Arsenic: Useful Yet Poisonous at Any Level
Arsenic (As) is the culprit in the largest poisoning of a population in history . The purpose of this paper is to describe this event that occurred in the late 20th century in Bangladesh and to review the history and present status of As poisoning in the global economy. Exposure to inorganic and organic As compounds from water, soil, and air pollution is a major public health problem that affects hundreds of millions of people worldwide, often without them being aware of the exposure. Many cases of such contamination are known, but none so extensive as that in Bangladesh. Increased mortality rates from chronic diseases in As-exposed populations have been reported in the U.S., Canada, Argentina, China, Chile, India, Taiwan, Bangladesh, and other nations [2-6]. Poisoning in these studies is mainly from drinking water contaminated by As, but is often found in areas contaminated by mining wastes.
Yellowknife, Northwest Territories, Canada provides an unfortunate example of the negative externality effects of As contamination during gold mining and processing during a period in the mid-20th century when few environmental controls were in place. The Yellowknife example will be described with the recognition that such contamination still exists in many cases globally where legislative regulations do not exist or are weakly enforced. Arsenic emissions with negative health effects are present in many mining and smelting operations worldwide involving sulfide ores .
Three additional cases of As exposure will be discussed: (1) the Bangladesh example, (2) exposure of a specific population in Chile to a high level of As in their drinking water for a known length of time, and (3) exposure of a large area in China to As contamination from industrial activity. China is of interest because a major share of arsenic trioxide (As2O3) production globally comes from that nation. In 2012, China produced 26,000 metric tons (mt); Chile, 10,000 mt; Morocco, 8000 mt; and all others < 2600 mt of As2O3. Arsenic metal and As2O3 have not been produced in the U.S. since 1985 . Arsenic pollution in China has been largely uncontrolled for many decades providing many examples of contamination of water, soil, and air. Finally, the effectiveness of traditional separation systems in recovering As from contaminated solutions will be evaluated and the case will be made that simplified green engineering/green chemistry approaches need to be developed to achieve effective As remediation.
What is Safe Arsenic Exposure in Drinking Water?
The simple and correct answer to the question about a safe exposure level of As in drinking water is zero. However, this is neither practicable nor enforceable. The U.S. Environmental Protection Agency (EPA) has summarized the situation as follows : In 1974, Congress passed the Safe Drinking Water Act. This law requires EPA to determine the level of contaminants in drinking water at which no adverse health effects are likely to occur. These non-enforceable health goals, based solely on possible health risks and exposure over a lifetime with an adequate margin of safety, are called maximum contaminant level goals (MCLG). Contaminants are any physical, chemical, biological or radiological substances or matter in water. The MCLG for arsenic is zero. EPA has set this level of protection based on the best available science to prevent potential health problems. Based on the MCLG, EPA has set an enforceable regulation for arsenic, called a maximum contaminant level (MCL), at 0.010 mg/L [10 µg/L] or 10 ppb. MCLs are set as close to the health goals as possible, considering cost, benefits and the ability of public water systems to detect and remove contaminants using suitable treatment technologies.
The MCL value of 10 µg/L for As became effective in 2002. Previously, the value had been 50 µg/L. The lower value of 10 µg/L is recommended by the World Health Organization (WHO) and other international bodies . However, the 50 µg/L level is still a goal to be achieved in many nations, including Bangladesh, West Bengal, India, China, and parts of South America. As will be pointed out, the potential environmental and public health cost of not achieving the lower goal is very large.
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Yellowknife, Northwest Territories, An Unfortunate Example of Negative Externality
Jamieson  presents an insightful discussion of the Giant Au mine of Yellowknife, Northwest Territories, that operated for about fifty years until its closure in 1999 leaving a complex legacy of As contamination and an estimated remediation cost of almost one billion Canadian dollars. It is estimated that the Au recovered from the Giant mine totaled CAD$2.75 billion. The history of the mine provides a remarkable example of how relations among mining companies, local population, and government authorities have evolved over the past 75 years. Local Aboriginal communities were not consulted when the mine was established even though they were affected by As contamination along with other community members. A Dene child died of As poisoning in 1951 resulting in installation of pollution controls. However, emissions and spills of As continued. An estimated 20,000 tons of As were released through stack emissions in the early years of the mine. Over the lifetime of the mine, most of the As2O3 emitted was collected and stored in underground chambers. This stored As2O3 is, perhaps, the largest concentrated source of As on Earth, and is a potential source of As contamination to groundwater and surface water . Giant mine went into receivership in 1999 and is now considered an abandoned mine with environmental liability being the responsibility of the public.
Beginning in 1951, tailings were deposited into several former lakes on mine property. Tailings dams and several impoundments were later constructed. Arsenic concentrations in tailings ranges from 1,100 to 5,000 mg/kg with an average of about 2,700 mg/kg. Jamieson  has described these storage facilities and has discussed the danger they hold for the surrounding environment. Palmer, et al.  analyzed surface water samples in 2012-2014 for As and a variety of other constituents from 98 lakes in a 40-km radius centered on the roaster stack of the Giant mine. Arsenic concentrations varied considerably between lakes within the study area (0.5 – 646 µg/L) and exceeded the drinking water standard of 10 µg/L for 45% of the lakes sampled. Concentrations of As declined sharply as a function of distance from the roaster stack at the Giant mine. Beyond 17 km, little As is deposited. There is considerable concern by the local population over As pollution of the culinary water supply, as might be expected. This is expressed in newspapers and on the internet.
Jamieson  observes that the economy of Yellowknife has been fueled for the past 15 years by diamond mining under environmental controls and community participation in a way that would have been unimaginable in the 1950s for the Giant mine. Waste generation as occurred with the Giant mine is an unfortunate example of negative externality. The burden of cleaning up the waste and any residual human/animal health effects are borne by society because of default by previous mine owners. Since metals are indestructible, can change their form, and move through ecological systems in uncontrolled, and often unpredictable ways when exposed to environmental conditions, the economic cost can be large. In this case, nearly half of the value of the Au produced. It is apparent that if the cost for As remediation had been added to the capital/operating costs for the mining operation the mining of the Au ore would have been problematic. However, as is usually done in mining operations, following mine closure, the responsibility for the extensive environmental and health damage devolved onto the local community. As indicated, the dollar amounts are very high, the stored As is a liability because it cannot be marketed, and the As that leaks into the environment from all causes is large and continuous with no adequate method for containing it. During operation, extremely large quantities of As were dispersed to the environment in addition to that collected and stored. Stack emissions of As2O3 decreased from more than 7 to 0.1 tonnes per day from 1949 to 1990, as As control measures were installed. The greater part of the emissions occurred prior to 1975. Total As2O3 emissions were estimated to be 20,824 tonnes.
Arsenopyrite-bearing Au ore was roasted from 1949 to 1999 as a pretreatment for cyanidation to recover the Au. The most important consequence of ore roasting at Giant, in terms of the environmental legacy, was the production of approximately 300,000 tonnes of As2O3 as waste during a time of few emission controls, few regulations, and limited options regarding re-use of the As2O3. Most of the Au in the Giant mine was refractory, incorporated sub-microscopically within aresenopyrite. The subsequent ore roasting step converted the As to As2O3 which led to large amounts of As2O3 being dispersed by stack emissions and accumulation of even larger amounts of As2O3 in the underground storage chambers. Production of ~300,000 tons of As2O3 as waste in a remote area created marketing problems. Arsenic is a valuable commodity and could have been marketed during the lifetime of the mine for use in herbicides, insecticides, or as chromated copper arsenate preservatives for pressure treating of lumber. These markets were active during the time the Giant mine was in operation but were not accessed. Recent worldwide tightening of regulations regarding As have made these markets much less available. A potential resource has become an environmental liability.
Arsenic Responsible for Largest Poisoning of a Population in History
According to the World Health Organization (WHO) , the largest poisoning of a population in history occurred in the latter part of the 20th century in Bangladesh because of contamination of groundwater by As. Bangladesh is one of the most densely populated countries on Earth with 165 million people (December 2017) and an annual growth rate of 1.6%. Thirty-one percent of the population lives below the national poverty line of USD$2/day (2010), the proportion of employed population below USD$1.90 purchasing power a day is 73.5% (2010), and for every 1000 babies born in 2015, 31 died before their first birthday . Bangladesh at 143,998 square kilometers (km2) is 1.2 times as large as Pennsylvania at 119,283 km2. Most of the nation consists of a delta plain fed by many large rivers flowing from the Himalayas. This plain is subject to flooding from these rivers and typhoons that regularly strike the country. The rivers over time have carried minerals containing As from distant mountains into the delta where they have been deposited and have contaminated the underlying aquifers. The As in these aquifers is not evenly distributed so neighboring regions may contain quite different concentrations of the metal.
Between 35 million and 75 million people in Bangladesh and many millions more in neighboring West Bengal, India are at risk of drinking water contaminated with As [1,12]. This situation resulted from a humanitarian effort with the best of intentions by WHO and others to provide a fresh water supply to the population decades ago. WHO officials in the late 20th century were successful in installing millions of tube-wells in Bangladesh that tapped into underground aquifers and provided instant fresh water to the delight of the population. The tube-wells consisted of tubes 5 cm in diameter that were inserted into the ground at depths of usually less than 200 meters. The tubes were capped with a cast iron or steel hand pump. The tube-wells were affordably priced at about USD$100 each. This effort was widely hailed as a great humanitarian accomplishment since it virtually eliminated the prevalent morbidity and mortality from gastrointestinal disease that had earlier constantly plagued much of the population and contributed to high mortality rates, especially among children. The affected population embraced the tube-wells with great enthusiasm because they provided a source of clean, fresh water that they had not had access to previously and their health improved dramatically. The tube-wells were initially installed in large numbers during the 1970s by the United Nations Children’s Fund (UNICEF) working with the Department of Public Health Engineering . During the 1980s, UNICEF support decreased as the private sector was able to supply and install millions more. UNICEF announced in 1997 that it had surpassed its goal of providing 80% of the population with access to safe drinking-water in the form of tube-wells. The number of tube-wells in Bangladesh is estimated to be from 8 to 12 million . In rural areas, 97% of the population relies on tube wells installed since the 1970s .
At the time these wells were installed beginning about 1970, As was not recognized as a problem in water supplies and, therefore, water testing procedures did not include tests for As. There is a latency period, sometimes lasting decades, between exposure to low levels of As and the onset of disease symptoms. In 1987, several cases of As-induced skin lesions were identified in Bangladesh. After ruling out other causes, water sources used by the patients were analyzed and the diagnosis of As-caused disease was confirmed. The magnitude of As contamination in Bangladesh was first realized in 1998 when an international conference on As was held at Dhaka, Bangladesh . A report from the conference stated that tens of millions of people were at risk for health effects and that 43,000 of 68,000 villages were at risk or could be at risk in the future. WHO personnel predicted that, within a few years, death across much of southern Bangladesh (1 in 10 adults) could be from cancers triggered by As.
The government of Bangladesh has made access to safe drinking water for its population a priority agenda item. Yunus, et al.  discuss this effort, but observe that pockets of the population continue to suffer from As toxicity due to contaminated water supplies. In one study, 50 of 64 districts were found to have groundwater As concentrations exceeding 50 mg/L . Another study showed 25% of the sample population had As-associated skin lesions. A second source of As poisoning is ingestion of As-contaminated food . Increased levels of As have been found in crops commonly grown in Bangladesh, including different varieties of rice, an important food source for the population. Rice selectively accumulates As from the environment in which it is grown. Rice is cooked with water from the tube wells affording additional opportunity for increasing the quantity of As in the final product.
In 2015, Chakraborti, et al.  summarized progress in attacking the As problem in Bangladesh as follows: At present due to mitigation efforts by the government, non-governmental organizations and international aid agencies, many individuals living in contaminated areas of Bangladesh have been drinking low levels of arsenic contaminated water. Also, our recent survey in arsenic-affected villages of Bangladesh show young children in affected areas up to 10 years are mostly free from arsenical skin lesions and new patients with skin lesions are few. During 1995 to 2002, in each survey we identified hundreds of severe arsenic patients. This indicates that now villagers are not exposed to highly arsenic contaminated water. This does not mean future generations are free from arsenic danger. One method used for over 20 years to distinguish relatively safe wells from contaminated ones was to paint those wells with As levels >50 µg/L red and those with As levels <50 µg/L green. People were advised to obtain water for drinking and food preparation from the green wells. One can imagine that determining which of 8-12 million wells fits in which category and painting these wells are near-impossible tasks, but what are the choices? No one wants to give up the fresh water they have. Remarkable progress has been made but the risk of As poisoning from drinking water in Bangladesh and West Bengal is still high. The latency period of As poisoning after exposure can be decades which compounds the problem.
Flanagan, et al.  estimated the economic losses in Bangladesh resulting from the As-related mortality burden over the next 20 years to be $USD 12.5 billion assuming an As exposure of >10 µg/L. These authors point out the advisability of reducing exposure of the population to high As levels by treatment of the water. They estimate that the cost of such treatment costs would be a fraction of the economic losses that would result from continued As exposure and the health benefits to generations not yet born would be incalculable. This estimate, of course, will rise if the exposure level considered is 50 µg/L or more. In 2009, the Bangladesh Multiple Indicator Cluster Survey (MICS) tested drinking water for As in 15,000 randomized households nationwide . For the national population of 164 million, it was estimated that 22 million and 5.6 million were drinking water with As concentrations of >50 ppb and >200 ppb, respectively. Similar results were obtained in a survey in 2011.
Arsenic Poisoning in Chile
In the late 1950s, river water from the nearby Andes Mountains containing high concentrations of naturally occurring arsenic was diverted to the largest city in northern Chile (Antofagasta) for drinking. This resulted in a 13-year period (1958–1970) with an average arsenic concentration of 860 µg/L in the city’s water supply. Installation of a treatment plant in 1970 reduced these concentrations to less than 10 µg/L which has continued to the present time. Because of its unique geology, limited water sources, and good historical records, lifetime exposure and long-term latency patterns can be assessed in this area with better accuracy than in other arsenic-exposed areas worldwide. Also, there is relatively little movement geographically among the population. The use of a water supply containing extremely high As levels illustrates how limited knowledge was in the 1950s about the toxicity of As. Northern Chile is the driest inhabited place on Earth. Because of the small number of water sources, lack of alternative water supplies, and good historical records, estimates of lifetime exposure to As can be generated that are more accurate than those from other large, highly exposed areas worldwide. Since the latency period between exposure and cancer onset is several decades or more and the population is relatively stable over time, it has been possible to study long-term latency patterns of As-related lung, bladder, and kidney cancers in this area .
Steinmaus, et al.  report evidence of four-fold increases in lung cancer and almost seven-fold increases in bladder cancer 35 to 40 years after high As exposures ended in the affected Chilean population. Ferreccio, et al.  found, in the same population, strong evidence that ingested As causes kidney and urethra transitional cell-carcinomas. These authors emphasize that based on the knowledge gained in Chile there is a need to reduce exposures for the millions of people who continue to drink As-contaminated water worldwide. Steinmaus, et al.  suggest that the results can be helpful to public health agencies in planning long-term strategies and obtaining resources needed to reduce long-term impacts of As-related disease. The mechanism by which As may increase long-term cancer risks is unknown, but may be linked to genetic changes induced by this toxic metal [4,15].
Could As poisoning such as that seen in Bangladesh and Chile happen in the U.S.? The United States Geological Survey (USGS) thinks so. In a study released by USGS dated October 18, 2017 it was estimated that about 2.1 million people in the contiguous U.S. may be getting their drinking water from private domestic wells, many of which are considered to have high concentrations of As, presumed to be from natural sources . Joe Ayotte, a USGS hydrologist and lead author of the study comments: About 44 million people in the lower 48 states use water from domestic wells. While we’re confident our research will help well owners understand if they live in an area of higher risk for arsenic, the only way for them to be certain of what’s in their water is to have it tested. After the experiences in Bangladesh and Chile, testing domestic water wells for As does sound like a good idea. Ayotte and his co-workers developed a statistical model based on water samples from more than 20,000 domestic wells that estimates the probability of having high As in domestic wells in a specific area. Some of the areas where it is predicted that people are likely to have high-levels of As in private domestic well water include much of the West, parts of the Northeast and Midwest, and some of the Atlantic southeast coastal states.
Arsenic Pollution in China
Jiang, et al.  point out that consumption of China’s mineral resources has grown rapidly as its industrial base and economy have developed in recent decades. The rapid development of China’s industry has not been without growth problems including tremendous damage to the environment. Heavy metal concentrations are high in the air, water, and soil around enterprises of nonferrous metallurgy, lead acid battery, coal-fired power plant, cement, and ferrous metallurgy operations. Varying degrees of heavy-metal pollution of underground water and soil in these areas affect crop growth, the security of drinking water, and the health of people living in the vicinity. Jiang, et al.  emphasize that environmental consciousness of people in China is also growing, causing them to pay more attention to their living environment. Chinese people are as interested as anyone else in having clean air, a drinkable water supply, and a pollution-free environment and are working toward that goal.
Arsenic is an important contaminant in heavy metal pollution found in China today [18,19]. Jiang, et al.  cite a study in which 39,514 wells were examined in areas where the drinking water was seriously poisoned by As. They state: If the number 50 µg/L is taken as the safety standard for maximum allowable arsenic concentration in drinking water, arsenic concentrations in Shanxi Province were over the limit by 50%. This province was followed by Jilin province (12.21%), Inner Mongolia province (11.30%), Qinghai province (8.33%), Xinjiang province (4.77%), and Ningxia province (21.06%). The number of wells that exceed WHO standards for arsenic in drinking water (10 µg/L) will be much greater, which is of great concern to people who live in the area. The high concentration of As in drinking water from wells in China portends increased incidence of a variety of chronic diseases in the future based on experiences in Bangladesh, Chile, West Bengal, and elsewhere.
Arsenic pollution in soil due to mining operations is also very serious in China. Jiang, et al.  describe one area as follows: In Hunan Chenzhou city, a large area of soil had an arsenic content as high as 1,217 mg/kg, caused by metal mining and smelting production. In an abandoned tungsten mine in Shantou city, the concentration of arsenic in surrounding soil was found to be 935 mg/kg, while in the groundwater it reached 325 µg/L.
Heavy metal (including As) pollution as atmospheric fine particulates is common in areas of China where industrial production is occurring. In 2012, the Chinese Ministry of Environmental Protection released ambient air quality standards that incorporated pollutant particles of 2.5 microns or lower (PM 2.5). In one study of the main pollution constituents in the PM 2.5 range in several urban areas, Jiang, et al.  report As to have the largest concentration exceeding those of Cu, Zn, Cd, and Cr. The highest As concentrations were found in Xi’an city (0.11 µg/m3) and Changchun city (0.09 µg/m3). However, these As concentrations were exceeded by Pb, 102.8 µg/m3 in X’ian city and 51.0 µg/m3 in Changchun city. In an earlier Investor Intel article, the serious health effects of Pb poisoning are described .
Health Effects from Chronic Arsenic Exposure: A Worldwide Public Health Problem
Rao, et al.  state: In case of acute poisoning, arsenic can inhibit up to 200 enzymes. The enzymes include those involved in critical cellular functions such as DNA synthesis and repair and cellular energy pathways. Symptoms of systemic acute poisoning include abdominal pain, nausea, vomiting, severe diarrhea, encephalopathy, and/or peripheral neuropathy. A lethal dose can lead to multi-organ systems failure, coma, and death. The acute minimal lethal dose is 100 to 300 mg in human adults.
The broad scope of health effects resulting from chronic As exposure have been summarized by Naujokas, et al. . These authors represent the Superfund Research Program of the National Institute of Environmental Health Sciences (NIEHS) of the U.S. National Institutes of Health and several universities involved in public health. Those who desire in-depth discussions of health effects associated with As exposure and references to the research they cite should consult the Naujokas, et al. paper. It is estimated that over 200 million people worldwide are at risk of As exposure at levels of concern for human health. The enormity of the potential public health impact of As poisoning is striking. Arsenic-associated health problems affect nearly every major organ and organ system in the human body . Human cancers identified include skin, lung, bladder, liver, and kidney with onset of the condition about 20 years after exposure in each case. Arsenic affects a broad range of organs and systems including skin with development of cutaneous lesions; developmental processes in children such as infant mortality, birth weight, neurological impairment; nervous system including motor function, neuropathy, and intellectual function; respiratory system including pulmonary tuberculosis and bronchiectasis; cardiovascular system including coronary and ischemic heart disease, acute myocardial infarction, and hypertension; liver, kidney, and bladder leading to cancers; immune system including altered immune-related gene expression and cytokine expression, inflammation, and increased infant morbidity from infectious diseases; and endocrine system including diabetes and impaired glucose tolerance in pregnant women.
Mechanisms for onset of symptoms from sub-acute As exposure levels over time are unclear. Rao, et al.  have discussed possible mechanisms, some involving DNA damage and modification, as these have been postulated from results of human and animal studies. The reader is referred to this in-depth review for further information.
Naujokas, et al.  comment with probable understatement: In light of accumulated research, there is increasing awareness that arsenic exposure might be affecting more persons and contributing to more chronic disease than previously thought. Argos, et al.  report a study in which trained physicians unaware of As exposure interviewed in person and clinically assessed 11,746 population-based participants (ages 18-75 years) from Araihazar, Bangladesh during a period beginning in 2000 with follow-ups through 2009. The conclusion from the study was that an estimated 21.4% of all deaths and 23.5% of deaths associated with chronic disease in this population could be attributed to arsenic exposure (>10 ppb) in drinking water. Considering the number of persons getting their drinking water from wells worldwide, it is likely that As exposure will lead to increased rates of chronic disease and death in the future. Arsenic pollution is a global public health problem of great magnitude. This evaluation is attested to by The Agency for Toxic Substances and Disease Registry (ATSDR) which publishes a priority list of substances determined to pose the most significant potential threat to human health due to their known or suspected toxicity and potential for human exposure at Environmental Protection Agency (EPA) National Priority List (NPL) hazardous waste sites in the United States. Arsenic is ranked number 1 on this list in 2017 .
Litter, et al.  have described the health effects of As poisoning in South America, especially in Argentina, Chile, and Peru. The As problem there is equivalent to that in southeast Asia. Exposure is from drinking water and mining waste which affects local drinking water and soils. These authors summarize the health effects as follows: The permanent ingestion of waters with high arsenic concentrations provokes the appearance of arsenicosis, an illness with high incidence in Asia and LA [Latin America]; in LA, the disease is named Chronic Endemic Regional Hydroarsenicism (in Spanish: HACRE). Symptoms of this illness are palmplantar hyperkeratosis, damage to the central neural system, hepatic damage, hair loss, skin cancer and cancer of internal organs (lungs, liver, kidney and bladder). So far, there is no treatment for HACRE, and prevention is the only way to combat the illness, which involves reduction of As concentration in water or avoidance of people to As exposure.
History of Arsenic Poisoning and Uses
Arsenic is one of the few elements in the periodic table that has a history of involvement with man stretching back thousands of years. Several accounts of this involvement are available [23,24]. Bentley and Chasteen  observe that Arsenic and arsenic compounds have had a long and Janus-type interaction with humanity; on the one hand they have been extensively utilized, but on the other hand their poisonous properties have caused misery and many deaths. Realgar (As4S4) and orpiment (As2S3) minerals have a long history of human use stretching back to Greek and Roman times, but elemental As was not conclusively identified until 1649 . The etymology of the name arsenic is complex tracing back to Greek, Syriac, and Persian origins. The highly poisonous nature of As compounds has been known for millennia and has been used effectively by many to accomplish nefarious schemes. There is evidence that the Medici family in Italy and keepers of Napoleon Bonaparte while in exile used As in a lethal manner. The colorless and tasteless compound arsenous oxide, As2O3, was at one time used as a rat poison because of its ready availability and effectiveness. This compound was also often used for criminal purposes in real life and in fiction such as Arsenic and Old Lace. In fact, to many people the word arsenic has become synonymous with the word poison. We now have a much better idea than our ancestors did of the poisonous nature of As and how widespread the danger of exposure to this metal is in the water we drink, the food we eat, our exposure at mining waste sites, and our contact with many other natural and anthropogenic sources. Recognition of this danger has led to regulations worldwide aimed at controlling human exposure to this metal and successive lowering of “safe” levels of exposure as our knowledge increases.
Arsenic has been used in a wide array of medical and non-medical uses over the centuries [24,25] and continues at a smaller scale in 2017. Until the 1970s, As was used in some medicinal applications . For example, inorganic As was used in the treatment of leukemia, psoriasis, and chronic bronchial asthma, and organic As was used in antibiotics for the treatment of spirochetal and protozoal disease. In previous centuries, As was used in many medical applications. It was effective, but the patient often died from the treatment instead of the disease.
Current and historical uses of As include cosmetics, pharmaceuticals, wood preservatives, agricultural chemicals for insecticides and rodenticides, and applications in the mining, metallurgical, glass-making, and semiconductor industries. As expected, there have been many cases of As poisoning due to its industrial uses. The principal use of As2O3 has been to produce arsenic acid that is used in the formulation of chromated copper arsenide (CCA) preservatives for the pressure treating of lumber used primarily in non-residential applications . This product is no longer used in residential applications, following a voluntary ban on its use in Canada and the U.S. in 2003. Inorganic As pesticides have not been used for agricultural purposes in the U.S. since 1993. In 2009, the EPA issued a cancellation order aimed at phasing out use of organic arsenical pesticides.
Arsenic has important applications in the manufacture of high technology products. High-purity arsenic (99.9999%) is used by the electronics industry for GaAs semiconductors that are used for solar cells, space research, and telecommunications. Arsenic also is used for germanium-arsenide-selenide specialty optical materials. Indium-gallium-arsenide is used for short-wave infrared technology. Discard of high technology products containing As when they reach their end-of-life state can lead to additional sources of environmental As pollution. The recycling rate of As is <1%  indicating that very little As is retrieved from these spent products or other As waste. There is a very large knowledge base for the As problem with over 1000 scientific papers published annually with “arsenic” in the title .
Technologies for Arsenic Separation and Recovery
Arsenic chemistry is complex, and this complexity is evident in its speciation in aqueous solution, soil, and atmosphere, and in its toxicity to humans [3,16,28-30]. The toxicity of As(III) is 60-100 times greater than that of As(V) while As in the organic form is much less toxic. The valence or oxidation state of As varies from 0 in the elemental form to -3 (such as AsH3 which is highly toxic), to +3 (such as As2O3), to +5 (such as in HAsO42-, or H2AsO4– depending on pH conditions).
The forms of As in water are mainly soluble species, which are closely related to the oxidation-reduction (redox) potential and pH of the water bodies involved. Under reducing conditions such as are found in the Bangladesh aquifers, arsenous acid (H3AsO3) is the largest component. In oxygen-enriched water bodies, arsenate species such as H2AsO4– and HAsO42- become the major components. Thus, the As species present in each system depends on the pH and redox potential present.
Hayat, et al.  point out that Appropriate treatment of industrial wastewater becomes increasingly essential to (i) recover freshwater from industrial wastewater for beneficial uses which is an ever increasing imperative due to ever increasing freshwater demand (irrigation water being the largest consumer) due to demographic and economic growth and (ii) reducing environmental impacts. They go on to say that the metalloid arsenic is of principal concern, since it is highly toxic to environment and humans and present in many industrial waste-water streams such as those from (i) mining and related activities (ore processing, smelters, etc.); (ii) wood processing industry and wood combustion; (iii) carbon and petroleum exploitation, processing, refining and combustion; (iv) geothermal exploitation; (v) agrochemical industry (e.g., related to impurities in pesticides) and agricultural wastewater due to their applications; (vi) water treatment sludge; and (vi) municipal solid waste incineration. To this list might be added separation of As from culinary water supplies including tube-wells or other wells and from samples prior to As analysis by ICP or graphite furnace ultraviolet spectroscopy.
Remediation techniques used for As removal from water have been summarized and their advantages and disadvantages discussed by Shakoor, et al.  and Litter, et al. . These techniques include precipitation, coagulation/flocculation, ion exchange, membrane filtration, flotation, phytoremediation, and sorption. Litter, et al.  observe that Arsenic removal from water for human consumption seems to be a difficult task. Not a universal method exists and the election is very dependent on the composition of waters to be treated. One complicating factor is that the As(III) present must be oxidized to As(V) for the methods to work. Hayat, et al.  promote the use of microbial remediation as a promising technology for As remediation from industrial wastewater and point out that conventional techniques have the disadvantage that they produce toxic residual waste which requires expensive management and often have limited efficiency, operational difficulty, and high operational cost. Shakoor, et al.  conclude that current treatment technologies for As-contaminated water have a number of disadvantages, and the wastes or sludge generated can be a potential source of secondary pollution. Thus, for better protection of our environment from As, new hybrid technologies are needed accompanied by safe disposal options for As-loaded wastes/sludge.
Litter, et al.  have discussed the need for simple, economical methods to provide a means for As detection and removal in poor, isolated and dispersed populations in Latin American regions. These authors point out that As-related diseases in South America affect mainly urban and rural poor populations not connected to drinking water networks. These authors have concisely stated the problem: Arsenic removal from waters is not an easy task. Economical aspects are perhaps the most important factors for the selection of the technology, taking into account size of the population, incidence of chronic illnesses, lack of safe water, poverty conditions, and other socioeconomic variables. In most cases, sophisticated, expensive techniques cannot be applied in populations with low economical resources. In addition, arsenic treatment units require very sensitive monitoring and maintenance arrangements, which falls far beyond the economic scope of poor isolated communities. Moreover, a number of cultural and political factors play deciding roles in the implementation of new technologies. A further difficulty is that As is usually present in multi micro gram per liter quantities. Current technologies are challenged to operate successfully at these low concentrations.
Rahman, et al.  describe a simple flow-based method for the selective separation of As species (+3 and +5) using a Molecular Recognition Technology (MRT) process that does allow separations at low As concentrations. In this process, a feed solution containing As was passed through a column containing an AnaLig® product. The AnaLig® product (marketed by IBC Advanced Technologies, Inc.) consists of a highly As-selective ligand bound by a tether to a solid support particle, such as silica gel. Any As(V) species present was selectively separated from the feed solution as an anion by the AnaLig® product. Any As(III) present went on to raffinate. The retention capacity of the AnaLig® product was found to be 0.25 ± 0.04 mmol/g. The method was applied to speciation analysis of tri- and pentavalent As in natural water with As recoveries of >98.7%. Arsenic determinations were made using a graphite furnace atomic absorption spectrometer.
The MRT process was checked against wastewater and groundwater reference standards for As provided by the European Commission Joint Research Centre, Institute of Reference Materials and Measurements. Agreement was excellent as seen in the following example. Effluent wastewater: MRT (sum of both As species) 9.0 ± 1.4 µg/L; Certified value (sum of both As species) 9.7 ± 1.1 µg/L. Groundwater: MRT (sum of both As species) 10.2 ± 1.6 µg/L; Certified value (sum of both As species) 10.8 ± 0.4 µg/L. MRT was able to provide values for both As(III) and As(V) species. The certified values were only for the sum of these species. The following values for As(III) and As(V) were determined for wastewater using MRT: As(III): 1.9 ± 0.3 µg/L, As(V): 7.1 ± 1.2 µg/L; and for groundwater: As(III): 3.3 ± 0.6 µg/L, As(V): 6.9 ± 1.1 µg/L.
Rahman, et al.  conclude: The process offers a single-step separation option of trivalent and pentavalent arsenic species that commonly exist in the natural aqueous matrix. Easy operation, rapid separation performance, and reusability for more than 100 cycles without loss of the analytical performance of the MRT–SPE [solid phase extraction] are some additional characteristics of the proposed process which make it a suitable and economic option for, particularly, the arsenic-prone nations suffering from natural arsenic contamination.
Shrestha and Spuhler  have discussed the sludge disposal problem associated with conventional As treatment technologies. Ultimately, these technologies concentrate As in sorption media, sludge, or liquid media. Indiscriminate disposal of these concentrated media will lead to environmental pollution, since additional chemicals have been added to the system and must be treated as waste. Thus, environmentally safe disposal of components rich in As is of high concern. Also, this treatment using conventional technologies is expensive and is usually not done, as has been the case with the Giant mine in Yellowknife, Canada.
MRT processes have important advantages over traditional separation technologies. One advantage is that individual species are separated at low concentration levels of mg/L to multi-µg/L. This is possible due to the high selectivity MRT ligands have for individual species and the high binding energy between the bound ligands and these species . MRT processes follow green chemistry principles. Because of the simple column design and high selectivity for As, minimal waste is generated. Thus, disposal of sludge or added chemicals is not an issue. MRT processes have much lower capital expenses and operating expenses compared to conventional separation processes, especially when the cost of conventional processes includes true expenses that incorporate negative externality costs. Externality costs can be very high as seen in the Giant mine example. MRT processes have been shown to be effective in recovering As from dilute solutions and in preparing As solutions for analytical determinations .
Conclusions that can be drawn from this paper are as follows:
- Arsenic poisoning is a major health problem that affects hundreds of millions of people worldwide through increased mortality rates from chronic diseases in As-exposed populations.
- Exposure to As may occur through contaminated drinking water; food, especially rice, raised on As-contaminated soil; inhalation of As-containing dust in industrial settings; inhalation of PM2 particles present as atmospheric pollutants; or other means. Many such exposures occur without the recipient’s knowledge highlighting the critical need for use of analytical measurements of As concentrations in food sources and drinking water sources, and for greater efforts at increasing public and governmental awareness of the dangers of As exposure.
- Health problems caused or augmented by acute or chronic exposure to As have increased as epidemiological and clinical knowledge have increased and now include cancers of the bladder, skin, lung, liver, and kidney as well as impairment of nearly every major organ and organ system in the human body. A range of clinical manifestations includes cutaneous lesions, childhood physical and mental developmental processes, respiratory problems, neurological impairment, cardiovascular malfunctions, altered immune function, impaired endocrine function, and reduced immune response.
- It is critical to reduce exposure to As by children to decrease immediate health problems and increased long-term problems including cancer as adults. Pre-natal exposure to As can create serious physical and developmental problems as organs form.
- The MCL level for As, set at 10 µg/L for drinking water, is not easily attained. Globally, greater efforts are needed to inform the public and policy makers of the harmful effects of As, its widespread occurrence, and the significant human health costs associated with allowing continuation of human exposure to drinking water levels greater than 10 µg/L. There is a latency period between exposure and disease occurrence, but the eventual damage to human health and resultant costs can be appreciable.
- Arsenic is especially challenging to remediate due to its complex chemistry. Despite this, MRT has been shown to be effective in removing As from polluted environments, especially when the As is present at mg/L and lower concentrations. In contrast to traditional remediation technologies, MRT is based on green chemistry and green engineering principles and offers dramatic improvements over traditional approaches to As remediation.
- Return on investment from reducing exposure to As by affected populations can be substantial when measured by reduced incidence of chronic disease and reduced rates of cancer worldwide.
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Reed M. Izatt received a BS degree in Chemistry from Utah State University (1951) and a PhD degree in Chemistry with an Earth Sciences minor ... <Read more about Reed M. Izatt, PhD>