[Geochemical Characteristics and Genesis Analyses of High-arsenic Groundwater in the Pearl River Delta]

To determine the main factors affecting the migration, enrichment, and sources of arsenic in the shallow groundwater of the Pearl River Delta (PRD), clustering analysis was used to partition the study area and then analyze the abnormal distribution of arsenic and groundwater storage environment in each part area based on the data obtained from the investigation of groundwater pollution in the PRD region. The results showed, in the study area, arsenic was mainly represented by As(Ⅲ), and its concentration ranged from under the detection limit to 560 μg·L^-1. High-arsenic groundwater was mainly distributed in the plain area covered by Quaternary loose sediment, with the Shunde District in Foshan City having the highest, followed by Zhongshan City and central Guangzhou. The hydrochemical type of groundwater in the study area was mainly HCO₃-Ca type water. The high-arsenic groundwater had the characteristics of high pH value; high concentrations of NH₄⁺, Fe, and Mn; and a high permanganate index, in addition to a low concentration of NO₃^-. Based on scatter plot and factor analysis of various indicators of arsenic in groundwater and the impact of human activities on the groundwater environment of the PRD, it was concluded in this study that under the common influence of natural sedimentary environment and pollution input, a neutral or weak-alkaline-reducing environment, which was conducive to the occurrence of high-arsenic groundwater, was formed in the plain area. The role of microorganisms and the input of organic pollutants in the shallow groundwater led to the reduction and dissolution of arsenic-containing Fe-Mn oxide, resulting in the release of arsenic. The source of arsenic contamination in the groundwater was mainly the industrial pollution in Shunde and other areas in southern Foshan City.