14. The Problem With Geogenic Arsenic and Global Effects
Prepared by:
Riccilee Keller, Integrated Science Education Major
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.
Figure 6. Environmental Health Perspectives Volume 108, Number 5, May 2000
Figure 8. Geologic, Hydrologic, and
Geochemical Characterization of the Deep
Ground Water Aquifer System In the Bengal
Delta of Bangladesh, 2010
Figure 3. Block Diagram showing principal geochemical processes involved in the generation of high-arsenic groundwater in Bangladesh
INTRODUCTION
HEALTH CONCERNS
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.
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
Figure 2. Different molecular
configurations of arsenic
Figure 7. 10-year old girl suffering from arsenic
poisoning, hyperkeratosis
Figure 9. Arsenic-induced hyperkeratosis causing
skin ulceration, which leads to skin cancer
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. Chili peppers, dried over coal were 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 10. Arsenic and other metal concentrations in chilli peppers and corn.
SUMMARY
Figure 11. Environmental Health Perspectives
Figure 1. Distribution of Arsenic Globally
in Oxidizing and Reducing Conditions
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 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
Figure 4. Keratosis on hands, 2008
Figure 5. Health Impact Visual
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
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 Cited
Naidu, R., and Nadebaum, P.R. “Geogenic Arsenic and Associate Toxicity Problems in the Groundwater-Soil-Plant-Animal-Human Continuum.” CSIRO Land and Water, 2001
Smedley, Pauline, and Kinniburgh, David G. “ Arsenic in Groundwater and The Environment. British Geological Survey, 2005
Wuyi, Wang, et al., “Mitigation of Endemic Arsencosis with Selenium: An Example in China.” Institute of Geographical Sciences and Natural Resources Research, 2003
Centeno, Jose A., “Global Impacts of Geogenic Arsenic: A Medical Geology Research Case.” Royal Sweedish Sciences, 2007
Also see www.wou.edu/~rkeller06 for a more complete list of references.