Short-term insecticide exposure amid co-occurring stressors reduces diversity and densities in north-east Indian experimental aquatic invertebrate communities.

Globally, river pesticide concentrations are associated with regional and local stream invertebrate diversity declines. Pesticides often co-occur with elevated nutrients (e.g. nitrogen and phosphorus) and sediments related to agriculture, making their individual effects difficult to disentangle. These effects are also less well studied in Asia, than in other geographic regions. Within Asia, India is one of the largest producers and users of pesticides and has approximately 60% of total land mass used for agriculture. Here we examine the responses of Indian river invertebrate communities subjected to malathion, nutrients, and sediment additions in a semi-orthogonal design, in three sequential (through time) short-term (120 h) mesocosm experiments. Additionally, a series of single-species toxicity tests were run that used 24 h exposure and 72 h recovery to examine the sensitivity of 13 local invertebrate taxa to malathion, and 9 taxa to cypermethrin, comparing these results to those from other biogeographic regions. Mesocosm results indicate that malathion exposure had a major effect compared to other stressors on communities, with a lesser effect of nutrients and/or sediments. In mesocosms, taxa richness, total abundance and the abundance of sensitive species all declined associated with malathion concentrations. Comparisons of organism sensitivities from other geographic locations and those in the current paper suggest taxa in India are relatively tolerant to malathion and cypermethrin. Our results further reinforce that the high observed aquatic pesticide concentrations known to occur in Asian freshwater ecosystems are likely to be negatively affecting biodiversity, homogenising biota towards those most stress tolerant.

Prey preferences of notonectids towards larval mosquitoes across prey ontogeny and search area.

BACKGROUND: Predatory biological control agents can be effective natural means of managing pests, vectors and invasive species. However, the strength of predator-prey interactions can be regulated through context-dependencies that often remain unquantified. In particular, refuge effects can influence the efficacy of biological agents towards target species, and such effects are often driven by prey size and search area differences. In this study, we quantify the prey preferences of two predaceous notonectids, Anisops breddini and Anisops sardeus, towards four different aquatic larval instar stages of the medically important mosquito Culex quinquefasciatus across variations in surface area and water depth. RESULTS: Consumption rates differed significantly among the four larval sizes but not between the notonectids. Search area variations also elicited differences in consumption rates. Both predators tended to prefer second-instar mosquito prey among surface area and water depth variations, while generally avoiding the largest (fourth instar) and smallest (first instar) prey instar stages. For both predators, differential selectivity traits were emergent across surface area variations and water depth, with refuge effects for small prey generally greatest at intermediate-large depths with high surface areas. We thus demonstrate that predatory impacts of notonectids towards mosquito larvae differ significantly according to prey size, and likely peak at intermediate size classes. CONCLUSION: Different mosquito size classes often coexist and compete, selectivity has important implications for adult mosquito proliferations. Further, in ephemeral aquatic habitats where surface areas and water depths are highly variable spatiotemporally, the efficacy of notonectids in controlling mosquito prey may differ substantially. © 2019 Society of Chemical Industry.

Water depth-dependent notonectid predatory impacts across larval mosquito ontogeny.

BACKGROUND: Context-dependencies can modulate the strength of predatory interactions and often remain unquantified. In particular, differences in water depth within aquatic systems could influence predator efficiencies towards prey which utilise three-dimensional space through the water column. Differences in prey size could drive prey size-refuge effects, influencing the efficacy of natural enemies towards vector species. We thus quantify the predatory impact of two notonectid predators, Anisops breddini and Anisops sardeus, towards four different larval instars of Culex quinquefasciatus prey across a water depth gradient, using functional responses (FRs). RESULTS: Consumption rates differed significantly between the predators, and interspecific differences in responses to variations in water depth were emergent. Both notonectids were able to handle C. quinquefasciatus prey across all instar stages, yet predation rates were generally higher towards early as opposed to late instar prey. Anisops sardeus was most voracious, and differential predation rates of this species were most pronounced in shallow waters. Type II FRs were displayed by notonectids in the majority of treatments; however, Type III FRs were emergent in specific treatment groups, with potential implications for prey population stability. Both capture rates and handling times were often greater at greater depths, and thus maximum feeding rates reduced as depth increased. Our results further demonstrate substantial predatory impacts of notonectid predators towards mosquito, and quantify biotic and abiotic context-dependencies which modulate their impact. CONCLUSION: Given notonectids are capable of aerial dispersal between ephemeral aquatic habitats of varied volumes, their promotion in aquatic systems could help reduce proliferations of medically important mosquitoes. © 2019 Society of Chemical Industry.

Nanomaterials as versatile adsorbents for heavy metal ions in water: a review.

Over the years, heavy metal pollution has become a very serious environmental problem worldwide. Even though anthropogenic sources are believed to be the major cause of heavy metal pollution, they can also be introduced into the environment from natural geogenic sources. Heavy metals, because of their toxicity and carcinogenicity, are considered to be the most harmful contaminants of groundwater as well as surface water, a serious threat to both human and aquatic life. Nanomaterials due to their size and higher surface area to volume ratio show some unique properties compared to their bulk counterpart and have drawn significant attention of the scientific community in the last few decades. This large surface area can make these materials as effective adsorbents in pollution remediation studies. In this review, an attempt has been made to focus on the applicability of different types of nanomaterials, such as clay-nanocomposites, metal oxide-based nanomaterials, carbon nanotubes, and various polymeric nanocomposites as adsorbents for removal of variety of heavy metals, such as As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sn, U, V, and Zn, from water as reported during the last few years. This work tries to analyze the metal-nanomaterial interactions, the mechanism of adsorption, the adsorption capacities of the nanomaterials, and the kinetics of adsorption under various experimental conditions. The review brings forward the relation between the physicochemical properties of the nanomaterials and heavy metal adsorption on them.

Impact of waste dump on surface water quality and aquatic insect diversity of Deepor Beel (Ramsar site), Assam, North-east India.

Water and aquatic insects were collected seasonally from site 1, the low-lying area of the dump near Deepor Beel, and from sites 2 and 3 of the main wetland and analysed. While dissolved oxygen (DO) increased from site 1 to site 3 in each season, electrical conductivity (EC), total dissolved solid (TDS), total alkalinity (TA) and free CO2 (F-CO2) decreased. Pb and Cd were found to exceed the limits set for drinking water in all the sites and seasons. Species richness (SpR) was found highest (23) at site 2 and lowest (14) at site 1. Sensitive species was absent. The Shannon (H') values at site 1 were < 1 while at sites 2 and 3 were > 1 in most of the seasons. Biological monitoring scores (Biological Monitoring Working Party and Stream Invertebrate Grade Number-Average Level) in different sites and seasons inferred severely poor to moderate water quality. At site 1, significant negative correlations were seen for Pb and Cr with SpR while Ni and Cu with insect density (ID). At site 2, TA had highly significant positive correlations with SpR and ID while Cu showed negative correlation with SpR. At site 3, ID had significant negative relationships with air temperature, water temperature, depth, TA, F-CO2, PO43- and Cr. Canonical correspondence analysis triplot has clearly separated site 1 associated with tolerant species and highly influenced by TA, TDS, EC, F-CO2, Cr, Ni, Cd and Zn confirming high anthropogenic activities on that site. Tolerant and semitolerant species were present at site 2 (influenced by depth and transparency) and site 3 (influenced by Pb and WT) both. Results of this study discerned that the dump site is the point source of pollution.

Acute toxicity of cadmium in Anisops sardeus (Heteroptera:Notonectidae): Effects on adult and nymphal survival and swimming behavior.

Adult female and male, and final instar nymph of Anisops sardeus (Heteroptera: Notonectidae) were exposed to graded concentrations of cadmium in 96h static-with-renewal acute toxicity tests, which were conducted in dry (March) and wet (May-June) seasons. The 96h LC50 values for instar V nymph, adult female and male were found to be 0.9, 0.59 and 0.51mgL-1 Cd, respectively, in wet season, while these were 26.7 and 20.2mgL-1 Cd for adult female and male, respectively, in dry season. Adult males were most sensitive to Cd, followed by females in both seasons, while highest tolerance in wet season was observed in instar V nymph. There was a steep decline in LC50 values from 24 to 96h in wet season. Besides mortality at higher concentrations of Cd, sublethal effects in terms of reduced 'velocity magnitude' (swimming speed) and mostly increased 'rotation angle' (turning angle) could be discerned at concentrations as low as 0.03mgL-1. The swimming pattern of Cd-exposed nymph and adults were also affected. Based on the bioaccumulation factor (BAF) values, A. sardeus could be designated as a macroconcentrator of Cd (BAF > 2), with highest Cd accumulation in instar V nymph, followed by that in female, and with lowest Cd accumulation in male.

RETRACTED: Adsorption of Crystal violet on raw and acid-treated montmorillonite, K10, in aqueous suspension.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor-in-Chief. After further consultation with the experts conducting research in the area of XRD and FTIR spectrum, it has been concluded that the appropriate action for this case is the full retraction of the article from the Journal of Environmental Management. The rationale for this decision is what the journal has concluded to be the fabrication of data associated with Figure 2a in the manuscript which shows three distinct areas in the noise patters with unusual similarities to be considered as coincidental. The data presented in Figure 2a jeopardizes the quality of the manuscript and the conclusions drawn based on the data presented in Figure 2.

(Metallo)porphyrins as potent phototoxic anti-cancer agents after irradiation with red light.

Novel photoactive (metallo)porphyrins were synthesised and characterised. When irradiated with light at a wavelength greater than 600 nm, these porphyrins act as photosensitisers and show high cytotoxicity towards two different human cancer cell lines with IC50 values down to 0.4 µM. A paramagnetic copper(II) porphyrin is the first photosensitiser to display excellent phototoxicity, explained by the electron paramagnetic resonance (EPR) spin trapping of hydroxy radicals and experimentally confirmed by the discovery of elevated levels of reactive oxygen species (ROS) inside A2780 cells after irradiation with red light. This finding indicates that paramagnetic compounds should be considered for photodynamic therapy (PDT). Furthermore, an additive effect of cisplatin and a zinc porphyrin, both at subtherapeutic concentrations of 0.22 µM, was observed.

Ecology of Baskandi anua, an oxbow lake of South Assam, North East India.

A study was made on the physico-chemical properties of water and phyto and zooplankton communities of Baskandi anua, an oxbow lake of South Assam during March to August, 2009. Analyses of water showed acidic to slightly alkaline pH (5.4-7.9) with dissolved oxygen ranging from 4.26 to 11.83 mgl(-1) and total alkalinity from 31.25 to 65 mg l(-1), indicating the productive nature of water. Free CO2 fluctuated from 2.93 to 15.04 mgl(-1). PO4 and NO3 concentration ranged from 0.15 to 1.4 mg l(-1) and 0.06 mg l(-1) to 4.94 mg l(-1), respectively. Conductivity, pH and free CO2 were found higher at the sites surrounded by paddy fields. Mean values of physico-chemical parameters significantly varied between the sites and were found to be influenced by one or more of the following factors viz. rainfall, depth and influx from adjacent paddy field. A total of 30 phytoplankton taxa and 12 zooplankton taxa with qualitative dominance of Chlorophyceae were recorded. The study revealed that water quality of the lake was good for aquaculture. Hence, the lake should be protected and best management practices should be implemented for sustainable production.

Two new species of Pleciobates (Hemiptera: Gerromorpha: Gerridae) from India, with a key to the species of Pleciobates.

Two new species of water striders in the genus Pleciobates are described from India and compared with allied species. Pleciobates bengalensis Jehamalar, Basu & Zettel sp. nov. is described from the Jalpaiguri District, West Bengal and Pleciobates expositus Jehamalar, Chandra & Zettel sp. nov. (Hemiptera: Gerridae) is described from the Dhubri District, Assam. A key to the species of Pleciobates and a distribution map of the species of Pleciobates from India are provided. For the first time the genitalia of Pleciobates females are described in detail.

Photo-catalytic decolourisation of toxic dye with N-doped titania: a case study with Acid Blue 25.

Dyes are one of the hazardous water pollutants. Toxic Acid Blue 25, an anthraquinonic dye, has been decolourised by photo-catalysing it with nitrogen doped titania in aqueous medium. The photo catalyst was prepared from 15% TiCl3 and 25% aqueous NH3 solution as precursor. XRD and TEM revealed the formation of well crystalline anatase phase having particle size in the nano-range. BET surface area of the sample was higher than that of pure anatase TiO2. DRS showed higher absorption of radiation in visible range compared to pure anatase TiO2. XPS revealed the presence of nitrogen in N-Ti-O environment. The experimental parameters, namely, photocatalyst dose, initial dye concentration as well as solution pH influence the decolourisation process. At pH 3.0, the N-TiO2 could decolourise almost 100% Acid Blue 25 within one hour. The influence of N-TiO2 dose, initial concentration of Acid Blue 25 and solution pH on adsorption-desorption equilibrium is also studied. The adsorption process follows Lagergren first order kinetics while the modified Langmuir-Hinselwood model is suitably fitted for photocatalytic decolourisation of Acid Blue 25.

Aquatic insect community of lake, Phulbari anua in Cachar, Assam.

An investigation on the water quality and aquatic insect community of an oxbow lake (Phulbari anua) of south Assam, North-East India was carried out during February to April, 2010. Aquatic insect community of the oxbow lake was represented by 9 species belonging to 9 families and 4 orders during the study period. Order Ephemeroptera and Hemiptera were found to be dominant. Record of 5 species and 5 families from the order Hemiptera showed that this is the largest order in terms of aquatic insect diversity of the lake. Computation of dominance status of different species of aquatic insects of the lake based on Engelmann's Scale revealed that Anisops lundbladiana and Cloeon sp. were eudominant in the system. The Shannon- Weiner's Diversity Index (H') and Shannon evenness values (J') were found to range from 0.3-0.69 and 0.53 -0.97, respectively indicating perturbation of the system. Again in terms of physico-chemical properties of water the lake is in a satisfactory condition where all the parameters are well within the range of IS 10500. The DO values were found to range from 6.8 to 14.8 mgl(-1). Free CO2 fluctuated from 1 to 4.98 mgl(-1) and nitrate in water ranged from 0.4 to 2.1 mgl(-1). Margalef's water quality index values of most of the samplings also indicated clean water condition of the lake. Correlation coefficient analyses of the environmental variables, aquatic insect diversity and density of the lake revealed that aquatic insect diversity of the lake is mainly governed by dissolved oxygen, nitrate, and free carbon dioxide.

Studies on the physico-chemical parameters in water of Keibul Lamjao National Park, Manipur, India.

A study on the physico- chemical parameters of Keibul Lamjao National Park (KLNP) on seasonal basis was carried out for parameters like temperature, pH, transparency, turbidity, dissolved oxygen, chloride, hardness, calcium and magnesium at six selected Stations. The temperature ranged from 10.4 to 28 degrees C showing subtropical nature. pH was consistent both spatially and temporally except at one Station where it was alkaline having value ranging from 6.9 to 7.26. There was a trend in dissolved oxygen to be more during cold season. Electrical conductivity ranged between 105.56 to 201 microS cm(-1). It was high during the dry season and low during rainy season. Transparency and turbidity values indicated that in most Stations water was clear and the two parameters were found to be negatively correlated (r = -0.381). Based on the hardness (41 to 78 mg l(-1)), water was soft. Significant negative correlation (r = -0.532) was found between rainfall and hardness. Calcium and magnesium ions were found to be below the prescribed value of WHO. These two parameters were found to be positively correlated with hardness. ANOVA showed a significant variation in the parameters recorded during winter and monsoon season.

Adsorption of heavy metals on kaolinite and montmorillonite: a review.

The process of adsorption is considered to be one of the best water treatment technologies around the world. Different heavy metals, due to their toxic and hazardous nature, are possibly the most widespread groundwater contaminants imposing a serious threat to human health. In this review, an attempt has been made to discuss the use of two common clay materials, namely kaolinite and montmorillonite, along with their modified forms for heavy metal removal on the basis of published reports (2008 onwards). The modifications of clays have been attempted by the process of pillaring, intercalation, acid/base activation, functionalization, etc. The adsorption of toxic metals, viz., As, Cd, Cr, Co, Cu, Fe, Pb, Mn, Ni, Zn, etc., has been studied predominantly. Montmorillonite and its modified forms have much higher metal adsorption capacity compared to that of kaolinite as well as modified-kaolinite. The modification often boosted the adsorption capacities of the clays, however, reverse trends are also reported in some cases.

Kinetics of adsorption of metal ions on inorganic materials: A review.

It is necessary to establish the rate law of adsorbate-adsorbent interactions to understand the mechanism by which the solute accumulates on the surface of a solid and gets adsorbed to the surface. A number of theoretical models and equations are available for the purpose and the best fit of the experimental data to any of these models is interpreted as giving the appropriate kinetics for the adsorption process. There is a spate of publications during the last few years on adsorption of various metals and other contaminants on conventional and non-conventional adsorbents, and many have tried to work out the kinetics. This has resulted from the wide interest generated on using adsorption as a practical method for treating contaminated water. In this review, an attempt has been made to discuss the kinetics of adsorption of metal ions on inorganic solids on the basis of published reports. A variety of materials like clays and clay minerals, zeolites, silica gel, soil, activated alumina, inorganic polymer, inorganic oxides, fly ash, etc. have been considered as the adsorbents and cations and anions of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn as adsorbate have been covered in this review. The majority of the interactions have been divided into either pseudo first order or second order kinetics on the basis of the best fit obtained by various groups of workers, although second order kinetics has been found to be the most predominant one. The discussion under each category is carried out with respect to each type of metal ion separately. Application of models as given by the Elovich equation, intra-particle diffusion and liquid film diffusion has also been shown by many authors and these have also been reviewed. The time taken for attaining equilibrium in each case has been considered as a significant parameter and is discussed almost in all the cases. The values of the kinetic rate coefficients indicate the speed at which the metal ions adsorb on the materials and these are discussed in all available cases. The review aims to give a comprehensive picture on the studies of kinetics of adsorption during the last few years.

Electrochemically derived redox molecular architecture: a novel electrochemical interface for voltammetric sensing.

Redox-active molecular architectures are electrochemically derived on the electrode surface by Michael addition reaction of o-quinone with surface adsorbed nucleophiles. Electrogenerated o-quinone undergoes facile Michael addition reaction with nucleophile mercaptotriazole (MTz) and mercaptoimidazole (MIm) preassembled on Au electrode. The Michael addition reaction yields redox molecular architectures of 4-(3-mercapto-[1,2,4]triazol-1-yl)-benzene-1,2-diol (MTBD) and 4-(2-mercapto-imidazol-1-yl)-benzene-1,2-diol (MIBD). Solution pH controls the Michael addition reaction; the reaction of o-quinone with MTz nucleophile is more favorable in neutral pH whereas it is favorable in pH >or=9 with MIm. Michael addition of electrogenerated o-quinone with the nucleophile is quantitatively followed in real time using electrochemical quartz crystal microbalance (EQCM). The redox molecular architecture on the electrode surface is characterized by attenuated total reflection (ATR) spectral and electrochemical measurements. ATR spectral measurement confirms the Michael addition with the nucleophile. The redox molecular architecture displays reversible voltammetric response at 0.2 V corresponding to the redox reaction surface confined catechol moiety. The surface coverage of MTBD and MIBD on the electrode surface at pH 7.2 is estimated to be (5.4 +/- 0.2) x 10(-10) and (2.0 +/- 0.2) x 10(-10) mol/cm(2), respectively. Both redox molecular assemblies efficiently mediate the oxidation of reduced nicotinamide adenine dinucleotide (NADH) at a favorable potential. A large decrease in the overpotential associated with an enhancement in the voltammetric peak current with respect to the unmodified electrode is observed. Flow injection amperometric sensing of NADH is performed at the potential of 230 mV. These modified electrodes could detect NADH at micromolar level. Mixed molecular architecture of cysteamine (CYST) and MTz/MIm are developed for the interference free voltammetric sensing of NADH.

Phytoplankton diversity and dynamics of Chatla floodplain lake, Barak Valley, Assam, North East India--a seasonal study.

A study was carried out in Chatla floodplain lake, Barak Valley, Assam, North East India on phytoplankton diversity, density and distribution in different seasons and their correlations with physico-chemical properties of water. A total of 34 phytoplankton taxa belonging to Chlorophyceae, Cyanophyceae, Bacillariophyceae and Euglenophyceae were recorded. Highest number of species was present in pre-monsoon (29) and lowest in winter (23). Members of Chlorophyceae were present in a reasonable number throughout the year while being most abundant in pre-monsoon and monsoon. Bacillariophycae and Cyanophyceae populations did not show much seasonal variation. Percentage composition of Euglenophyceae showed clear seasonal change, being most dominant in post monsoon, moderate in pre-monsoon and winter and nearly absent in monsoon. Total phytoplankton density showed highly significant positive correlation with transparency (p<0.01) and significant positive correlation with total suspended solids, total hardness and calcium (p<0.05). Shannon-Wiener diversity index (H') value (2.66) was found to be the highest during pre-monsoon while the highest evenness (J') value (0.89) was recorded during winter. Berger-Parker index of dominance (0.45) was highest in post-monsoon. Our study revealed that the growth of phytoplankton is governed by transparency, total suspended solids, calcium and total hardness. These types of studies are prerequisites for evolving fish culture programmes and management of water resources.

Adsorption of a few heavy metals on natural and modified kaolinite and montmorillonite: a review.

The feasibility of using two important and common clay minerals, kaolinite and montmorillonite, as adsorbents for removal of toxic heavy metals has been reviewed. A good number of works have been reported where the modifications of these natural clays were done to carry the adsorption of metals from aqueous solutions. The modification was predominantly done by pillaring with various polyoxy cations of Zr4+, Al3+, Si4+, Ti4+, Fe3+, Cr3+or Ga3+, etc. Preparation of pillared clays with quaternary ammonium cations, namely, tetramethylammonium-, tetramethylphosphonium- and trimethyl-phenylammonium-, N'-didodecyl-N, N'-tetramethylethanediammonium, etc, are also common. Moreover, the acid treatment of clays often boosted their adsorption capacities. The adsorption of toxic metals, viz., As, Cd, Cr, Co, Cu, Fe, Pb, Mn, Ni, Zn, etc., have been studied predominantly. Montmorillonite and its modified forms have much higher metal adsorption capacity compared to that of kaolinite as well as modified-kaolinite.

Ferrocene-linked thymine/uracil conjugates: base pairing directed self-assembly and supramolecular packing.

Ferrocene-linked bis(nucleobase) (1a-c) and chimeric nucleobase (1d) conjugates have been synthesized from mono- and bis(hydroxybutyl)ferrocene 6 via Mitsunobu reaction as the key step. X-ray crystallographic studies of ferrocene bis(nucleobase) conjugates reveal two-dimensional supramolecular organizations of backbones through self-assembled Watson-Crick and reverse Watson-Crick type pairs. Ferrocene-bis(thymine) conjugate self-assembles by reverse Watson-Crick pairing, while the corresponding bis(uracil) conjugate self-assembles by alternating WC and reverse WC type pairing. Such continuous assemblies are not seen in monosubstituted ferrocene nucleobase conjugates which form only planar sheets. The results are interesting from the point of understanding and engineering supramolecular assemblies through rational design of base pairing patterns.