1.1 Introduction
Arsenic is a naturally occurring metalloid with the chemical symbol As, known for its toxic properties and ability to contaminate groundwater through both natural geological processes and anthropogenic activities. Arsenic contamination of subsurface water is a significant environmental and public health issue, particularly in regions where groundwater serves as the primary source of drinking water. Arsenic, a naturally occurring element found in the earth's crust, can dissolve into groundwater through natural geological processes or due to human activities such as mining, agricultural practices, and industrial waste disposal. The widespread occurrence of arsenic contamination in groundwater, especially in countries like Bangladesh, India, and parts of Southeast Asia, has resulted in large-scale public health crises. According to the World Health Organization (WHO), prolonged exposure to arsenic-laden water can lead to severe health conditions, including skin lesions, various cancers, cardiovascular diseases, and developmental problems in children (Smith et al., 2000).
The mobility and concentration of arsenic in groundwater are influenced by several factors, including the geochemical properties of the soil, the redox potential, and the pH levels. Regions with high concentrations of arsenic-bearing minerals are particularly vulnerable to contamination, especially in areas with specific hydrogeological conditions that promote arsenic release into aquifers. While naturally occurring sources of arsenic are predominant, anthropogenic activities have exacerbated the problem in several locations, leading to higher contamination levels.
As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Limitation of the study and Definition of terms.
1.2 Background of Study
Water is one of the major means of transport of arsenic in the environment. Soil erosion and leaching have been reported to contribute to the quantity of arsenic in dissolved and suspend form. Soil erosion and agricultural runoff are large contributors to the arsenic concentration in sediments too. Arsenic in its various chemical forms and oxidation states is released into the aquatic environment by natural erosion processes, sewage, refuse and industrial discharges. On release to the aquatic environment, the arsenic species enter into a methylation/ demethylation cycle, while some are bound to the sediments or taken up by biota where they could undergo metabolic conversion to other organoarsenicals (Islam and Tanaka, 2004). The history of arsenic pollution in subsurface water traces back to ancient times, but it became a global concern only in recent decades due to its widespread impact on public health. Arsenic has been known for centuries as a toxic substance, historically used as a poison. However, its environmental significance was not fully recognized until the late 20th century when large-scale groundwater contamination was discovered, particularly in South Asia.
In the early 1970s and 1980s, large numbers of tube wells were installed in Bangladesh and parts of India to provide safe drinking water as an alternative to surface water sources, which were contaminated with pathogens causing waterborne diseases. Unfortunately, this shift led to an unintended consequence exposure to arsenic from naturally occurring sources in the subsurface layers of sediment. The discovery of this contamination in the 1980s marked the beginning of what the World Health Organization later described as “the largest mass poisoning in history” (Smith et al., 2000). Arsenic pollution in groundwater was not limited to South Asia; it has also been detected in parts of China, Southeast Asia, and Latin America. in the United States, arsenic contamination was identified in areas with specific geological formations, particularly in regions like the Southwest and parts of the Midwest (Smedley & Kinniburgh, 2002). The increased awareness of arsenic’s presence in groundwater prompted extensive research into its sources, and health impacts.
Historically, the contamination primarily arose from natural geological processes. Arsenic-bearing minerals, when exposed to certain redox conditions, dissolve and release arsenic into groundwater. However, human activities such as mining, industrial waste disposal, and the use of arsenic-based pesticides have further contributed to the pollution in many areas (Nordstrom, 2002). Efforts to mitigate the issue began in the late 20th century with the development of various technologies for arsenic removal and the establishment of drinking water standards. The World Health Organization set a guideline value of 10 µg/L for arsenic in drinking water, which has been adopted by many countries as the permissible limit. Despite these measures, millions of people in affected regions continue to face chronic exposure due to inadequate infrastructure and limited access to safe water (WHO, 2020).
The problem of arsenic pollution in subsurface water has garnered significant global attention over the past few decades due to its severe public health implications. Arsenic, a toxic metalloid, is naturally present in the earth’s crust and can leach into groundwater through natural geochemical processes. This contamination is especially prevalent in regions with specific geological conditions, such as the alluvial and deltaic plains of South Asia. Notably, countries like Bangladesh and India have faced catastrophic consequences, where millions of people have been exposed to arsenic through drinking water sourced from contaminated wells (Smedley & Kinniburgh, 2002).
The recognition of arsenic as a public health threat can be traced back to the 1980s when large-scale testing of tube wells in Bangladesh revealed widespread contamination. The problem was exacerbated by the extensive reliance on groundwater as a safe alternative to surface water, which was previously plagued by microbial contamination. While the shift to groundwater initially reduced waterborne diseases, it inadvertently exposed vast populations to arsenic poisoning. This phenomenon, described as the “largest mass poisoning in history,” highlighted the complex interplay between public health initiatives and environmental risks (Smith et al., 2000).
Several factors influence the concentration and mobility of arsenic in subsurface water, including the redox conditions, pH levels, and the presence of competing ions. The reduction of arsenic-bearing minerals under anaerobic conditions is a primary mechanism by which arsenic is released into groundwater. Additionally, human activities such as mining, agricultural runoff, and industrial waste disposal have intensified arsenic pollution in certain regions (Nordstrom, 2002).
Therefore, in Nigeria where the research was carried out, the activities that was conducted is to know the arsenic pollution of the subsurface water.
1.3 Statement of Problems
Investigation revealed that arsenic pollution in subsurface water presents a critical environmental and public health challenge, particularly in regions heavily reliant on groundwater for drinking purposes. The problem stems from the widespread presence of naturally occurring arsenic in geological formations, which leaches into aquifers under certain geochemical conditions. This issue is particularly severe in South Asia, where millions of people have been exposed to arsenic-contaminated water, resulting in severe health outcomes such as cancer, skin lesions, and cardiovascular diseases (Smith et al., 2000). Despite the global awareness of this crisis, significant gaps remain in the detection, prevention, and remediation of arsenic contamination.
One of the major problems is the difficulty in detecting arsenic pollution in groundwater. Unlike pathogens that cause immediate health effects, arsenic exposure leads to chronic conditions that develop over years, making early detection and intervention challenging. Furthermore, low-cost and accessible testing methods for arsenic in groundwater are often unavailable in rural and resource-limited settings, leaving communities vulnerable to prolonged exposure (Smedley & Kinniburgh, 2002).
Another issue is the socio-economic impact of arsenic contamination. In many affected regions, the population relies heavily on groundwater for drinking, irrigation, and daily use. Once a water source is found to be contaminated, communities are often left without affordable and accessible alternatives. The cost of installing arsenic-free wells or filtration systems is typically beyond the reach of low-income households, exacerbating inequalities in access to safe water (WHO, 2020).
Additionally, there are challenges related to the sustainable management of contaminated areas. While mitigation technologies such as filtration systems and chemical treatments exist, their long-term effectiveness and scalability remain concerns. Moreover, many of these interventions require regular maintenance and monitoring, which are often lacking in the affected regions. Policy implementation and enforcement are also inconsistent, particularly in areas with weak governance structures (Nordstrom, 2002). This study investigates concentration of Arsenic in surface and subsurface water within Onitsha metropolis and possible impact on populace.
1.4 Aim and Objectives of Study
The aim of this study is to analyze the arsenic pollution of the subsurface water in Onitsha. The specific objective of the study can be subdivided into the following:
- To evaluate the health risks associated with long-term exposure to arsenic-contaminated water and its socio-economic impacts on local communities;
- To analyze the geochemical and anthropogenic factors contributing to arsenic release and mobility in groundwater;
- To assess the spatial distribution and concentration levels of arsenic in subsurface water across affected regions;
- To explore and recommend sustainable technologies and practices for the removal of arsenic from groundwater; and
- To interpret through observations made in the field and laboratory results the history and processes that lead to the sources of Arsenic pollution in this region.
1.5 Significance of Study
This study will provide critical data and insights for government agencies and policymakers to develop targeted regulations and initiatives aimed at mitigating arsenic contamination in groundwater, leading to safer water supplies for communities. Also, the findings will assist public health organizations in designing and implementing effective health intervention programs to reduce arsenic exposure, thereby decreasing the prevalence of arsenic-related diseases in affected populations.
Furthermore, the findings of this study will aid in making existing education programs more effective and in reducing the risk of developing Arsenic-related illnesses. Also, it will assist policy makers in considering the effectiveness of current education efforts and in crafting future public awareness campaigns of Arsenic risks.
Finally, the study will benefit local communities by raising awareness about the dangers of arsenic contamination and offering practical guidance on alternative water sources and low-cost purification methods. NGOs and non-profit organizations working in water and sanitation will be better equipped with evidence-based strategies to advocate for improved infrastructure, testing, and education initiatives to protect vulnerable populations from arsenic exposure.
1.6 Scope of the Study
The scope of the research is focused on arsenic pollution of the subsurface water. An extract of Onitsha map was made from the Google Earth (map). The map covers Onitsha North and South Local Government Area, Okpoko in Ogbaru Local Government Area and part of Obosi and Nkpor, both in Idemili North Local Government Area.
Some of the boreholes from which water samples were collected are located in residential buildings, markets, churches and boreholes close to dump sites.
The study method employed was the direct observation, sampling and carrying out in-situ test right there in the field.
1.7 Limitations of the Study
The limitations of this study included several challenges that affected the scope and depth of the research.
- Financial Constraints: The cost of extensive field testing, laboratory analyses, and procuring advanced equipment for detecting arsenic levels in groundwater was higher than anticipated, resulting in a reduced sample size and limited geographical coverage. Additionally, the study's financial limitations restricted the deployment of more comprehensive interventions and technologies that could have provided deeper insights into the problem.
- Time Constraints: The study was conducted within a limited timeframe, which restricted the ability to perform longitudinal analyses or assess seasonal variations in arsenic concentrations. This time limitation also meant that some potential areas of investigation, such as in-depth community health assessments and broader regional studies, were not fully explored. Consequently, while the findings provide valuable insights, they reflect only a snapshot of the broader arsenic pollution issue.
1.8 Definition of Terms
Arsenic:
A naturally occurring metalloid with the chemical symbol As, known for its toxic properties and ability to contaminate groundwater through both natural geological processes and anthropogenic activities (Smith et al., 2000).
Subsurface Water:
Groundwater located below the earth’s surface, which is a crucial source of drinking water and can become contaminated by various pollutants, including arsenic (Smedley & Kinniburgh, 2002).
Arsenic Contamination:
It refers to the presence of arsenic in groundwater at levels exceeding safe drinking water standards, leading to potential health risks. This contamination typically results from the dissolution of arsenic-bearing minerals in geological formations or through anthropogenic activities such as mining and industrial waste disposal (Nordstrom, 2002).
Geochemical Factors:
Natural processes and conditions, including pH levels, redox potential, and mineral composition, that influence the mobility and concentration of arsenic in subsurface water (Smedley & Kinniburgh, 2002).
