Biogeochemistry of mercury and methylmercury in sediment cores from Sundarban mangrove wetland, India—a UNESCO World Heritage Site

This study was performed to elucidate the distribution, concentration trend and possible sources of total mercury (Hg(T)) and methylmercury (MeHg) in sediment cores (<63 μm particle size; n?=?75) of Sundarban mangrove wetland, northeastern part of the Bay of Bengal, India. Total mercury was determined by atomic absorption spectrometry (AAS) in a Leco AMA 254 instrument and MeHg by gas chromatography-atomic fluorescence spectrometry (GC-AFS). A wide range of variation in Hg(T) (0.032-0.196 μg g(-1) dry wt.) as well as MeHg (0.04-0.13 ng g(-1) dry wt.) concentrations revealed a slight local contamination. The prevalent low Hg(T) levels in sediments could be explained by sediment transport by the tidal Hugli (Ganges) River that would dilute the Hg(T) values via sediment mixing processes. A broader variation of MeHg proportions (%) were also observed in samples suggesting that other environmental variables such as organic carbon and microbial activity may play a major role in the methylation process. An overall elevated concentration of Hg(T) in surface layers (0-4 cm) of the core is due to remobilization of mercury from deeper sediments. Based on the index of geoaccumulation (I (geo)) and low effects-range (ER-L) values, it is considered that the sediment is less polluted by Hg(T) and there is less ecotoxicological risk. The paper provides the first information of MeHg in sediments from this wetland environment and the authors strongly recommend further examination of Hg(T) fluxes for the development of a detailed coastal MeHg model. This could provide more refine estimates of a total flux into the water column.     

Microbial siderophores and their potential applications: a review

Siderophores are small organic molecules produced by microorganisms under iron-limiting conditions which enhance the uptake of iron to the microorganisms. In environment, the ferric form of iron is insoluble and inaccessible at physiological pH (7.35–7.40). Under this condition, microorganisms synthesize siderophores which have high affinity for ferric iron. These ferric iron-siderophore complexes are then transported to cytosol. In cytosol, the ferric iron gets reduced into ferrous iron and becomes accessible to microorganism. In recent times, siderophores have drawn much attention due to its potential roles in different fields. Siderophores have application in microbial ecology to enhance the growth of several unculturable microorganisms and can alter the microbial communities. In the field of agriculture, different types of siderophores promote the growth of several plant species and increase their yield by enhancing the Fe uptake to plants. Siderophores acts as a potential biocontrol agent against harmful phyto-pathogens and holds the ability to substitute hazardous pesticides. Heavy-metal-contaminated samples can be detoxified by applying siderophores, which explicate its role in bioremediation. Siderophores can detect the iron content in different environments, exhibiting its role as a biosensor. In the medical field, siderophore uses the “Trojan horse strategy” to form complexes with antibiotics and helps in the selective delivery of antibiotics to the antibiotic-resistant bacteria. Certain iron overload diseases for example sickle cell anemia can be treated with the help of siderophores. Other medical applications of siderophores include antimalarial activity, removal of transuranic elements from the body, and anticancer activity. The aim of this review is to discuss the important roles and applications of siderophores in different sectors including ecology, agriculture, bioremediation, biosensor, and medicine.     

Development and modification of permanent magnet brushed DC motor for hybrid photovoltaic-operated solar systems

A modified brushed permanent magnet DC (PMDC) motor has been developed and fabricated for a photovoltaic (PV)-operated solar systems. The conventional PMDC motor has been plagued with constraints, the most critical being ingestion of vapours of working fluid inside the rotor and stator, damaging the insulation of windings and forming a thin film of moisture between commutator and brushes. This flaw results into a very low mean time between failures of the motor. In the past, many attempts have been made where-in variety of seals to isolate the working fluid vapours from inner parts of motor have been tried out, but to no avail. Even Brushless DC motors have been designed in the past but their exorbitant cost makes the entire arrangement not viable economically. The modification attempted in this article overcomes the problem of working fluid ingestion inside the motor. It is found that mass flow rate of working fluid obtained at maximum peak sunshine hours is 17.5 l/min at 3030 rpm of motor driven by a PV module of 40 W at 16.20 V. This low-cost modified PMDC motor has been robust with high mean time between failures as no breakdown observed during 18 months of operation.     

Hydrogeochemical comparison and effects of overlapping redox zones on groundwater arsenic near the Western (Bhagirathi sub-basin, India) and Eastern (Meghna sub-basin, Bangladesh) margins of the Bengal Basin

Although arsenic (As) contamination of groundwater in the Bengal Basin has received wide attention over the past decade, comparative studies of hydrogeochemistry in geologically different sub-basins within the basin have been lacking. Groundwater samples were collected from sub-basins in the western margin (River Bhagirathi sub-basin, Nadia, India; 90 samples) and eastern margin (River Meghna sub-basin; Brahmanbaria, Bangladesh; 35 samples) of the Bengal Basin. Groundwater in the western site (Nadia) has mostly Ca-HCO(3) water while that in the eastern site (Brahmanbaria) is much more variable consisting of at least six different facies. The two sites show differences in major and minor solute trends indicating varying pathways of hydrogeochemical evolution However, both sites have similar reducing, postoxic environments (p(e): +5 to -2) with high concentrations of dissolved organic carbon, indicating dominantly metal-reducing processes and similarity in As mobilization mechanism. The trends of various redox-sensitive solutes (e.g. As, CH(4), Fe, Mn, NO(3)(-), NH(4)(+), SO(4)(2-)) indicate overlapping redox zones, leading to partial redox equilibrium conditions where As, once liberated from source minerals, would tend to remain in solution because of the complex interplay among the electron acceptors.     

Quantifying monthly water balance to estimate water deficit in Mayurakshi River basin of Eastern India

Environment, Development and Sustainability - Recorded seasonal variation and uneven distribution of rainfall is one of the major issues to the agrarian society and the domestic water users today....     

Coastal flood management in rural planning unit through land-use planning: Kaikhali, West Bengal, India

The Indian subcontinent is highly prone to the detrimental impacts of hazards viz. cyclones, floods and storm surges. Of late, these events have become extreme in nature and intensity. While occurrence and severity of the events is being linked to the phenomenon of climate change, their devastating potentialities are also getting triggered due to lack of resilience and coping capacity of the human community. That in turn depends on distribution of activities over the land i.e. land use pattern, affecting the socio -economic conditions directly. A coastal village often lacks infrastructural support, administrative attention and planning standards compared to a coastal city, thereby making it more vulnerable to disasters like flood. In a coastal city it is easy to govern and manage livelihood as land use depends highly on anthropogenic decisions. While in a coastal village, activities would highly depend on its natural characteristics viz. coastal geomorphology, soil, vegetation cover i.e. governance of livelihood by the eco-system. Hence, managing disaster through in-situ pro-active or developmental measures in a rural planning unit though imperative, is a challenging task. This paper focuses on spatial planning techniques for Restoration of ecological buffers and livelihood enhancement that would sustainably combat the impact of flood at village level in a coastal area. Geographic Information System (GIS) and Remote Sensing (RS) techniques have been used extensively in this study as application tools.     

Social cost‐benefit analysis of intensive versus traditional shrimp farming: A case study from India

This paper attempts a social cost‐benefit analysis of intensive versus traditional shrimp farming in West Bengal, India. Using primary data, the paper shows that although intensive shrimp farming yields high returns as compared to traditional shrimp farming, when the opportunity costs and environmental costs of shrimp farming, including disease risk, are accounted for, intensive shrimp farming loses its advantage. Sensitivity analysis shows that if the expected benefits were to fall short by 15% and costs rise by a similar proportion, intensive shrimp farmers would report higher losses than traditional shrimp farmers. Large traditional shrimp farmers continue to report positive net returns. These results are also most pronounced for small and marginal intensive shrimp farmers. Further, if the probability of disease risk is also accounted for, intensive shrimp farming reports significant losses whereas traditional shrimp farming in most cases shows positive net returns. In light of the high social costs and risks, this paper questions the rationale behind promoting intensive shrimp farming, especially among small and marginal holdings, as an income‐generating activity or poverty alleviation measure in the absence of an enabling environment. It suggests that policymakers need to factor in sustainability concerns and the local context when formulating policies to promote intensive shrimp farming.     

How to engineer biological processes that neutralize hazardous wastes

Because bioremediation must satisfy the fundamental biological tastes of specific organisms, environmental engineers must create a nutritious waste stew. Waste-hungry organisms need a proper electron acceptor. Oxygen is preferred; if it is not available, nitrate, sulfate, or carbon dioxide may work. The waste itself is a source of carbon and energy. Macronutrients are next—including phosphorus, nitrogen, and certain metals, if they are not already present in the wastewater—as well as micronutrients. Other factors, including pH, temperature, aeration, and mixing must suit the organisms' natural temperaments. This article explores how bioengineers can combine these ingredients in precise quantities and proportions in both conventional and innovative aerobic and anaerobic bioprocesses, including in situ treatment and even composting, to make the organisms healthy, happy, and inexpensive.     

Comparison of drinking water,raw rice and cooking of rice as arsenic exposure routes in three contrasting areas of West Bengal,India

Remediation aimed at reducing human exposure to groundwater arsenic in West Bengal, one of the regions most impacted by this environmental hazard, are currently largely focussed on reducing arsenic in drinking water. Rice and cooking of rice, however, have also been identified as important or potentially important exposure routes. Quantifying the relative importance of these exposure routes is critically required to inform the prioritisation and selection of remediation strategies. The aim of our study, therefore, was to determine the relative contributions of drinking water, rice and cooking of rice to human exposure in three contrasting areas of West Bengal with different overall levels of exposure to arsenic, viz. high (Bhawangola-I Block, Murshidibad District), moderate (Chakdha Block, Nadia District) and low (Khejuri-I Block, Midnapur District). Arsenic exposure from water was highly variable, median exposures being 0.02 μg/kg/d (Midnapur), 0.77 μg/kg/d (Nadia) and 2.03 μg/kg/d (Murshidabad). In contrast arsenic exposure from cooked rice was relatively uniform, with median exposures being 0.30 μg/kg/d (Midnapur), 0.50 μg/kg/d (Nadia) and 0.84 μg/kg/d (Murshidabad). Cooking rice typically resulted in arsenic exposures of lower magnitude, indeed in Midnapur, median exposure from cooking was slightly negative. Water was the dominant route of exposure in Murshidabad, both water and rice were major exposure routes in Nadia, whereas rice was the dominant exposure route in Midnapur. Notwithstanding the differences in balance of exposure routes, median excess lifetime cancer risk for all the blocks were found to exceed the USEPA regulatory threshold target cancer risk level of 10⁻⁴–10⁻⁶. The difference in balance of exposure routes indicate a difference in balance of remediation approaches in the three districts.     

Impact of Eco-restoration on the Biodiversity of Sundarbans Mangrove Ecosystem, India

A comprehensive study on biodiversity and environmental characteristics of three different selected study sites located on different estuarine networks viz. Matla, Saptamukhi, and Hooghly on eastern, central, and western regions, having different environmental features of Sundarbans Mangrove Ecosystem, India, a World Heritage Site, was conducted through six seasons of consecutive 2 years. The different sites understudy have shown variable species composition. Special emphasis was made to record the population structure of benthic fauna, which exhibited maximum density during pre-monsoon followed by monsoon and post-monsoon. Physicochemical parameters displayed a wide range of fluctuation through different seasons and also revealed differences among different study sites. Biotic community structures of different study sites have been analyzed using different community indices like similarity index, dominance index, diversity index, and evenness index. Moreover, in order to evaluate the environmental stress on the environmental health of this dynamic mangrove ecosystem of global importance, species pollution value and community pollution value have been deduced as a new model of biotic indices based on the distribution patterns of both zooplanktons and benthic fauna. Canonical correspondence analysis revealed the cumulative influence of a group of environmental parameters on the abundance of different components of biodiversity. The study site II (Saptamukhi), encircled by undisturbed mangrove islands, revealed the least pollution stress and higher biological diversity followed by Jharkhali (study site I), which is in the process of eco-restoration and Bokkhali (study site III), which has been under anthropogenic stress especially from ecotourism.