Md. Jahangir Alam

Comparison of fecal indicators with pathogenic bacteria and rotavirus in groundwater

Groundwater is routinely analyzed for fecal indicators but direct comparisons of fecal indicators to the presence of bacterial and viral pathogens are rare. This study was conducted in rural Bangladesh where the human population density is high, sanitation is poor, and groundwater pumped from shallow tubewells is often contaminated with fecal bacteria. Five indicator microorganisms (E. coli, total coliform, F+RNA coliphage, Bacteroides and human-associated Bacteroides) and various environmental parameters were compared to the direct detection of waterborne pathogens by quantitative PCR in groundwater pumped from 50 tubewells. Rotavirus was detected in groundwater filtrate from the largest proportion of tubewells (40%), followed by Shigella (10%), Vibrio (10%), and pathogenic E. coli (8%). Spearman rank correlations and sensitivity-specificity calculations indicate that some, but not all, combinations of indicators and environmental parameters can predict the presence of pathogens. Culture-dependent fecal indicator bacteria measured on a single date did not predict total bacterial pathogens, but annually averaged monthly measurements of culturable E. coli did improve prediction for total bacterial pathogens. A qPCR-based E. coli assay was the best indicator for the bacterial pathogens. F+RNA coliphage were neither correlated nor sufficiently sensitive towards rotavirus, but were predictive of bacterial pathogens. Since groundwater cannot be excluded as a significant source of diarrheal disease in Bangladesh and neighboring countries with similar characteristics, the need to develop more effective methods for screening tubewells with respect to microbial contamination is necessary.

Fecal Contamination of Shallow Tubewells in Bangladesh Inversely Related to Arsenic

The health risks of As exposure due to the installation of millions of shallow tubewells in the Bengal Basin are known, but fecal contamination of shallow aquifers has not systematically been examined. This could be a source of concern in densely populated areas with poor sanitation because the hydraulic travel time from surface water bodies to shallow wells that are low in As was previously shown to be considerably shorter than for shallow wells that are high in As. In this study, 125 tubewells 6−36 m deep were sampled in duplicate for 18 months to quantify the presence of the fecal indicator Escherichia coli. On any given month, E. coli was detected at levels exceeding 1 most probable number per 100 mL in 19−64% of all shallow tubewells, with a higher proportion typically following periods of heavy rainfall. The frequency of E. coli detection averaged over a year was found to increase with population surrounding a well and decrease with the As content of a well, most likely because of downward transport of E. coli associated with local recharge. The health implications of higher fecal contamination of shallow tubewells, to which millions of households in Bangladesh have switched in order to reduce their exposure to As, need to be evaluated.

Advection of surface-derived organic carbon fuels microbial reduction in Bangladesh groundwater

Chronic exposure to arsenic (As) by drinking shallow groundwater causes widespread disease in Bangladesh and neighboring countries. The release of As naturally present in sediment to groundwater has been linked to the reductive dissolution of iron oxides coupled to the microbial respiration of organic carbon (OC). The source of OC driving this microbial reduction—carbon deposited with the sediments or exogenous carbon transported by groundwater—is still debated despite its importance in regulating aquifer redox status and groundwater As levels. Here, we used the radiocarbon (14C) signature of microbial DNA isolated from groundwater samples to determine the relative importance of surface and sediment-derived OC. Three DNA samples collected from the shallow, high-As aquifer and one sample from the underlying, low-As aquifer were consistently younger than the total sediment carbon, by as much as several thousand years. This difference and the dominance of heterotrophic microorganisms implies that younger, surface-derived OC is advected within the aquifer, albeit more slowly than groundwater, and represents a critical pool of OC for aquifer microbial communities. The vertical profile shows that downward transport of dissolved OC is occurring on anthropogenic timescales, but bomb 14C-labeled dissolved OC has not yet accumulated in DNA and is not fueling reduction. These results indicate that advected OC controls aquifer redox status and confirm that As release is a natural process that predates human perturbations to groundwater flow. Anthropogenic perturbations, however, could affect groundwater redox conditions and As levels in the future.

Efficacy of Hollow-Fiber Ultrafiltration for Microbial Sampling in Groundwater

The goal of this study was to test hollow-fiber ultrafiltration as a method for concentrating in situ bacteria and viruses in groundwater samples. Water samples from nine wells tapping a shallow sandy aquifer in a densely populated village in Bangladesh were reduced in volume approximately 400-fold using ultrafiltration. Culture-based assays for total coliforms and Escherichia coli, as well as molecular-based assays for E. coli, Bacteroides, and adenovirus, were used as microbial markers before and after ultrafiltration to evaluate performance. Ultrafiltration increased the concentration of the microbial markers in 99% of cases. However, concentration factors (CF = post-filtration concentration/pre-filtration concentration) for each marker calculated from geometric means ranged from 52 to 1018 compared to the expected value of 400. The efficiency was difficult to quantify because concentrations of some of the markers, especially E. coli and total coliforms, in the well water (WW) collected before ultrafiltration varied by several orders of magnitude during the period of sampling. The potential influence of colloidal iron oxide precipitates in the groundwater was tested by adding EDTA to the pre-filtration water in half of the samples to prevent the formation of precipitates. The use of EDTA had no significant effect on the measurement of culturable or molecular markers across the 0.5 to 10 mg/L range of dissolved Fe(2+) concentrations observed in the groundwater, indicating that colloidal iron did not hinder or enhance recovery or detection of the microbial markers. Ultrafiltration appears to be effective for concentrating microorganisms in environmental water samples, but additional research is needed to quantify losses during filtration.

Implications of Fecal Bacteria Input from Latrine-Polluted Ponds for Wells in Sandy Aquifers

Ponds receiving latrine effluents may serve as sources of fecal contamination to shallow aquifers tapped by millions of tube-wells in Bangladesh. To test this hypothesis, transects of monitoring wells radiating away from four ponds were installed in a shallow sandy aquifer underlying a densely populated village and monitored for 14 months. Two of the ponds extended to medium sand. Another pond was sited within silty sand and the last in silt. The fecal indicator bacterium E. coli was rarely detected along the transects during the dry season and was only detected near the ponds extending to medium sand up to 7 m away during the monsoon. A log-linear decline in E. coli and Bacteroidales concentrations with distance along the transects in the early monsoon indicates that ponds excavated in medium sand were the likely source of contamination. Spatial removal rates ranged from 0.5 to 1.3 log(10)/m. After the ponds were artificially filled with groundwater to simulate the impact of a rain storm, E. coli levels increased near a pond recently excavated in medium sand, but no others. These observations show that adjacent sediment grain-size and how recently a pond was excavated influence the how much fecal contamination ponds receiving latrine effluents contribute to neighboring groundwater.

Analysing the lacunae in planning and implementation: spatial development of Dhaka city and its impacts upon the built environment

This article explores the causes of rapid increase in land and housing development projects and their effects on the restricted areas of Greater Dhaka, Bangladesh, using a global positioning system (GPS) survey and socio-economic data. Rapidly increasing housing projects are contravening the urban containment policy stipulated in the Dhaka Metropolitan Development Plan (DMDP). These findings show that most of the projects do not have any kind of plan approval and many projects have encroached on restricted areas, for example, flood flow zones (FFZs), high-value agricultural land and retention ponds, through massive land filling, which has resulted in rapid changes of land use, with wide range of impacts on environment and habitat quality. Furthermore, the article analyses the inherent lack of integrated urban planning, the lacunae within agencies in charge of urban management and the resultant externalities in the built environment.

Impacts of environmental laws on land development and developers in Dhaka City, Bangladesh

The fast paced land and housing development projects in Dhaka City since 1980s had generated irregularities in developers’ real estate projects and policy deviations in the Dhaka Metropolitan Development Plan (DMDP). This paper explores the causes of the irregularities and reasons that trapped many buyers in the developers’ unauthorised housing projects and violation of some regulations. The study argues that the untimely promulgation of laws, namely: The Natural Water Body, Open Space, Park/Play Ground Preservation Rule 2000, Private Housing Project Land Development Rules 2004 (PHPLD Rules 2004), and Real Estate Development and Management Act 2010 (REDM Act 2010) could be largely responsible for the present crisis. This paper suggests that modification of the DMDP policies and relevant laws should be urgently undertaken in order to bring about solidity and smooth functioning of the land and real estate market in Dhaka. The study also suggests that an independent assessment agency could be commissioned to assess the situation and minimise the risks of buyers and the irregularities of developers by disseminating the relevant information to respective agencies and concerned persons.