Shallow Groundwater Manganese Merits Deeper Consideration.
Shallow Groundwater Manganese Merits Deeper Consideration.
复制标题
DOI：
10.1021/acs.est.0c08065
复制
发表时间：
2021-03-16
影响因子：
11.4
通讯作者：
Ying SC
中科院分区：
文献类型：
--
作者：
Ramachandran M;Schwabe KA;Ying SC
锰是地球上第十二大最丰富的元素，也是S结壳中的一种基本微量营养素，通常不被视为主要的饮用水污染物。然而，美国地质调查局(USGS)在1991年至2010年间调查的所有美国地下水井中，有四分之一的锰含量超过了美国环境保护局(USEPA)设定的次要最大污染物水平(SMCL)0.05毫克/L。1在同一时期，美国地质勘探局抽样的水井中，有7%的水井中的锰浓度超过了0.3毫克/升的健康筛选水平。在过去十年中，不断有报告称，美国各地的当地地下水供应中存在锰污染，经常接近或超过健康筛选水平。然而，由于锰被归类为二次污染物，SMCL只是一个审美指南，SMCL和HBSL都不是可执行的标准。2越来越多的研究指出，摄入饮用水中过量的锰会产生神经毒性：长期过量接触会损害幼儿的智力和运动技能。3、4由于这些挫折不易扭转，过量接触锰对儿童的健康构成重大威胁。尽管水是孕妇和幼儿接触锰的主要途径，5但环境保护局目前并不要求公共供水系统或私人水井使用者监测和报告锰含量。私人水井为大约4300万人提供饮用水，占美国人口的15%。鉴于毒性问题、经常超过建议限量，再加上很大一部分美国人可能接触到锰，有理由相信在美国，锰可能需要更严格的监管标准，锰是一种基本营养素，建议成年人每天最高摄入量为10毫克，大部分锰是通过饮食摄入的。6需要监测饮用水中的浓度，以防止过量摄入锰。要将锰浓度保持在安全水平，特别是在地下水中，一个具体的挑战是了解地源锰的空间异质性以及影响地下地球化学和锰氧化态的过程。锰可在多种原生矿物中找到，通常在土壤和沉积物的细粒中含量较丰富，与层状硅酸盐和碳酸盐伴生。9原生矿物的风化释放出Mn2+，经氧化生成次生的Mn(III/IV)氧化物。这些二次锰(III/IV)氧化物随后可以在亚氧或缺氧条件下被还原溶解。溶解的锰(II)然后可以通过沉积物孔隙网络被动员，并最终被输送到含水层中。虽然Mn2+是低氧条件下的主要形态，但在水处理过程中，它很容易被氯化转化为难溶的Mn(IV)氧化物，并通过过滤去除。如果摄入，体内的锰(II)会被氧化成锰(III)。虽然锰(II)和锰(III)都是生物相关的物种，但锰(III)更容易通过膜和血脑屏障运输。…说，在地下地层含有锰的浅层地下水中，最容易将锰以锰(II)的形式转移到地下水中，这些浅层地下水中有足够的溶解氧来触发锰还原(例如，锰(IV)到锰(II))，同时仍保持足够高的氧化还原状态，使锰仍然溶解在井水中。
Manganese, the twelfth-most abundant element in the earth, s crust and an essential micronutrient, is not frequently viewed as a major drinking water contaminant. Yet, a quarter of all US groundwater wells surveyed by the US Geological Survey (USGS) between 1991 and 2010 contained manganese at concentrations above the secondary maximum contaminant level (SMCL) of 0.05 mg/L set by the United States Environmental Protection Agency (USEPA). 1 Over the same period, 7% of the wells sampled by the USGS had manganese concentrations above the health-based screening level (HBSL) of 0.3 mg/L. In the past decade, there have been recurring reports of manganese contamination in local groundwater supplies around the US, frequently at levels approaching or exceeding the HBSL. 1 However, because manganese is classified as a secondary contaminant, the SMCL is only an aesthetic guideline, and neither the SMCL nor the HBSL are enforceable standards. 2 A growing body of research points to the neurotoxic effects of ingesting excessive manganese in drinking water: chronic overexposure is shown to damage intellectual function and motor skills in young children. 3, 4 Because these setbacks are not easily reversed, overexposure to manganese poses a significant health threat to children. Although water is the principal route of manganese exposure for pregnant women and young children, 5 the EPA does not currently oblige public water systems or private well users, to monitor and report manganese levels. Private wells provide drinking water for approximately 43 million people, which is 15% of the US population. Given the toxicity concerns, the frequent exceedances of advisory limits coupled with potential exposure for a large proportion of the US population, there is reason to believe that manganese may warrant a stricter regulatory standard in the US Manganese is an essential nutrient with a recommended maximum daily intake of 10 mg/day for an adult, with most manganese consumed via diet. 6 Concentrations in drinking water need to be monitored in order to prevent excessive manganese intake. A specific challenge to keeping manganese concentrations at safe levels, particularly in groundwater, is to understand the spatial heterogeneity of geogenic sources of manganese and the processes influencing subsurface geochemistry and manganese oxidation states. 7, 8 Manganese can be found in a wide range of primary minerals and is generally more abundant in finer fractions of soils and sediments where it is associated with layered silicates and carbonates. 9 Weathering of primary minerals releases Mn2+ which undergoes oxidation to form secondary Mn (III/IV) oxides. These secondary Mn (III/IV) oxides can subsequently be reductively dissolved under suboxic or anoxic conditions. Dissolved Mn (II) can then be mobilized through sediment pore-networks and eventually transported into aquifers. Though Mn2+ is the predominant species under low oxygen conditions, it can be readily converted to insoluble Mn (IV) oxides during water treatment via chlorination and removed by filtering. If ingested, Mn (II) can become oxidized to Mn (III) in the body. While both Mn (II) and Mn (III) are biologically relevant species, Mn (III) is more readily transported across membranes and the blood brain barrier. Mobilization of manganese as Mn (II) into groundwater occurs most readily in shallow groundwaters where subsurface strata possess Mn content, with enough dissolved oxygen to trigger manganese reduction (eg, Mn (IV) to Mn (II)), while still maintaining a high enough redox status to allow manganese to remain dissolved in well water …
影响因子：
11.4
作者：
Ying, Samantha C.;Schaefer, Michael V.;Fendorf, Scott
通讯作者：
Fendorf, Scott
影响因子：
11.4
作者：
McMahon, Peter B.;Belitz, Kenneth;Johnson, Tyler D.
通讯作者：
Johnson, Tyler D.
影响因子：
10.4
作者：
Schullehner J;Thygesen M;Kristiansen SM;Hansen B;Pedersen CB;Dalsgaard S
通讯作者：
Dalsgaard S