Arsenic Neurotoxicity in Humans
砷对人类的神经毒性

Abstract 抽象的

Arsenic (As) contamination affects hundreds of millions of people globally. Although the number of patients with chronic As exposure is large, the symptoms and long-term clinical courses of the patients remain unclear. In addition to reviewing the literature on As contamination and toxicity, we provide useful clinical information on medical care for As-exposed patients. Further, As metabolite pathways, toxicity, speculated toxicity mechanisms, and clinical neurological symptoms are documented. Several mechanisms that seem to play key roles in As-induced neurotoxicity, including oxidative stress, apoptosis, thiamine deficiency, and decreased acetyl cholinesterase activity, are described. The observed neurotoxicity predominantly affects peripheral nerves in sensory fibers, with a lesser effect on motor fibers. A sural nerve biopsy showed the axonal degeneration of peripheral nerves mainly in small myelinated and unmyelinated fibers. Exposure to high concentrations of As causes severe central nervous system impairment in infants, but no or minimal impairment in adults. The exposure dose–response relationship was observed in various organs including neurological systems. The symptoms caused by heavy metal pollution (including As) are often nonspecific. Therefore, in order to recognize patients experiencing health problems caused by As, a multifaceted approach is needed, including not only clinicians, but also specialists from multiple fields.
砷 (As) 污染影响着全球数亿人。尽管慢性砷暴露患者数量较多，但患者的症状和长期临床病程仍不清楚。除了回顾有关砷污染和毒性的文献外，我们还提供有关砷暴露患者医疗护理的有用临床信息。此外，还记录了代谢途径、毒性、推测的毒性机制和临床神经症状。描述了在砷诱导的神经毒性中起关键作用的几种机制，包括氧化应激、细胞凋亡、硫胺素缺乏和乙酰胆碱酯酶活性降低。观察到的神经毒性主要影响感觉纤维的周围神经，对运动纤维的影响较小。腓肠神经活检显示周围神经的轴突变性主要发生在小有髓鞘和无髓鞘纤维中。接触高浓度的砷会导致婴儿中枢神经系统严重受损，但成人不会受到或轻微损害。在包括神经系统在内的各种器官中观察到暴露剂量-反应关系。重金属污染（包括砷）引起的症状往往是非特异性的。因此，为了识别因砷引起的健康问题的患者，需要采取多方面的方法，不仅包括临床医生，还包括来自多个领域的专家。

1. Introduction 一、简介

Arsenic (As) has a long history of use as a pigment and as a homicidal agent. However, in the past 100 years, As has been used as a pesticide, medicine, and component of a number of products [1]. As the global population increasingly relies on aquifers for drinking water, and because some aquifers are contaminated by heavy metals, the population exposed to As has increased dramatically [2]. In addition, reliance on the excavation of deep strata when mining rare metals has increased human contact with heavy metals. Volcanic eruptions can also affect heavy metal exposure, and together, these causes dramatically increase the chances of human contact with heavy metals in amounts far above acceptable thresholds for human health.
砷 (As) 用作颜料和杀人剂有着悠久的历史。然而，在过去的100年里，砷已被用作农药、药物和许多产品的成分[ 1 ]。随着全球人口越来越依赖含水层获取饮用水，并且由于一些含水层受到重金属污染，接触砷的人口急剧增加[ 2 ]。此外，开采稀有金属时依赖深层地层开挖，增加了人类与重金属的接触。火山喷发也会影响重金属暴露，这些原因共同导致人类接触重金属的机会大大增加，重金属的含量远远超过人类健康可接受的阈值。

Among heavy metals, As is attracting media attention owing to its high toxicity. At least 140 million people in more than 50 countries are exposed to As-contaminated drinking water [3]. However, although a small number of acute As exposure patients have been studied in detail, relatively few studies have been performed on a detailed neuropathy of patients chronically exposed to As [4,5,6]. Although patients with chronic As exposure are numerous, their symptoms and clinical courses remain unclear. Medical care of patients with chronic As exposure is often performed through trial and error. In this review, we describe not only the research on As toxicity, but also clinical aspects and case studies with the goal to make this review useful to physicians who examine patients with arsenicosis as well as to researchers.
在重金属中，As因其高毒性而引起了媒体的关注。 50 多个国家至少有 1.4 亿人接触受 As 污染的饮用水 [ 3 ]。然而，尽管对少数急性砷暴露患者进行了详细研究，但对长期暴露于砷的患者的详细神经病变进行的研究相对较少[ 4,5,6 ]。尽管慢性砷暴露患者数量众多，但他们的症状和临床病程仍不清楚。对慢性砷暴露患者的医疗护理通常是通过反复试验来进行的。在这篇综述中，我们不仅描述了砷毒性的研究，还描述了临床方面和案例研究，目的是使这篇综述对检查砷中毒患者的医生以及研究人员有用。

2. Arsenic in the Environment
2. 环境中的砷

Arsenic is widely distributed throughout the earth. In the crust, it often exists in its trivalent atomic state, inorganic As (III), together with other metals such as copper, lead, and iron. In soil and water, it is generally oxidized to pentavalent As (V). In low oxygen environments, such as deep well water or deep seawater, it is reduced to trivalent As (III). Sea water has an As concentration of approximately 2 ppb [7], whereas rain and river water have almost 0 ppb [6]. Despite these levels, the area most prescient for researchers remains As contamination of aquifers due to exposure risk.
砷广泛分布于地球各地。在地壳中，它通常以三价原子态、无机砷 (III) 与铜、铅和铁等其他金属一起存在。在土壤和水中，它通常被氧化成五价As（V）。在低氧环境中，例如深井水或深层海水，它被还原为三价As(III)。海水中砷的浓度约为 2 ppb [ 7 ]，而雨水和河水中的砷浓度几乎为 0 ppb [ 6 ]。尽管存在这些水平，但研究人员最有先见之明的领域仍然是由于暴露风险而导致含水层污染。

Arsenic accumulation in animals sheds light on the significance of the different chemical species of As. Land animals contain 0.06–0.4 ppm of As, whereas fish and shellfishes contain 0.78–25 ppm [8]. Although the As quantities in fish and shellfish are much higher than that in land animals, the form in fish and shellfish is mostly organic As of arsenobetaine (C5H11AsO2). Arsenobetaine is neither metabolized by nor accumulated in humans, and thus, it is considered non-toxic to humans [9].
动物体内砷的积累揭示了不同砷化学形态的重要性。陆地动物含有 0.06–0.4 ppm 的砷，而鱼类和贝类含有 0.78–25 ppm [ 8 ]。尽管鱼类和贝类中的砷含量远高于陆地动物，但鱼类和贝类中的砷形式大多是有机砷砷甜菜碱（C5H11AsO2）。砷甜菜碱在人体中既不代谢也不积累，因此被认为对人体无毒[ 9 ]。

3. Arsenic Metabolic Pathway and Toxicity
3.砷的代谢途径和毒性

3.1. Metabolic Pathway 3.1.代谢途径

Arsenic metabolites exist both in organic and inorganic forms, and both types can exist in either trivalent or pentavalent oxidation states. Thus, there are a variety of molecular species that have different biological effects, which further complicates diagnoses.
砷代谢物以有机和无机形式存在，两种类型都可以三价或五价氧化态存在。因此，存在多种具有不同生物学效应的分子种类，这使得诊断进一步复杂化。

The exact metabolic pathways of As are yet to be confirmed in humans and food animals, although the proposed metabolic pathway of As is shown in Figure 1 [10,11]. Oxidative methylation and glutathione conjugation are believed to be the primary pathways of As metabolism [12,13]. Inorganic As (V) is known to reduce to As (III), which is a prerequisite for methylation in mammals. Inorganic As (III) is methylated to methylarsonic acid (MMA) and dimethylarsinic acid (DMA) by alternating the reduction of pentavalent As to trivalent As (Figure 1). In some species (though not in humans), DMA can be converted into trimethylarsine oxide during oxidative methylation [14].
尽管砷的拟议代谢途径如图 1所示 [ 10 , 11 ]，但砷在人类和食用动物中的确切代谢途径尚未得到证实。氧化甲基化和谷胱甘肽结合被认为是砷代谢的主要途径[ 12 , 13 ]。已知无机 As (V) 会还原为 As (III)，这是哺乳动物甲基化的先决条件。通过五价 As 交替还原为三价 As，无机 As (III) 被甲基化为甲基胂酸 (MMA) 和二甲基胂酸 (DMA)（图 1 ）。在某些物种中（但在人类中则不然），DMA 可以在氧化甲基化过程中转化为三甲基胂氧化物 [ 14 ]。

Figure 1. Proposed metabolic pathways for the conversion of inorganic Aresenic (As) into organic As. The mechanism involved in the oxidation and reduction of As is shown.
图 1.将无机砷 (As) 转化为有机砷的拟议代谢途径。显示了 As 氧化和还原所涉及的机制。

In humans, the bioavailability of inorganic As is 60%–87% [15,16], and inorganic As and its metabolites are mainly excreted in urine and bile. The biological half-life of As is approximately 4 days, depending on the form: arsenite is believed to have a shorter half-life compared to arsenate [17]. The most frequently detected As compounds in human urine are DMA (V) (40%–80%), MMA (V) (10%–25%), and inorganic As (10%–30%) [18,19]. Arsenosugar and/or arsenobetaine are other concerning forms of As that people may be exposed to when eating algae or seafood—these forms are excreted in the urine.
在人体中，无机砷的生物利用度为60%~87%[ 15 , 16 ]，无机砷及其代谢物主要通过尿液和胆汁排泄。砷的生物半衰期约为 4 天，具体取决于形式：亚砷酸盐被认为比砷酸盐的半衰期更短 [ 17 ]。人尿液中最常检测到的砷化合物是 DMA (V) (40%–80%)、MMA (V) (10%–25%) 和无机砷 (10%–30%) [ 18 , 19 ]。砷糖和/或砷甜菜碱是人们在食用藻类或海鲜时可能接触到的砷的其他形式，这些形式会通过尿液排出。

3.2. Toxic LD50 Concentrations
3.2.有毒 LD50 浓度

Methylation is generally considered to be the primary detoxification pathway for inorganic As, however, the toxicity levels of inorganic and organic As metabolites are mixed. For example, several studies have demonstrated that trivalent As is more toxic than the pentavalent state [1]. Trivalent As compounds, As (III), MMA (III), and DMA (III) are thought to interact with thiol groups of proteins and enzymes and inhibit the catalytic activity of enzymes [20]. The toxicity of these metabolites were investigated in Chang human hepatocytes using a lethal dose, 50% (LD50) in the three cytotoxicity assays (LDH, K+ and XTT) [21]. The order of toxicity obtained was as follows: MMA (III) > As (III) > As (V) > MMA (V) = DMA (V). Similar findings were observed in another study in which LD50 concentrations of As (III), As (V), MMA (III), MMA (V), DMA (III), and DMA (V) were 50 µM, 180 µM, 8 µM, 60 mM, 8 µM, and 15 mM, respectively [22]. This stands in contrast to other As chemical species—arsenobetaine and arsenosugar—that were judged as non-toxic. In animal experiments, it was concluded that MMA (III) and DMA (III) are more toxic than inorganic As compounds and induce chromosomal mutations but not gene mutations [23].
甲基化通常被认为是无机砷的主要解毒途径，然而，无机砷和有机砷代谢物的毒性水平是混合的。例如，一些研究表明三价砷比五价态砷的毒性更大[ 1 ]。三价砷化合物 As (III)、MMA (III) 和 DMA (III) 被认为与蛋白质和酶的硫醇基团相互作用并抑制酶的催化活性 [ 20 ]。在三种细胞毒性测定（LDH、K+ 和 XTT）中使用致死剂量 50% (LD50) 在 Chang 人肝细胞中研究了这些代谢物的毒性 [ 21 ]。获得的毒性顺序如下：MMA(III)>As(III)>As(V)>MMA(V)=DMA(V)。在另一项研究中观察到类似的结果，其中 As (III)、As (V)、MMA (III)、MMA (V)、DMA (III) 和 DMA (V) 的 LD50 浓度分别为 50 µM、180 µM、8分别为 µM、60 mM、8 µM 和 15 mM [ 22 ]。这与其他被认为无毒的砷化学物质（砷甜菜碱和砷糖）形成鲜明对比。在动物实验中，得出结论，MMA（III）和DMA（III）比无机砷化合物毒性更大，并且会诱导染色体突变，但不会诱导基因突变[ 23 ]。

The residents of Kamisu City, Japan (n = 157) were orally exposed to diphenylarsinic acid (DPAA; C₁₂H₁₁AsO₂) via the ingestion of contaminated groundwater. Subsequently, a clinical syndrome associated with cerebellar and brainstem symptoms was observed in 20 of the 30 residents who consumed high concentrations of DPAA in the contaminated well water [24]. After this DPAA leak accident, the toxicity of organic and inorganic As were examined using human cervical carcinoma HeLa cells by the Japanese government [25]. Using a relative scale, with the toxic level of DPAA defined as “1,” the levels of As (III), As (V), MMA (V) and DMA (V) were 96, 5.8, 0.18, and 1.0, respectively.
日本神栖市的居民（ n = 157）通过摄入受污染的地下水而口服接触二苯胂酸（DPAA；C ₁₂ H ₁₁ AsO ₂ ）。随后，在饮用受污染井水中高浓度 DPAA 的 30 名居民中，有 20 名居民观察到与小脑和脑干症状相关的临床综合征 [ 24 ]。这次DPAA泄漏事故后，日本政府利用人宫颈癌HeLa细胞检查了有机砷和无机砷的毒性[ 25 ]。使用相对量表，将 DPAA 的毒性水平定义为“1”，As (III)、As (V)、MMA (V) 和 DMA (V) 的水平分别为 96、5.8、0.18 和 1.0 。

4. Toxic Mechanisms 4. 毒性机制

The underlying mechanisms of As-induced neurotoxicity mostly remain unknown, though several mechanisms have been proposed, mainly from animal experiments. Metabolites exert their toxic effect by inactivating a host of enzymes, especially those involved in the cellular energy pathway as well as DNA synthesis and repair [26]. Several mechanisms—oxidative stress, thiamine deficiency, and decreased acetyl cholinesterase activity—seem to play key roles in As-induced neurotoxicity [27,28].
尽管已经提出了几种主要来自动物实验的机制，但砷引起的神经毒性的基本机制仍然未知。代谢物通过使许多酶失活来发挥毒性作用，特别是那些参与细胞能量途径以及DNA合成和修复的酶[ 26 ]。氧化应激、硫胺素缺乏和乙酰胆碱酯酶活性降低等多种机制似乎在砷诱导的神经毒性中发挥着关键作用 [ 27 , 28 ]。

4.1. Mitochondrial Dysfunction
4.1.线粒体功能障碍

One of the most important mechanisms involved in the neurotoxicity of As is its ability to cause oxidative stress and mitochondrial dysfunction [29,30]. Arsenic decreased the activities of mitochondrial complexes I, II-III, and IV in the rat brain and increased the levels of reactive oxygen species (ROS) [31]. The accumulation of ROS is responsible for lipid bi-layer damage and it causes mitochondrial swelling and a drop in the membrane potential [32]. It has also been shown that oxidative stress and mitochondrial dysfunction may cause neurodegeneration [33].
砷神经毒性最重要的机制之一是其引起氧化应激和线粒体功能障碍的能力[ 29 , 30 ]。砷降低大鼠大脑中线粒体复合物 I、II-III 和 IV 的活性，并增加活性氧 (ROS) 的水平 [ 31 ]。 ROS 的积累导致脂质双层损伤，并导致线粒体肿胀和膜电位下降[ 32 ]。研究还表明，氧化应激和线粒体功能障碍可能导致神经退行性变[ 33 ]。

4.2. Lipid Peroxidation 4.2.脂质过氧化

Oxidative stress and the resulting lipid peroxidation are involved in various pathological states including inflammation, atherosclerosis, neurodegenerative diseases, and cancer [34]. Lipid peroxidation is a basic cellular deterioration process induced by oxidative stress [35]. Lipid peroxidation induced by oxidative stress due to As exposure leads to DNA damage and subsequent brain cell death, and it induces the degeneration of the central nervous system (CNS) [36]. In addition, plasma lipid peroxidation has been shown to be positively correlated with As levels in urine [37].
氧化应激和由此产生的脂质过氧化与多种病理状态有关，包括炎症、动脉粥样硬化、神经退行性疾病和癌症[ 34 ]。脂质过氧化是氧化应激诱导的基本细胞恶化过程[ 35 ]。 As暴露引起的氧化应激诱导的脂质过氧化导致DNA损伤和随后的脑细胞死亡，并诱导中枢神经系统（CNS）的退化[ 36 ]。此外，血浆脂质过氧化已被证明与尿液中的砷水平呈正相关[ 37 ]。

4.3. Apoptosis 4.3.细胞凋亡

Apoptosis is a cellular response to maintain normal cell development and proper function of multicellular organisms. Arsenic neurotoxicity involves the induction of apoptosis by activating p38 mitogen-activated protein kinase and JNK3 pathways [38]. In another study using HepaRG cells, the DMA (III) exposure increased the activity of caspase-9, an apoptosis initiator caspase [39]. Exposure to As reduced rat cerebellar neuron viability and induced nuclear fragmentation and condensation as well as DNA degradation to oligonucleosome fragments, which are processes associated with apoptosis. Together, these studies indicate that As-induced apoptosis may be related to As neurotoxicity in humans.
细胞凋亡是维持正常细胞发育和多细胞生物体正常功能的细胞反应。砷的神经毒性涉及通过激活p38丝裂原激活蛋白激酶和JNK3途径诱导细胞凋亡[ 38 ]。在另一项使用 HepaRG 细胞的研究中，DMA (III) 暴露增加了 caspase-9（一种凋亡启动子 caspase）的活性 [ 39 ]。砷暴露会降低大鼠小脑神经元的活力，诱导核断裂和浓缩，以及 DNA 降解为寡核小体片段，这些过程与细胞凋亡相关。总之，这些研究表明砷诱导的细胞凋亡可能与砷对人类的神经毒性有关。

4.4. Increased Calpain 4.4.钙蛋白酶增加

Inorganic As (III) causes compositional changes in sciatic nerve proteins, such as reduction in NF-L expression [40]. Furthermore, in vitro studies with various As metabolites have shown that MMA (V) and DMA (V) affect the expression of neurofilaments and tau genes, but not inorganic As (III) [41]. In animal experiments, As exposure reduced the expression of the neurofilament protein and induced destabilization and disruption of the cytoskeletal framework which may eventually lead to the axonal degeneration of peripheral nerves [42]. It has been speculated that the cleavage of p35 is caused by calpain activation, which is induced by Ca²⁺. The inhibition of calpain by calpeptin prevents the cleavage of p35 to p25. These results suggest that cleavage of p35 to p25 by calpain, likely promotes As-induced Ca²⁺-influx, and therefore, it may be the mechanism by which As induces its neurotoxic effects [41].
无机砷 (III) 会导致坐骨神经蛋白的成分发生变化，例如 NF-L 表达减少 [ 40 ]。此外，各种砷代谢物的体外研究表明，MMA (V) 和 DMA (V) 影响神经丝和 tau 基因的表达，但不影响无机砷 (III) [ 41 ]。在动物实验中，砷暴露降低了神经丝蛋白的表达，并引起细胞骨架框架的不稳定和破坏，最终可能导致周围神经的轴突变性[ 42 ]。据推测p35的裂解是由Ca ²⁺诱导的钙蛋白酶激活引起的。 calpeptin 对钙蛋白酶的抑制可防止 p35 裂解为 p25。这些结果表明，钙蛋白酶将 p35 裂解为 p25，可能会促进 As 诱导的 Ca ²⁺内流，因此，这可能是 As 诱导其神经毒性作用的机制 [ 41 ]。

4.5. Thiamine Deficiency 4.5.硫胺素缺乏症

The deficiency of thiamine (vitamin B1) induces neuronal complications, and As causes thiamine deficiency and inhibits pyruvate decarboxylase [43], an enzyme responsible for converting glucose to energy. Trivalent As inhibits enzyme complexes through ROS. ROS production causes pyruvate dehydrogenase inactivation through oxidation, which can occur at a much lower concentration than arsenite binding directly to the critical thiols [44,45]. Axonal neuropathy, which is similar to beriberi neuropathy or mild Wernicke’s encephalopathy, may be induced by thiamine deficiency and the inhibition of pyruvate decarboxylase due to As exposure.
硫胺素（维生素 B1）的缺乏会引起神经元并发症，而 As 会导致硫胺素缺乏并抑制丙酮酸脱羧酶 [ 43 ]，丙酮酸脱羧酶是一种负责将葡萄糖转化为能量的酶。三价 As 通过 ROS 抑制酶复合物。 ROS 的产生通过氧化导致丙酮酸脱氢酶失活，其发生浓度比直接与关键硫醇结合的亚砷酸盐低得多 [ 44 , 45 ]。轴突神经病与脚气病神经病或轻度韦尼克脑病相似，可能是由于硫胺素缺乏和砷暴露导致的丙酮酸脱羧酶抑制所致。

4.6. Decreased Acetylcholinesterase Activity
4.6.乙酰胆碱酯酶活性降低

Acetylcholinesterase is one of the many important enzymes needed for the proper functioning of the human nervous system. In rats, As trioxide significantly decreased the activity of serum acetylcholinesterase in a dose-dependent manner [46]. The decreased acetylcholinesterase activity caused cholinergic crisis, which may be associated with peripheral neuropathy or CNS damage [28,46]. There are several possible mechanisms of toxicity, and the correspondence between the mechanisms and the symptoms remains unclear.
乙酰胆碱酯酶是人类神经系统正常运作所需的众多重要酶之一。在大鼠中，三氧化二砷以剂量依赖性方式显着降低血清乙酰胆碱酯酶的活性[ 46 ]。乙酰胆碱酯酶活性降低引起胆碱能危象，这可能与周围神经病变或中枢神经系统损伤有关[ 28 , 46 ]。有几种可能的毒性机制，但机制与症状之间的对应关系仍不清楚。

5. Clinical Neurological Symptoms
5. 临床神经症状

Peripheral neuropathy due to chronic As exposure is caused by drinking water with As concentrations as low as 10–50 ppb [6]. The resulting impairment is observed predominantly in sensory fibers, and less so in motor fibers [5,47]. Sural nerve biopsies revealed a reduction in both small myelinated and unmyelinated fibers, which occurred with the axonal degeneration of peripheral nerves [47,48]. CNS impairment may occur at 50 ppb or more in children [49], though in adults, CNS impairments are only known to be caused by As exposure at high concentrations [50]. Peripheral neuropathy due to As exposure may recover in the long term, however, CNS impairments are less likely to recover. Organ damage is related not only to As exposure concentrations, but also to acute or chronic factors (Figure 2).
慢性砷暴露引起的周围神经病变是由砷浓度低至 10-50 ppb 的饮用水引起的 [ 6 ]。由此产生的损伤主要出现在感觉纤维中，而运动纤维中则较少[ 5 , 47 ]。腓肠神经活检显示小有髓鞘和无髓鞘纤维均减少，这与周围神经的轴突变性有关[ 47 , 48 ]。儿童中的中枢神经系统损伤可能会在 50 ppb 或更高浓度下发生 [ 49 ]，但在成人中，中枢神经系统损伤已知仅是由高浓度砷暴露引起的 [ 50 ]。砷暴露引起的周围神经病变可能会在长期内恢复，但中枢神经系统损伤则不太可能恢复。器官损伤不仅与砷暴露浓度有关，还与急性或慢性因素有关（图2 ）。

Figure 2. Duration and concentration of As pollution and As exposure incidents. Speculated thresholds for organ impairments are shown as a thick gray dotted line.
图 2.砷污染和砷暴露事件的持续时间和浓度。器官损伤的推测阈值显示为粗灰色虚线。

5.1. Acute As Poisoning 5.1.急性中毒

Oral exposure to As is associated with gastrointestinal symptoms including cramps, nausea, vomiting, and diarrhea and with cardiovascular and respiratory symptoms such as hypotension, shock, pulmonary edema, and heart failure [51]. In acute As poisoning, death is usually due to cardiovascular collapse and hypovolemic shock. The fatal human dose for ingested As trioxide is 70–300 mg [18,26]. After the ingestion of a lethal dose, death occurs after 12–24 h. Acute As exposure also includes neurological symptoms such as light-headedness, delirium, encephalopathy, muscle weakness or cramping, and peripheral neuropathy [52]. Peripheral neuropathy occurs as symmetrical sensory-motor polyneuropathy one or more weeks after the initial toxic exposure, which usually shows axonal degeneration but sometimes shows demyelinating polyradiculoneuropathy-like Guillain–Barré syndrome [53].
口服砷与胃肠道症状（包括痉挛、恶心、呕吐和腹泻）以及心血管和呼吸道症状（如低血压、休克、肺水肿和心力衰竭）有关[ 51 ]。急性砷中毒时，死亡通常是由于心血管衰竭和低血容量性休克。人体摄入三氧化二砷的致命剂量为 70–300 毫克 [ 18 , 26 ]。摄入致死剂量后，12-24 小时后就会死亡。急性砷暴露还包括神经系统症状，如头晕、谵妄、脑病、肌肉无力或痉挛以及周围神经病变[ 52 ]。周围神经病变在初次中毒暴露后一周或几周内以对称性感觉运动性多发性神经病的形式发生，通常表现为轴突变性，但有时表现为脱髓鞘性多发性神经根神经病，如吉兰-巴利综合征[ 53 ]。

5.2. Toroku As Pollution 5.2.作为污染的Toroku

Toroku is a small village in a narrow valley in Miyazaki prefecture, Japan with a total population of less than 300. Arsenic was mined intermittently and refined at the Toroku mine between 1920 and 1941 and between 1955 and 1962. The roasters used at the mine’s refinery were primitive and lacked dust-collecting systems. Therefore, residents were exposed to very high concentration of As via air, food, water, and skin contact. Dozens of people died at a young age, mainly the workers and residents near the mine. Although As concentrations in the environment were not measured until 1962, they were investigated by Miyazaki prefecture in 1972 [54]. The average As concentrations in the neighboring soil and in the water percolating from the slag were 2,760 mg/kg and 180 mg/L, respectively.
Toroku 是日本宫崎县一个狭窄山谷中的一个小村庄，总人口不到 300 人。1920 年至 1941 年间以及 1955 年至 1962 年间，Toroku 矿间歇性开采和精炼砷。该矿精炼厂使用的焙烧炉原始且缺乏除尘系统。因此，居民通过空气、食物、水和皮肤接触接触到非常高浓度的砷。数十人年纪轻轻就死亡，主要是矿井附近的工人和居民。尽管直到 1962 年才测量环境中的砷浓度，但宫崎县于 1972 年对其进行了调查[ 54 ]。邻近土壤和炉渣渗滤水中的平均砷浓度分别为 2,760 毫克/千克和 180 毫克/升。

Since 1974, Miyazaki prefecture has been conducting medical examinations for residents in the district, and according to the data, subjective symptoms such as sensory disturbances, skin lesions, upper airway symptoms, hearing impairments and dizziness have been present in over 85% of chronically exposed patients [5]. In terms of sensory impairments, only 30% of the patients were judged to be objectively abnormal by neurological examination. Studies using somatosensory-evoked potentials showed that the prolongation of the central sensory conduction time, which indicates sequelae in the CNS, may remain even after more than 40 years post-As exposure [50]. Similarly, more than 40 years after the final As exposure, 50% of the residents had hearing impairment, however, no significant differences were observed in auditory brainstem response from the normal group [55]. In the determination of sequelae in elderly patients, it is difficult to distinguish them from typical age-related phenomena.
自1974年起，宫崎县就对该地区居民进行体检，数据显示，超过85%的长期接触者存在感觉障碍、皮肤损伤、上呼吸道症状、听力障碍、头晕等主观症状。患者[ 5 ]。在感觉障碍方面，只有30%的患者经神经系统检查判断为客观异常。使用体感诱发电位的研究表明，中枢感觉传导时间的延长（表明中枢神经系统的后遗症）甚至可能在砷暴露后 40 多年后仍然存在[ 50 ]。同样，在最终砷暴露40多年后，50%的居民出现听力障碍，但与正常组的听觉脑干反应没有观察到显着差异[ 55 ]。在确定老年患者的后遗症时，很难将其与典型的年龄相关现象区分开来。

5.3. Arsenic Poisoning in Morinaga Dry Milk
5.3.森永奶粉砷中毒

In the early summer of 1955, physicians in the western part of Japan became worried about outbreaks of an unusual disease characterized by anorexia, skin pigmentation, diarrhea, vomiting, fever, and abdominal distention among infants, most less than 12 months of age [56]. It was determined that Arsenic (V) was inadvertently added to powdered milk products made by the Tokushima plant of the Morinaga Milk Industry. The company used an alternative low-cost industrial dibasic sodium phosphate as a stabilizer which was added to the infant powdered milk products. It was found that As was also used as a catalyst in the manufacturing process. The As concentration in the milk was 4–7 mg/L (4000–7000 ppb) [56]. The As intake for the exposed infants was estimated to be 1.3–3.6 mg/day, and the total intake was estimated to be 90–140 mg. In a long-term follow-up study, skin disorders such as keratosis, as well as central nervous disorders such as deafness, mild brain damage, mental retardation, and epilepsy remained [56,57]. Generally speaking, neurological impairment induced by As has been reported as peripheral neuropathy [4,5,58]. However, in the Morinaga milk incident, severe CNS impairments were induced, likely due to the very high concentration of As and the immature blood-brain-barrier of the infants.
1955 年初夏，日本西部地区的医生开始担心婴儿中会爆发一种不寻常的疾病，其特征是厌食、皮肤色素沉着、腹泻、呕吐、发烧和腹胀，大多数婴儿不到 12 个月大 [ 56] ]。经确定，森永乳业德岛工厂生产的奶粉中无意中添加了砷（V）。该公司使用替代的低成本工业磷酸氢二钠作为稳定剂添加到婴儿奶粉产品中。人们发现砷在制造过程中也被用作催化剂。牛奶中砷的浓度为 4–7 mg/L (4000–7000 ppb) [ 56 ]。暴露婴儿的砷摄入量估计为 1.3-3.6 毫克/天，总摄入量估计为 90-140 毫克。在一项长期跟踪研究中，角化病等皮肤疾病以及耳聋、轻度脑损伤、智力低下和癫痫等中枢神经疾病仍然存在[ 56 , 57 ]。一般来说，砷引起的神经功能损害已被报道为周围神经病变[ 4,5,58 ]。然而，在森永牛奶事件中，可能由于砷浓度极高和婴儿血脑屏障不成熟，导致了严重的中枢神经系统损伤。

5.4. Arsenic Contamination in Groundwater
5.4.地下水砷污染

Unfortunately, As contamination in groundwater is now a common phenomenon being reported from various countries, including Bangladesh, India, Myanmar, Argentina, Chile, China, Hungary, Mexico, Nepal, Taiwan, the United States, and others. At least 140 million people from 50 countries are exposed to As through low-dose As-contaminated groundwater at levels above 10 ppb [3]. Several studies have shown that As exposure induces peripheral neuropathy or neuritis [4,58,59,60]. The type of neuropathy caused by such extremely long exposure to low As concentrations in water has gradually become clear over the last decade. For neurological impairments, it has been suggested that mild peripheral neuropathy may occur by drinking As-contaminated water at the level of 10 ppb [6]. On the other hand, there is no study showing that CNS impairments occur due to drinking As-contaminated groundwater in adults [4,6,61] except the DPAA exposure of the Kamisu city incident [24]. In a study in Cambodia, neurobehavioral function was found to be affected in the group of children that consumed more than 50 ppb of As-contaminated drinking water compared to those in the normal control groups [49]. The long-term prognosis for the above impairments is unknown.
不幸的是，地下水污染现已成为孟加拉国、印度、缅甸、阿根廷、智利、中国、匈牙利、墨西哥、尼泊尔、台湾、美国等国家的普遍现象。来自 50 个国家的至少 1.4 亿人通过浓度高于 10 ppb 的低剂量砷污染地下水接触到砷[ 3 ]。多项研究表明砷暴露会诱发周围神经病变或神经炎[4,58,59,60 ] 。在过去的十年中，由于长时间接触低砷浓度的水中而引起的神经病变类型已逐渐变得清晰。对于神经系统损伤，有人建议饮用 10 ppb 水平的 As 污染水可能会导致轻度周围神经病变 [ 6 ]。另一方面，除了神栖市事件中的 DPAA暴露外，没有研究表明成年人因饮用受 As 污染的地下水而导致中枢神经系统损伤 [4,6,61 ] 。柬埔寨的一项研究发现，与正常对照组相比，饮用砷污染饮用水超过 50 ppb 的儿童组的神经行为功能受到影响 [ 49 ]。上述损伤的长期预后尚不清楚。

6. Exposure Dose–Response Relationship in Various Organs
6. 各器官的暴露剂量-反应关系

Exposure dose–response relationships of As have been described in previous studies [62]. There are significant As exposure dose–response relationships for the occurrence of skin lesion, internal malignancies, vascular diseases, and elevated hepatic enzyme levels [62,63,64]. However, the comparisons of these studies are difficult because the exposure period is different among these studies, and acute and chronic As exposure have distinct clinical symptoms [26]. Furthermore, the longer the exposure period, the lower is the threshold at which organ impairments might occur (Figure 2) [26,61]. However, the damage and the mechanism of the effects of high As concentrations with short-term exposure would be different from those of low concentrations with long-term exposure.
先前的研究已经描述了砷的暴露剂量-反应关系[ 62 ]。砷暴露与皮肤病变、内部恶性肿瘤、血管疾病和肝酶水平升高的发生存在显着的剂量反应关系[62,63,64 ] 。然而，这些研究的比较很困难，因为这些研究的暴露时间不同，而且急性和慢性砷暴露具有不同的临床症状[ 26 ]。此外，暴露时间越长，可能发生器官损伤的阈值就越低（图2 ）[ 26 , 61 ]。然而，高浓度砷短期暴露与低浓度长期暴露的损害和影响机制会有所不同。

In the studies of chronic As exposure, an increased prevalence of skin lesions was observed in people drinking As-contaminated groundwater at a level of 5–10 ppb [62,65]. In the analysis of internal malignancies and As exposure, the dose–response relationships for the occurrence of lung, bladder, and kidney cancers were linear [62,66,67]. A threshold level for inorganic As in the drinking water for these cancers is estimated to be between 50 and 150 ppb [68]. In a survey of 1,185 people in the United States, those who consumed As-contaminated water of more than 10 ppb were statistically more likely to report a history of circulatory problems [69]. Long-term exposure to As from drinking water has been shown to have a dose–response relationship with an increased risk of diabetes, mellitus, and hypertension [70]. A significant As exposure dose–response relationship was also observed in serum hepatic enzyme levels, with statistically higher levels found in subjects who consumed As-contaminated water of more than 34 ppb [63]. In the context of neurological impairments, subjective neurological impairments occurred at As contamination levels of around 10 ppb, and objective peripheral nerve disturbances occurred at more than 50 ppb [6].
在慢性砷暴露的研究中，在饮用砷污染浓度为 5-10 ppb 的地下水的人中，观察到皮肤损伤的患病率增加 [ 62 , 65 ]。在对内部恶性肿瘤和砷暴露的分析中，肺癌、膀胱癌和肾癌发生的剂量反应关系是线性的[62,66,67 ] 。这些癌症的饮用水中无机砷的阈值水平估计在 50 至 150 ppb 之间 [ 68 ]。在对美国 1,185 人进行的一项调查中，饮用砷污染水超过 10 ppb 的人在统计上更有可能报告有循环系统问题的病史 [ 69 ]。长期接触饮用水中的砷已被证明具有剂量反应关系，会增加患糖尿病、糖尿病和高血压的风险[ 70 ]。在血清肝酶水平中也观察到了显着的砷暴露剂量-反应关系，在饮用砷污染水超过 34 ppb 的受试者中发现具有统计学上更高的水平[ 63 ]。在神经损伤的情况下，当砷污染水平约为 10 ppb 时，会出现主观神经损伤，当砷污染水平超过 50 ppb 时，会出现客观周围神经障碍 [ 6 ]。

7. Effect on Children 7. 对儿童的影响

There are no conclusions as to whether the intake of low concentration As-contaminated drinking water adversely affects the brain of children. An epidemiological study indicated that CNS impairments such as cognitive or intellectual deficits were associated with As exposure in children [71,72,73]. However, a study in West Bengal showed no association between long-term As exposure in water and intellectual functions in children [74].
关于摄入低浓度砷污染饮用水是否会对儿童大脑产生不利影响，目前尚无定论。一项流行病学研究表明，认知或智力缺陷等中枢神经系统损伤与儿童接触砷有关[71,72,73 ] 。然而，西孟加拉邦的一项研究表明，长期接触水中的砷与儿童智力功能之间没有关联[ 74 ]。

To discuss the effect of As exposure on children, we will contrast a few differences between adults and children. First, exposure durations in children are shorter than those in adults. If toxic effects are cumulative, adults would be affected more severely than children. Second, children may have a higher As methylation capacity than adults [75,76], resulting in more efficient detoxification [76] and a lower incidence of neuropathy. In fact, in the case of the Wakayama curry-poisoning cases, the majority of the children were in the process of recovery approximately 1 week to 10 days after the high dose As-contaminated curry intake, whereas the poisoning symptoms in adults were exacerbated [77]. Third, compared with adults, children have an immature defense system of the blood–brain–barrier against toxic substances. Therefore, CNS damage due to As may occur easily in children. Therefore, when determining the reference value of drinking water, it is necessary to carefully consider whether the value for children is the same as that for adults.
为了讨论砷暴露对儿童的影响，我们将对比成人和儿童之间的一些差异。首先，儿童的暴露时间比成人短。如果毒性作用累积，成人受到的影响将比儿童更严重。其次，儿童可能比成人具有更高的 As 甲基化能力 [ 75 , 76 ]，从而导致更有效的解毒 [ 76 ] 和更低的神经病变发生率。事实上，在和歌山咖喱中毒事件中，大多数儿童在摄入高剂量受砷污染的咖喱后约1周至10天处于恢复过程，而成人的中毒症状则加剧。 77 ]。第三，与成人相比，儿童针对有毒物质的血脑屏障防御系统尚不成熟。因此，儿童很容易发生砷引起的中枢神经系统损伤。因此，在确定饮用水的参考值时，需要仔细考虑儿童的值是否与成人相同。

8. Factors to Consider 8. 需要考虑的因素

When considering the effects of As on humans, the degree of injury varies depending on the route, concentration and duration of exposure, the total amount, and the target organ. Patient factors such as nutrition, age and general health status may also amplify or diminish the ill effects of As exposure [78]. The protection provided to the CNS by the blood–brain barrier is impaired if exposed to high concentrations, however, if exposed to low concentrations, damage may not occur easily, even if exposed for a long time. Among the damaged organs are those that can be expected to regenerate, such as peripheral nerves and the liver, and those that are difficult to regenerate, such as the CNS. It is also necessary to consider the effects of heavy metals other than As. At the As polluted area, there is often contamination with other toxic heavy metals such as lead, manganese, cadmium, chromium, uranium, and copper [49,54,79] which may have compounding effects on As contamination.
当考虑砷对人体的影响时，伤害程度因暴露途径、浓度和持续时间、总量和靶器官而异。营养、年龄和一般健康状况等患者因素也可能放大或减少砷暴露的不良影响[ 78 ]。如果暴露在高浓度下，血脑屏障对中枢神经系统的保护作用会受到损害，但如果暴露在低浓度下，即使长时间暴露，也不容易发生损害。受损的器官包括那些可以再生的器官，例如周围神经和肝脏，以及那些难以再生的器官，例如中枢神经系统。还需要考虑As以外的重金属的影响。在砷污染地区，经常存在其他有毒重金属的污染，如铅、锰、镉、铬、铀和铜[ 49,54,79 ]，这些重金属可能对砷污染产生复合效应。

9. Conclusions 9. 结论

Arsenic-contaminated drinking water has long been a global problem, especially in South Asia. To evaluate the health damage caused by heavy metals in drinking water, we estimated the residents’ clinical findings based on past data. However, several factors such as exposure route, As quantity, characteristics of the patients and their organs are intricately intertwined. The emerging symptoms are often nonspecific and the diagnoses require a different public health approach than the conventional clinical approach. To determine whether health problems in certain residents or patients caused by As, a multifaceted approach is needed, including not only clinicians but also specialists from multiple fields.
饮用水砷污染长期以来一直是一个全球性问题，特别是在南亚。为了评估饮用水中重金属对健康造成的损害，我们根据过去的数据估算了居民的临床结果。然而，暴露途径、砷数量、患者及其器官的特征等几个因素错综复杂地交织在一起。新出现的症状通常是非特异性的，诊断需要采用与传统临床方法不同的公共卫生方法。为了确定某些居民或患者的健康问题是否由砷引起，需要采取多方面的方法，不仅包括临床医生，还包括来自多个领域的专家。