Arsenic Pollution

A Global Synthesis

Peter Ravenscroft, Hugh Brammer, Keith Richards

• Publisher: Wiley-Blackwell
• Year: 2011
• ISBN:
  9781444355468
• Edition: 1
• Topic: Medicine
• Subtopic: Toxicology

Arsenic Pollution summarizes the most current research on the distribution and causes of arsenic pollution, its impact on health and agriculture, and solutions by way of water supply, treatment, and water resource management.

• Provides the first global and interdisciplinary account of arsenic pollution occurrences
  
• Integrates geochemistry, hydrology, agriculture, and water supply and treatment for the first time
  
• Options are highlighted for developing alternative water sources and methods for arsenic testing and removal
  
• Appeals to specialists in one discipline seeking an overview of the work being done in other disciplines

Chapter One

Introduction

1.1 Background

Arsenic, a notorious poison, is now recognised to be one of the world’s greatest environmental hazards, threatening the lives of several hundred million people. Andrew Meharg (2005), in his book Venomous Earth, presents fascinating accounts of the use of arsenic for murder, medicine and wallpaper¹. Sometimes known as the King of Poisons, arsenic has been known to humankind for thousands of years, being used to harden bronze in the Middle East around 3000 BC, and prized as a dye by the Egyptians, Greeks and Romans. In the fifth century BC, Hippocrates suggested using arsenic compounds as an ulcer treatment, while in the first and second centuries AD, the Roman Emperor Nero and Mithridates, King of Pontus, both used arsenic to murder their enemies. However, we will not describe the human use and abuse of arsenic further, because that is not the purpose of this book. Here, we are concerned with the insidious, creeping effects of naturally occurring arsenic in rocks and soils, which finds its way into underground water and streams, or is drawn into the roots of plants. This arsenic, withdrawn from the ground by wells and used for drinking, does not kill suddenly, but in the past 20 or 30 years has surely accounted for many more deaths than all the arsenical poisonings in history.

Long-term exposure to low levels of arsenic in food and water produces a broad array of effects on human health that are often described by the catch-all term arsenicosis. Early symptoms are non-specific effects such as muscular weakness, lassitude and mild psychological effects. These are followed by characteristic skin ailments such as changes in skin pigmentation and progressively painful skin lesions, known as keratosis. At the same time, arsenic causes a wide range of other effects on health, including diseases of the liver and kidney, cardio-vascular and peripheral vascular diseases, neurological effects, diabetes and chronic and acute lung disease. Continued exposure to arsenic can lead to gangrene, cancers of the skin, lung, liver, kidney and bladder, and thereby to death.

Because the effects of arsenic depend on cumulative exposure, the symptoms are most commonly seen in adults and, because of lifestyle, in men more than in women. As symptoms develop, a person’s ability to live a normal life is reduced. Sufferers may become unable to work, severely affecting the welfare of their families. Meanwhile, so long as exposure continues, the patient’s condition will continue to deteriorate, while their ability to cope with the illness is reduced. The stigma of arsenic poisoning revealed in the symptoms of arsenicosis, and even of simply owning a polluted well, gives rise to social impacts such as ostracism and social and economic exclusion, with the burden falling disproportionately on women.

Naturally occurring arsenic in groundwater used for drinking and cooking is a catastrophe of global proportions. The World Health Organization (WHO) described the situation in Bangladesh as ‘the largest poisoning of a population in history’ (Smith et al., 2000). It is estimated that in 1998-99 around 27 million people were drinking water containing more than the national standard of 50 parts per billion (ppb) of arsenic. To this total should be added another 6 million people in the adjoining area of West Bengal in India. Worse, the WHO and many countries now consider 50 ppb unsafe, and recommend a limit of only 10 ppb. At this level, around 50 million people in Bangladesh, about 40% of the total population, and about 12 million people in West Bengal, are consuming dangerous concentrations of arsenic. If the statistics were not dire enough, these countries, striving to reduce the burden of poverty, are desperately ill-equipped to cope with the additional disease burden of arsenicosis. Moreover, suffering falls disproportionately on the poor, who are malnourished, drink more well-water, eat more arsenic in their diet and are less able to resist the toxic effects of arsenic than their better-off counterparts. Indeed, there is evidence that, within affected regions, the poor are most likely to show clinical symptoms of arsenicosis.

1.2 The Nature of Arsenic Pollution

Some of the features that made arsenic such an attractive poison – that it is colourless, tasteless and odourless – also contributed to its late discovery as an environmental contaminant. Further, when exposure is continuous over a period of years, arsenic is toxic at very low concentrations. In the past, it was no simple task to measure arsenic concentrations in water, and so, because it was not recognised as a problem, it was not routinely tested for. Unfortunately, in many parts of the world, arsenic is naturally present in groundwater that is easily accessible and otherwise fit for drinking. Because it is in water used for drinking and cooking, and sometimes in staple foods as well, arsenic may be consumed in large quantities and for long periods. However, arsenic is almost never found in natural waters at concentrations that are acutely poisonous². Chronic poisoning involves a long latent period before clinical symptoms develop. When water containing tens to a few hundreds of ppb is consumed continuously, symptoms of arsenicosis typically become apparent after periods of 2–10 years.

Natural arsenic pollution occurs in diverse geological and climatic conditions. It occurs most commonly in sands deposited by large rivers, and most of the worst cases are found in the tropical river basins of Asia. However, arsenic-contaminated groundwater is found in unconsolidated sediments and sedimentary, igneous and metamorphic rocks ranging in age from a few thousand to more than a billion years old. Arsenic pollution is found in climates ranging from the hot and humid tropics, to Arctic Alaska and hyperarid deserts. Despite this diversity, in any given location, contamination usually has a well-defined relationship to particular strata, or to particular depths of wells.

In many areas where groundwater contains high levels of arsenic, so too do the soils. Although the quantities vary greatly, most plants take up arsenic through their roots and into the edible parts. Where arsenic-rich groundwater is used for irrigation, the arsenic content of soils gradually builds up, and leads to more arsenic being taken up by plants. Thus, the effects of arsenic in food and water are both additive and cumulative. The worst conditions occur in the subsistence rice economies of Asia, where rice is irrigated with arsenic-contaminated water. The diet of the rural poor typically comprises locally grown rice with little fruit, vegetables or meat, and so a deficiency of vitamins, minerals and protein reduces their ability to resist the toxic effects of arsenic. If their food is cooked in, and washed down with, polluted well-water, the daily intake of arsenic can be ten times the recommended maximum. Thus, poverty and environmental hazards combine to exacerbate the suffering of poor, rural populations.

1.3 History of Natural Arsenic Contamination

1.3.1 Early discoveries

Although almost unknown 25 years ago, natural arsenic contamination affects more than 70 countries in the world (Figure 1.1). Unlike arsenic in minerals, such as orpiment and realgar, the occurrence of arsenic in natural waters has been known for barely 100 years. The earliest measurement of arsenic in natural water was by the famous German chemist Fresenius at Wiesbaden Spa in 1885 (Schwenzer et al., 2001). Although historically interesting, this water was not consumed in sufficient quantities to cause illness. The earliest report of arsenic poisoning from well-water, which apparently caused skin cancer, was from Poland in 1898 (Mandal and Suzuki, 2002), although ironically there are no later reports from Poland. The first major case of endemic disease caused by arsenic in drinking water was reported in the 1920s in Cordoba Province of Argentina (Bado, 1939), where it is associated with a type of skin cancer known as Bel Ville disease. Although this affected thousands, perhaps tens of thousands, of people, it was little known outside Argentina until the end of the 20th century.

Figure 1.1 Global distribution of arsenic contamination. Note that the size of each affected area should not confused with either the intensity and severity of pollution, or the numbers of people affected, which are elaborated in Chapters 8–10. The map numbers are detailed in Table 1.2. Where the numbered locations are too close to show on the map, groups of affected regions are identified by letter. Asia: A, 37, 39–41 & 43; B, 10, 11, 31–33, 154–157 and 205; C, 13, 14, 16–20, 22–24, 26; D, 12, 58, 201 and 202; E, 9, 28, 30, 47, 48 and 49 (see Fig. 8.1). Europe: F, 92, 93, 96 and 200; G, 80, 82, 83, 191 and 198; H, 79, 81, 166, 194, 195 and 215; I, 65, 78, 90, 91, 151, 161, 223; J, 97, 98, 216–220; K, 69–72, 152, 164; L, 73–75, 84, 165, 192 (see Fig. 9.17). Africa: M, 6–8, 190 (see Fig. 10.6). North America: N, 100, 101, 123, 133; O, 99, 104, 131, 132 and 187; P, 121, 170–174, 182; Q, 116, 117, 130, 175, 177, 188, 193; R, 126, 169, 176, 183, 186; S, 107, 119, 168, 184; T, 122, 178, 179, 181, 185; U, 128, 167; V, 106, 110–112, 115 (see Fig. 9.1). South America: W, 135–138 (see Fig 10.1).

1.3.2 The mid-twentieth century

From the 1930s to the 1970s, there were few discoveries of natural arsenic contamination, although minor occurrences were noted in Canada (Wyllie, 1937) and New Zealand (Grimmett and McIntosh, 1939). In the 1960s, arsenic poisoning from well-water became well known in Taiwan, which has a special place in the history of epidemiological studies of arsenic. In Taiwan, arsenic caused a range of severe illnesses, including Blackfoot Disease, which is almost unique to southwest Taiwan. However, there were no international publications concerning the science of its occurrence, and the Taiwan case was largely unknown amongst water scientists³. Arsenic contamination is not only an issue in the developing world. The USA is, in fact, one of the most widely affected countries in the world, although the health impacts are quite small. The USA has been curiously slow to recognise and respond to the extent of contamination. A classic paper on the geochemistry of arsenic by Onishi and Sandell (1955) only recorded arsenic in hot springs and volcanic exhalations. A 1969 survey of 1000 water supplies reported that only 0.5% exceeded 10 ppb and 0.2% exceeded 50 ppb, and stated that arsenic represented ‘no current threat to public health in the US’ (Ferguson and Gavis, 1972). However, later surveys of water supplies reported that 1% exceeded 50 ppb and 8% exceeded 10 ppb (Ryker, 2003). In the 1970s, arsenic contamination was identified in Nova Scotia in Canada, where 25% of people drinking water with >50 ppb showed mild clinical symptoms (Grantham and Jones, 1977). Around the same time, almost the whole population of Antofagasta in northern Chile was exposed to 800 ppb As between 1958 and 1971, resulting in widespread and severe illness. However, the death toll attributed to arsenic-induced cancer, lung and heart disease in the decades following commissioning of a municipal treatment plant was about four times higher than during the period of peak exposure (Yuan et al., 2007).

1.3.3 The late twentieth century

Until the 1980s, the picture that emerges is one of isolated problems that did not attract international attention. The reasons are unclear, but there are probably three main explanations. First, arsenic was not routinely tested for in many countries, and second, there was a relatively poor knowledge of the health effects of low levels of arsenic. The third reason is cultural. The two major problems at the time (Argentina and Taiwan) were poorly known in Europe and North America and did not resonate with public health officials. Also, because arsenic was not perceived to be a problem in the home territories of the former colonial powers of Europe, they did not ‘export’ arsenic-testing protocols to their former colonies.

With hindsight, the 1980s may be seen as the period when the extent of pollution began to be recognised. Arsenic poisoning related to well-water was discovered in West Bengal (India) in 1983⁴, although it took the rest of the decade for the size of the affected area to be appreciated. At about the same time, arsenic pollution was recognised in Hungary (Varsányi et al., 1991) and Xinjiang Province in China (Sun, 2004). However, in the political climate of the Cold War, there was apparently little awareness of the two latter problems in the west. Meanwhile, there was growing recognition of arsenic pollution in North America, with investigations of glacial aquifers in the mid-west by Matisoff et al. (1982), and a landmark publication by Welch et al. (1988) that documented 28 occurrences of groundwater arsenic in the southwest USA. While investigations in India and China had been triggered by medical diagnoses, the occurrences in the USA were not associated with clinical symptoms of arsenic poisoning.

In tropical Asia, drinking water was traditionally drawn from surface water or very shallow dug wells, and bacterial pollution of these water sources gave rise to epidemics of diarrhoeal diseases such as cholera and dysentery. Although the use of groundwater supplies began in the 1930s, it accelerated particularly after 1970 and into the 1990s, partly as a result of a deliberate policy promoted by UNICEF to reduce child mortality associated with enteric diseases. Tens of millions of cheap, shallow tubewells were drilled to obtain microbiologically safe drinking water. The major aim was to avoid polluted surface water sources that had caused widespread diarrhoeal disease. To this end, there was considerable success: in Bangladesh, between 1960 and 1996, child mortality dropped from 151 to 83 per thousand (Meharg, 2005). However, the switch from surface water did not occur without cost. For while the policy was largely successful in reducing enteric disease, and millions of deaths from this cause were prevented, in some areas the shallow tubewells that were substituted tapped arsenic-polluted groundwater, leading to chronic poisoning on a massive scale.

In the 1990s, arsenic pollution of groundwater burst from obscurity to receive the attention of the international press (e.g. Bearak, 1998), and radio and television networks such as CNN and the BBC. This transformation essentially took place in India and Bangladesh between 1994 and 1998, thanks particularly to the efforts of Dipankar Chakraborti and his colleagues at the School of Environmental Studies (SOES) at Jadavpur University in Kolkata, who described arsenic pollution in six districts of West Bengal as ‘the biggest arsenic calamity in the world’ (Das et al., 1994). For 10 years this was effectively unknown, even in neighbouring Bangladesh, except to a handful of individuals who chose to ignore or suppress the information. The tipping point was an international conference organised by Chakraborti in Kolkata in 1995. Almost overnight, the plight of millions of people in West Bengal was brought to the attention of the world’s scientists, aid agencies and international media. The message was carried to Bangladesh, where geologists knew that the contamination must extend across the border, although none anticipated it would cover more than half of the country. Unlike its gradual revelation in West Bengal, Bangladesh progressed from discovery to comprehensive national mapping in two and a half years, and doctors soon began to recognise the symptoms of arsenic poisoning. From indifference in 1995, by the end of 1997, United Nations agencies, the World Bank and five bilateral donors were ready to commit millions of dollars to assist the Bangladesh Government implement a mitigation programme.

A second landmark conference took place in Dhaka in February 1998, organised by SOES and the Dhaka Community Hospital (DCH), which reiterated the magnitude of the problem in West Bengal, and revealed the even greater scale of contamination in Bangladesh. For the first time, the current scientific explanation of the pollution in Bengal was presented (Ahmed et al., 1998), showing that the cause was geological, and not anthropogenic, and acted as a stimulus for testing in surrounding countries. Over the next few years, extensive pollution was discovered in the river basins of Nepal, Myanmar, Cambodia, Vietnam and Pakistan (e.g. Jain and Ali, 2000; Nordstrom, 2002). Ironically, it was not until later that arsenic pollution was identified upstream from West Bengal in the Indian States of Bihar, Uttar Pradesh and Assam on the Ganges and Brahmaputra floodplains. Meanwhile, expanding studies in China discovered severe arsenic pollution in Inner Mongolia and Shanxi Provinces.

1.3.4 The twenty-first century

Since 2000, arsenic contamination has been found in other parts of the world, and new discoveries are regularly reported. In many parts of the world, especially Africa and South America, there is still a grave shortage of information, and it seems inevitable that more cases will be found in the future. However, new discoveries have also been driven by the lowering of drinking water standards in many countries. From the middle of the 20th century, most countries specified a standard of 50 ppb, but in 1993, the WHO reduced its guideline value for drinking water to 10 ppb. Beginning with Germany in 1996, many countries have adopted the new guideline as a legal standard, leading to major testing programmes, so that countries that previously did not have an arsenic problem suddenly acquired one, and were obliged to retrofit arsenic treatment to many existing public supplies. However, the countries that face the most severe problems, mostly poor and in Asia, have retained 50 ppb as the standard for drinking water.

Where arsenic contamination has been discovered recently, one of the puzzles is to know how long the poisoning has been going on. Is it a new phenomenon, or has it always been present, and why was it not recognised before? In most cases, there are no clear answers to these questions, yet it is widely perceived that extensive arsenicosis is a recent phenomenon, and this has led many people to assume an anthropogenic cause. While this is generally incorrect, and arsenic has been present in groundwater for thousands of years, there is a human connection because of the deliberate shift towards groundwater supply in the 20th century.

1.3.5 The growth of knowledge

Knowledge of arsenic contamination has expanded enormously in the past two to three decades. Commenting on the first diagnosis of arsenic poisoning due to well-water in India, Datta and Kaul (1976) noted that the only equivalent reports of arsenical skin lesions were from Chile and Taiwan. While overlooking Argentina, they were correct in principle. Likewise, Fowler (1977), summarising the conclusions of an international conference intended to ‘assess the current level of scientific knowledge about arsenic as an environmental toxicant and to identify areas of needed research’, observed that the most important sources of arsenic exposure were non-ferrous smelting and burning of arsenic-rich coal. He ‘suggested’ that steel smelters, burning of impregnated wood, and abandoned mines should be studied. Finally, he noted that ‘natural sources of environmental arsenic release such as volcanoes and hotsprings were also recognised as important.’ The occurrence of nongeothermal arsenic in aquifers or soils received no mention.

The subsequent growth of knowledge is reflected in the literature consulted during the preparation of this book. Although far from comprehensive, a database of 1100 publications explicitly concerning arsenic was compiled, for the period up to the end of 2006. Classified by decade (Table 1.1), over 90% of all publications were produced after 1990. The database included 789 geographically related publications, of which the largest group, 444 publications, concerned arsenic in Asia, of which 83% had been published since the year 2000.

Table 1.1 Publications concerning arsenic by decade

Source: Authors’ database

Because of the history of arsenic as a p...