Nutrient-limited toxin production and the dynamics of two phytoplankton in culture media: A mathematical model

In this paper we have proposed and analyzed a simple mathematical model consisting of four variables, viz., nutrient concentration, toxin producing phytoplankton (TPP), non-toxic phytoplankton (NTP), and toxin concentration. Limitation in the concentration of the extracellular nutrient has been incorporated as an environmental stress condition for the plankton population, and the liberation of toxic chemicals has been described by a monotonic function of extracellular nutrient. The model is analyzed and simulated to reproduce the experimental findings of Graneli and Johansson [Graneli, E., Johansson, N., 2003. Increase in the production of allelopathic Prymnesium parvum cells grown under N- or P-deficient conditions. Harmful Algae 2, 135–145]. The robustness of the numerical experiments are tested by a formal parameter sensitivity analysis. As the first theoretical model consistent with the experiment of Graneli and Johansson (2003), our results demonstrate that, when nutrient-deficient conditions are favorable for the TPP population to release toxic chemicals, the TPP species control the bloom of other phytoplankton species which are non-toxic. Consistent with the observations made by Graneli and Johansson (2003), our model overcomes the limitation of not incorporating the effect of nutrient-limited toxic production in several other models developed on plankton dynamics.     

Bio-mediated silver nanoparticle synthesis: mechanism and microbial inactivation

Even though plenty of literature is available on the biosynthesis of metal nanoparticles, there are serious lacunae on the mechanisms of their formation. In the present study, the mechanism of formation of mono-crystalline silver nanoparticles using a fruit extract of the ornamental tree Thevetia peruviana is emphasized, i.e. how the pH of the reaction mixture affected reaction kinetics and size of the nanoparticles. The facilitation of formation of Ag₂O at higher pH resulted in a faster rate of particle formation. The diameter of the bare particles at neutral pH determined by field emission scanning electron microscopy and the hydrodynamic diameter determined by dynamic light scattering were 53 and 104 nm, respectively. The silver nanoparticles exhibited good inactivation of Escherichia coli due to participation of free radicals as evidenced by electron spin resonance spectroscopy.     

Influence of coal ash on the concrete properties and its performance under sulphate and chloride conditions

Environmental Science and Pollution Research - This study investigated the influence of coal bottom ash (CBA) on the concrete properties and evaluate the effects of combined exposure of sulphate...     

Long-range atmospheric transport of persistent organochlorinated compounds from south and mainland south-eastern Asia to a remote mountain site in south-western China

A range of organochlorinated compounds have been consumed in China, India and the countries of mainland southeast Asia (MSA). Considering their persistence in the environment and ability in long-range atmospheric transport (LRAT), the potential outflow of these compounds from this region is therefore of great concern in the context of the global distribution of toxic chemicals. As part of a monitoring campaign aimed at investigating the LRAT of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) from southern China, MSA and northern India, atmospheric levels of OCPs and PCBs were measured once a week from October 2005 through December 2006 at Tengchong Mountain (TM), a remote site located in south-western China. The average concentrations of OCPs were found to be higher than those in other remote stations in the Arctic and the Tibetan plateau, except for α-hexachlorocyclohexane (α-HCH). A high level of β-HCH and low α-HCH/β-HCH ratio was attributed to an accidental release of β-HCH from unknown sources, besides obvious evidence of lindane (γ-HCH) and technical HCH usage. Temporal variations of chlordanes and endosulfan were related to the usage pattern of these compounds, as well as LRAT. In contrast, dichlorodiphenyltrichloroethane (DDT) exhibited a relatively minor seasonal variation. The OCP levels at the monitoring site were found to be related to the air parcel back trajectories on the basis of four distinct clusters. Elevated levels of HCHs and DDTs were observed when air parcels originated from northern India where considerable OCP usage was reported recently, while high levels of γ-HCH and TC (trans-chlordane) were mainly associated with air masses from southern China and northern MSA. The study highlighted the high background level of OCPs as well as their temporal patterns of trans-boundary LRAT in the MSA region.     

Stagnant surface water bodies (SSWBs) as an alternative water resource for the Chittagong metropolitan area of Bangladesh: physicochemical characterization in terms of water quality indices

The concern over ensuing freshwater scarcity has forced the developing countries to delve for alternative water resources. In this study, we examined the potential of stagnant surface water bodies (SSWBs) as alternative freshwater resources in the densely populated Chittagong metropolitan area (CMPA) of Bangladesh??where there is an acute shortage of urban freshwater supply. Water samples were collected at 1-month intervals for a period of 1 year from 12 stations distributed over the whole metropolis. Samples were analyzed for pH, water temperature (WTemp), turbidity, electrical conductivity (EC), total dissolved solids, total solids, total hardness, dissolved oxygen (DO), chloride, orthophosphates, ammonia, total coliforms (TC), and trace metal (Cd, Cr, Cu, Pb, As, and Fe) concentrations. Based on these parameters, different types of water quality indices (WQIs) were deduced. WQIs showed most of CMPA-SSWBs as good or medium quality water bodies, while none were categorized as bad. Moreover, it was observed that the minimal water quality index (WQI_m), computed using five parameters: WTemp, pH, DO, EC, and turbidity, gave a reliable estimate of water quality. The WQI_m gave similar results in 72% of the cases compared with other WQIs that were based on larger set of parameters. Based on our finding, we suggest the wider use WQI_m in developing countries for assessing health of SSWBs, as it will minimize the analytical cost to overcome the budget constraints involved in this kind of evaluations. It was observed that except turbidity and TC content, all other quality parameters fluctuated within the limit of the World Health Organization suggested standards for drinking water. From our findings, we concluded that if the turbidity and TC content of water from SSWBs in CMPA are taken care of, they will become good candidates as alternative water resources all round the year.     

Exploring the relationship between residential segregation and thermal inequity in 20 U.S. cities

A combination of the urban heat island effect and a rising temperature baseline resulting from global climate change inequitably impacts socially vulnerable populations residing in urban areas. This article examines racial/ethnic and socioeconomic inequities in the spatial distribution of exposure to urban heat in the context of climate justice and residential segregation in the U.S. An urban heat risk index (UHRI) is calculated from measures of land surface temperature, structural density, and vegetation abundance, acquired from summer 2010 remote sensing imagery. Twenty of the largest metropolitan statistical areas (MSAs) in the U.S. are selected and analysed using census tract-level socio-demographic data from the U.S. Census. Multilevel modelling is utilised to examine the statistical associations between urban heat, minority status, socioeconomic disadvantage, and MSA-level segregation of racial/ethnic minority groups. Variables representing socioeconomic status (i.e. household income, home ownership, and education level) are consistently and significantly associated with greater urban heat exposure. Minority status and measures of segregation have a significant but varied relationship with urban heat exposure, indicating that there are inconsistent associations with urban heat due to differing social geographies. Urban heat and social vulnerability present a varying landscape of thermal inequity in different metropolitan areas, associated in many cases with residential segregation.     

Elevated level of arsenic negatively influences nifH gene expression of isolated soil bacteria in culture condition as well as soil system

Environmental Geochemistry and Health - Comprehensive studies on the effect of arsenic (As) on free-living diazotrophs that play a crucial role in soil fertility by nitrogen fixation are still...     

A comparative study on intertidal faunal biodiversity of selected beaches of Mumbai coast

Comparative study has been done to examine the biodiversity and ecological status of the intertidal region of Tata Institute of Fundamental Research (TIFR), Bandstand and National Centre for Performing Arts (NCPA) rocky beaches in Mumbai, West coast of India. A total of 50 species of intertidal organisms were recorded from these shores. Shannon and Simpson's diversity index, Margalefs richness index and Pielou's evenness index indicated different level of ecological state of the shore in different months. Dendrograms and 2-D non metric MDS ordination from Bray-Curtis similarity matrix of occurrence of intertidal organisms from these sites showed highest similarity and combination pattern of occurrence between Nerita oryzarum and Planaxis sulcatus in TIFR and Bandstand shore. Nerita oryzarum and Tactarius malaccanus at NCPA shore. Abundance/biomass comparison (ABC) method of determining level of disturbance also pointed towards the polluted status of these shores. Study concludes that though these beaches are highly disturbed due to anthropogenic activities, they still support a rich intertidal biodiversity which need immediate attention for protection and conservation.     

Comparison of a plant based natural surfactant with SDS for washing of As(Ⅴ) from Fe rich soil

This study explores the possible application of a biodegradable plant based surfactant, obtained from Sapindus mukorossi, for washing low levels of arsenic （As） from an iron （Fe） rich soil. Natural association of As（Ⅴ） with Fe（Ⅲ） makes the process difficult. Soapnut solution was compared to anionic surfactant sodium dodecyl sulfate （SDS） in down-flow and a newly introduced suction mode for soil column washing. It was observed that soapnut attained up to 86% efficiency with respect to SDS in removing As. Full factorial design of experiment revealed a very good fit of data. The suction mode generated up to 83 kPa pressure inside column whilst down-flow mode generated a much higher pressure of 214 kPa, thus making the suction mode more efficient. Micellar solubilisation was found to be responsible for As desorption from the soil and it followed 1st order kinetics. Desorption rate coefficient of suction mode was found to be in the range of 0.005 to 0.01, much higher than down-flow mode values. Analysis of the PT-IR data suggested that the soapnut solution did not interact chemically with As, offering an option for reusing the surfactant. Soapnut can be considered as a soil washing agent for removing As even from soil with high Fe content.