珠江三角洲高砷地下水赋存环境特征及成因分析

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

为了弄清珠江三角洲地区浅层地下水中砷迁移、富集的主控因素及砷的来源,利用珠江三角洲地区地下水污染调查所取得数据资料,运用聚类分析方法对研究区进行分区,分别对砷异常分布特征以及地下水赋存环境进行分析.结果表明,研究区地下水砷浓度范围为从未检出至560μg·L-1,主要以As(Ⅲ)的形式存在;高砷地下水主要分布在第四系松散沉积物覆盖的平原区,其中佛山顺德地区最高,广州市中部与中山市次之;研究区地下水水化学类型以HCO3-Ca型水为主,高砷地下水具有p H值较高,NH+4、Fe、Mn、耗氧量浓度较高,且NO-3浓度低的特征.通过对高砷地下水各指标散点图与因子分析,结合人类活动对珠三角地下水环境影响推断:在天然沉积环境与污染输入的共同影响下,平原区形成有利于高砷地下水赋存的中性至弱碱性还原环境.浅层地下水在微生物作用与有机污染物输入下,引起含砷铁锰氧化物的还原溶解,导致砷的释放.而佛山市南部顺德等地区工业污染则是地下水中砷污染的主要来源.

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 560μg·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 hydrochemieal 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 NH; , 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 atheas in southern Foshan City.