Dark-Black Stains on Rooftops: Implications on the Quality of Water Harvested from Rooftops

Mechanics, Materials Science & Engineering, May 2017

ISSN 2412-5954

Dark-Black Stains on Rooftops: Implications on the Quality of Water Harvested from Rooftops in Uyo Metropolis-Nigeria27 Ihom A.P.1,a,b, Uko D.K. 1, Markson I.E. 1, Eleghasim O.C. 1 1

Department of Mechanical Engineering, University of Uyo, Uyo, PMB 1017 Uyo-Nigeria

a

ihom@uniuyo.edu.ng

b

paulihom@yahoo.co.uk DOI 10.2412/mmse.100.67.317 provided by Seo4U.link

Keywords: rainwater, quality, harvest, WHO, dark-black stains, rooftops.

ABSTRACT. The study Dark-Black Stains on Rooftops: Implications on the Quality of Water Harvested from Rooftops in Uyo Metropolis-Nigeria has been undertaken. The study took samples of harvested rainwater from the rooftops of buildings in four different locations in Uyo Metropolis. The samples were taken for analysis at the Ministry of Science and Technology Laboratory-Uyo. The parameters of the harvested rainwater investigated covered physical and chemical properties, heavy metals, total organic carbon (TOC) and total coliform count (TCC). Gravimetric, titrimetric and instrumental methods of analysis were used in determining the various parameters investigated. The result was analysed by comparing it with WHO and Ministry of Environment standard specifications for drinking water. The result was equally compared with the composition of the dark-black stains on the rooftops to establish whether the stains on the rooftops were from the rainwater. Findings were astounding; the rainwater was acidic in all the four stations and could not meet up with WHO standard for drinking water. Lead values of 0.75 mg/l and 0.22 mg/l in stations 2 and 3 respectively exceeded WHO standard specification of 0.01mg/l for drinking water. The iron content in the water from stations 2, 3, and 4 all exceeded WHO standard specification for drinking water of 0.30mg/l. All the four stations had cadmium content in the rainwater, which was more than WHO specification for drinking water of 0.003mg/l. The water showed bacteria contamination with total coliform count of 118MPN/100ml in station 4. Some of the parameters in the rainwater also reported in the composition of the dark-black stains on the rooftops an indication that the rain contributed to the darkblack stains on the rooftops in Uyo metropolis. The study concluded that harvested rainwater from the rooftops of buildings in Uyo metropolis is polluted and is not suitable for drinking, bathing and even for use in fish farming. The study therefore recommended that the health implication of this study be carried out by relevant agencies of government.

Introduction. Dark-black stains on rooftops are a common sight in Uyo metropolis. Nwokocha [1] in his work has attributed oil and gas flaring as being responsible for the menace. He said this can be seen in most oil producing states in Nigeria; particularly the Niger Delta region. Dara [2], agrees with Nwokocha [1], but goes further to explain the mechanism of the formation for these stains. Gas flaring produces smoke and soot including other particulates and gases. According to [1] these is discharged into the atmosphere, which already have other particulates like Fe2O3, V2O3, CaO, PbCl2, PbBr 2, fly ash, aerosols, etc. soot is a highly condensed product of polycyclic aromatic hydrocarbons (PAH) compounds and can itself adsorb many PAH compounds and toxic trace metals e.g., Be, Cd, V, Cr, Ni, and Mn, as well as carcinogenic organics such as benzo- pyrenes. The air speed determines the settling of this mixture unto surfaces and rain also washes the mixture from the air unto surfaces, and roofs are normally readily available surfaces for such deposits from the air.

This position is corroborated by several authors [3], [4], [5]. When water mixes with the mixture it forms the dark-black stain that is seen on rooftops in oil and gas flaring areas [6], [7], [8], [9].

In an address presented by the governor of Akwa Ibom State, Mr Udom Emmanuel Gabriel at the environment summit organized by the state government at Le Meridien Hotel and Golf Resort, Uyo. The governor lamented the adverse effects of environmental pollution caused by oil flaring and fossil fuels combustion on humans and the environment, he specifically mentioned darkening roof-tops in Uyo metropolis which has taken away the aesthetics of many buildings in the state. According to the governor, the problem is so serious that many people are now using dark and black coloured roofing sheets to conceal the black deposits on their roof-tops [10]. The -NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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nature of this black deposit is not understood, it is only assumed that it is from gas flaring and combustion of fossil fuels from generators and automobiles. Olajire [11] and Nwokocha [1] also in their respective studies have linked the dark black stains on the roofs to pollution from gas flaring and other industrial activities. Figs.

1-5 clearly captures the menace.

Fig. 1. Building in Uyo Metropolis: The Roof is Completely Covered with Dark-Black Deposit.

Fig. 2. Building Roof Completely Covered with Dark-Black Coating/Deposit.

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Fig. 3. Building Roof Completely Covered with Dark-Black Deposit.

Fig. 4. The Roof Top of the Building in the Front is covered with Dark-Black Deposit, the Storey Buildings Behind are Roofed with Dark-colored Roofing Sheets to Conceal the Effect of the Dark-Black Deposit.

Fig. 5. Dark-Black Deposit on Colored Roofs in a Housing Estate in Uyo Town.

Dara [2] any human activity that impairs the use of water as a resource is called water pollution. With exploding population and increasing industrialization and urbanization, water pollution by agricultural, municipal and MMSE Journal. Open Access www.mmse.xyz

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industrial sources has become a major concern for the welfare of mankind. Water is essential for the survival of any form of life. On an average, a human being consumes about 2 litres of water every day. Water accounts f million hectares in area) is covered by water. Out of the estimated 1,011 million km3 of the total water present on earth, only 33,400m3 of water is available for drinking, agriculture, domestic and industrial consumption.

The rest of the water is locked up in oceans as salt water, polar ice-caps and glaciers and underground. Owing to increasing industrialization on one hand and exploding population on the other, the demands of water supply have been increasing tremendously. Moreover, considerable part of this limited quantity of water is polluted by sewage, industrial wastes and a wide array of synthetic chemicals. The menace of water-borne diseases and epidemics still threatens the well-being of population, particularly in underdeveloped and developing countries like Nigeria. Thus, the quality as well as the quantity of clean water supply is of vital significance for the welfare of mankind [12], [13], [14], [15], [16]. Uyo receives 2000-4000mm of rainfall annually. It is estimated that 96% of this water is used for agriculture, 3% for domestic use and 1% for industrial activity [16]. The various types of water pollution are broadly classified as organic, inorganic, suspended solids and sediments, radioactive materials and heat pollutants.

Water harvesting is a common practice in different parts of the world including Uyo metropolis. Water harvested from the rooftops of buildings is used for cooking, bathing, and washing, flushing of toilettes, drinking, and agriculture. Fish farmers who have to be changing water for their fishes quite often, do find raining season very convenient. Studies have shown that most of the rain water collected from rooftops is polluted; to what extent? This may also depend on the area and the kind of natural and anthropogenic activities going on in the area [1], [11], [17]. Definitely the pollution level in the oil and gas producing areas will be more than that of serene and pristine areas where gas flaring, automobiles, and generating sets are lacking. he composition of the dark black deposit on the rooftops? Answering these questions is important because the health implications may be disastrous and should be understood. There are reports of people who have complained of soapy-feelings and itching skin after bathing with rain water from dark-black stained rooftops.

The objective of this work is to establish the quality of water harvested from dark-black stained rooftops of buildings in Uyo metropolis.

MATERIALS AND METHOD Materials. The materials used for this research work included, chemicals of various types like potassium hydrogen phythalate buffer, sodium chloride, barium chloride, sodium sulphate, concentrated sulphuric acid etc., which were used in the analyses of the samples, and rain water which was collected from different parts of the metropolis from rooftops.

Equipment. The equipment used for the research work included sample collecting plastics buckets, specimen bottles (McCartney), Scanning Electron Microscope (SEM), pH meter, electrical conductivity meter, turbidity tube, conical flasks, test tubes, pipette, burette, spectrophotometer, steam bath, systronics flame photometer 128, coliform bottles, and as required by the various standard tests for the samples at the Ministry of Science and Technology, Uyo Analytical Laboratory.

The Study Area. The study area of this research work is Uyo metropolis. Uyo is the Capital of Akwa Ibom state. It is a major oil producing state in Nigeria, with a lot of gas flaring activities going on from the oil exploiting companies. The population of Uyo according to the 2006 Nigerian census which comprises Uyo and Itu is 436,606. The metropolitan area covers an estimated area of 168 km2 (65sq.mi). Uyo is a fast-growing city and has witnessed some infrastructural growth in recent years. It is located on coordinates 5 02`N and 70 The average annual rainfall in the study area is between 2000-4000mm with the period of fall usually between April and October. The rainfall reaches its peak in the months of June and September, while the dry period falls between November to March. The relative humidity of the area varies between 75% and 95% with mean annual temperatures of about 26 to 36oC. Fig. 6 is the map of the study area. The samples for the work were taken in different areas of the metropolis covering, Use Offot on Nwanniba road (station 2), University of Uyo, main campus on Nwanniba road (station 1), Ikot-Okubo on Abak road (station3), and Mbaibong on Oron road (station 4). The town is characterized by high usage of generators as a result of incessant power failure from the national grid and high vehicular traffic typical of a growing metropolis.

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Fig. 6. The Map of Uyo Metropolis the Study Area.

Method. The rain water samples which were harvested from rooftops in four different areas of Uyo Metropolis as indicated by the research study area above were sent to ministry of Science and Technology, Uyo for various tests and analysis. Both wet and instrumental analysis were used for the testing of the test specimens. The samples from the different locations were subjected to pH test using pH meter, which was calibrated earlier on using standard buffer solutions. Standard procedures were adopted in carrying out the following tests on the rain water samples collected from the rooftops of buildings in Uyo metropolis, electrical conductivity test, turbidity test, temperature, total suspended solid, salinity, chloride, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, total dissolved solid, hydrogen carbonate, hardness, calcium, magnesium, lead, iron, copper, zinc, cadmium sodium, nitrogen, total organic carbon, nitrate, sulphate, phosphate, and total coliform count which constituted the microbiological analysis of the water. The determination of the heavy metals was done through digestion method using perchloric acid according to the standard methods proposed

by Association of Analytical Chemists. The Scanning Electron Microscope micrograph of the dark black deposit on the rooftops was also carried out at Defence Industries Corporation of Nigeria (DICON).

RESULTS AND DISCUSSION Results. The various results of the tests which were carried out on the rain water samples from various parts of Uyo metropolis are here displayed in Tables1-4. Table 5 is the WHO and Ministry of Environment specification for drinking water. Table 6 is the chemical composition of the dark-black deposit on rooftops.

Plates I-VI shows the plates of cultured rain water from the four stations with coliform growth. The SEM micrograph of the rooftop coated dark black deposit is also shown in Plate VII.

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Table 1. Physical and Chemical Properties of Rain Water Collected from Four Different Locations from Rooftops in Uyo Metropolis.

S/No

Parameter

SAMPLE

IDENTIFICATION

Station 1

Station 2

Station 3

Station 4

1

pH

5.49

5.24

6.41

5.92

2

Temperature oC

24.6

24.95

25.1

28.15

3

Electrical conductivity 35.12

50.41

82.6

50.6

4

Total suspended solid (TSS) (mg/l)

0.01

<0.01

0.01

5

Salinity (mg/l)

15.41

23.4

35.1

23.4

6

Chloride (Cl) (mg/l)

10.65

14.2

21.3

14.2

7

Dissolved oxygen (DO) 7.17 (mg/l)

8.3

6.37

8.22

8

Biochemical oxygen 2.0 demand (mg/l)

4.2

2.2

4.44

9

Chemical oxygen 3.9 demand (COD) (mg/l)

8.1

4.4

8.3

10

Turbidity (NTU) (mg/l) 0.14

0.3

0.19

0.26

11

Total dissolved solid 17.55 (TDS) (mg/l)

25.3

41.4

25.3

12

Hydrogen Carbonate 18.3 (HCO3) (mg/l)

18.3

12.2

24.4

13

Hardness (mg/l)

1.5

1.0

2.0

14

Calcium (Ca) (mg/l)

23.47

1.87

1.07

2.93

15

Magnesium (mg/l)

(Mg) 11.73

0.93

0.53

1.47

(CaCO3) 1.5

Table 2. Heavy Metals and Metals in Rain Water collected from Four Different Locations from Rooftops in Uyo Metropolis. s/No

Parameter

Sample identification Station 1

Station 2

Station 3

Station 4

1

Lead (Pb) (mg/l)

<0.01

0.75

0.22

<0.01

2

Iron (Fe) (mg/l)

0.12

0.79

0.53

0.55

3

Copper (Cu) (mg/l)

0.11

0.21

0.2

0.19

4

Zinc (Zn) (mg/l)

0.33

0.91

0.91

1.16

5

Cadmium (Cd) (mg/l)

<0.01

0.82

0.61

0.02

6

Sodium (Na) (mg/l)

<0.01

1.79

1.86

1.65

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Table 3. Nitrogen and Salts in Rain Water Collected from Four Different Locations from Rooftops in Uyo Metropolis. s/No

Parameter

Sample identification Station 1

Station 2

Station 3

Station 4

1

Nitrogen (N) (mg/l)

<0.01

<0.01

<0.01

<0.01

2

Nitrate (NO3) (mg/l)

<0.01

<0.01

0.01

<0.01

3

Sulphate (SO3) (mg/l)

0.01

0.01

<0.01

<0.01

4

Phosphate (PO4) (mg/l)

0.01

<0.01

<0.01

<0.01

Table 4. Total Organic Content (TOC) and Total Coliform (TCC) in Rain Water Collected from Four Different Locations from Rooftops in Uyo Metropolis. s/No

Parameter

Sample identification Station 1

Station 2

Station 3

Station 4

1

Total Organic Content 50 (TOC) %

75

75

66.67

2

Total Coliform (TCC) 105 (18hrs) (MPN/100 ml)

61 (18hrs)

6 (18hrs)

118 (18hrs)

Key: Station 1: University of Uyo, main campus on Nwanniba road, Station 2: Use Offot on Nwanniba road, Station 3:Ikot-Okubo on Abak road Station 4: Mbaibong on Oron road.

Table 5. World Health Organization and Federal Ministry of Environment Drinking Water Standards. s/No.

Parameter

WHO (2008)

FMEnv (2007)

1

Appearance

Clear

Clear

2

Colour (HU)

15

15.00

3

Taste

Inoffensive

Inoffensive

4

Odour

Inoffensive

Inoffensive

5

Temperature (oC)

27-28

6

Ph

6.5-8.5

6.5-8.5

7

Turbidity (NTU)

5.00

5.00

1000

1000

8 9

Total dissolved solids (mg/l)

500

500

10

Alkalinity as (CaCO3) (mg/l)

200

-

11

Hardness (mg/l)

100

150.00

12

Dissolved oxygen (mg/l)

6.00

7.50

13

BOD (mg/l)

6.00

10.00

14

Chloride (mg/l)

250.00

250.0

15

Nitrates (mg/l)

10.00

10.00

16

Nitrite (mg/l)

0.20

0.20

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17

Fluoride (mg/l)

1.00

1.50

18

Sulphate (mg/l)

250

200.00

19

Phosphate (mg/l)

3.50

<5.00

20

Residual chloride (mg/l)

0.2-0.4

0.2-0.4

21

Sodium (mg/l)

200.00

200.00

22

Calcium (mg/l)

75.00

200.00

23

Magnesium (mg/l)

150.00

150.00

24

Potassium (mg/l)

15.00

150.00

25

Nickel (mg/l)

0.07

-

26

Lead (mg/l)

0.01

0.01

27

Copper (mg/l)

0.05

1.00

28

Cadmium (mg/l)

0.003

0.003

29

Chromium (mg/l)

0.01

0.05

30

Zinc (mg/l)

0.10

5.00

31

Iron (mg/l)

0.30

0.30

32

Manganese (mg/l)

0.10

0.20

33

Cyanide (mg/l)

0.05

0.07

34

Mercury (mg/l)

0.001

0.006

35

Molybdenum (mg/l)

0.07

0.07

36

Selenium (mg/l)

0.01

0.01

Source: WHO (2008), FMEnv (2007) Table 6. Chemical Composition of Dark-Black Material Scrapped from Roof-Tops (Analysed at NMDC Jos).

Parameters (in %) S/No

Sample

Al2O3

SiO2

P2O5

SO3

K2O

CaO

TiO2

V2O5

1

Blackish powder from roof-top

16.00

43.80

1.20

2.71

3.20

1.62

2.93

0.11

Cr2O3

MnO

Fe2O3

NiO

Co2O3

CuO

ZnO

Br

Rb2O

SrO

0.10

0.31

10.55

0.05

ND

0.09

0.22

0.07

0.03

0.05

ZrO2

Yb2O3

Re2O7

PbO

Carbonaceous and volatile matter

0.20

0.001

0.06

0.11

16.59

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Plate I: coliform growth on sample rain water collected from rooftops at station 4 Mbiaobong Etoi Uyo, after 18hrs of culture.

Plate II: Coliform growth on sample rain water collected from rooftops at station 1 Uniuyo main campus after 18 hrs of culture.

Plate III: Coliform growth on sample rain water collected from rooftops in station 3 Ikot Ukuubo Uyo after 18hrs of culture

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Plate IV: Coliform growth on sample rain water collected from the rooftop at station 2 use offot after 18hrs of culture.

Plate V: Coliform growth on sample rain water collected from rooftops at station 1 Uniuyo main campus after 18hrs of culture.

Plate VI: Coliform growth on sample rain water collected at station 4 Mbiaobong Etoi Uyo after 18 hrs of culture

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Plate VII: Scanning Electron Microscope (SEM) Micrograph of Dark-Black Deposit on Aluminium-Base Roofing Sheet. The light shining areas are where the deposit of the material is low and the dark areas are where the deposit has covered the aluminium sheet completely.

Discussion. Previous works carried out by several researchers have established that the sources of dark black deposits on rooftops are normally from rain, (which washes the air content of particles, soot, gases and aerosols down unto the rooftops) dry air, and wet air. These three sources transport the deposits onto the rooftops [3], [4], [5], [18], [19]. The discussion of the result of this present paper (which is part of a global research work sponsored by TETFUND to investigate the root causes and possible remedies of quick corrosion and formation of dark- black deposits on rooftops in Uyo metropolis) is going to be tailored in two directions. The result of the harvested rain water from rooftops is going to be compared with WHO and Federal Ministry of Environment quality standards for drinking water and on the second front, the composition of the water is going to be compared to the chemical composition of the dark-black deposit on the rooftops which was analysed in the earlier part of this ongoing research work.

Table 1 shows the Physical and Chemical Properties of Rain Water Collected from Four Different Locations from Rooftops in Uyo Metropolis labelled station 1, station 2, station 3 and station 4. Looking at the result in the Table and comparing it with WHO and Federal Ministry of Environment standards in Table 6 the only parameters of concern are; pH, electrical conductivity, and chemical oxygen demand. The pH of rainwater is normally 5.6, which is acidic, and this is because of the dissolution of carbon dioxide, sulphur dioxide and other gases in rain water. Station 2 has the highest acidity of 5.24, which is even lower than normal rainwater value of 5.6. Station 1 has pH value of 5.49 this is also lower than the normal rainwater value of 5.6. These two stations have indicated pollution; the effect of these is that the water will affect the mucous membrane, and give rise to increase leaching and corrosion of rooftops. If the water is passed through water supply system it will corrode the system. The water has low electrical conductivity with station 1 having the lowest electrical is as a result of the absences of plenty dissolved ion species in the rain water. Although in all the four stations the chemical oxygen demand is less than the WHO standard of 10mg/l, the closeness of the values of stations 2 and station 4 to the standard value of 10mg/l is worrisome. They have the values of 8.1mg/l and 8.3mg/l respectively. This is an indication of pollution but looking at the BOD values it cannot be of organic nature but must be coming from the oxidisable inorganic components in the water [2], [6], [7], [8], [9], [19].

Table 2 Heavy Metals and Metals in Rain Water collected from Four Different Locations from Rooftops in Uyo Metropolis and labeled station 1, station 2, station 3, and station 4. Looking at the result of Table 2, the metals of concern are lead, iron, zinc, and cadmium. Lead content in stations 2 and 3 are worrisome this is because the values are greater than WHO standard value of 0.01mg/l. Station 2 has the value of 0.75 mg/l and station 3 has the value of 0.22 mg/l. Expected side effects is that this water is toxic. Lead causes an endemic acting and subtle. The major biochemical effect of lead is its interference with heme synthesis; leading to hematological damage. Lead inhibits several important enzymes involved in the overall process of heme synthesis. It disrupts the synthesis of haemoglobin and other respiratory pigments such as cytochromes which require heme. Iron content in stations 2, 3, and 4 are greater than WHO 0.3mg/l although the permissible range is up to 1 mg/l. The value for station 2 is 0.79 mg/l, station 3 is 0.53 mg/l and station 4 is 0.55 mg/l, these values are greater than the standard and therefore indicates pollution which will affect taste, appearance and also have adverse effects on domestic uses and water supply structures, and promote iron bacteria. Zinc content MMSE Journal. Open Access www.mmse.xyz

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in the rain water from stations 1-4 all exceed the WHO standard of 0.1mg/l but not higher than the permissible range of 3 mg/l. Station 1 has the value of 0.33mg/l, station 2 value is 0.91mg/l, station 3 value is 0.91mg/l and station 4 value is 1.16mg/l. These values all exceed WHO standard. This may lead to astringent taste and an opalescence in water. Cadmium content in rain water from the four stations exceed WHO standard value of 0.003mg/l this is worrisome. Station 1 has the value of <0.01mg/l, station 2 has the value of 0.82mg/l, station 3 has the value of 0.61mg/l and station 4 has the value of 0.02mg/l. The water becomes toxic beyond the WHO standard. Cadmium acts as inhibitor of sulphydryl enzymes. It has also got affinity for other ligands in cells, such as hydroxyl, carboxyl, phosphatyl, cysteinyl, and histidyl sidechains of proteins, purines and porphyrin.

It can disrupt pathways of oxidative phosphorylation. Cadmium is highly toxic because of the absence of homeostatic control for this metal in the human body. Cadmium in water at 10 ppm level can kill fishes in one day while at 2 ppm level they will be killed in 10 days. This water therefore cannot be recommended for fish farming [2], [12], [13], [14], [15], [16].

Table 3 shows Nitrogen and Salts in Rain Water Collected from Four Different Locations from Rooftops in Uyo Metropolis and labeled as station 1, station 2, station 3 and station 4. Looking at the Table all the parameters in the Table did not exceed or compromise WHO standards specifications and therefore did not create any worrisome situation.

Table 4 shows Total Organic carbon Content (TOC) and Total Coliform (TCC) in Rain Water Collected from Four Different Locations from Rooftops in Uyo Metropolis and labeled station 1, station 2, station 3 and station 4. Looking at the Table the values of total organic carbon and total coliform count are high in some of the stations and therefore indicate some level of pollution of the rainwater collected from the rooftops. The total organic carbon in station 1 is 50%, station 2 is 75%, station 3 is 75% and station 4 is 66.67%. This carbon cannot be from natural source but from anthropogenic activities such as gas flaring, generating sets, burning of fossil fuels and vehicular emissions. It is most likely that the black colour of the deposit on the rooftop is from the carbon. Their connection to poly-aromatic hydrocarbons (PAHs) makes them poisonous. The total coliform count in the four stations is as shown in Table 4. Station 4 has the highest total coliform count (TCC) of 118 MPN/100ml followed by station 1 with 105 MPN/ 100 ml, the total coliform count shows the level of contamination of the rainwater with coliform. This poses health hazard and pollution of the water harvested from the rooftops; the availability of coliforms in any sample indicates the presence of the potential harmful threats to man and environment. Coliforms are a broad class of bacteria that are readily available in our environment. They can survive on roofs and walls of buildings [2], [20], [17].

Although, bacteria and fungi colonies have many characteristics and some can be rare, there are a few elements that you can identify for all colonies. Most bacteria colonies appear white, cream or yellow in colour, and fairly circular in shape. Yeast species such as candida, can grow as white patches with a glossy surface. We equally have round, and pink yeast colonies, molds are actually fungi and they often appear whitish, with fuzzy edges.

They usually turn into a different colour from the centre outwards. Fungi are mostly green colonies, a white cloud or a ring of spores [16], [19], [20], [21]. Plates I-VI shows cultures of rain water samples collected from four different stations the micrographs show colonies of different organisms which grew during the culture and incubation period of 18 hrs at 20oC for the total coliform count test.

Plate VII is the SEM micrograph of the dark black deposit on the rooftops. The dark black deposit was removed and analysed using ED-XRF and the result is shown in Table 6. Comparing Tables 1-4 with Table 6 we can see that the elements and some of the compounds in Tables 1-4 actually reported in the composition of the dark black deposit on the rooftops confirming that rain is one of the sources of the dark black deposit on rooftops. The composition of the rain water also show that it flushes microbial and chemical contaminants from the rooftops. Several authors have agreed with the above discussions [2], [6], [7], [8], [9], [19]. Nwokocha Nigeria and other authors have worked on the effect of vehicular emissions, generating set emissions, and burning of fossil fuels. And all the authors have agreed that these sources release particulates, soot, and gases of various chemical composition into the air which are washed-down to the rooftops the rain gets polluted even before getting to the rooftops, the situation is only worsen by leaching of the roofing material by acidic rain [2], [3], [4], [5], [12], [13], [14], [15], [16]. The rain also contributes in the dark black deposit on the rooftop in addition to what has been deposited by both dry and wet air. The quantity of atmospheric deposition depends on the amount and types of air pollutants emitted in the vicinity and upwind of the site [13].

Summary.

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from rooftops of dark-black stain coated roofs in different parts of Uyo metropolis was considered during the research and the following conclusions were drawn I. The study revealed that the water harvested from dark-black stained rooftops in Uyo metropolis is polluted.

It is worrisome the levels of metals, acidity and coliforms measured in the water.

II. Lead values of 0.75 mg/l and 0.22 mg/l in stations 2 and 3 respectively exceeded WHO standard specification of 0.01mg/l for drinking water.

III. The iron content in the water from stations 2, 3, and 4 all exceeded WHO standard specification for drinking water of 0.30mg/l IV. All the four stations had cadmium content in the rain water which was more than WHO specification for drinking water of 0.003mg/l V. All the four stations had pH that did not meet WHO standard specification for drinking water. The water will affect the mucous membrane and increase the leaching of the roofing material if in direct contact.

VI. The study has shown that the water has contributed to the dark-black deposit of the rooftops of buildings in Uyo metropolis. The total organic carbon must have been responsible for the dark-black colour and its source is from the soot of fossil fuels combustion from gas flaring, vehicular emissions, and generating sets used everywhere in the metropolis.

VII. The result of this work calls for serious action from government to further investigate the health implications of this findings on the masses.

Acknowledgements. The authors of this work wish to acknowledge the contributions of Engr. Nicholas Agbo of the Defence Industries Corporation of Nigeria, Kaduna and Mr Musa Chaga of the National Metallurgical Development Center Jos which led to the successful completion of this work. The authors equally extend their unfathomable thanks to Mr. Monday Inyang of the state Ministry of Science and Technology Uyo, Akwa Ibom State for his contribution in sampling and analyzing the test specimens.

Sponsorship. This research work is sponsored by TETFUND under the Institutional Based Research Grant for University of Uyo-Nigeria.

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