Mobilisation of arsenic and other trace elements in fluviolacustrine aquifers of the Huhhot Basin, Inner Mongolia
Mobilisation of arsenic and other trace elements in fluviolacustrine aquifers of the Huhhot Basin, Inner Mongolia
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DOI：
10.1016/s0883-2927(03)00062-3
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发表时间：
2003-09-01
影响因子：
3.4
通讯作者：
Luo, Z
中科院分区：
文献类型：
--
作者：
Smedley, PL;Zhang, M;Luo, Z
在中国北方内蒙古呼和浩特盆地的钻孔和威尔斯地下水中观测到的砷浓度范围在< 1 μ g l（-1）和1480 μ g l（-1）之间。含水层由第四纪（主要是全新世）湖泊和河流沉积物组成。在浅井和深井以及一些挖好的威尔斯井（井深在10米至400米之间）的地下水中发现了高浓度。来自受影响地区的人群经历了许多与砷相关的健康问题，其中最显著的是皮肤病变（角化病、黑变病、皮肤癌），但也有报告称发生了内脏癌（肺癌和膀胱癌）。在浅层和深层含水层中，地下水沿水流梯度从沿着盆地边缘的氧化条件向盆地中部低洼处的还原条件发展。高As浓度发生在这个低洼地区的厌氧地下水，并与中度高溶解铁以及高Mn，NH 4，溶解有机C（DOC），HCO 3和P浓度。许多深层地下水具有特别富集的DOC浓度（高达30毫克l（-1）），并且由于有机酸的高浓度而常常呈棕色。在还原性地下水中，无机As（III）通常占总溶解As的60%以上。最高的As浓度往往是在地下水中发现的低SO 4浓度，并表明，作为动员发生在强烈的还原条件下，SO 4还原一直是一个积极的过程。高浓度的Fe、Mn、NH 4、HCO 3和P是减少高砷地下水省份（例如孟加拉国、西孟加拉）的共同特征。高浓度的有机酸（腐殖酸、富里酸）并不是这类含水层的普遍特征，但在台湾和匈牙利的地下水中也发现了这种现象。沉积物中总As的浓度范围为3-29 mg kg（-1）（n = 12），与总Fe的浓度呈正相关。高达30%的砷是可萃取的，并采取了主要与铁氧化物。在还原条件下As向溶液中的释放被认为是通过解吸结合Fe氧化物矿物的还原溶解。溶解As与HCO 3，DOC和P等成分的关联可能与普遍的还原条件和缓慢的地下水流有关，但它们也可能直接参与，因为它们与As竞争Fe氧化物上的结合位点。呼和浩特地下水也有一些高浓度的溶解U（高达53 μ g l（-1））和F-（尖端到6.8 mg l（-1））。与As相反，U主要发生在沿着盆地边缘的氧化条件下。氟主要存在于以Na和HCO 3为优势离子的浅层地下水中。地下水流动缓慢和含水层沉积物年代较轻也被认为是造成高水位的潜在重要原因。溶解砷浓度观察到的沉积物可能含有新形成的和活性矿物，并没有很好地冲洗，因为埋葬。(C)2003年由Elsevier Science Ltd.出版
Observed As concentrations in groundwater from boreholes and wells in the Huhhot Basin of Inner Mongolia, northern China, range between < 1 mug l(-1) and 1480 mug l(-1). The aquifers are composed of Quaternary (largely Holocene) lacustrine and fluvial sediments. High concentrations are found in groundwater from both shallow and deep boreholes as well as from some dug wells (well depths ranging between 10 m and 400 m). Populations from the affected areas experience a number of As-related health problems, the most notable of which are skin lesions (keratosis, melanosis, skin cancer) but with internal cancers (lung and bladder cancer) also having been reported. In both the shallow and deep aquifers, groundwaters evolve down the flow gradient from oxidising conditions along the basin margins to reducing conditions in the low-lying central part of the basin. High As concentrations occur in anaerobic groundwaters from this low-lying area and are associated with moderately high dissolved Fe as well as high Mn, NH4, dissolved organic C (DOC), HCO3 and P concentrations. Many of the deep groundwaters have particularly enriched DOC concentrations (up to 30 mg l(-1)) and are often brown as a result of the high concentrations of organic acid. In the reducing groundwaters, inorganic As(III) constitutes typically more than 60% of the total dissolved As. The highest As concentrations tend to be found in groundwater with low SO4 concentrations and indicate that As mobilisation occurs under strongly reducing conditions, where SO4 reduction has been an active process. High concentrations of Fe, Mn, NH4, HCO3 and P are a common feature of reducing high-As groundwater provinces (e.g. Bangladesh, West Bengal). High concentrations of organic acid (humic, fulvic acid) are not a universal feature of such aquifers, but have been found in groundwaters from Taiwan and Hungary for example. The observed range of total As concentrations in sediments is 3-29 mg kg(-1) (n = 12) and the concentrations correlate positively with total Fe. Up to 30% of the As is oxalate-extractable and taken to be associated largely with Fe oxides. The release of As into solution under the reducing conditions is believed to be by desorption coupled with reductive dissolution of the Fe oxide minerals. The association of dissolved As with constituents such as HCO3, DOC and P may be a coincidence related to the prevalent reducing conditions and slow groundwater flow, but they may also be directly involved because of their competition with As for binding sites on the Fe oxides. The Huhhot groundwaters also have some high concentrations of dissolved U (up to 53 mug l(-1)) and F- (tip to 6.8 mg l(-1)). In contrast to As, U occurs predominantly under the more oxidising conditions along the basin margins. Fluoride occurs dominantly in the shallow groundwaters which have Na and HCO3 as the dominant ions. The combination of slow flow of groundwater and the young age of the aquifer sediments are also considered potentially important causes of the high. dissolved As concentrations observed as the sediments are likely to contain newly-formed and reactive minerals and have not been well flushed since burial. (C) 2003 Published by Elsevier Science Ltd.