article · Applied Geochemistry
Groundwater analysis in the Pearl River Delta reveals the specific hydrogeochemical mechanisms controlling arsenic enrichment in shallow aquifers. Testing of 77 groundwater samples identified peak arsenic levels of 57 micrograms per litre, with nine percent of samples surpassing drinking water standards. The prevailing well-oxygenated conditions keep overall concentrations relatively low and cause the pentavalent form, As(V), to predominate. Statistical and structural equation modelling demonstrates that As(V) accumulation is largely driven by competitive desorption from phosphate and silicate, which account for 65.2 percent and 31.5 percent of variance respectively. In contrast, the emergence of trivalent arsenic, As(III), is primarily governed by iron reduction facilitated by dissolved organic matter, alongside competitive desorption. The findings confirm that controlling and reducing phosphate and reactive organic matter inputs can serve as a targeted mechanism to suppress arsenic contamination in such groundwater environments.
Arsenic contamination in drinking water poses serious health hazards to more than one hundred million people globally. By pinpointing the precise chemical triggers that release toxic arsenic into shallow aquifers, this research clarifies how agricultural or municipal inputs of phosphate and organic matter exacerbate water pollution. Understanding these exact mechanisms assists environmental authorities in designing targeted water safety interventions to protect dependent communities.
This early-stage research provides diagnostic criteria that could inform catchment management and remediation programmes run by water authorities and environmental engineering consultants. By identifying phosphate and reactive organic matter as the primary drivers of arsenic release, the work points towards water treatment and land management protocols designed to limit these inputs. However, the study remains an observational hydrogeochemical investigation, meaning practical remediation technologies or monitoring products require further development before field deployment.
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Arsenic (As) contamination in groundwater is a global environmental geochemical problem that threatens over 100 million people around the world. Although groundwater As enrichment has been demonstrated to result from some major complex processes, including competitive desorption by anions and reductive release of As from iron (Fe) oxyhydroxides due to microbial respiration of dissolved organic matter (DOM), knowledge of the detailed interactions among these processes and their respective contributions is still limited. In this study, we aimed to elucidate the key variables that regulate the evolution of dissolved As in shallow groundwater from a typical As-contaminated region of the Pearl River Delta (PRD) after comprehensive statistical analysis of hydrogeochemical characteristics. The results showed that the highest concentration of As in the groundwater samples (n = 77) was 57 μg/L, with 9% of samples exceeding the drinking water standard. In comparison with other regions with geogenic As contamination in groundwater, the relatively low As concentration range is primarily controlled by the well-oxygenated environment, which also contributed to the dominance of As(V) (19.5–100.0%, median of 100.0%). Hierarchical cluster analysis (HCA) and principal component analysis (PCA) suggested that the presence of As in groundwater may be impacted by the reduction process of Fe/Mn oxyhydroxides and by competitive anions. Further analysis using structural equation modeling (SEM) indicated that the increased concentration of As(V) in the shallow groundwater was primarily induced by the competitive roles of phosphate and silicate, explaining 65.2% and 31.5% of total As(V), respectively. In contrast, the presence of As(III) was strongly explained by DOM (23.8%, 12.4%, and 5.7% from microbial humic-like, terrestrial humic-like, and protein-like components, respectively) and Fe (31.8%), followed by competitive desorption (26.3%), revealing the dominant contribution from DOM-facilitated Fe reduction to As(III) enrichment. Our study empirically demonstrated that decreasing the concentrations of phosphate and reactive organic matter can effectively alleviate As contamination in groundwater. • Phosphate, Fe reduction, and organic matter trigger As release in PRD groundwater. • As species in As(V)-dominated groundwater are controlled by the oxidizing environment. • Phosphate and silicate contributed substantially to the competitive desorption of As(V). • Release of As(III) is probably facilitated by iron (oxyhydr)oxide reduction. • Increased As(III) was related to increasing microbial humic-like components.
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DOI: 10.1016/j.apgeochem.2023.105602
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