Arsenic Contamination in Groundwater and Potential Health Risk in Western Lampang Basin, Northern Thailand

Nipada Santha,Schradh Saenton,Saowani Sangkajan

doi:10.3390/w14030465

Abstract

This research aimed to investigate the spatial distribution of arsenic concentrations in shallow and deep groundwaters which were used as sources for drinking and domestic and agricultural uses. A geochemical modeling software PHREEQC was used to simulate equilibrium geochemical reactions of complex water–rock interactions to identify arsenic speciation and mineral saturation indices based on groundwater quality and hydrogeochemical conditions. In addition, the potential health risk from arsenic-contaminated groundwater consumption was assessed based on the method developed by the U.S. Environmental Protection Agency. The study area is located at the western part of the Lampang Basin, an intermontane aquifer, Northern Thailand. The area is flat and situated in a floodplain in the Cenozoic basin. Most shallow groundwater (≤10 m depth) samples from dug wells were of Ca-Na-HCO3 and Ca-HCO3 types, whereas deep groundwater from Quaternary terrace deposits (30–150 m depth) samples were of Na-HCO3 and Ca-Na-HCO3 types. High arsenic concentrations were found in the central part of the study area (Shallow groundwater: <2.8–35 mg/L with a mean of 10.7 mg/L; Deep groundwater: <2.8–480 mg/L with a mean of 51.0 mg/L). According to geochemical modeling study, deep groundwater contained toxic As(III), as the dominant species more than shallow groundwater. Arsenic in groundwater of the Lampang Basin may have been derived from leaching of rocks and could have been the primary source of the subsurface arsenic in the study area. Secondary source of arsenic, which is more significant, could be derived from the leaching of sorbed arsenic in aquifer from co-precipitated Fe-oxyhydroxides in sediments. Quantitative risk assessment showed that the average carcinogenic risk values were as high as 2.78 × 10−3 and 7.65 × 10−3 for adult and child, respectively, which were higher than the acceptable level (1 × 10−4). The adverse health impact should be notified or warned with the use of this arsenic-contaminated groundwater without pre-treatment.

Highlights

Groundwater is the main freshwater resource for consumption and utilization in many parts of the world because of its large amount reserves and less microbial contamination [1,2], but it can be naturally contaminated by heavy metals
The results from this study indicate that arsenic concentration in deep groundwater wells was higher than the regulated standard of 50 μg/L [5] and some groundwater wells contained arsenic concentrations greater than the WHO’s standard for drinking water, 10 μg/L [6]
Most shallow groundwater samples showed Ca-Na-HCO3 and Ca-HCO3 water types, whereas deep groundwater samples were of Na-HCO3 and Ca-Na-HCO3 types

Summary

Introduction

Groundwater is the main freshwater resource for consumption and utilization in many parts of the world because of its large amount reserves and less microbial contamination [1,2], but it can be naturally contaminated by heavy metals. As(V) is predominant under oxidizing conditions, and As(III) is mainly present in reducing environment and both can coexist in groundwater [15,16]. The mobility of these species is controlled by pH, redox potential, and the presence of adsorbents, such as iron and manganese (hydr)oxides and clay minerals [17,18]. The complexity of spatial distribution, fate, and transport of arsenic in groundwater are mainly controlled by geochemical conditions and processes depending on geologic setting characters. The unique and individual features of the source rocks, aquifer materials, and hydrogeochemical conditions are the key characteristics of the study of arsenic contamination

Objectives

Results

Conclusion