Pond management in rural Bangladesh: problems and possibilities in the context of the water supply crisis

Today, Bangladesh is confronted with an immense water supply crisis: the decline of surface water bodies as well as a fall in the water table, together with the multiple pollution of the water in general, has put pressure on a precious resource that needs to meet the demand of a growing population. However, the most serious problem became public just four years ago—the contamination of the groundwater with arsenic. Considering the extent of the water supply problem, solutions for the future provision of safe drinking water are urgently needed. This article argues that ponds, a traditional water source in Bangladesh, could contribute to a solution. However, it is essential to recognise the problems and advantages of ponds in order to make suggestions on how to integrate ponds into the national water policy. Therefore, this paper analyses pond management—the use, maintenance and control of ponds—and its change from the past to the present. A holistic, dynamic and actor-oriented approach on a small scale was proved to be the appropriate instrument for this analysis.     

Three Different Topics for Bioremediation Application on Soils and Waters Contaminated with Aromatic Compounds, by Using Immobilized Bacteria

Molecular techniques and modelling are presented as powerful tools required in the performance of efficient soil and water bioremediation systems. An Escherichia coli CC118-D strain was constructed by inserting the Klebsiella pneumoniae hpa B gene, coding for the unstable 3,4-dihydroxyphenylacetate 2,3-dioxygenase, into its chromosome. When the constructed strain was immobilized, both enzyme stability and viability increased along the studied period, in absence of antibiotic. We proposed this strategy as an approach to overcoming plasmid instability and to enhance enzyme activity and stability, avoiding antibiotic utilization. A model was developed to understand and predict the behaviour of bacteria and pollutants in a bioreactor system, considering: fluid dynamics, molecular/cellular scale processes and biofilm formation.     

Mobilization of arsenic in groundwater of Bangladesh: evidence from an incubation study

The extensive extraction of arsenic (As)-contaminated groundwaters for drinking, household and agricultural purposes represents a serious health concern in many districts of Bangladesh. This laboratory-based incubation study investigated the sources and mechanisms of As mobilization in these groundwaters. Several incubation studies were carried out using sediments collected from the Bangladesh aquifer that were supplemented, or not, with different nutrients, followed by an analysis of the sediment suspensions for pH, ORP (oxidation-reduction potential), EC (electrical conductivity) and As and Fe(ΙΙ) concentrations. In the substrate-amended sediment suspensions incubated under anaerobic environment, there was a mobilization of As (maximum: 50–67 μg/l) and Fe(ΙΙ) (maximum: 182 μg/l), while the ORP value decreased immediately and drastically (as much as −468 mV to −560 mV) within 5–6 days. In the sediment suspensions incubated under control and aerobic conditions, no significant As mobilization occurred. The simultaneous mobilization of As and Fe(ΙΙ) from sediments is a strong indication that their mobilization resulted from the reduction of Fe oxyhydroxide by the enhanced activity of indigenous bacteria present in the sediments; this phenomenon also provides insights on the mobilization mechanism of As in groundwater. The concentrations of As in the sediments used in the incubation studies were strongly linked to the gradients of redox potential development that was stimulated by the quantity of organic nutrient (glucose) used. The penetration of surface-derived organic matter into the shallow aquifer may stimulate the activity of microbial communities, thereby leading to a reduction of iron oxyhydroxide and As release.     

城市土壤污染研究现状与趋势

城市土壤是城市生态环境系统的有机组成部分,对城市的可持续发展有着重要的意义.城市化和工业化进程的加快,造成城市土壤污染、侵蚀、酸化和硬化以及土壤生物和植被退化等一系列较为严重的城市环境问题,直接危及到城市居民的健康和安全;因此,城市土壤污染问题已经引起人们的高度重视.近10多年来,国内外有关城市土壤重金属污染,微有机物污染,生源要素污染和城市土壤污染的环境与健康风险评价等诸多研究取得了一系列的研究成果.本文主要就以上研究成果进行了较为系统地总结与阐述,并且在此基础上提出了今后有关城市土壤污染研究的发展重点与趋势,以期为改善城市生态环境质量提供重要的科学依据.     

近岸海域石油污染生物修复技术的研究进展

生物修复技术是治理大面积污染区域的一种有价值的修复方法。对国内外最新的生物刺激和生物强化技术进行调研,总结了该技术对治理近岸海域石油污染的研究进展,分析总结了施加营养盐技术对海洋环境的影响,以及生物修复技术尚存在的一些局限性。     

Reaction mechanism of arsenic capture by a calcium-based sorbent during the combustion of arsenic-contaminated biomass: A pilot-scale experience

Pilot-scale combustion is required to treat arsenic-enriched biomass in China. CaO addition to arsenic-enriched biomass reduces arsenic emission. CaO captures arsenic via chemical adsorption to form Ca₃(AsO₄)₂. Large quantities of contaminated biomass due to phytoremediation were disposed through combustion in low-income rural regions of China. This process provided a solution to reduce waste volume and disposal cost. Pilot-scale combustion trials were conducted for in site disposal at phytoremediation sites. The reaction mechanism of arsenic capture during pilot-scale combustion should be determined to control the arsenic emission in flue gas. This study investigated three Pteris vittata L. biomass with a disposal capacity of 600 kg/d and different arsenic concentrations from three sites in China. The arsenic concentration in flue gas was greater than that of the national standard in the trial with no emission control, and the arsenic concentration in biomass was 486 mg/kg. CaO addition notably reduced arsenic emission in flue gas, and absorption was efficient when CaO was mixed with biomass at 10% of the total weight. For the trial with 10% CaO addition, arsenic recovery from ash reached 76%, which is an ~8-fold increase compared with the control. Synchrotron radiation analysis confirmed that calcium arsenate is the dominant reaction product.     

The nature and significance of public exposure to arsenic: a review of its relevance to South West England

In South West England, more than two hundred years of intensive exploitation of metalliferous ore deposits, combined with the natural processes of pedogenesis from mineral-rich parent rocks, has resulted in the creation of a aignificant area of arsenic-contaminated wastes and soils. The scale of arsenic dispersion by natural and anthropogenic processes is such that 722 km² of land contains concentrations of arsenic in excess of 110 g g^–1, more than twice the maximum that might be expected in a normal soil.The general rationale for the clean-up of derelict and contaminated mining sites often includes aesthetic factors and the desirability of preventing the dispersion of contaminants beyond the site boundaries. Only in extreme cases is public health directly invoked as justification for remediation. In South West England, if arsenic constitutes a genuine threat to the public, an increased rate of site remediation would be justified. The primary purpose of this review is to establish whether or not widespread arsenic contamination (principally of soils) has any measurable effects on public health in South West England, and how this might affect current contaminated site remediation policy. The review is based on data from previous research in the region, and other relevant international studies of mining and smelting communities, and other populations exposed to elevated arsenic concentrations. The literature reviewed also includes the determination of the extent and sources of contamination, and pathways between source and man.While the contamination of potable waters in some countries has led to measurable health effects, this scenario has not yet been identified in South West England, and there is little reason to believe that significantly contaminated potable water supplies would escape detection for extended periods of time under the current monitoring regime.In relative terms (based on both globaland local data), one of the most significant links between contaminated soils and humans appears to be contaminated food stuffs. In absolute terms, such exposure is low due to the natural constraints on arsenic uptake by herbage, cereal crops and vegetables, and the food chain does not appear to have been significantly compromised in South West England. Chronic health effects are unlikely as excessive arsenic concentrations in locally grown food crops remain rare.With the problems of confounding medical and social factors, it is not surprising that studies in South West England have failed to identify chronic exposure to arsenic at very low concentrations as a significant health risk. Those studies that indicate otherwise do not stand up to close scrutiny. It appears that the number of additional deaths arising from the widespread arsenic contamination in South West England is small. The relative benefits of a costly statistical study to actually determine the number of additional deaths might be considered minimal, but one major area could benefit from further studies: the sensitivity of certain population sub-groups to environmental arsenic exposure. Of particular interest are children, for whom significant exposure to arsenic via soil ingestion may be occurring.Based on available information, there appears to be no justification for a large programme of site remediation. Resources should, however, be expended on enlightening the general public, and private and governmental organisations as regards the gap between the perceived and actual significance of arsenic contamination in South West England.To whom correspondence should be addressed.     

A Preliminary Study of Geographic Influence on Arsenic Concentrations in Human Hair

Past mining activities in the county of Cornwall in the United Kingdom, has exposed the local environment to raised levels of As. Previous research has shown an increased concentration of As in crops grown in such areas and the subsequent take-up of As through the food chain may lead to an increased body burden in man. In an attempt to evaluate this, a pilot study was carried out using Particle Induced X-ray Emission to compare the hair As concentration of a group of Cornish residents to that of a control group consisting of residents in the counties of Oxfordshire and Wiltshire. The null hypothesis being that there is no significant difference between the hair As concentrations of the two groups.Each group comprised thirty six age and sex matched subjects. The mean hair As concentration for the Cornish group was 2.51 g g-1, which is significantly greater than that of 0.7 g g-1 found in the control group (p = 0.004). The World Health Organisation suggests a hair As value greater than 1 g g-1 as evidence of increased exposure to As and 5 g g-1 is quoted by the Canadian Government as evidence of significant ingestion of As. Twenty one Cornish subjects registered a value at or above 1 g As g-1 compared to nine in the control group (p = 0.0003). Five subjects in the Cornish group had values that exceed 5 g As g-1, compared to only two in the control group (p = 0.23). We use the results of this study as evidence to support our continued work in this area in order to evaluate possible health implications.     

土壤和地下水中多环芳烃生物降解研究进展

多环芳烃是一类普遍存在于环境中的难降解的危险性"三致"有机污染物。受污染的土壤和地下水中的多环芳烃,生物降解是其归宿的主要途径。研究表明,对于土壤中低分子量多环芳烃类化合物,微生物一般以唯一碳源方式代谢;而大多数细菌和真菌对四环或四环以上的多环芳烃的降解作用一般以共代谢方式开始。文章重点论述了多环芳烃的来源、降解多环芳烃的微生物、生物降解机理、影响生物降解的因素以及生物修复方法。认为今后的研究方向是高分子量多环芳烃的降解机理与降解途径,基因工程技术在多环芳烃生物降解方面的应用,以及生物表面活性剂产生的机理及其在实际处理中的应用等。     

Temporal dynamics of arsenic uptake and distribution: food and water risks in the Bengal basin

Abstract

Contaminated food chain is a serious contender for arsenic (As) uptake around the globe. In Nadia, West Bengal, we trace possible means of transfer of As from multiple sources reaching different trophic levels, and associated seasonal variability leading to chronic As uptake. This work considers possible sources-pathways of As transfer through food chain in rural community. Arsenic concentration in groundwater, soil, rice, and vegetable-samples collected detected in different harvest seasons of 2014 and 2016. Arsenic level in shallow groundwater samples ranged from 0.1 to 354?µg/L, with 75% of the sites above the prescribed limit by WHO (10?µg/L) during the boro harvest season. High soil As content (～20.6?mg/kg), resulted in accumulation of As in food crops. A positive correlation in As conc. with increase over period in all sites indicating gradual As accumulation in topsoil. Unpolished rice samples showed high As content (～1.75?mg/kg), polishing reduced 80% of As. Among vegetables, the plant family Poaceae with high irrigation requirements and Solanaceae retaining high moisture, have the highest levels of As. Contaminated animal fodder (Poaceae) and turf water for cattle are shown to contaminate milk (0.06 to 0.24?µg/L) and behoves strategies, practices to minimize As exposure.