High-Arsenic Groundwater in Paleochannels of the Lower Yellow River, China: Distribution and Genesis Mechanisms

Chuanshun Zhi,Zhen Wang,Zeyan Li,Wengeng Cao

doi:10.3390/w13030338

Chuanshun Zhi, Zhen Wang + Show 2 more

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https://doi.org/10.3390/w13030338

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Abstract

High–arsenic (As) groundwater poses a serious threat to human health. The upper and middle reaches of the Yellow River are well–known areas for the enrichment of high–arsenic groundwater. However, little is known about the distribution characteristics and formation mechanism of high-As groundwater in the lower reach of the Yellow River. There were 203 groundwater samples collected in different groundwater systems of the lower Yellow River for the exploration of its hydrogeochemical characteristics. Results showed that more than 20% of the samples have arsenic concentrations exceeding 10 μg/L. The high-As groundwater was mainly distributed in Late Pleistocene–Holocene aquifers, and the As concentrations in the paleochannels systems (C2 and C4) were significantly higher than that of the paleointerfluve system (C3) and modern Yellow River affected system (C5). The high-As groundwater is characterized by high Fe2+ and NH4+ and low Eh and NO3−, indicating that reductive dissolution of the As–bearing iron oxides is probably the main cause of As release. The arsenic concentrations strikingly showed an increasing tendency as the HCO3− proportion increases, suggesting that HCO3− competitive adsorption may facilitate As mobilization, too. In addition, a Gibbs diagram showed that the evaporation of groundwater could be another significant hydrogeochemical processes, except for the water–rock interaction in the study area. Different sources of aquifer medium and sedimentary structure may be the main reasons for the significant zonation of the As spatial distribution in the lower Yellow River.

Highlights

High-As (>10 μg/L) groundwater is distributed worldwide, including Vietnam, India, Bangladesh, Thailand, China, USA, Argentina, and Mexico, among others [1]
The distribution of samples was relatively spaced in the C5 groundwater system, with the water types of Na–Mg–HCO3 or Ca–Mg–HCO3
High–As groundwater mainly occurred in paleochannel aquifers (C2 and C4) with a high permeability, compared with the paleointerfluve aquifer (C3) and modern Yellow River affected zone

Summary

Introduction

High-As (>10 μg/L) groundwater is distributed worldwide, including Vietnam, India, Bangladesh, Thailand, China, USA, Argentina, and Mexico, among others [1]. The mechanisms of As release into groundwater mainly include reductive dissolution of As–bearing iron oxide minerals, arsenic desorption in high pH conditions, bicarbonate and phosphate competitive adsorption with arsenic, and oxidation of pyrite [4,5,6,7,8,9]. In the Red River delta plain, areas with high-As groundwater (10–810 μg/L) are distributed in a 20-km-wide band along the NW–SE boundary of the plain, which is consistent with the location of the Red River paleochannels (9 ka B.P.) [20]. The paleochannel aquifers are characterized by high permeability and reductive conditions

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Conclusion