The human environment is the basis for any economic, social and Cultural development. It is therefore important that its quality be maintained in a good state to ensure a high level of social performance, which can be achieved by closer monitoring of pollution factors (Avwiri and Ebeniro, 1998). The quest for oil fields development and exploration in the Niger Delta of Nigeria has led to various forms of activities that tend to perturb the fragile ecological, biophysical systems and the Socio-economic and political structures.
Oil and gas industry in the Niger Delta is a multi-faceted Industry that includes the construction, exploration, production, downstream and marketing sectors. In most of these sectors, radioactive materials and radiation generators are used on a large scale. The application of radioactive materials in both the onshore and offshore oil and gas industries includes industrial radiography, automated ionizing radiation gauge, well logging, use of radiotracers, mapping and evaluation of geological formations and the extraction of other natural hydrocarbon resources (Arogunjo et al., 2004).
Foland et al. (1995) reported that human activities, that have led to the depletion of the ozone layer, increased the cosmic rays reaching the earths surface thereby affecting the background radiation.
Kuroda (1991) reported that the background radiation levels are from a combination of terrestrial (40K, 232Th, 226Ra etc.) and cosmic radiation (Photons, Muons etc.). He reported that the level is fairly constant over the world, being 0.008-0.015 mR h-1. But Brazil, India and China have higher background ionizing radiation, primarily due to the high concentrations of radioactive minerals (Monozite) in the soil (Ron Kathren, 1991):
Ebong and Alagoa (1992a and b) studied the background radiation pattern of the Pre- and Post-Industrial pattern of a fertilizer plant and reported an increase in the background radiation.
Avwiri and Ebeniro (1998) studied the external environmental radiation in an industrial area of Rivers State. They reported an average of 0.014 mR h-1 of background. The results indicated significant elevation from the standard background radiation of 0.013mR h-1.
Arogunjo et al. (2004) studied the impact of oil and gas industry to the natural radioactivity distribution in the Niger Delta region of Nigeria and revealed that, the mean activity concentrations for 40K, 238U and 234Th radionuclides are 34.8±2.4, 16.2±3.7 and 24.4±4.7 Bq kg-1, respectively, with oil extraction activities areas having activity concentration values greater than areas without any known oil extraction activity in the region. The environmental Radioactive levels in Ikot Ekpene area of Akwa Ibom State of Nigeria have also been studied by Louis et al. (2005) and reported a value average activity level of 201.0±0.05 mBq. An outdoor gamma radiation exposure dose rate of 0.067x10-2 μR h-1 was recorded at Ikot Ekpene.
On the effect of oil and gas activities on the radiation level of the environment,
Stanislav and Elena (1998) carried out studies on the environmental impact of
the offshore oil and gas facilities and showed that produced waters from oil
and gas production contain naturally occurring radioactive elements (uranium
and thorium) and their daughter products (Ra-226 and Ra-228).
Also, the Rail Road Commission of Texas (RRC, 2007) showed that Naturally Occurring Radioactive Materials (NORM) associated with oil and gas production originate in sub-surface formations which may contain radioactive materials like uranium and thorium and their daughter products, Ra-226 and Ra-228.
According to United States Environmental Protection Agency (http://www.epa.gov/radiation),
field surveys have shown that petroleum pipe scale originating from oil production
may have very high Ra-226 concentration,and on disposal exposes the environment
to associated radioactive contaminants.
Ughelli and its environs are major oil producing communities in the Niger Delta region of Nigeria. The areas are criss-crossed with network of pipelines carrying either oil or gas to the flow stations from many locations (oil wells). Excessive exposure to background radiation by staff and host communities can result to associated known health-hazards. Research findings on the level of background radiation in respect to these areas are lacking. The need to properly document the level of background ionizing radiation of the areas and provide a base-line data for future studies lay credence to this study. The health implications of the obtained information were also carefully examined.
MATERIALS AND METHODS
This study was conducted in November, 2006 around oil and gas facilities in Ugheli, Nigeria.
The study areas lie within longitude 6°.04E and 5°.56E
and latitude 5° 38N and 5°.30N. An insitu approach
of background radiation measurement was adopted and preferred to enable samples
maintain their original environmental characteristics. A Digilert nuclear radiation
monitor and a Geographical Positioning System (GPS) were used. The tube of the
radiation monitoring meter was raised to a standard height of 1.0 m above the
ground (Ebong and Alagoa, 1992b) with its window facing first the oil facility
and then vertically downward while the GPS readings taken at that spot. Readings
were obtained between the hours of 1300 and 1600 h, since the exposure rate
meter has a maximum response to environmental radiation within these hours as
recommended (Ebong and Alagoa, 1992b). Three readings were taken at each facility
and the average calculated. For adequate coverage of the various facilities,
four to six different facilities radiation levels were taken within a field.
Measurements were also taken within the host communities outside the oil installations.
The count rate per minute was converted to micro-roentegen per hour (μR
h-1) using the relation:
where Q.F is the quality factor which is unity.
The Exposures dose equivalent in micro-Sieverts per week were obtained using the relation.
RESULTS AND DISCUSSION
Table 1 shows exposure rate determined for the twenty-one facilities within the four fields. The values obtained range from 12.00 to 22.00, μR h-1 for exposure rate and 5.34 to 9.79 μSv/week for dose equivalent. Eriemu
obtained from stations studied
fields and host communities data
count rate, compared with count rate for standard and host communities
N.G.C station recorded the highest radiation levels of 22.00±0.1 μR h-1 while the least radiation levels of 12.00±0.1 μR h-1 was recorded in Afiesere flare knock-out vessel. Table 2 shows the average exposure rate in the fields and Host Communities with Eriemu field recording the highest average and percentage deviation of 17.5±3.6 μR h-1 and 88.9% respectively.
Figure 1 shows the comparison between the radiation levels within the fields, standard background radiation and Host Communities radiation levels. In all the four fields the exposure rates exceeded the standard background and the previous values reported by Avwiri and Ebeniro (1998). Also, there is a significant elevation of the radiation levels in agreement with previous study in a similar environment (Arogunjo et al., 2004; Louis et al., 2005). The difference in the exposure rates between Host Communities and fields could be due to the input, outputs or effects associated with the activities of the facilities.
Furthermore, the levels recorded for gas flare stations and natural gas stations are fairly higher than other stations. This could be attributed to the heavy metals, normally associated with gas flares (Arogunjo et al., 2004).
These results obtained do not indicate any immediate health side-effects on
the staff and the host communities. The highest radiation exposure level of
9.79 μSv/week (recorded for NGC Station) is below the recommended value
of 0.2 mSv/week by the Texas Regulation for Control of Radiation (above background)
and protection of public health (RRC, 2007; UNSCEAR, 1998).
There is still likelihood of future health- side effects due to precipitation of produced formation waters (which contain radioactive elements) which on condensation as rain constitute radioactive pollution of rain water. Unfortunately, this serves as a major source of water for drinking and agriculture in the surveyed area. Also a greater proportion of these formation waters are leached from the oil/gas reservoir and carried to the sub- surface where they can make contact with sea water. The associated radionuclides interact with sulphates in the sea water where they partly precipitate and the rest consumed by aquatic animals and hence pose a radioactive risk to the aquatic family (Stanislav et al., 1998) and beyond.
As a result of this indirect ingestion of these radionuclides, the level of exposure by the host communities is enhanced. According to Ballinger (1991), most radiation biology researches describing the quantitative relationship between the radiation dose and biological effect indicates a threshold dose level below which no health side-effect occurs(for short term exposure). Late effects of low level radiation exposure do not have threshold dose level rather every small exposure exacerbates the health side-effect response curve.
The measurements of the external environmental radiation around oil and gas facilities in four oil fields and Host Communities have been carried out. The study revealed that the terrestrial radiation level of the areas have been affected by the activities of the oil company. Though the dose equivalent is still within the safe radiation limit of 0.02 mSv/week recommended by UNSCEAR (1998), the radiation levels within the facilities are far above the normal background levels.
Generally, the high values obtained can be attributed to the operation of the oil company in the environment, since the geology of the area shows no trace of (monazite) radionuclide bearing mineral (Ron, 1991; Arogunjo et al., 2004).
We therefore recommend as follows.
||The oil operating companies in the area should device means of reducing
their radionuclide input.
||In the interim, both life and health insurance policies should be acquired
for employers and contract staff of these multi-national companies working
within these fields, to take care of their long-term health problems.
||There should be a regular monitoring of radiation level in these environments.