Future study

References

ABSTRACT

Introduction

Optimization of a spectrophotometric method to determine ammonia in groundwater to understand the arsenic and manganese occurrence in aquifers of Chittagong, a

rapidly expanding coastal city of Bangladesh

Discussion /Summary

Laboratory Activities

ACKNOWLEDGEMENT The field samples were collected by the students of Engineering University of Chittagong, Bangladesh in Summer 2014. Thanks to School of Arts and Sciences and York College Academic Affairs for facilities and additional supports.

Results

While serious health effects due to elevated arsenic (As) consumption have been documented in several South Asian countries, the source and mechanisms of  As mobilization in aquifers remain poorly understood. In the study area of Chittagong, Bangladesh, the northern part of the city is a part of Anticline associated with Tertiary aquifers and the southern part of the city is plain land associated with Quaternary aquifers. Preliminary studies have reported elevated As and manganese (Mn) in those aquifers. However, as to date,  no hydro-geochemical study has been conducted to understand the geochemical processes that control the As distribution in groundwater. This study reports the ammonia concentration in a set of 9(nine) groundwater samples collected from both and shallow aquifers of Chittagong area. The preliminary results showed high level of ammonia is associated with elevated level of As and Mn, suggests that reducing condition may control the As and Mn release in groundwater. The study is in progress to improve the understanding of detail geochemical processes.

Groundwater aquifers are a main source of drinking water for billions of people worldwide. There is, however, growing public concern about chronic exposure to natural and geogenic contaminants that can be released from contaminated sediment to groundwater. Arsenic and manganese of natural origin contribute to a globally significant environmental and public concern. The metalloid arsenic (As) has received attention as a contaminant over the past two decades, particularly in south and Southeast Asia. For example, elevated groundwater arsenic concentrations in many parts of Bangladesh have been described as the “largest poisoning of a population in history.” Estimates of the rural population exposed to unsafe arsenic levels by drinking water in India, China, Myanmar, Pakistan Vietnam, Nepal and Cambodia has grown to over 100 million people. The spatial extent of the problem and the fact that the most severely contaminated areas are in the geologically distinct low-lying flood plain, support the idea that the sediments themselves are the most likely As source. Available data for As in sediments from Bangladesh, including those bearing high-As groundwater, show the concentration of As to be closely similar to those for average sediments and are ranged from 0.4 mgkg-1

to 16 mgkg-1 in different parts of Bangladesh [1]. However, the mobility of arsenic in the subsurface is influenced by a combination of the dissolved species present, minerals in aquifer solids, microbiological activity, and by ambient geochemical parameters such as Eh and pH [2]. The proposed study area of Chittagong, is the commercial and industrial capital of Bangladesh, lying in the south eastern part of Bangladesh (Figure-1). Total population of the city is ~4 million and the rate of urbanization is 42.4%. The groundwater system in the study area is more complex than the other cities, because the northern part of Chittagong city is a part of Anticline (Sitakund- a Tertiary Hills) whereas the southern part of it is more or less plain land. The city is surrounded by the Bay of Bengal in the west and the Karnaphuli River in the east and south [3]. Earlier BGS-DPHE study did not include the Chittagong City in their nation-wide arsenic survey [4]. Recently CUET (Chittagong University of Engineering and Technology) conducted an arsenic screening survey using field test kits in municipal areas of Chittagong and reported elevated arsenic level in several wells in different parts of Chittagong [5,6]. Last summer, PI contacted CUET and organized a brief field screening on a set of nine existing wells in different parts of Chittagong for nutrients and manganese during his visit in Bangladesh. The data (Table-1) showed extremely high amount of ammonia and manganese in most of the wells (depth 35-260 ft) (unpublished data). Because of this threat, it is critically important to understand the factors controlling arsenic migration in natural systems, both to assess risks posed by As-enriched sites and to design effective mitigation strategies. The main research objectives in initiating to investigate the site are to study: 1) source of arsenic and manganese to groundwaters, 2) mechanisms of arsenic and manganese mobilization, and 3) prospects for remediating this and other similar sites.

Sasha Heralall(Environmental Health Science Major)

Mentor: Dr. Ratan Kumar DharDepartment of Earth and Physical Sciences, School of Arts and Sciences

Standard Addition Calibration curve was valid with a regression value (r2) of 99.8%.

Most of the ammonia results match with the field chemetric measurements. However, saamples with differing results have to be re-run by colorimetry to asses the sample preservation for long time.

Depth profile consistently showed the higher ammonia concentration in shallow environment, suggesting the nutrients inflow from localized environment.

Elevated concentration of arsenic and manganese were also found in shallow environment where ammonia reducing condition exist.

The Aqualog Fluorescence instrument showed consistently low level of instrumental noise and high reproducibility.

The study will be extended to investigate the detailed geochemical properties of the groundwater. Groundwaters are being analyzed by High Resolution Inductively Coupled Plasma Mass Spectrometry (HR ICPMS) at Lamont-Doherty Earth Observatory, Columbia University for a suit of 32 elements including As, Mn, Fe, Pb, Se, Hg.

•[1] Dhar, R. K., Y. Zheng, K.A. Radloff, B. Mailloux, K. M. Ahmed and A. van Geen. 2011. Microbes Enhance Mobility of Arsenic in Pleistocene Aquifer Sand from Bangladesh. Environmental Science and Technology. 45 (7), p. 2648–2654 • [2] Hossain M.S., K.Bashar, and N. Ahmed, 2008, An approach to hydrogeological zonation: a case study for the Chittagong City, Bangladesh Geoscience Journal, v. 14, p. 33-55. •[3] BGS & DPHE. 2001. Arsenic contamination of groundwater in Bangladesh. In D. G. Kinniburgh & P. L. Smedley (eds), British Geological survey Technical Report WC/00/19. Keyworth, UK.•[4] Palit, S. and M.A. Ashraf, 2010, Arsenic screening of tube-wells within the city wards: East Sholashahar and North Halishahar under Chittagong City Corporation, Arsenic Research Report-2, The Institution of Engineers Bangladesh (IEB). • [5] Uddin A. M. and T. Islam, 2013, Arsenic screening of groundwater from tube-wells located within Chittagong City, International Journal of Scientific and Engineering Research, v. 4(10), p. 73-81.

Selection of sites: To cover different geological sites of Chittagong, total nine samples were collected from four different locations. For further detailed hydro-geochemical study, samples from existing wells will be collected from three different areas: Tertiary aquifer system with no reported As, Quaternary coastal plain with high As, and Quaternary river flood plain with high As.  Future Sample Collection Plan: Collection of sediments and groundwater from boreholes: The profiles of aquifer materials and groundwater will be collected with the needle-sampler, a simple device developed to allow drillers in Bangladesh to test groundwater before installing a well [8]. It consists of an evacuated sample chamber capped with a silicone stopper, a long needle and plunger assembly to transfer groundwater and sediment from a depth slightly greater than that of the drill hole to the sample chamber, and a housing unit that connects the needle and plunger assembly to the sample chamber. The device is deployed by drilling to the targeted depth using the entirely manual method (hand flapper method) that has been used to install the vast majority of the millions of wells in Bangladesh [1]. The chamber fills almost entirely with groundwater and some sediment during deployment. Groundwater samples will be filtered under nitrogen and acidified for As and other heavy metals by HR-ICPMS. Sediment cuttings at every 3-5 feet interval will also be collected whenever possible for texture and bulk analysis.  Collection of groundwaters from existing tube-wells: Groundwater samples from the selected existing wells will be collected from three sites . Each well will be pumped for at least 15 minutes by a battery-driven submersible pump (Geotech geosquirtTM 12V DC Purge Pump) at a rate of ~ 2 L/min to remove at least one well-bore volume before sampling. However, 15 minutes of pumping usually allows conductivity and temperature readings to stabilize prior to sampling. Samples for As, Fe, Mn and other ions will be collected in 30-ml or 60-ml acid-cleaned HDPE bottles and acidified to 1.2 N HCl (Fisher Optima) immediately after collection and without filtration. Prior studies have shown that the standard monitoring well screens in Bangladesh are typically sufficient to exclude particles that might dissolve upon acidification, whereas filtration can produce artifacts unless carried out under nitrogen [9]. Samples for common anions and cations will be collected in nanopure-washed 30 ml HDPE bottles without filtration.

Sampling Protocol and Methodology

Table-1: Groundwater chemistry of As contaminated aquifers in 2014 (Dhar, unpublished data)

Ward Ward Name Depth

No. (m) As* Mn NH4+ NO2

- NO3-

6 East Sholashahar 18 0.4-0.5 0.30-0.64 8.09-10.2 8.40-24.1 0.04-0.09 0.09-0.11

11 South Kattali 37-43 0.1-0.2 0.55-0.68 0.12-0.27 3.79-4.09 0.05-0.05 0.09-0.17

19 South Bakalia 67-79 0.3-0.4 0.87-10.3 0.32-0.49 1.20-4.60 0.07-0.29 0.15-0.36

26 North Halishahar 11-18 0.4-0.5 0.78-1.49 8.64-10.1 8.95-16.6 0.05-0.11 0.16-0.19* Arsenic data are obtained from Palit and Ashraf, 2010.

Concentration (mg/L)

PO43-

y = 0.4128x + 0.1153R² = 0.9977

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

Mea

n Ab

sorb

ance

Uni

t

Concentration (ppm)

Ammonia Standard Addition Calibration Curve

0

50

100

150

200

250

300

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00

Dept

h of

the

wel

l (ft

)

concentration (ppm)

Depth Profile of Ammonia in groundwater of Bangladesh

Aqualog

Chemetrics(Field)

Table-1: Field data by Vacua-Vial Chemetric method (using V-2000)

Sample Depth NH4+ PO4

2- Mn2+ NO2- NO3

-

ID (Ft) (ppm) (ppm) (ppm) (ppm) (ppm)

1 220 0.910 0.410 1.010 1.002 0.030

2 240 1.460 0.320 0.870 0.013 0.044

3 260 3.540 0.490 10.340 0.188 0.081

4 60 6.530 8.080 0.297 0.011 0.020

5 60 18.740 10.170 0.639 0.014 0.024

6 120 3.080 0.115 0.681 0.014 0.038

7 140 3.180 0.267 0.551 0.015 0.021

8 40 12.910 8.640 1.487 0.033 0.044

9 60 6.960 10.040 0.778 0.014 0.036

0.000

0.005

0.010

0.015

0.020

0 2 4 6 8 10 12 14 16

Mea

n Ab

sorb

ance

Uni

t

Nanopure blank measurement

Drift Monitoring during the analysis by Aqualog