Thesis Abstract

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.

Thesis Overview

INTRODUCTION 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  

General Description:

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.

Compound

Chemical Abstracts

Service Number

Molecular formula

Arsenic

7440-38-2

As

Arsenic trioxide

1327-53-3

As2O3

Arsenic pentoxide

1303-28-2