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Nitrate and nitrite levels of potable water supply in Warri, Nigeria: a public health concern.


Nitrate in drinking water has long been considered a health threat for its ability to induce methemoglobinemia, and this health outcome is the basis of the U.S. Environmental Protection Agency's (U.S. EPA's) maximum contaminant level (Bruning-Fann & Kaneene, 1993). Groundwater underlying agricultural areas often has elevated nitrate levels due to runoff of nitrogen fertilizers. Intake of nitrate from drinking water and dietary sources may cause increased exposure to N-nitroso compounds through endogenous nitrosation (Mirvish, 1995). N-nitroso compounds, which are known animal carcinogens, are formed endogenously from drinking water and dietary sources of nitrate and nitrite. In their study, Coss and co-authors (2004) suggest that long-term exposure to drinking water nitrate at levels below the maximum contaminant level of nitrate nitrogen (10 mg/L) is not associated with pancreatic cancer. The work of Niagolova and co-authors (2005) explored two hypotheses relating elevated concentrations of nitrogen species in drinking water and the disease Balkan Endemic Nephropathy (BEN). Their results clearly establish an exposure pathway between anthropogenic activity and drinking water supplies, suggesting that the causative agent for BEN could result from surface contamination. Turkdogan and co-authors (2003) investigated nitrate and nitrite levels in some traditional foods and drinking water in Van, an endemic upper gastrointestinal (esophageal and gastric) cancer region of eastern Turkey. Their findings suggest that the influence of a traditional diet rich in nitrate and nitrite is significant in the development of endemic upper gastrointestinal (esophageal and gastric) cancers in the Van region of Turkey.

Pregnant women who drink nitrate-contaminated water may be at increased risk of having spontaneous abortions or giving birth to infants with congenital malformations, especially of the central nervous system (Centers for Disease Control and Prevention [CDC], 1996; Croen, Todoroff, & Shaw, 2001). Although the role of nitrate in drinking water as a risk for cancer is controversial, high levels of nitrate and nitrosamines in drinking water have been associated with increased mortality (Cantor, 1997) and incidence of some cancers and lesions (Gulis, Czompolyova, & Cerhan, 2002). Spontaneous abortion, ectopic pregnancy (Gbaroro & Igbafe, 2002), malignant lymphomas (Omoti, 2006; Omoti & Halim, 2005), and soft tissues sarcomas (Seleye-Fubara, Nwosu, & Yellowe, 2005) have been reported in the Niger Delta region of Nigeria.

While empirical evidence exists to substantiate increased levels of nitrate pollution of groundwater, the pattern of pollution in Nigeria is poorly understood. Since these groundwater supplies are the main source of potable water in the Niger Delta, they constitute a major source of exogenous nitrate and nitrite to the population. The study area is located within the mangrove swamp in the equatorial rainforest belt of Nigeria, which is marshy and has a shallow water aquifer.

The poor health conditions of the people of the Niger Delta area, who often blame their woes on environmental damage by oil prospecting and oil producing activities, have led to political restiveness, claims, negotiations, and so forth between the local people and successive governments. The goal of this study is to investigate the impact of industrialization on the nitrate and nitrite burden of potable water supply in Warri. This is why we have divided the sampling sites into market areas, characterized by refuse dumps, and industrialized areas, characterized by crude oil pollution such as spillages and leakages.

Materials and Methods

A borehole is a well drilled into the subsurface aquifer for the purpose of exploiting groundwater. An aquifer is a porous and permeable rock hosting water or a water-saturated geologic unit or formation that may be exploited for water for economic use. It is drilled solely to provide water for drinking, domestic, and industrial uses. The depth of boreholes in the study area is between 150 m and 200 m. Boreholes are situated in an unconfined sedimentary basin that exceeds 2000 m. Hand-dug wells are between 16 m and 45 m deep. With hand-dug wells, seasonal fluctuation occurs in that the water column rises in the rainy season but decreases or may dry up in the dry season.

A total of 30 water samples was divided into two subsets of 15: five each of surface water, shallow wells, and boreholes from industrial areas; and five each of surface water, shallow wells, and boreholes from market areas. Nitrate was analyzed using the Bruccine colorimetric method of the Association of Official Analytical Chemists (1980), while nitrite was spectrophotometrically determined according to the Greiss method of Montgomery and Dymock (1961). Spectrophotometric readings were taken at 543 nm in a DR/4000 UV-Vis spectrophotometer and concentrations were read from the standard curve. Triplicate determinations of nitrates and nitrites were made.


Table 1 shows the nitrate and nitrite level in water samples from the industrialized area of the city. Surface water from Ubeji had the highest level of nitrate and nitrite, 4.28 and 1.34 mg/L, respectively; whereas the Ubeji borehole had the lowest level of nitrate at 0.18 mg/L. Aladja and Ubeji boreholes showed the lowest levels of nitrite, 0.03 mg/L.

Nitrate and nitrite levels in water samples from the market area are shown in Table 2. The Udu River had the highest nitrate level of 8.36 mg/L, while the lowest nitrate level was found in the Marcava River at 0.22 mg/L. The highest level of nitrite was seen in the Udu River, 1.12 mg/L, and the lowest level of nitrite was found in the Agbarho borehole, 0.02 mg/L.

Taken together, the samples from the market area of Warri tended to show higher levels of nitrate and nitrite than the water samples from the industrialized area.


In a continuation of our geochemical and mineralogical study of potable water in Warri, we have investigated the levels of nitrate and nitrites in the market and industrialized areas of the community.

Warri is a densely populated metropolitan city that generates high volume of municipal waste and sewage. A high percentage of the population in Warri depends on an interwoven network of surface water (characteristics of the Niger Delta region of Nigeria), shallow (16--45 m deep) dug wells, and boreholes for their regular water supply. Water treatment is rarely carried out at the household level, yet adequate and safe drinking water provisions are not priorities for the federal and state governments. No water delivery protection exists in most cities in Nigeria. Poor sanitation, littered compost heaps, fertilizer application, sewage, abattoirs, large organic waste from the market and industrial effluents, and especially intense oil exploration and exploitation are major sources of nitrate and nitrite in water sources of the study area.

Average nitrate levels of 110 and 224 mg/L for surface water bodies and shallow aquifers, respectively, were reported by Egboka and Ezeonu in southeastern Nigeria (Egboka & Ezeonu, 1990). It was observed that all the water samples from the two areas contain some amount of nitrate and nitrite. In our study, the highest nitrate level was in the Udu and Enerhen rivers, followed by the Pessu and Ubeji rivers. The highest level of nitrite was in the Ubeji River, Udu well, Udu River, and Enerhen well. These values were lower than both the levels found by Egboka and Ezeonu in the eastern part of Nigeria and the WHO maximum contamination level of 45mg/L (World Health Organization [WHO], 1985). As a result, these findings may have possible public health implications given the poor nutrition and poor hygiene of the local Nigerian people. The maximum allowable nitrate level for drinking water under WHO's and the European Union's maximum admissible concentration standards is 50 mg/L nitrate ion (European Economic Community, 1980). (The U.S. EPA drinking water standard is 10 mg/L as nitrate-nitrogen, roughly equivalent to 45 mg/L nitrate ion.)

The higher levels of nitrate and nitrites from the market area seen in this study are an indication of the environmental burden of nitrate from the decaying matter and refuse dumps, which is a common feature of most cities in developing nations like Nigeria (Chukwuma, 1994). The pollution load of nitrate from household and market wastes into our water resources constitute an important consideration in determining environmental exposure to these chemical entities. These contaminated water sources are most frequently used untreated for direct drinking or in our food and beverage industry (Ezeonu, Egboka, & Okaka, 1992). Water is largely untreated in most cities in Nigeria, hence water regulation policy is almost nonexistent. Households and industries resort to private arrangements for their water supply. A major concern arises from the danger posed by the chronic effect of continued ingestion of contaminated water sources, since drinking water in large volumes is a daily practice in the tropics due to excessive temperature and perspiration.

Health workers need to educate the residents on the implications of nitrate pollution and help ensure improved sanitation by disposing municipal wastes and sewages so that runoff water will not pollute the potable waterways.

In conclusion, contrary to the claims of many, the poor health conditions of the Niger Delta people may not be completely blamed on oil producing activities in the area. The present study suggests that indiscriminate disposal of waste and poor sanitation may be additional contributing factors of nitrate pollution of water supply in the Niger Delta area of Nigeria. With no public health educators, high infant mortality and poverty in Nigeria accentuate the importance of more epidemiological investigations of the health of the Niger Delta people of Nigeria.


Association of Official Analytical Chemists. (1980). Official methods of analysis (13th ed.). Washington, DC: Author.

Bruning-Fann, C.S., & Kaneene, J.B. (1993). The effects of nitrate, nitrite, and N-nitroso compounds on human health: A review. Veterinary Human Toxicology, 35(6), 521-538.

Cantor, K.P. (1997). Drinking water and cancer. Cancer Causes Control, 8(3), 292-308.

Centers for Disease Control and Prevention. (1996). Spontaneous abortions possibly related to ingestion of nitrate-contaminated well water--LaGrange County, Indiana, 1991-1994. Morbidity Mortality Weekly Report, 45(26), 569-572.

Chukwuma, C., Sr. (1994). Health concepts, issues, and experience in the Abakaliki area, Nigeria. Environmental Health Perspectives, 102(10), 854--856.

Coss, A., Cantor, K.P., Reif, J.S., Lynch, C.F., & Ward, M.H. (2004). Pancreatic cancer and drinking water and dietary sources of nitrate and nitrite. American Journal of Epidemiology, 159(7), 693-701.

Croen, L.A., Todoroff, K., & Shaw, G.M. (2001). Maternal exposure to nitrate from drinking water and diet and risk for neural tube defects. American Journal of Epidemiology, 153(4), 325-331.

Egboka, B.C.E., & Ezeonu, F.C. (1990). Nitrate and nitrite pollution and contamination in parts of South Eastern Nigeria. A case study of developing economy. Water Resources (Nigeria), 2, 101-110.

European Economic Community. (1980). Council Directive 80/778/ EEC of 15 July 1980 relating to the quality of water intended for human consumption. Retrieved July 2, 2008, from http://faolex.fao. org/docs/texts/eur37618.doc

Ezeonu, F.C., Egboka, B.C.E., & Okaka, A.N.C. (1992). Nitrate and nitrite in some non-alcoholic beverages and water supplies in Onitsha, Nigeria. Journal Food Science Technology, 29(5), 329-330.

Gharoro, E.P., & Igbafe, A.A. (2002). Ectopic pregnancy revisited in Benin City, Nigeria: Analysis of 152 cases. Acta Obstetrics Gynecology Scandinivica, 81(12), 1139-1143.

Gulis, G., Czompolyova, M., & Cerhan, J.R. (2002). An ecologic study of nitrate in municipal drinking water and cancer incidence in Trnava District, Slovakia. Environmental Research, 88(3), 182-187.

Mirvish, S.S. (1995). Role of N-nitroso compounds (NOC) and N-nitrosation in etiology of gastric, esophageal, nasopharyngeal and bladder cancer and contribution to cancer of known exposures to NOC. Cancer Letters, 93(1), 17-48.

Montgomery, H.A.C, & Dymock, J.F. (1961). The determination of nitrate in water. Analyst, 86, 414-416.

Niagolova, N., McElmurry, S.P., Voice, T.C., Long, D.T., Petropoulos, E.A., Havezov, I., Chou, K., & Ganev, V. (2005). Nitrogen species in drinking water indicate potential exposure pathway for Balkan Endemic Nephropathy. Environment Pollution, 134(2), 229-237. Omoti, C.E. (2006). Socio-demographic factors of adult malignant lymphomas in Benin City, Nigeria. Nigeria Postgraduate Medical Journal, 13(3), 256-260.

Omoti, C.E., & Halim, N.K. (2005). Adult lymphomas in Edo state, Niger Delta region of Nigeria - Clinicopathological profile of 205 cases. Clinical Laboratory Haematology, 27(5), 302-306.

Seleye-Fubara, D., Nwosu, S.O., & Yellowe, B.E. (2005). Soft tissue sarcomas in the Niger Delta Region of Nigeria (a referral hospital's study). Nigeria Journal of Medicine, 14(2), 188-194.

Turkdogan, M.K., Testereci, H., Akman, N., Kahraman, T., Kara, K., Tuncer, I., & Uygan, I. (2003). Dietary nitrate and nitrite levels in an endemic upper gastrointestinal (esophageal and gastric) cancer region of Turkey. Turkey Journal of Gastroenterology, 14(1), 50-53.

World Health Organization. (1985). Health hazards from nitrates in drinking water. Copenhagen: Author.

Corresponding Author: Orish Ebere Orisakwe, Nnamdi Azikiwe University, Nnewi Campus, Toxicology Unit, Department of Pharmacology, College of Health Sciences, Anambra State, PMB 5001 Nigeria. E-mail:
Nitrates and Nitrites in Water Samples from Industrialized Area

Location of Sampling Point    Nitrate (mg/L)    Nitrite (mg/L)

Ekpan River                        1.43              0.18
Ekpan well                         1.18              0.12
Ekpan borehole                     2.63              0.03
Ubeji River                        4.28              1.34
Ubeji well                         1.12              0.14
Ubeji borehole                     0.18              0.03
NPA River                          1.08              0.42
NPA well                           1.48              0.32
NPA borehole                       1.13              0.08
Aladja River                       0.70              0.25
Aladja well                        1.82              0.15
Aladja borehole                    1.20              0.03
Otokutu River                      0.40              0.30
Otokutu well                       1.42              0.08
Otokutu borehole                   1.10              0.06


Nitrate and Nitrite in Water Samples from Market Area

Location of Sampling Point    Nitrate (mg/L)    Nitrite (mg/L)

Agbarho River                      0.93              0.12
Agbarho well                       2.40              0.18
Agbarho borehore                   1.18              0.02
Udu River                          8.36              1.12
Udu well                           2.17              1.14
Udu borehole                       1.35              0.10
Marcava River                      0.22              0.16
Marcava well                       2.20              0.14
Marcava borehole                   1.40              0.08
Pessu River                        4.29              0.62
Pessu well                         2.28              0.60
Pessu borehole                     1.27              0.06
Enerhem River                      4.65              0.64
Enerhem well                       2.19              1.10
Enerhem borehole                   1.38              0.05
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Article Details
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Author:Nduka, John Kanayochukwu; Orisakwe, Orish Ebere; Ezenweke, Linus Obi
Publication:Journal of Environmental Health
Article Type:Report
Geographic Code:6NIGR
Date:Jan 1, 2010
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