Study shows heavy metal contamination of Lagos ground water
By Chukwuma Muanya
THE recent upsurge in kidney failure, hypertension, cancers, mental decline, memory loss, hearing loss, skin diseases may be due to heavy metal contamination of ground water such as from wells and boreholes.
In Nigeria today, the use of ground water has become an agent of development because the government is unable to meet the ever-increasing water demand. Thus, inhabitants have had to look for alternative ground water sources such as shallow wells and boreholes.
A recent assessment of water from boreholes in Lagos State has shown heavy metal contamination. The new study titled, "Heavy Metal Contamination of Ground Water: The Surulere Case Study," was published in Research Journal Environmental and Earth Sciences by Dr. Chimezie A. Anyakora and M.A. Momodu of the Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Lagos.
Previous studies have been shown that the most common heavy metals that humans are exposed to are Aluminium, Arsenic, Cadmium, Lead and Mercury.
Aluminium has been associated with Alzheimer's and Parkinson's disease, senility and pre-senile dementia. Alzheimer's disease is a brain disorder named for German physician, Alois Alzheimer, who first described it in 1906. Alzheimer's destroys brain cells, causing memory loss and problems with thinking and behaviour severe enough to affect work, lifelong hobbies or social life.
Parkinson's disease (also known as Parkinson disease or PD) is a degenerative disorder of the central nervous system that often impairs the sufferer's motor skills, speech, and other functions.
Arsenic exposure has been shown to cause among other illness or symptoms cancer, abdominal pain and skin lesions. Cadmium exposure produces kidney damage and hypertension.
Lead has been found to be a cumulative poison and a possible human carcinogen while for Mercury, toxicity results in mental disturbance and impairment of speech, hearing, vision and movement. In addition, Lead and Mercury may cause the development of autoimmunity in which a person's immune system attacks its own cells. This can lead to joint diseases and ailment of the kidneys, circulatory system and neurons. At higher concentrations, Lead and Mercury can cause irreversible brain damage.
It has been shown that the quality of these ground water sources are affected by the
characteristics of the media through which the water passes on its way to the ground water zone of saturation, thus, the heavy metals discharged by industries, traffic, municipal wastes, hazardous waste sites as well as from fertilisers for agricultural purposes and accidental oil spillages from tankers can result in a steady rise in contamination of ground water.
The study assessed heavy metal contamination of the groundwater in middle class neighbourhood of Lagos. About 49 well, and borehole water samples were analyzed using Atomic Absorption Spectrophotometer for their Aluminium, Cadmium and Lead content and their levels compared with the World Health Organisation (WHO) specified maximum contaminant level.
According to the WHO, the Maximum Contaminant Level (MCL) for Aluminium, Cadmium and Lead are 0.2mg/L, 0.003mg/L and 0.01mg/L respectively. From the results obtained, none of the samples analysed contained Aluminium in concentrations above the MCL, however, the metal was found to be present in 93.88 per cent of the samples analysed. Over 38 per cent of the samples had Cadmium present in them and 32.65 per cent of the samples had Cadmium concentrations above the MCL. Almost 60 per cent of the samples had detectable level of Lead while 36.73 per cent of the sample had Lead concentration above the MCL.
In general, 97.96 per cent of all samples analysed contained one or more of the three heavy metals studied each in varying concentrations. The results obtained from this study suggest a significant risk to this population given the toxicity of these metals and the fact that for many, hand dug wells and bore holes are the only sources of their water supply in this environment.
The researchers concluded: "These results show high concentration of these heavy metals and in some cases the levels were above WHO specified Maximum Contaminant level. This suggests a significant risk to this population given the toxicity of these metals and the fact that for many, hand dug wells and bore holes are the only sources of their water supply in this environment."
Indeed, one of the most important environmental issues today is ground water contamination and between the wide diversity of contaminants affecting water resources, heavy metals receive particular concern considering their strong toxicity even at low concentrations.
Heavy metals are elements having atomic weights between 63.546 and 200.590 and a specific gravity greater than 4.0, that is, at least five times that of water. They exist in water in colloidal, particulate and dissolved phases with their occurrence in water bodies being either of natural origin (example eroded minerals within sediments, leaching of ore deposits and volcanism extruded products) or of anthropogenic origin (that is solid waste disposal, industrial or domestic effluents, harbour channel dredging).
Some of the metals are essential to sustain life-calcium, magnesium, potassium and sodium must be present for normal body functions. Also, cobolt, copper, iron, manganese, molybdenon and zinc are needed at low levels as catalyst for enzyme activities, however, excess exposure to heavy metals can result in toxicity.
Heavy metal can cause serious health effects with varied symptoms depending on the nature and quantity of the metal ingested. They produce their toxicity by forming complexes with proteins, in which carboxylic acid (-COOH), amine (-NH2), and thiol (-SH) groups are involved. These modified biological molecules lose their ability to function properly and result in the malfunction or death of the cells. When metals bind to these groups, they inactivate important enzyme systems or affect protein structure, which is linked to the catalytic properties of enzymes. This type of toxin may also cause the formation of radicals, which are dangerous chemicals that cause the oxidation of biological molecules.
Previous studies have shown that the main threats to human health from heavy metals are associated with exposure to lead, cadmium, mercury and arsenic. These metals have been extensively studied and their effects on human health regularly reviewed by international bodies such as the WHO.
Heavy metals have been used by humans for thousands of years. Although several adverse health effects of heavy metals have been known for a long time, exposure to heavy metals continues, and is even increasing in some parts of the world, in particular in less developed countries, though emissions have declined in most developed countries over the last 100 years.
Cadmium compounds are currently mainly used in re-chargeable nickel-cadmium batteries. Cadmium emissions have increased dramatically during the 20th century, one reason being that cadmium-containing products are rarely re-cycled, but often dumped together with household waste. Cigarette smoking is a major source of cadmium exposure. In non-smokers, food is the most important source of cadmium exposure.
Recent data indicate that adverse health effects of cadmium exposure may occur at lower exposure levels than previously anticipated, primarily in the form of kidney damage but possibly also bone effects and fractures. Many individuals in Europe already exceed these exposure levels and the margin is very narrow for large groups. Therefore, measures should be taken to reduce cadmium exposure in the general population in order to minimise the risk of adverse health effects.
The general population is primarily exposed to mercury via food, fish being a major source of methyl mercury exposure, and dental amalgam. The general population does not face a significant health risk from methyl mercury, although certain groups with high fish consumption may attain blood levels associated with a low risk of neurological damage to adults. Since there is a risk to the fetus in particular, pregnant women should avoid a high intake of certain fish, such as shark, swordfish and tuna; fish (such as pike, walleye and bass) taken from polluted fresh waters should, especially be avoided.
There has been a debate on the safety of dental amalgams and claims have been made that mercury from amalgam may cause a variety of diseases. However, there are no studies so far that have been able to show any associations between amalgam fillings and ill health.
The general population is exposed to lead from air and food in roughly equal proportions. During the last century, lead emissions to ambient air have caused considerable pollution, mainly due to lead emissions from petrol. Children are particularly susceptible to lead exposure due to high gastrointestinal uptake and the permeable blood-brain barrier. Blood levels in children should be reduced below the levels so far considered acceptable, recent data indicating that there may be neurotoxic effects of lead at lower levels of exposure than previously anticipated. Although lead in petrol has dramatically decreased over the last decades, thereby reducing environmental exposure, phasing out any remaining uses of lead additives in motor fuels should be encouraged. The use of lead-based paints should be abandoned, and lead should not be used in food containers. In particular, the public should be aware of glazed food containers, which may leach lead into food.
Exposure to arsenic is mainly via intake of food and drinking water, food being the most important source in most populations. Long-term exposure to arsenic in drinking-water is mainly related to increased risks of skin cancer, but also some other cancers, as well as other skin lesions such as hyperkeratosis and pigmentation changes. Occupational exposure to arsenic, primarily by inhalation, is causally associated with lung cancer. Clear exposure-response relationships and high risks have been observed.
