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Lake pollution in Ibadan, Nigeria
Environment International, Vol. 11, pp. 419-423, 1985 Printed in the USA. All rights reserved.
0160-4120/85 $3.00 + .00 Copyright ©1985 Pergamon Press Ltd.
LAKE POLLUTION IN IBADAN, NIGERIA M. K. C. Sridhar and A. O. Bammeke Department of Preventive and Social Medicine, College of Medicine, University of Ibadan, Ibadan, Nigeria
(Received 31 July 1984;Accepted 3 January 1985) An investigation was made of the sources and degree of pollution of Ogunpa lake, situated in Ibadan, Nigeria. It was shown that the lake receives a variety of waste effluents from domestic and industrial sources which discharge into the Ogunpa stream. These waste effluents have caused an odour nuisance in the lake, and little or no dissolved oxygen is present. The discharge of nutrients (N and P) to the lake has resulted in excessivegrowth of aquatic weeds. All these impacts on the lake have resulted in a reduced fish production. Some suggestions for the prevention of pollution and the recovery of the lake are presented.
M a t e r i a l s and M e t h o d s
Introduction
Materials Nigeria, the most populous country in Black Africa, is fast developing towards self-reliance. In this direction, agriculture, animal husbandry, fisheries, and a variety of industries are developing. In addition, the government is actively considering p r o m o t i o n of tourism a m o n g the country's 44 game reserves, 17 m a j o r waterfalls, 13 beaches, 45 lakes and riverine resorts, and 22 hilly and mountainous areas. All of these activities result in increasing pollution and pose environmental problems with economic and productivity losses. One of the cities that has been facing the wrath of pollution at a fast rate is the city of Ibadan, the capital of the most populous Oyo State. A m o n g the different lakes and streams, Ogunpa lake is perhaps the most popular and worst polluted. The lake was at one time a rich source of fish, and the area around it, including a zoological garden, is being used by visitors and tourists as a picnic and recreational spot. The Ogunpa lake is formed out of the Ogunpa stream, which travels through a m a j o r part of the city and receives a variety o f waste effluents. One o f the m a j o r effluents is treated sewage f r o m the University College Hospital, located close to the lake (Fig. 1); this poses a potential and probable adverse effect on the water quality and the future of Ogunpa lake. With a view to studying the sources and effects of different pollutants entering the lake, an investigation was undertaken; this paper presents the results obtained.
Ogunpa lake: Ogunpa lake is a m a n - m a d e lake formed along the path of the Ogunpa stream, which traverses a m a j o r portion of the city including Ashi village. The lake has an area of 13 ha, stretching about 1 k m with a m a x i m u m depth of about 5 m. Samples of water were collected at different points (Fig. 1). Ogunpa stream: Samples of water f r o m Ogunpa stream as it enters the lake and samples f r o m upstream up to about 10 km were collected. Sewage effluent: The sewage of University College Hospital, Ibadan, amounting to about 14,400 L / d a y is treated conventionally. The sewage is domestic in character and passes through a screen, two comminutors, three primary clarifiers, three trickling or percolating filters, and an activated sludge plant. The final effluent is chlorinated and discharged into a stream. The sludge obtained f r o m the primary clarifier and the activated sludge plant is digested anaerobically and dried in sludge drying beds; the dried powder is then made available for use on the f a r m as a manure. The samples of sewage at every stage of treatment were collected for analysis. Fishes: The types o f fishes found in the lake were recorded. A dominant fish found in the lake, Hemichromis 419
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/t Fig. 1. Map showing the Ogunpa lake receiving waste effluents through various feeder streams (Numbers in the lake show the sampling points).
bimaculatus, was used in the toxicity tests using the waste effluents entering the lake. Methods The samples of lake water and waste effluents were analyzed for pH value, biochemical oxygen demand (BOD), 4-h permanganate value representing the difficultly oxidizable organic matter, dissolved oxygen, total alkalinity, total hardness, ammonia nitrogen, total phosphorus, and chloride. The analyses were carried out according to the standard methods (APHA, 1975; Ministry of Housing and Local Government, 1956). Results
Characteristics of water in Ogunpa lake The characteristics of water in Ogunpa lake at five different points (Fig. 1) in the course of its flow were
determined, and the results are presented in Table 1. The results indicate that the lake water is polluted with organic matter showing low dissolved oxygen levels. In
Table 1. Characteristics of water at different points in Ogunpa Lake. ~ i n g Characteristi~
points
pH value Dissolved oxygen (mg/L) Biochemical oxygen demand (mg/L) 4-h Permanganate value (rag/L) Ammonia N (mg/L) Total alkalinity (mg/L) Total hardness (mg/L) Chloride (mg/L)
Mean Value
1
2
3
4
5
6.4 2.0 13.4
6.4 0.9 8.8
6.3 0.9 8.8
6.9 1.1 9.0
6.7 2.3 7.2
6.54 1.44 9.44
2.5
2.0
1.4
2.2
1.9
2.00
2.0 116 100 30
2.5 96 120 22
0.5 76 140 24
1.0 100 144 26
2.5 112 164 24
1.70 I00.00 134.00 25.20
421
Lake pollution in Nigeria Table 2. Weekly variation in the characteristics of water in Ogunpa stream entering the lake. Characteristic
Sunday
Monday
Tuesday
pH value Dissolved oxygen(mg/L) BOD (mg/L) 4-h permanganate value (mg/L) Ammonia N (mg/L) Total PO4 (mg/L) Total alkalinity (mg/L) Total hardness (mg/L) Chloride, C1 (mg/L)
6.7 6.3 8.8
6.8 5.8 13.0
6.8 Nil 30.8
6.5 3.7 27.2
6.4 1.0 2.0 108 116 20
10.4 Nil 1.0 112 116 24
8.8 Nil 1.0 120 120 22
10.8 -100 100 22
addition, the lake has been fully covered with aquatic vegetation and the width has been constricted to a great extent.
Characteristics o f water in Ogunpa stream before entering the lake The results o f analysis of water in Ogunpa stream before entering into the lake on different days of the week are given in Table 2. The results indicate that the water is grossly polluted; this is evident from high organic matter, ammonia nitrogen, and phosphorus. It was interesting to note that the BOD value was the lowest on Sunday.
Characteristics o f the sewage effluent before entering the lake The characteristics of sewage effluent from the University College Hospital on different days of the week before entering the lake are given in Table 3. The results indicate that the quality was variable on different days and showed higher values for ammonia nitrogen and chloride.
Sources of pollution in Ogunpa lake The two major streams that are entering the Ogunpa lake are (a) Ogunpa stream, and (b) sewage effluent from University College Hospital. To determine which is responsible for the major pollution, these two sources were examined more intensively.
Wednesday
Friday
Saturday
Weekly Mean
6.7 1.2 16
6.6 1.4 16.4
6.9 4.2 26.0
6.7 3.2 19.7
2.8 -116 120 24
10.0 1.0 4.0 100 128 26
8.0 3.0 2.0 128 112 22
8.2 1.0 2.0 112 116 22.9
Thursday
Ogunpa upstream: The upstream of Ogunpa travels a long distrance and collects a variety o f effluents from open drains, industries, slaughterhouses, and other sources. The samples were collected at 4 different areas, and the results are given in Table 4. The results indicate that the stream receives a variety of industrial wastes with high BOD. It was also observed that, at times, the stream appears viscous with oily slicks. Sewage treatment plant at University College Hospita# A series o f samples was collected and analyzed to determine to what extent the sewage was treated at various stages, and its influence on the character of the final effluent entering the Ogunpa lake. The results (Table 5) indicate that the sewage treatment plant is able to remove the organic matter to a great extent but was not able to remove ammonia and phosphorus. This is understandable because only the trickling filters are functional; the activated sludge plant is inoperative due to lack of spare parts. It was also found that the effluent coming out of the activated sludge plant was much inferior in quality than its influent, which consists o f the effluents from the trickling filter. The comparison between these two sources revealed that the Ogunpa stream has been carrying a heavy load of pollution as compared to that of the sewage effluent. This was also in conformity with the observations made by the Ministry of Agriculture and Natural Resources, indicating that the low dissolved oxygen was a result of
Table 3. Weekly variation in the characteristics of sewage effluent entering the lake. Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Weekly Mean
Characteristic
Sunday
pH x;alue Dissolved oxygen(mg/L) BOD (mg/L) 4-h permanganate value (rag/L) Ammonia N (mg/L) Total PO4 (mg/L) Total alkalinity (mg/L) Total hardness (mg/L) Chloride, C1 (mg/L)
6.8 5.6 8.4
6.9 5.7 10.4
6.8 5.0 11.8
6.9 4.0 13.2
6.9 3.5 5.8
6.9 4.1 4.2
7.0 5.9 14.0
6.9 4.8 9.7
6.8 5.0 1.0 92 96 26
3.6 6.0 2.8 100 120 36
4.4 10.0 4.0 108 116 34
5.2 -116 124 36
2.8 92 128 44
1.6 5.0 0.2 100 144 42
6.4 5.5 4.8 104 124 40
4.4 6.3 2.6 102.0 121.7 36.9
422
M.K.C. Sridhar and A. O. Bammeke Table 4. Characteristics of water from Ogunpa upstream. Flow Direction Characteristic Appearancea Dissolved oxygen (mg/L) BOD (mg/L) 4-h Permanganate value (mg/L) Ammonia, N (rag/L) Total phosphorus, PO, (rag/L) Total alkalinity (mg/L) Total hardness (mg/L) Chloride (mg/L)
Aderinola Road
Oduduwa Road
Francis Okediji Road
Bodija Area
Viscous, black and stinking Nil 325.0 46.8 1.5 4.0 132.0 136.0 32.0
Fairly clear
Dark
Dark
7.7 6.0 3.6 1.0 1.0 96.0 1190.0 20.0
0.5 76.0 13.6 2.0 1.0 112.0 112.0 22.0
1.1 96.0 14.4 2.5 1.5 116.0 112.0 22.0
aDomestic discharges from open drains and industrial discharges from a beverage factory, tannery and a slaughter house were noticed.
d o m e s t i c sewage a n d r u n - o f f l a d e n with a n i m a l wastes a n d b l o o d . T h e r e was n o p o s s i b i l i t y t h a t a n y a n i m a l wastes a n d b l o o d w o u l d be in the sewage effluent, since it was essentially o r i g i n a t i n g f r o m the residential a n d hospital community.
Further toxicity studies using fish T h e O g u n p a l a k e has a b o u t nine varieties o f fish, as given in T a b l e 6. O f these, while the delicate varieties have r e d u c e d in n u m b e r , Hemichromis bimaculatus is the d o m i n a n t v a r i e t y at this time. T h e s e fish were collected f r o m the lake; a n d five e a c h were i n t r o d u c e d i n t o f o u r 10-L b u c k e t s c o n t a i n i n g t a p w a t e r , O g u n p a l a k e water, w a t e r o f O g u n p a s t r e a m t h a t enters the lake, a n d
sewage e f f l u e n t t h a t enters the lake. T h e fish were exa m i n e d f o r 4 h. T h e results ( T a b l e 7) i n d i c a t e t h a t the O g u n p a s t r e a m h a d the highest p o l l u t i o n l o a d to kill the fish in 4 h as c o m p a r e d to o t h e r sources. T h e high a m m o n i a n i t r o g e n c o n c e n t r a t i o n in the sewage effluent seems to be r e s p o n s i b l e for the fish kills. L a c k o f dissolved o x y g e n in the t r e a t m e n t p l a n t effluent also c o u l d h a v e a f f e c t e d the fish.
Discussion A large a m o u n t o f w o r k was d o n e o n the p o l l u t i o n levels o f n a t u r a l waters in Nigeria, the sources, a n d their effects ( O l u w a n d e et al., 1983, S r i d h a r et aL, 1981;
Table 5. Characteristics of wastewater at different stages of treatment. ~
C
ters Temp )
1. After the comminutor (combined influent) 2. After primary settling tank 3. After the trickling filter 4. Activated Sludge plant effluent 5. Chlorine contact basin effluent 6. Upstream of discharge point 7. Downstream of discharge point 8. Laundry wastewater
Suspended Solids pH Value (mg/L)
Dissolved Solids (rag/L)
Total Solids (rag/L)
BOD (mg/L)
NH~N (rag/L)
Total P PO, Coliforms (mg/L) (MPN/100 mL)
Residual Chlorine for 5, 6, 7 only
32
7.00
200
289
489
243
12.0
4.8
80,000,000
31
6.80
133
172
305
185
8.5
3.2
65,000,000
30
6.60
19
150
169
7.5
4.0
1.6
900
31
6.80
46
103
149
8.3
4.5
4.8
900
31
6.85
41
145
186
8.3
4.5
2.4
Nil
1.0
27
7.00
29
115
144
3.6
2.0
0.8
175
Nil
30
7.00
83
101
184
7.0
4.5
2.4
Nil
0.5
33
9.65
52
152
204
2.6
1.0
0.8
4
Lake pollution in Nigeria
423
Table 6. The varieties of fishes found in the lake.
Table 7. Influence of the different waters on the fish.
Variety
Water Quality Number of Fish
Sarotherodon inloticus Sarotherodon qalilaeus Tilapia zillii Tilapia rnelanopleura Glarias lazera Gymnarchus niloticus Barbus occidentalis Hemichromis bimaculatus Hemichromis fasciatus
Sridhar and Sharma, 1980; Mombeshora et al., 1981). Pollution has been c o m m o n in every urban centre as a result of population migration, industrial development, and lack of sanitary disposal of sewage and pollution control regulations. As in this study, people often raise sporadic objections, but no effective measures are taken thereafter. At a site such as Ogunpa lake, the origin of pollutants into the lake is multifarious. Though a sewage treatment plant is contributing to some extent, the greater pollution is coming through Ogunpa stream. This stream does not carry any pure water. It acts as a sewer for many waste effluents from slaughterhouses, and a beverage factory, tannery, and laundry. This stream is also misused for dumping o f refuse which leaches organic and inorganic pollutants, besides causing floods. The result many times is that the lake emits bubbles of hydrogen sulphide in the dry periods; the entire lake surface is also covered with gigantic water lettuce. The authorities have even given up on removing this weed. In 1971, Nigeria experienced its worst cholera epidemic, in which 14,158 suspected cases and 162 deaths were reported. The epidemic was attributed to the contaminated water supplies, and Ogunpa stream was no exception. To avoid such incidents, what is needed today is the introduction of sanitary disposal of sewage and other waste waters as a matter of urgency, at least in 10 of the
Dissolved At At the end Percent Oxygen Ammonia Water Source Start of 4 h Died (mg/L) N (rng/L) Tap (Control) Ogunpa lake Ogunpa stream entering the lake Sewage effluent entering the lake
5 5
5 4
0 20
7.7 0.8
0.0 4.5
5
1
80
0.0
4.5
5
3
40
0.8
7.0
Nigeria's major cities. This should be followed by the introduction of pollution control legislation with effective monitoring. The experiences o f Britain and other developed countries in the years of the Industrial Revolution should be wisely utilized to prevent the repetition o f the irrevocable death of the rivers and the associated health and economic losses. Acknowledgements-We thank O. Ojo and J. Olaniyan, Fisheries
Division, Ministry of Agriculture and Natural Resources, Oyo State, for their cooperation and assistance in carrying out this work.
References American Public Health Association/American Water Works Association (1975) Standard Methods for the Examination of Water and Wastewater, 14th ed. APHA/AWWA, Washington, D.C. Ministry of Housing and Local Government (1956) Methods of Chemical Analysis as Applied to Sewage and Sewage Effluents,
2nd ed. Her Majesty's Stationery Office, London. Mombeshora, C., Ajayi, S. O. and Osibanjo, O. (1981) Pollution studies on Nigerian Rivers: Toxic heavy metal status of surface waters in Ibadan city, Environ. Int. 5, 49-53. Oluwande, P. A., Sridhar, M. K. C., Bammeke, A. O., and Okubadejo, A. O. (1983) Pollution levels in some Nigerian Rivers, Water Res. 17, 957-963. Sridhar, M. K. C. and Sharma, B. M. (1980) Pistia stratiotes L. in Nigerian waters, Experientia 36, 953-954. Sridhar, M. K. C., Oluwande, P. A., and Okubadejo, A. O. (1981) Health hazards and pollution from open drains in a Nigerian city. Ambio 10, 29-33.
0160-4120/85 $3.00 + .00 Copyright ©1985 Pergamon Press Ltd.
LAKE POLLUTION IN IBADAN, NIGERIA M. K. C. Sridhar and A. O. Bammeke Department of Preventive and Social Medicine, College of Medicine, University of Ibadan, Ibadan, Nigeria
(Received 31 July 1984;Accepted 3 January 1985) An investigation was made of the sources and degree of pollution of Ogunpa lake, situated in Ibadan, Nigeria. It was shown that the lake receives a variety of waste effluents from domestic and industrial sources which discharge into the Ogunpa stream. These waste effluents have caused an odour nuisance in the lake, and little or no dissolved oxygen is present. The discharge of nutrients (N and P) to the lake has resulted in excessivegrowth of aquatic weeds. All these impacts on the lake have resulted in a reduced fish production. Some suggestions for the prevention of pollution and the recovery of the lake are presented.
M a t e r i a l s and M e t h o d s
Introduction
Materials Nigeria, the most populous country in Black Africa, is fast developing towards self-reliance. In this direction, agriculture, animal husbandry, fisheries, and a variety of industries are developing. In addition, the government is actively considering p r o m o t i o n of tourism a m o n g the country's 44 game reserves, 17 m a j o r waterfalls, 13 beaches, 45 lakes and riverine resorts, and 22 hilly and mountainous areas. All of these activities result in increasing pollution and pose environmental problems with economic and productivity losses. One of the cities that has been facing the wrath of pollution at a fast rate is the city of Ibadan, the capital of the most populous Oyo State. A m o n g the different lakes and streams, Ogunpa lake is perhaps the most popular and worst polluted. The lake was at one time a rich source of fish, and the area around it, including a zoological garden, is being used by visitors and tourists as a picnic and recreational spot. The Ogunpa lake is formed out of the Ogunpa stream, which travels through a m a j o r part of the city and receives a variety o f waste effluents. One o f the m a j o r effluents is treated sewage f r o m the University College Hospital, located close to the lake (Fig. 1); this poses a potential and probable adverse effect on the water quality and the future of Ogunpa lake. With a view to studying the sources and effects of different pollutants entering the lake, an investigation was undertaken; this paper presents the results obtained.
Ogunpa lake: Ogunpa lake is a m a n - m a d e lake formed along the path of the Ogunpa stream, which traverses a m a j o r portion of the city including Ashi village. The lake has an area of 13 ha, stretching about 1 k m with a m a x i m u m depth of about 5 m. Samples of water were collected at different points (Fig. 1). Ogunpa stream: Samples of water f r o m Ogunpa stream as it enters the lake and samples f r o m upstream up to about 10 km were collected. Sewage effluent: The sewage of University College Hospital, Ibadan, amounting to about 14,400 L / d a y is treated conventionally. The sewage is domestic in character and passes through a screen, two comminutors, three primary clarifiers, three trickling or percolating filters, and an activated sludge plant. The final effluent is chlorinated and discharged into a stream. The sludge obtained f r o m the primary clarifier and the activated sludge plant is digested anaerobically and dried in sludge drying beds; the dried powder is then made available for use on the f a r m as a manure. The samples of sewage at every stage of treatment were collected for analysis. Fishes: The types o f fishes found in the lake were recorded. A dominant fish found in the lake, Hemichromis 419
420
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bimaculatus, was used in the toxicity tests using the waste effluents entering the lake. Methods The samples of lake water and waste effluents were analyzed for pH value, biochemical oxygen demand (BOD), 4-h permanganate value representing the difficultly oxidizable organic matter, dissolved oxygen, total alkalinity, total hardness, ammonia nitrogen, total phosphorus, and chloride. The analyses were carried out according to the standard methods (APHA, 1975; Ministry of Housing and Local Government, 1956). Results
Characteristics of water in Ogunpa lake The characteristics of water in Ogunpa lake at five different points (Fig. 1) in the course of its flow were
determined, and the results are presented in Table 1. The results indicate that the lake water is polluted with organic matter showing low dissolved oxygen levels. In
Table 1. Characteristics of water at different points in Ogunpa Lake. ~ i n g Characteristi~
points
pH value Dissolved oxygen (mg/L) Biochemical oxygen demand (mg/L) 4-h Permanganate value (rag/L) Ammonia N (mg/L) Total alkalinity (mg/L) Total hardness (mg/L) Chloride (mg/L)
Mean Value
1
2
3
4
5
6.4 2.0 13.4
6.4 0.9 8.8
6.3 0.9 8.8
6.9 1.1 9.0
6.7 2.3 7.2
6.54 1.44 9.44
2.5
2.0
1.4
2.2
1.9
2.00
2.0 116 100 30
2.5 96 120 22
0.5 76 140 24
1.0 100 144 26
2.5 112 164 24
1.70 I00.00 134.00 25.20
421
Lake pollution in Nigeria Table 2. Weekly variation in the characteristics of water in Ogunpa stream entering the lake. Characteristic
Sunday
Monday
Tuesday
pH value Dissolved oxygen(mg/L) BOD (mg/L) 4-h permanganate value (mg/L) Ammonia N (mg/L) Total PO4 (mg/L) Total alkalinity (mg/L) Total hardness (mg/L) Chloride, C1 (mg/L)
6.7 6.3 8.8
6.8 5.8 13.0
6.8 Nil 30.8
6.5 3.7 27.2
6.4 1.0 2.0 108 116 20
10.4 Nil 1.0 112 116 24
8.8 Nil 1.0 120 120 22
10.8 -100 100 22
addition, the lake has been fully covered with aquatic vegetation and the width has been constricted to a great extent.
Characteristics o f water in Ogunpa stream before entering the lake The results o f analysis of water in Ogunpa stream before entering into the lake on different days of the week are given in Table 2. The results indicate that the water is grossly polluted; this is evident from high organic matter, ammonia nitrogen, and phosphorus. It was interesting to note that the BOD value was the lowest on Sunday.
Characteristics o f the sewage effluent before entering the lake The characteristics of sewage effluent from the University College Hospital on different days of the week before entering the lake are given in Table 3. The results indicate that the quality was variable on different days and showed higher values for ammonia nitrogen and chloride.
Sources of pollution in Ogunpa lake The two major streams that are entering the Ogunpa lake are (a) Ogunpa stream, and (b) sewage effluent from University College Hospital. To determine which is responsible for the major pollution, these two sources were examined more intensively.
Wednesday
Friday
Saturday
Weekly Mean
6.7 1.2 16
6.6 1.4 16.4
6.9 4.2 26.0
6.7 3.2 19.7
2.8 -116 120 24
10.0 1.0 4.0 100 128 26
8.0 3.0 2.0 128 112 22
8.2 1.0 2.0 112 116 22.9
Thursday
Ogunpa upstream: The upstream of Ogunpa travels a long distrance and collects a variety o f effluents from open drains, industries, slaughterhouses, and other sources. The samples were collected at 4 different areas, and the results are given in Table 4. The results indicate that the stream receives a variety of industrial wastes with high BOD. It was also observed that, at times, the stream appears viscous with oily slicks. Sewage treatment plant at University College Hospita# A series o f samples was collected and analyzed to determine to what extent the sewage was treated at various stages, and its influence on the character of the final effluent entering the Ogunpa lake. The results (Table 5) indicate that the sewage treatment plant is able to remove the organic matter to a great extent but was not able to remove ammonia and phosphorus. This is understandable because only the trickling filters are functional; the activated sludge plant is inoperative due to lack of spare parts. It was also found that the effluent coming out of the activated sludge plant was much inferior in quality than its influent, which consists o f the effluents from the trickling filter. The comparison between these two sources revealed that the Ogunpa stream has been carrying a heavy load of pollution as compared to that of the sewage effluent. This was also in conformity with the observations made by the Ministry of Agriculture and Natural Resources, indicating that the low dissolved oxygen was a result of
Table 3. Weekly variation in the characteristics of sewage effluent entering the lake. Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Weekly Mean
Characteristic
Sunday
pH x;alue Dissolved oxygen(mg/L) BOD (mg/L) 4-h permanganate value (rag/L) Ammonia N (mg/L) Total PO4 (mg/L) Total alkalinity (mg/L) Total hardness (mg/L) Chloride, C1 (mg/L)
6.8 5.6 8.4
6.9 5.7 10.4
6.8 5.0 11.8
6.9 4.0 13.2
6.9 3.5 5.8
6.9 4.1 4.2
7.0 5.9 14.0
6.9 4.8 9.7
6.8 5.0 1.0 92 96 26
3.6 6.0 2.8 100 120 36
4.4 10.0 4.0 108 116 34
5.2 -116 124 36
2.8 92 128 44
1.6 5.0 0.2 100 144 42
6.4 5.5 4.8 104 124 40
4.4 6.3 2.6 102.0 121.7 36.9
422
M.K.C. Sridhar and A. O. Bammeke Table 4. Characteristics of water from Ogunpa upstream. Flow Direction Characteristic Appearancea Dissolved oxygen (mg/L) BOD (mg/L) 4-h Permanganate value (mg/L) Ammonia, N (rag/L) Total phosphorus, PO, (rag/L) Total alkalinity (mg/L) Total hardness (mg/L) Chloride (mg/L)
Aderinola Road
Oduduwa Road
Francis Okediji Road
Bodija Area
Viscous, black and stinking Nil 325.0 46.8 1.5 4.0 132.0 136.0 32.0
Fairly clear
Dark
Dark
7.7 6.0 3.6 1.0 1.0 96.0 1190.0 20.0
0.5 76.0 13.6 2.0 1.0 112.0 112.0 22.0
1.1 96.0 14.4 2.5 1.5 116.0 112.0 22.0
aDomestic discharges from open drains and industrial discharges from a beverage factory, tannery and a slaughter house were noticed.
d o m e s t i c sewage a n d r u n - o f f l a d e n with a n i m a l wastes a n d b l o o d . T h e r e was n o p o s s i b i l i t y t h a t a n y a n i m a l wastes a n d b l o o d w o u l d be in the sewage effluent, since it was essentially o r i g i n a t i n g f r o m the residential a n d hospital community.
Further toxicity studies using fish T h e O g u n p a l a k e has a b o u t nine varieties o f fish, as given in T a b l e 6. O f these, while the delicate varieties have r e d u c e d in n u m b e r , Hemichromis bimaculatus is the d o m i n a n t v a r i e t y at this time. T h e s e fish were collected f r o m the lake; a n d five e a c h were i n t r o d u c e d i n t o f o u r 10-L b u c k e t s c o n t a i n i n g t a p w a t e r , O g u n p a l a k e water, w a t e r o f O g u n p a s t r e a m t h a t enters the lake, a n d
sewage e f f l u e n t t h a t enters the lake. T h e fish were exa m i n e d f o r 4 h. T h e results ( T a b l e 7) i n d i c a t e t h a t the O g u n p a s t r e a m h a d the highest p o l l u t i o n l o a d to kill the fish in 4 h as c o m p a r e d to o t h e r sources. T h e high a m m o n i a n i t r o g e n c o n c e n t r a t i o n in the sewage effluent seems to be r e s p o n s i b l e for the fish kills. L a c k o f dissolved o x y g e n in the t r e a t m e n t p l a n t effluent also c o u l d h a v e a f f e c t e d the fish.
Discussion A large a m o u n t o f w o r k was d o n e o n the p o l l u t i o n levels o f n a t u r a l waters in Nigeria, the sources, a n d their effects ( O l u w a n d e et al., 1983, S r i d h a r et aL, 1981;
Table 5. Characteristics of wastewater at different stages of treatment. ~
C
ters Temp )
1. After the comminutor (combined influent) 2. After primary settling tank 3. After the trickling filter 4. Activated Sludge plant effluent 5. Chlorine contact basin effluent 6. Upstream of discharge point 7. Downstream of discharge point 8. Laundry wastewater
Suspended Solids pH Value (mg/L)
Dissolved Solids (rag/L)
Total Solids (rag/L)
BOD (mg/L)
NH~N (rag/L)
Total P PO, Coliforms (mg/L) (MPN/100 mL)
Residual Chlorine for 5, 6, 7 only
32
7.00
200
289
489
243
12.0
4.8
80,000,000
31
6.80
133
172
305
185
8.5
3.2
65,000,000
30
6.60
19
150
169
7.5
4.0
1.6
900
31
6.80
46
103
149
8.3
4.5
4.8
900
31
6.85
41
145
186
8.3
4.5
2.4
Nil
1.0
27
7.00
29
115
144
3.6
2.0
0.8
175
Nil
30
7.00
83
101
184
7.0
4.5
2.4
Nil
0.5
33
9.65
52
152
204
2.6
1.0
0.8
4
Lake pollution in Nigeria
423
Table 6. The varieties of fishes found in the lake.
Table 7. Influence of the different waters on the fish.
Variety
Water Quality Number of Fish
Sarotherodon inloticus Sarotherodon qalilaeus Tilapia zillii Tilapia rnelanopleura Glarias lazera Gymnarchus niloticus Barbus occidentalis Hemichromis bimaculatus Hemichromis fasciatus
Sridhar and Sharma, 1980; Mombeshora et al., 1981). Pollution has been c o m m o n in every urban centre as a result of population migration, industrial development, and lack of sanitary disposal of sewage and pollution control regulations. As in this study, people often raise sporadic objections, but no effective measures are taken thereafter. At a site such as Ogunpa lake, the origin of pollutants into the lake is multifarious. Though a sewage treatment plant is contributing to some extent, the greater pollution is coming through Ogunpa stream. This stream does not carry any pure water. It acts as a sewer for many waste effluents from slaughterhouses, and a beverage factory, tannery, and laundry. This stream is also misused for dumping o f refuse which leaches organic and inorganic pollutants, besides causing floods. The result many times is that the lake emits bubbles of hydrogen sulphide in the dry periods; the entire lake surface is also covered with gigantic water lettuce. The authorities have even given up on removing this weed. In 1971, Nigeria experienced its worst cholera epidemic, in which 14,158 suspected cases and 162 deaths were reported. The epidemic was attributed to the contaminated water supplies, and Ogunpa stream was no exception. To avoid such incidents, what is needed today is the introduction of sanitary disposal of sewage and other waste waters as a matter of urgency, at least in 10 of the
Dissolved At At the end Percent Oxygen Ammonia Water Source Start of 4 h Died (mg/L) N (rng/L) Tap (Control) Ogunpa lake Ogunpa stream entering the lake Sewage effluent entering the lake
5 5
5 4
0 20
7.7 0.8
0.0 4.5
5
1
80
0.0
4.5
5
3
40
0.8
7.0
Nigeria's major cities. This should be followed by the introduction of pollution control legislation with effective monitoring. The experiences o f Britain and other developed countries in the years of the Industrial Revolution should be wisely utilized to prevent the repetition o f the irrevocable death of the rivers and the associated health and economic losses. Acknowledgements-We thank O. Ojo and J. Olaniyan, Fisheries
Division, Ministry of Agriculture and Natural Resources, Oyo State, for their cooperation and assistance in carrying out this work.
References American Public Health Association/American Water Works Association (1975) Standard Methods for the Examination of Water and Wastewater, 14th ed. APHA/AWWA, Washington, D.C. Ministry of Housing and Local Government (1956) Methods of Chemical Analysis as Applied to Sewage and Sewage Effluents,
2nd ed. Her Majesty's Stationery Office, London. Mombeshora, C., Ajayi, S. O. and Osibanjo, O. (1981) Pollution studies on Nigerian Rivers: Toxic heavy metal status of surface waters in Ibadan city, Environ. Int. 5, 49-53. Oluwande, P. A., Sridhar, M. K. C., Bammeke, A. O., and Okubadejo, A. O. (1983) Pollution levels in some Nigerian Rivers, Water Res. 17, 957-963. Sridhar, M. K. C. and Sharma, B. M. (1980) Pistia stratiotes L. in Nigerian waters, Experientia 36, 953-954. Sridhar, M. K. C., Oluwande, P. A., and Okubadejo, A. O. (1981) Health hazards and pollution from open drains in a Nigerian city. Ambio 10, 29-33.