ARSENIC POLLUTION OF THE SUBSURFACE WATER
This work investigates the extent of Arsenic pollution of borehole waters in Onitsha and environs. Fifteen samples of drinking water sourced from boreholes were randomly collected and analyzed using Atomic Absorption Spectrometry (AAS) and the technique employed is wet oxidation method. The results of Arsenic concentration obtained from the boreholes ranged from 0.00 mg/L (53.33% of boreholes) to 1.099mg/L (46.67% of boreholes). Seven out of the fifteen samples were observed to be concentrated with Arsenic ranging from 0.16mg/L to 1.099mg/L with majority of the concentrations occurring at areas adjacent to River Niger and Nwangene Lake. The results were found to be above the Maximum Contamination Level (MCL) of 0.01mg/L set by the World Health Organization (W.H.O, 2011) therefore, the sources were found to be contaminated with abnormal concentration of arsenic and the inhabitants who consume this water without proper treatment are vulnerable to severe health hazards. The high Arsenic concentrations in the study area could be attributed to both natural and anthropogenic processes such as improper discharge of untreated industrial effluents and sewage, urban storm runoff dissolving and leaching organic and inorganic matter into the subsurface ground, undersurface weathering, agro products, automobile workshops and emissions. The discharge of these effluents into water bodies leads to the bioaccumulation of heavy metals in fishes consequently, when humans feed on these aquatic organisms it results to serious health issues therefore, there is need for effluents to be treated before being discharged into the environment.
1.1 SUBSURFACE WATER
70% of the Earth’s surface is covered with water and 97% of the water is saline the quantity and the quality of water is equally important. Subsurface (groundwater) makes about 30.1% of the Earths freshwater as compared to 0.3% surface water and 68.7% Ice caps and Glaciers. Water is referred to as a universal solvent because it can dissolve many types of substances, but human and animal require water that contains fewer impurities. Drinking water comes from ground (subsurface) sources such as ground water and aquifers. It can also be obtained from surface water bodies such as rivers, streams and glacier other sources including rain, hail, snow and sea through desalination, surface water picks up different minerals resulting from the presence of animal or human activities. While for the subsurface water, the contaminants come from leachate, landfills, septic systems and the ambient rocks. Similarly, indiscriminate disposal from agricultural chemicals (Pesticides, Herbicides, Insecticides and Fertilizers) and household cleaning products. The contaminants in ground water take more time to be cleaned because it moves slowly and isn’t exposed to the natural cleansing benefits of air, sunlight and micro-organism.
Generally, the quality of drinking water is determined based on the appearance, taste, colour and odour of the water but all these do not really tell if the water should be free from hazardous compounds as the Geology of an area, its rock types, their weathered products, precipitation from rainfall, urban storm-water runoff and human activities in an environment contributes immensely to the chemistry of subsurface and surface water. Also, the quality of water is a measure of the suitability of the water for a designated use such as; drinking, agriculture, recreation, laundry and industrial usage based on selected physical, chemical and biological characteristics. The N.I.S (Nigerian Industrial standard), S.O.N (StandardOrganization of Nigeria) and W.H.O (World Health Organization) set a maximum contaminant level in drinking water supplied to municipal or population. When a standard or guideline is exceeded in the municipal or community water system, the state is required to take proper action to improve water quality level including treating the water through filtration or aeration blending water from several sources to reduce contaminants including inorganic chemicals such as salts, metals and mineral. These substances occur naturally in geological structures or sometimes caused by mining, industrial and agricultural activities. These chemical can badly affect human health when they are consumed in large amount.
There are two main sources of water supply that are available to man, surface water that includes: rivers, lakes, stream, drainage areas which funnels water toward the holding reservoirs and subsurface or ground water which includes wells, springs and horizontal galleries. The water resources are stressed by a number of factors, including cattle grazing, pollution and rapidly-growing urban areas. Over a billion people lack access to safe portable water supply globally and out of this number, more than 300 million people living in rural areas of SubSaharan Africa are being affected (Bresine, 2007).
1.2 ARSENIC POLLUTION
Arsenic is an element that exists in oxidation states of 5, 4, 3, 2, 1, 0, -1, -2, and -3, that is found naturally in air, water, soil, rocks and minerals, food, and even living organisms in low concentrations. In water, it is most likely to be present as arsenate, with an oxidation state of 5, if the water is oxygenated. However, under reducing conditions (<200 mV), it is more likely to be present as Arsenite, with an oxidation state of 3.
Dimethylarsenic acid (DMA)
Monomethylarsonic acid (MMA)
Table 1.21 Occurrence of Arsenic (Source: Adapted from W.H.O., 2011).
Arsenicals are used commercially and industrially as alloying agents in the manufacture of transistors, lasers and semiconductors, as well as in the processing of glass, pigments, textiles, paper, metal adhesives, wood preservatives, paints, dyes and ammunition. They are also used in the hide tanning process and, as well as pesticides, herbicides, feed additives and pharmaceuticals.
Environmental Levels (Water, Soil and Food):
The level of Arsenic in natural waters, including open ocean seawater, generally ranges between 1 and 2 µg/l. Concentrations may be elevated, however, in areas with volcanic rock and sulfide mineral deposits; in areas containing natural sources, where levels as high as 12 mg/l have been reported; near anthropogenic sources, such as mining and agrochemical manufacture; and in geothermal waters (mean 500 µg/l, maximum 25 mg/l). Mean Arsenic concentrations in sediment range from 5 to 3000 mg/kg; the higher levels occur in areas of contamination but are generally unrelated to Arsenic concentrations in water. The total estimated daily dietary intake of Arsenic may vary widely, mainly because of wide variations in the consumption of fish and shellfish. Most data reported are for total arsenic intake and do not reflect the possible variation in intake of the more toxic inorganic arsenic species. Limited data indicate that approximately 25% of the Arsenic present in food is inorganic, but this is highly dependent upon the type of food. Fish and meat are the main sources of dietary intake of Arsenic levels ranging from 0.4 to 118 mg/kg have been reported in marine fish sold for human consumption, and concentrations in meat and poultry can be as high as 0.44 mg/kg.
Health Effects of Arsenic:
Many scientific studies conclude that long term exposure to inorganic Arsenic through drinking water is associated with relatively high risks of cancer of the lungs and bladder and, to a lesser extent, with an increased risk of cancer of the skin, liver, and kidneys. Recent studies have also associated chronic Arsenic exposure through drinking water with a number of other serious health effects, including developmental defects, stillbirth, and spontaneous abortion as well as heart attacks, strokes, diabetes mellitus, and high blood pressure. Arsenic can also cause liver damage, nerve damage, and skin abnormalities (for example; discoloration and unusual growths, which may eventually turn cancerous). Some of these effects may take years to develop. Arsine is considered to be the most toxic form, followed by the Arsenites (Arsenic (III)), the arsenates (Arsenic (V)) and organic arsenic compounds.
Early clinical symptoms of acute intoxication include abdominal pain, vomiting, diarrhoea, muscular pain and weakness, with flushing of the skin. These symptoms are often followed by numbness and tingling of the extremities, muscular cramping and the appearance of a papular erythematous rash. Within a month, symptoms may include burning paraesthesias of the extremities, palmoplantar hyperkeratosis, Mee’s lines on fingernails and progressive deterioration in motor and sensory responses.
Signs of chronic Arsenicism, including dermal lesions such as hyperpigmentation and Hypopigmentation, peripheral neuropathy, skin cancer, bladder and lung cancers and peripheral vascular disease, have been observed in populations ingesting Arsenic contaminated drinking-water. Dermal lesions were the most commonly observed symptom, occurring after minimum exposure periods of approximately 5 years. Effects on the cardiovascular system were observed in children consuming Arsenic contaminated water (mean concentration 0.6 mg/l) for an average of 7 years.
There have been numerous epidemiological studies that have examined the risk of various cancers associated with arsenic ingestion through drinking-water. Many of these studies are ecological-type studies, and many suffer from methodological flaws, particularly in the measurement of exposure. However, there is overwhelming evidence that consumption of elevated levels of arsenic through drinking water is causally related to the development of cancer at several sites, particularly skin, bladder and lung. In several parts of the world, arsenic-induced disease, including cancer, is a significant public health problem. Because trivalent inorganic Arsenic has greater reactivity and toxicity than pentavalent inorganic arsenic, it is generally believed that the trivalent form is the carcinogen. However, there remain considerable uncertainty and controversy over both the mechanism of carcinogenicity and the shape of the dose–response curve at low intakes. Recently, the trivalent methylated metabolites, MMA (III) and DMA (III), have been found to be more genotoxic than inorganic arsenic.
1.3 AIM AND OBJECTIVES OF STUDY
The objective of the study can be subdivided into the following:
• To create both individual and public awareness of Arsenic pollution in the study area.
• To have knowledge regarding the diseases caused by Arsenic poisoning and mitigating measures available to prevent contamination.
• To identify Arsenic risk region, level of education, gender and age as important determinants of Arsenic knowledge.
• To know the extent of Arsenic pollution of the subsurface water in the study area.
• To prepare a study report that integrates observations made in the field.
• To interpret through observations made in the field and laboratory results the history and processes that lead to the sourcesof Arsenic pollution in this region.
1.4 SIGNIFICANCE OF STUDY
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.
1.5 SCOPE OF STUDY
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.
1.6 STUDY AREA
1.6.1 LOCATION AND ACCESSIBILITY
Onitsha is a commercial, industrial, educational and ecclesiastical city on the East bank of the River Niger in Anambra State, Southeastern Nigeria with a high population density of over 1million. It lies between latitude 06002I56II and 06038I34IINorth of the Equator and longitude 06037I30II and 06059I30II East of the Greenwich meridian and occupies an area of about 49,000km2. It is bounded by Anambra West and East local government area and Oyi in the North, Idemili North and South in the East, Ogbaru local government area in the South and inthe West by the River Niger.
Onitsha and environs is accessible by major roads such as the Onitsha-Asaba express way through the Niger Bridge linking the Eastern states to the Western part of the country, Onitsha-Enugu express way to the North and Onitsha-Owerri express way to the South and East. There are many minor and street roads that interconnect the towns within and outside the city.
1.6.2 TOPOGRAPHY, DRAINAGE AND HYDROGEOLOGY
The relief features of the study area are unique. The elevation ranges from 33m to 450m above sea level with average elevation of 250m. Onitsha falls into two main landform regions: a highland region of moderate elevation that covers most of the North central-Northeast, East-Southeast and a low plain to the Northwest-WestSouthwest of the highland. The highland region is a low asymmetrical ridge or cuesta in the Northern portion of the Awka-Orlu uplands, which trend roughly Southeast to Northwest, it is highest in the Southeast about 450m above sea level and gradually decreases in height to only 33m in the Northwest on the banks of the Anambra River and the Niger.
The drainage shows that the basin is having low relief of the terrain and is oval tending towards elongated shape and the network of the drainage is the dendritic pattern which indicates homogeneity in texture and lack of structural control. Dumping of refuse along culverts and channels has eventually blocked the channel of flow into the River Niger. The Niger River flows in the North-South direction.
The flow direction of the ground water direction of the ground water is multidirectional which was influenced by the piezo metric heights, there is also a depression (sinkhole) at the middle aquifer; this is as result of the population density with several functional boreholes taping its water from the middle aquifer on an hourly basis.
1.6.3 CLIMATE, VEGETATION AND OCCUPATION
Onitsha climate is classified as tropical. When compared with winter, the summers have much more rainfall. The average temperature in Onitsha is 27.00C while the average rainfall is 1828mm. Rainfall (precipitation) is lowest in December, with an average of 12mm. In September precipitation reaches its peak, with an average of 316mm. At an average temperature of 28.90C March is the hottest month of the year while at 25.40C on average, July is the coldest month of the year. Between the driest and wettest months, the difference in precipitation is 304mm and the variation in annual temperature is around 3.50C. Relative humidity is generally high throughout the year, between 70% and 180%. The highest figures are experienced during the wet season and the lowest during the dry season.
The vegetation of this region is light forest interspersed with tall grasses. The trees are not too tall and include both hardwood and softwood varieties; domesticated trees such as the mango, palm tree, guava, orange and almond are found. Much of the natural vegetation has been felled and the land utilized for development.
The occupation in Onitsha and its environs is mainly trading, services (tourism, hospitality, and civil service),and manufacturing, industrial and religious activities. The Onitsha Main market is reputed as the largest market in Africa which attracts people from different parts of the continent while, the city is also reputed as the number one (1) transit city in the country because most of the road transport services have their headquarters at Onitsha and it hosts the largest River port in the country which is on the River Niger.
1.7 LITERATURE REVIEW
An assessment of heavy metal pollution of effluents from three food industries within Onitsha in Anambra state, Nigeria (Nwosu et al, 2014) showed that the mean levels of all the heavy metals were above the limit allowed by the Nigeria Federal Ministry of Environment (FMENV, 1991) and the World Health Organization (W.H.O, 2011) in industrial effluent. It also revealed that apart from Arsenic, the concentrations of Mercury, Iron, Lead, Chromium, and Cadmium were not significant when the effluents were compared to each other. Arsenic concentration ranges from 0.205mg/L to 1.387mg/L.
Arsenic pollution of surface and subsurface water in Onitsha, Nigeria (Ezeabasili et al, 2014) revealed the pollution status of Onitsha metropolis water which indicates that the concentration of both surface and subsurface water is above the World Health Organization (W.H.O, 2011) standard. Surface concentration ranges from 0.2001mg/L (River Niger upstream) to 1.5883mg/L (River Niger central drainage surface) while Groundwater concentration ranges from 0.00mg/L to 1.2507mg/L. This also shows that the pollution of surface water is greater than that of the subsurface sources.
Furthermore, Histopathological alterations in the liver and kidney of the fish Chrysichthys nigrodigitatus due to heavy metals in Niger River (Nsofor et al, 2014) revealed the harmful effects of chemical pollutants like heavy metals in the fish Chrysichthys nigrodigitatus of Niger River Onitsha as well as pathological alterations in liver and kidney tissues of the fish. Also, Arsenic in water column is significantly lower than those in the fish.
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