Publications (9)25.89 Total impact
-
Article: Toxicity of organoclays to microbial processes and earthworm survival in soils.
[show abstract] [hide abstract]
ABSTRACT: Organoclays have wide spread application in environmental remediation and nanocomposites synthesis. Some of the quaternary ammonium compounds (QACs) commonly used to prepare organoclays are toxic to biota. However, information on the toxicity of organoclays is rarely available in the literature. This study assessed the toxicity of three laboratory prepared bentonite organoclays on the soil microbially mediated processes (such as dehydrogenase activity and potential nitrification) and soil inhabiting animals, such as earthworms. Toxicity to both microbial processes and earthworm followed the order: hexadecyltrimethyl ammonium modified bentonite>octadecyltrimethyl ammonium modified bentonite>arquad modified bentonite>unmodified bentonite. The organoclays were able to cause slight improvement (up to 25%) in the potential nitrification in some soils when they were added at low application rates up to 5%, but caused reduction (3-86%) in the dehydrogenase activity in all the soils irrespective of loading rates. The organoclays were extremely toxic to the survival and vigour of the earthworms. The average body weight loss of the worms reached as high as 62% in hexadecyltrimethyl ammonium modified bentonite treated soil even at 1% loading. This study holds utmost importance in assessing the toxicity of organoclays to soil microbially mediated processes and earthworms.Journal of hazardous materials 12/2012; · 4.14 Impact Factor -
Article: Bioreactive Organoclay: A New Technology for Environmental Remediation
[show abstract] [hide abstract]
ABSTRACT: Organoclays, which are synthesized by introducing organic molecules into the clay structure, have been proven effective for remediation of many contaminants in soil and water. The underlying principle for this is sorption. However, a new remediation approach that combines sorption and biodegradation/biotransformation has evolved in recent years. Contaminants sorbed on organoclays can be successfully degraded or transformed into less toxic forms by specific microorganisms, provided the participating microbes thrive well on the organoclays. Thus, bioreactive organoclays are prepared. The authors present a critical review of the scientific principles and scope of integrating microorganisms with organoclays to develop a new environmental friendly, risk–based, and cost-effective remediation technology. Furthermore, they propose new research directions in the field.Critical Reviews in Environmental Science and Technology 03/2012; 42(5):435-488. · 4.84 Impact Factor -
Article: Structural characterisation of Arquad® 2HT-75 organobentonites: surface charge characteristics and environmental application.
[show abstract] [hide abstract]
ABSTRACT: Organoclays are increasingly being used to remediate both contaminated soils and waste water. The present study was attempted to elucidate the structural evolution of bentonite based organoclays prepared from a commercially available, low-cost alkyl ammonium surfactant Arquad(®) 2HT-75. XRD, FTIR, SEM and zeta potential measurement were used to characterise the organoclays. In particular, the relationship between surface charge characteristics of the organoclays and their ability to remediate organic contaminants such as phenol and p-nitrophenol was investigated. The investigation revealed that the arrangement and conformation of surfactant molecules in the bentonite became more regular, ordered and solid-like as of Arquad(®) 2HT-75 loading increased. This also led to the formation of a positive zeta potential on the surface of organobentonites prepared with 3.57:1 and 4.75:1 surfactant-clay (w/w) ratio. The zeta potential values decreased with increasing pH of the suspension. The adsorption data of phenol and p-nitrophenol were best fitted to Freundlich isotherm model. The adsorption was controlled by multiple mechanisms of partitioning, physico-sorption and chemisorption. The outcomes of this study are useful for the synthesis of low cost organobentonite adsorbents for the remediation of ionisable organic contaminants such as phenol and p-nitrophenol from waste water.Journal of hazardous materials 08/2011; 195:155-61. · 4.14 Impact Factor -
Article: Sorption of quaternary ammonium compounds in soils: implications to the soil microbial activities.
[show abstract] [hide abstract]
ABSTRACT: Despite their widespread use in household activities and various industries, information on the toxicity of quaternary ammonium compounds (QACs) to microbial activities in soil is scant. This study investigated the effect of three commonly used QACs namely hexadecyltrimethyl ammonium bromide (HDTMA), octadecyltrimethyl ammonium bromide (ODTMA) and Arquad on dehydrogenase and potential nitrification activities in three different soils. The toxicity of QACs on the dehydrogenase activity and potential nitrification in these soils followed the order: HDTMA>ODTMA>Arquad and Arquad>HDTMA>ODTMA, respectively. HDTMA, ODTMA and Arquad exhibited toxicity to dehydrogenase activity at concentration of 50, 100 and 750 mg kg(-1) soil, respectively, whereas potential nitrification was inhibited by HDTMA and ODTMA even at 50 mg kg(-1) soil. Arquad exhibited toxicity to potential nitrification at comparatively higher concentration of 250 mg kg(-1) soil, with the severity of toxicity very intense at higher concentrations. The nature of QACs and soil properties influenced the toxicity. The toxic effect of QACs on soil microbial activities was more influenced by the relative release of sorbed QACs in soils. This study provides valuable information on the toxicological properties of some widely used QACs on important soil microbial activity parameters. To our knowledge, this is the first report.Journal of hazardous materials 12/2010; 184(1-3):448-56. · 4.14 Impact Factor -
Article: Remediation of hexavalent chromium through adsorption by bentonite based Arquad® 2HT-75 organoclays.
[show abstract] [hide abstract]
ABSTRACT: Unlike hydrophobic organic pollutants, the potential of organoclays to adsorb inorganic ionic contaminants is relatively underexplored. The present study attempts to characterise bentonite (QB) based organoclays synthesised from a commercially available, low-cost alkyl ammonium surfactant Arquad® 2HT-75 (Aq) and test their ability to adsorb hexavalent chromium (Cr (VI)) in aqueous solution. XRD, FTIR and TGA characterisation techniques prove successful modification of the bentonite structure and reveal that higher surfactant loadings gives rise to more ordered surfactant conformation in the organoclays. The zeta potential values indicate that higher surfactant loadings also create positive charges on the organoclay surfaces. Detailed isothermal and kinetic studies show that the organoclays effectively remove hexavalent chromium (Cr (VI)) from aqueous solution by both physical and chemical adsorption processes. Higher surfactant loadings provide better adsorption efficiency. The adsorption performance is reasonably efficient under the levels of pH, temperature, electrolyte concentration and natural organic matter concentration that generally prevail in contaminated soil and water. This study shows that organoclay sorbents offer good potential for remediating Cr (VI) under real environmental conditions.Journal of hazardous materials 11/2010; 183(1-3):87-97. · 4.14 Impact Factor -
Article: Synthesis and characterisation of novel organopalygorskites for removal of p-nitrophenol from aqueous solution: isothermal studies.
[show abstract] [hide abstract]
ABSTRACT: Organopalygorskites were synthesised by using dimethyldioctadecylammonium bromide (DMDOA) and cetylpyridinium chloride (CP) with surfactant loadings equivalent to 100% and 200% CEC of the palygorskite. The four organopalygorskites, thus produced, were characterised by Fourier Transform Infrared Spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and zeta potential measurement. FTIR and TGA data demonstrated that higher surfactant loadings as well as long branched chain DMDOA produced highly ordered surfactant conformation. SEM morphological results showed that the organopalygorskites had less entangled fibres than the unmodified palygorskite. The zeta potential values showed positive charge formation on the organopalygorskites surface when they were synthesised with surfactant loadings equivalent to 200% CEC of the palygorskite. The organopalygorskites were tested for adsorption of p-nitrophenol (PNP) with a special focus on the adsorption isotherms. The adsorption data could be fitted with multiple isothermal models indicating that the adsorption was controlled by multiple mechanisms. Sorbent loading rate, initial pH, temperature and ionic strength might all affect the adsorption process. Also, DMDOA modified organopalygorskites reduced desorption/redispersal of adsorbed PNP back into the environment to a great extent. This study will be helpful in designing palygorskite-based organoclay adsorbents for remediating organic environmental contaminants which are ionic in nature.Journal of Colloid and Interface Science 10/2010; 350(1):295-304. · 3.07 Impact Factor -
Article: Assessment of biological and biochemical indicators in soil under transgenic Bt and non-Bt cotton crop in a sub-tropical environment.
[show abstract] [hide abstract]
ABSTRACT: There is concern that transgenic Bt-crops carry genes that could have undesirable effects on natural and agro-ecosystem functions. We investigated the effect of Bt-cotton (expressing the Cry 1Ac protein) on several microbial and biochemical indicators in a sandy loam soil. Bt-cotton (MRC-6301Bt) and its non-transgenic near-isoline (MRC-6301) were grown in a net-house on a sandy clay loam soil. Soil and root samples were collected 60, 90, and 120 days after sowing. Soil from a control (no-crop) treatment was also included. Samples were analysed for microbial biomass C, N and P (MBC, MBN, MBP), total organic carbon (TOC), and several soil enzyme activities. The microbial quotient (MQ) was calculated as the ratio of MBC-to-TOC. The average of the three sampling events revealed a significant increase in MBC, MBN, MBP and MQ in the soil under Bt-cotton over the non-Bt isoline. The TOC was similar in Bt and non-Bt systems. Potential N mineralization, nitrification, nitrate reductase, and acid and alkaline phosphatase activities were all higher in the soil under Bt-cotton. Root dry weights were not different (P > 0.05), but root volume of Bt-cotton was higher on 90 and 120 days than that of non-Bt cotton. The time of sampling strongly affected the above parameters, with most being highest on 90 days after sowing. We concluded from the data that there were some positive or no negative effects of Bt-cotton on the studied indicators, and therefore cultivation of Bt-cotton appears to be no risk to soil ecosystem functions.Environmental Monitoring and Assessment 09/2008; 156(1-4):595-604. · 1.40 Impact Factor -
Article: Adsorption of Phenol by HDTMA-modified Organoclay
[show abstract] [hide abstract]
ABSTRACT: Naturally occurring clay materials can be modified organically by quaternary ammonium cations resulting into clay products commonly known as organoclays. Such organic modification alters the nature of clay from hydrophilic to hydrophobic, imparting enhanced interaction of the clay products towards hydrophobic pollutants in the environment. These materials can also be used to remediate ionisable organic contaminants such as phenol. The present study presents the adsorption of phenol by hexadecyl trimethyl ammonium (HDTMA) modified bentonite in aqueous medium. It was found that modification of bentonite by HDTMA hugely improved the adsorption of phenol as compared to the unmodified bentonite. Adsorption kinetics and isotherms were also studied. -
Article: Sorption of quaternary ammonium compounds in soils: Implications to the soil microbial activities
[show abstract] [hide abstract]
ABSTRACT: Despite their widespread use in household activities and various industries, information on the toxicity of quaternary ammonium compounds (QACs) to microbial activities in soil is scant. This study investigated the effect of three commonly used QACs namely hexadecyltrimethyl ammonium bromide (HDTMA), octadecyltrimethyl ammonium bromide (ODTMA) and Arquad on dehydrogenase and potential nitrification activities in three different soils. The toxicity of QACs on the dehydrogenase activity and potential nitrification in these soils followed the order: HDTMA > ODTMA > Arquad and Arquad > HDTMA > ODTMA, respectively. HDTMA, ODTMA and Arquad exhibited toxicity to dehydrogenase activity at concentration of 50, 100 and 750 mg kg−1 soil, respectively, whereas potential nitrification was inhibited by HDTMA and ODTMA even at 50 mg kg−1 soil. Arquad exhibited toxicity to potential nitrification at comparatively higher concentration of 250 mg kg−1 soil, with the severity of toxicity very intense at higher concentrations. The nature of QACs and soil properties influenced the toxicity. The toxic effect of QACs on soil microbial activities was more influenced by the relative release of sorbed QACs in soils. This study provides valuable information on the toxicological properties of some widely used QACs on important soil microbial activity parameters. To our knowledge, this is the first report.Journal of Hazardous Materials.
Top co-authors
Top Journals
Institutions
-
2010–2012
-
University of South Australia
- Centre for Environmental Risk Assessment and Remediation
Adelaide, South Australia, Australia
-
-
2008
-
Indian Agricultural Research Institute
- Division of Soil Science and Agricultural Chemistry
New Delhi, NCT, India
-
