DSpace at VNU: Arsenic contamination in groundwater and its possible sources in Hanam, Vietnam

Environ Monit Assess (2012) 184:4501–4515 DOI 10.1007/s10661-011-2281-6 Arsenic contamination in groundwater and its possible sources in Hanam, Vietnam Nguyen Minh Phuong & Yumei Kang & Katsutoshi Sakurai & Miyuki Sugihara & Chu Ngoc Kien & Nguyen Dinh Bang & Ha Minh Ngoc Received: November 2010 / Accepted: 27 July 2011 / Published online: 10 August 2011 # Springer Science+Business Media B.V 2011 Abstract This study investigated the arsenic (As) level in groundwater, and the characteristics of aquifer sediment as related to the occurrence of As in groundwater in Hanam, Vietnam The deposition and transport of As-containing substances through rivers were also examined Arsenic concentrations in 88% of the groundwater samples exceeded the As limit for drinking water based on the WHO standards The dominating form of arsenic was As(III) The maximum total As content in bore core sediment was found in a peat horizon of the profiles and generally, elevated levels of As were also found in other organic matter-rich horizons Total As contents of the bore core sediments were significantly correlated with crystalline iron oxide, silt and clay contents, suggesting that As in aquifer sediment was mainly associated with iron (hydr)oxides and clay mineral In the groundwater, As concentration showed significant correlations with the total concentrations of Fe and HCO − Significant correlations between HClextractable As and non-crystalline Fe oxide, total C, N, and S were also observed in the profiles The results support the hypothesis that under favorable reductive conditions established by the degradation of organic matter, the dissolution of iron (hydr)oxides releases adsorbed As into the groundwater The deposition of As in the sediments from the Red River were significantly higher than that in the Chau Giang River, suggesting that the Red River is the main source of As-containing substances deposited in the study area Keywords Arsenic Bore core Groundwater River Sediment Vietnam N M Phuong : C N Kien United Graduate School of Agricultural Sciences, Ehime University, Matsuyama 790-8566, Japan Y Kang : K Sakurai : M Sugihara Faculty of Agriculture, Kochi University, Monobe, Nankoku, Kochi 783-8502, Japan N M Phuong (*) : N D Bang : H M Ngoc Faculty of Chemistry, Hanoi University of Science, Hanoi, Vietnam e-mail: nmphuong81@yahoo.com Introduction Arsenic is unique among the heavy metalloids and oxyanion-forming elements (e.g., As, Se, Mo) in its susceptibility to mobilization under the pH conditions typically found in groundwater (pH=6.5–8.5) and over a wide range of redox conditions (Hossain 2006) Tens of millions of people in South and Southeast Asia routinely consume groundwater that has unsafe As levels (Smith et al 2000; Chowdhury et al 2000; Berg et al 2001, 2007; Hossain 2006) As a main water 4502 source for local communities, groundwater has been exploited in Vietnam since the 1900s The first publication on As contaminations in groundwater of Hanoi, Vietnam, in 2001 reported contamination levels from to 3,050 μg l−1 (average 159 μg l−1) (Berg et al 2001) Such elevated As concentrations were found in numerous regions throughout Vietnam (Berg et al 2001; Chander et al 2004; Agusa et al 2006; Nguyen et al 2009) A random survey of As levels in tube well water from 12 Vietnamese provinces indicated that Hanam is one of the most seriously As-contaminated area in the Red River Delta In this area, As concentrations exceeded the WHO guideline for As in drinking water (10 μg l−1) (Chander et al 2004) in 52% of the tube wells surveyed Arsenic-bearing groundwater in Vietnam has been noted because of the geological similarity with the Ganges–Brahmaputra, Mekong, and Red River basins which are built up with alluvium from the rapidly weathering Himalayas and are characterized by complex lithological structures of the aquifers which not show a full separation between upper and lower aquifers (Laurent and David 2006) Some researchers have argued that oxidation of As-rich sulfide minerals is one possible mechanism for the release of As into groundwater Others have suggested that reductive dissolution of iron oxyhydroxides or arsenate sorbed by detrital organic carbon is another possible mechanism of As mobilization (Nickson et al 1998; Smedley and Kinniburgh 2002) However, the dissolution of iron oxide is regarded the primary process responsible for high As concentrations in the groundwater in some areas Arsenic is naturally derived from eroded Himalayan sediments, and is believed to become mobile following reductive release from solid phases under anaerobic conditions (Polizzotto et al 2008) A study of the hydrological and sedimentary conditions of river bank deposits in the Hanoi area indicated that elevated groundwater levels of As are caused by reductive dissolution under iron-reducing conditions (Berg et al 2008) Hanam Province with a total area of 849.5 km2 and a population of 820,100 is a productive agricultural region located in the lower part of the Red River Delta The topography is dominated by limestone mountains, hills, and forests with some sloping areas in the west (10–15% of the total area), whereas the east is a plain that mainly consists of alluvium from the Red River (85–90% of the total area) About 38.6 Environ Monit Assess (2012) 184:4501–4515 km of the Red River form the eastern border of the province The Red River plays an important role in the fertility and irrigation of the roughly 10,000 of agricultural land However, there is little information on the characteristics and degree of As contamination, and the causes of As release to the groundwater in this area In this study, we examined As concentrations in groundwater and the geochemical parameters of aquifer sediment related to the occurrence of As in the groundwater Our study area in the Lynhan district of Hanam Province represents alluvium from two rivers, the Red River and the Chau Giang River Therefore, we also investigated the deposition and transport of pollutants through these streams Materials and methods Sample collection and preparation This survey was conducted in the Xuan Khe (XK), Hop Ly (HL) and Chan Ly (CL) communes of the Lynhan district, Hanam Province, in November 2006 (dry season) (Fig 1) Hop Ly and Xuan Khe are located near the Chau Giang River, while Chan Ly is located near the Red River Groundwater samples were taken from 31 randomly chosen tube wells in the three communes (Hop Ly, n=12; Xuan Khe, n=11; Chan Ly, n=8) Prior to sampling, water from tube wells was flushed away until crystal clear water was obtained (Berg et al 2001) Immediately after collection, pH, electrical conductivity (EC), oxidation–reduction potential (Eh), and dissolved oxygen (DO) were measured The samples were passed through small disposable ion exchange cartridges packed with 2.5 g selective aluminosilicate adsorbent (Metalsoft Center, Highland Park, NJ; Meng and Wang 1998) This adsorbent retained As(V) but not As(III) The filtrates then were acidified with 1% (volume) concentrated HCl for As (III) analysis The cartridges have been widely used in the field to separate As(V) from As(III) in water samples because of their convenience and reliability The average recovery of As(III) in the filtrates was 98% (Meng and Wang 1998) Water samples for the analysis of total As, Fe, and Mn were acidified with ml concentrated HCl acid and preserved in 100-ml polypropylene bottles For major ions analysis, polypropylene bottles were filled completely with Environ Monit Assess (2012) 184:4501–4515 Fig The study area, Ly Nhan district, Ha Nam province, Vietnam Further details of the location of sampling sites (bore core, groundwater, river water, and river sediment sampled site) are as in Figs 2, 3, 4, 8, and 4503 106o05' 106o00' Lynhan 106o10' 106o15' 106o20' Hop Ly Chan Ly 20o60' Hanam 20o55' Hanoi km Chau Giang River Legend Xuan Khe 20o50' river, canal commune border Vietnam sampled water, all bubbles were removed, and the bottles were tightly capped A set of 50-ml samples was used to determine HCO3− in the laboratory (see below for details) Another set of 50-ml samples were filtered through 0.45-μm membrane filters to remove suspended organic matter and acidified to pH