ABSTRACT

The 20th most abundant element found in the Earth is Arsenic (As). This element naturally occurs as As (III) and As (V). These two oxidation states determine toxicity levels and control its fate and transport into the human body, via geologic processes. Sources of arsenic exposure include contaminated ground water, coal, geothermal springs, volcanic sediments, and anthropogenically-related releases. Arsenite (H3AsO3) is the dominant species of As (III) in solution and is strongly absorbed onto iron oxides and other soil constituents (e.g. clay). Arsenate (H3AsO4) is the most common form of As (V) and highest absorption rates occur when pH falls between 4 and 7. As is highly mobile in the hydrosphere and poses a widespread public health concern. Exposure to Arsenic can come from both natural and anthropogenic activities. The most common toxic pathway is via groundwater, where the most acute cases are associated with Asian countries. West Bengal and Bangladesh, in particular, suffer from rampant arsenic poisoning, often interpreted as the result of agricultural irrigation. In heaviest impacted areas, concentration levels range up to 500 ppb (parts per billion), whereas background levels usually average between 3 and 20 ppb. China’s Guizhou Province suffers from As poisoning via lithologic pathways, thought to be intensified by use of domestic coal fuel associated with concentrations up to 3500 ppb. Long term exposure to As, whether air born, in food supplies, or drinking water, may result in cardiovascular disease, neurological disorders, skin depigmentation, rhagades, hyperkeratosis and Bowen’s Disease (squamous cell carcinoma). This paper examines the global impact of environmental arsenic and its range of human health effects.

INTRODUCTION

Arsenic is a naturally occurring element that can be found within the lithosphere. There is scientific research that has been documented depicting areas in which especially high concentrations of As have been found. Due to natural geologic processes, concentrated arsenic is able to infiltrate the hydrological cycle and enter the human body. Another way human health is impacted via geologic processes is by use of coal containing high concentrations of As. Health impacts from Arsenic vary immensely, such as squamous cell carcinoma and cardiovascular disease. The variety is a result of concentration levels of the consumed element in its different ionization states. Concentration levels are dependent upon geologic processes that have occurred in the past or are currently ongoing; these processes can be influenced and enhanced by humans.

GEOLOGIC SOURCE, FATE, AND TRANSPORT OR ARSENIC

Arsenic’s mobility in the lithosphere is a direct impact of the geologic setting it resides in. Arsenic has different ways it mobilizes through the environment. AS(III), Arsenite is considerably more toxic than Arsenate, As(V) because it is less soluble. (Naidu and Naderbaum, 2003) Pyrite is a type of rock that is formed under sedimentary conditions, at low temperatures, in reducing conditions. This type of rock is found alluvial deposits, sediments of rivers, lakes, oceans, and many aquifers. The depth of sedimentary deposits affects the concentrations of arsenic that occur. (Smedley and Kinniburgh, 2005). Found in mud and clays, pyrite is significant because it generally contains high levels of As(V). Pyrite is unstable in aerobic systems and undergoes which releases iron oxides while it desorbs the previously adsorbed arsenic. (Smedley and Kinniburgh, 2005) Redox potential and pH are the most important factors of arsenic speciation in aqueous systems. ( Smedley and Kinniburgh, 2005) Alluvial and deltaic plains as well as large inland basins are at a much greater risk to encounter high arsenic concentrations because of their interaction with aqueous environments. In strongly reducing aquifers, typified by Fe(III) and sulfate reduction, As(III) typically dominates. ( Smedley and Kinniburgh, 2005) See Figures 1, 2, 3

HEALTH CONCERNS

There are various health concerns related to scientifically recorded high concentrations of geogenic arsenic. Significantly high prevalence of skin cancer was observed in all arsenicosis-endemic areas around the world. (Centento et al, 2007) Squamous cell carcinoma, rhagades and hyperkeratosis are a few of the skin problems that have been the most noticeable health complications caused by arsenic poisoning. Inhalation of arsenic can occur near mining areas and in places where the burning of coal is used as an energy source. When arsenic becomes a systemic toxicant it is known to induce cardiovascular disease, neurobehavioral disorders, and respiratory disorders, and various cancers like liver and kidney. (Centneto et al, 2007) See Figures 4, 5, 7, 9

SUMMARY

1. Arsenic is geogenic and can be found at different ionization states throughout the lithosphere. Geologic processes that have influenced or currently do influence the area in question determine the mobility of arsenic in the groundwater and in the land.

2. Geogenic Arsenic is found to be associated mostly with alluvial and deltaic sedimentary deposits which contain pyritic rock types. Arsenic is most commonly associated with pyrite, which can be found in clays and mud, and in environments where there are high levels of iron oxides.

3. There are various human health concerns related to exposure of concentrated levels of As. The most commonly found health degenerates are related to skin disorders such as Hyperkeratosis, Bowen’s Disease, hyper pigmentation, and various cancers.

4. There are many cases of arsenic poisoning world wide. In the Bengal Basin area, the most severe cases are caused by exposure to arsenic via groundwater, which is used for drinking and irrigation. In China, chili peppers are believed to be the main cause of exposure. The Chinese population in this area uses contaminated to coal to roast their chili peppers for which are used for every day consumption.

References CitedNaidu, R., and Nadebaum, P.R. “Geogenic Arsenic and Associate Toxicity Problems in the Groundwater-Soil-Plant-Animal-Human Continuum.” CSIRO Land and Water, 2001Smedley, Pauline, and Kinniburgh, David G. “ Arsenic in Groundwater and The Environment. British Geological Survey, 2005Wuyi, Wang, et al., “Mitigation of Endemic Arsencosis with Selenium: An Example in China.” Institute of Geographical Sciences and Natural Resources Research, 2003Centeno, Jose A., “Global Impacts of Geogenic Arsenic: A Medical Geology Research Case.” Royal Sweedish Sciences, 2007Also see www.wou.edu/~rkeller06 for a more complete list of references.

14. The Problem With Geogenic Arsenic and Global EffectsPrepared by:

Riccilee Keller, Integrated Science Education Major

Figure 4. Keratosis on hands, 2008

WEST BENGAL/BANGLADESH

Addressing population at risk, the West Bengal/Bangladesh groundwater arsenic problems are by far the most serious cases recorded world wide. Approximately 35 million people, in the West Bengal/Bangladesh area, are exposed to levels of arsenic in their drinking water above the US EPA recommendation of 0.10ppm and also above the Indian recommendation for 0.05mg per liter. “The source of exposure is primarily from potable water used for drinking and irrigation. The Bengal Basin groundwater problems with arsenic generally occur within young, mainly Holocene, shallow aquifers(<150m depth), composed of alluvial and deltaic sediments deposited by the vast river systems of the Ganges, Brahmaputra, and Meghna…” (Smedley and Kinniburgh, 2005) The lower parts of the basin are covered in clays and fine silts; these silts are responsible for the widespread development of reducing conditions. Concentrations range from <0.05 to around 3200µ per liter. (Smedley and Kinniburgh, 2005) See Figures 3, 6, 8

Figure 6. Environmental Health Perspectives Volume 108, Number 5, May 2000

Figure 7. 10-year old girl suffering from arsenic poisoning, hyperkeratosis

CHINA’S GUIZHOU PROVINCE

China does not experience high levels of arsenic in drinking water however they do use geogenic coal from the area. Coal in this area contains extraordinarily high concentrations of arsenic because it is bound to the organic components and can contain up to 35,000µ per gram of coal. (Centeno et al, 2007) Chili peppers dried over coal burning stoves are believed to be the main source of poisoning. The dried peppers have been found to have up to 500µ per gram while chili peppers freshly picked contained as little as 1 µ per gram. (Centeno et al, 2007) Chili peppers are a main ingredient in the Chinese diet so the population in this area is at risk of poisoning. Other ways arsenic infiltrates the human body is by inhalation of combusted coal and dust from the local area. The population infected is in the thousands, a much smaller case than Bangladesh, but a relevant one. Those who are infected show typical symptoms of As poisoning such as Bowen’s Disease and hyperkeratosis. (Centeno et al, 2007) See Figures 9, 10, 11

Figure 8. Geologic, Hydrologic, and Geochemical Characterization of the Deep Ground Water Aquifer System In the Bengal Delta of Bangladesh, 2010

Figure 11. Environmental Health Perspectives

Figure 9. Arsenic-induced hyperkeratosis causing skin ulceration, which leads to skin cancer

Figure 2. Different molecular configurations of arsenic

Figure 5. Health Impact Visual

Figure 10. Arsenic and other metal concentrations in chilli peppers and corn.

Figure 3. Block Diagram showing principal geochemical processes involved in the generation of high-arsenic groundwater in Bangladesh

Figure 1. Distribution of Arsenic Globally in Oxidizing and Reducing Conditions