it could be used for control of weeds tailored to different crops.

134Cs transfer factors to green gram and soybean as influenced by waste mica.

Greenhouse pot culture experiment was carried out to study the (134)Cs transfer factors from soils to green gram and soybean as influenced by waste mica application (@ 0, 10, 20, 40 g mica kg(-1) soil) and compared with muriate of potash (MOP) application (0.17 g kg(-1) soil). For the study, the soils were contaminated with (134)Cs radionuclide @ 37 kBq kg(-1) soil. The shoot biomass and K uptake by crops were significantly improved with waste mica application (@ 40 g kg(-1) soil). Compared to control, waste mica and MOP application significantly improved the yield, K content in plant and its uptake. Amongst the soils, crops grown in vertisol recorded higher shoot biomass compared to inceptisol and ultisol. Irrespective of the treatments, higher (134)Cs transfer factors were seen in ultisol (0.30) as compared to inceptisol (0.16) and vertisol (0.13). It was observed that higher the K concentration in soil and plant, lowered (134)Cs transfer to green gram and soybean. The study recommended that waste mica @ 20 g kg(-1) would be useful for checking the (134)Cs transfer factors from soils to green gram and soybean.

Effect of nitrogen, potassium and humic acid on ( 134 )Cs transfer factors to wheat from tropical soils in Neubauer growth units.

A Neubauer plantlet experiment was carried out using Inceptisol (Typic Haplustept) and Vertisol (Typic Chromustert) soils contaminated with 134Cs at 74 kBq kg(-1) soil to study the transfer factor to wheat crop (Triticum aestivum) as influenced by four levels of humic acid (100, 200, 300, 400 mg HA kg(-1) soil), potassium and NH4-N (36.4, 54.5, 72.7 and 90.9 mg K or NH4 kg(-1) soil) under tropical climate. The biomass yield and K uptake by wheat were significantly improved in Vertisol with NH4-N and K application. The potassium application significantly increased the potassium concentration in wheat plants. The increase in the levels of each of the treatments dramatically improved the yield, K content and K uptake parameters, irrespective of the soils. The 134Cs transfer factors, irrespective of the treatments were observed to be higher in Vertisols as compared to Inceptisols. Among the treatments, the effect of HA was significantly greater than that of K and NH4-N application in Inceptisol, however, in Vertisols both HA and NH4-N were observed to be superior as compared to K application. With each increment in the levels of the treatments, a significantly lowered TF value was found, higher in Inceptisols (56.3%) than Vertisols (48.5%). Comparison of treatments indicates that in general higher potassium concentration in plant drastically lowered radiocesium transfer to wheat. Neubauer plant culture study, a rapid laboratory experimental model based on simple soil-plant system was quite clearly brought out the potential effectiveness of N, K and HA on soil-to-wheat transfer of radiocesium. Such screening technique needs to be extended to cover wider crop species, different climatic conditions and factors governing/modifying the mobility of radiocesium in soil and its absorption by crop plants.

Transfer factors of (134)Cs to crops from Typic Haplustept under tropical region as influenced by potassium application.

Under greenhouse condition a pot culture investigation was carried out using Inceptisol soil (Typic Haplustept) contaminating with (134)Cs @ 1microCikg(-1) soil to study the transfer factor to Mustard, Gram, Spinach and Wheat crops as influenced by potassium application (0, 27.3, 54.6 and 81.9mgKkg(-1) soil). Potassium application in general improved the biomass, grain yield and also the potassium concentration in all the crops. Irrespective of the crops, (134)Cs transfer factor to straw and grain was highest in control treatment (no K addition) and found to decrease significantly with increase in K application levels. The (134)Cs uptake was highest in Spinach followed by Mustard, Gram and Wheat crops. The weighted transfer factor values (straw plus grain) to Spinach, Mustard, and Gram were observed to be 5.54, 4.38 and 2.20 times higher as compared to Wheat crop.