The quality of public sources of drinking water in oil-bearing communities in the Niger Delta region of Nigeria

Background: Studies carried out in the Niger Delta region of Nigeria have demonstrated a link between oil exploration and poor-quality drinking water. However, many of these studies have been limited by small coverage and focus on few parameters. This study thus aimed at a comprehensive assessment of the quality of public sources of drinking water in three gas flaring and three non-gas flaring communities in the Niger Delta region of Nigeria. Methods: A total of 13 samples were collected from the major sources of drinking water in six communities in Rivers, Bayelsa and Delta States, Nigeria. These were stored and transported in line with International standards to a certified environmental laboratory where physical, chemical, bacteriological and petro-chemical assessments were conducted for 27 parameters. Results: Some samples had a pH below the normal range for drinking water, with median pH value of 4.63. All chemical parameters assessed fell below the normal acceptable range with exception of magnesium which exceeded the acceptable range. There were11 samples (91.7%) with microbial contamination; total and faecal coliform demonstrated at values ranging between 15 and 90 most probably number (MPN)/100 ml for total coliform and 9 to 23 MPN/100 ml for faecal coliforms. Oil, grease and total petroleum hydrocarbons (TPH) were identified in water samples from all communities. Values for oil and grease ranged between <0.001 and 0.015 mg/l, while TPH values were between <0.001 and 0.046 mg/l. There was no significant difference between median values in gas flaring and non-gas flaring communities. Conclusion: Distortion of physico-chemical properties, and hydrocarbon and faecal contamination of drinking water are a major challenge in oil-bearing communities in the Niger Delta region of Nigeria irrespective of gas flaring status. This calls for urgent interventions to improve the quality of drinking water for the people of the Niger Delta.


Introduction
Nigeria is Africa's largest producer of crude oil and the sixth largest producer in the world, (Egwurugwu et al., 2013;Ikeke, 2013;Oni & Oyewo, 2011) with a capacity to produce approximately 2.5 million barrels per day. (Nigerian National Petroleum Corportaion, 2015) A large proportion (97%) of the revenue from foreign trade that comes to Nigeria is from export of crude oil. As much as 20% of the country's GDP and 65% of the revenue budget is sourced from crude oil. Alongside the vast deposit of crude oil are even more vast deposits of natural gas located in the Niger Delta. (American Association for the Advancement of Science, 2011; Friends of the Earth Limited, 2004) In spite of this, the country is currently ranked by the World Bank as the 'poverty capital of the world' with up to half of its population said to be surviving on less than 1.90 dollars a day. (Kharas et al., 2018) The nine oil-bearing states in the country are collectively known as the Niger Delta. They are: Abia, Akwa Ibom, Bayelsa, Cross River, Delta, Edo, Imo, Ondo and Rivers States. Together they occupy 7.5% of the land mass of the country and are home to 31 million people speaking 250 different dialects from over 40 ethnic groups and 185 Local Government Areas (LGAs). These states though socially and culturally diverse, share in common the deleterious consequences of crude oil exploration and gas flaring. (Yakubu, 2017a) Oil exploration and gas flaring, which are routinely carried out by local and international oil companies in Nigeria, poses a significant hazard to the health of populations exposed to it. It has the potential to pollute the environment, heat up the atmosphere and releases greenhouse gases. (Ite & Ibok, 2013;McMichael et al., 2003) The process of oil exploration often involves gas flaring which results in the dissemination of greenhouse gases and other air pollutants such as carbon dioxide (CO 2 ), methane (CH 4 ), ethane, propane, butane hydrogen sulfide (H 2 S), and nitrous oxide (NO 2 ). Greenhouse gases have long been implicated in global warming and climate change. (Ajugwo, 2013;World Health Organization, 2003a;World Health Organization, 2003b) Apart from the effect on atmospheric temperature, the gases flared serve as pollutants to air and water. Greenhouse gases also precipitate the formation of acid rain. Acid rain runs off into surface water and percolates into ground water, causing a reduction in the pH of water and contamination with pollutants. (Efe & Mogborukor, 2014;Nwankwo & Ogagarue, 2011) There have also been various incidents of oil spills in several locations in the Niger Delta from accidents during drilling and transportation of crude oil. Oil spills contaminate soil, vegetation and water sources and contribute to reduction in the portability of drinking water through the introduction of total petroleum hydrocarbon (TPH). (Hagras, 2013;Kponee et al., 2015;Taiwo et al., 2012;WHO, 2005) Microbial contamination is also a common feature as a result of poor sanitation practices which persists despite the fact that oil-bearing communities generate a lot of revenue for oil exploration companies specifically and the nation generally.
The negative effect of oil exploration and gas flaring on the quality of drinking water in specific locations in the Niger Delta has been documented. Studies carried out in the Niger Delta region of Nigeria and elsewhere have demonstrated changes in the quality of drinking water in comparison to International standards. However, these studies have mostly been conducted in one or two communities in a state with focus on only a few parameters. (Efe & Mogborukor, 2012;Hagras, 2013;Ite & Ibok, 2013) This study thus aimed at a comprehensive assessment of the quality of public sources of drinking water in three gas flaring and three non-gas flaring communities in three states of the Niger Delta region of Nigeria.

Study background
This research was carried out between April and May 2016 in the Niger Delta region of Nigeria. A cross-sectional study design was employed. Communities that had been host to oil exploration activities with gas flaring for a minimum of ten years were included as well as communities without any history of oil exploration activities. A multistage sampling was used in recruiting the study communities. Purposive sampling of Rivers state, Bayelsa state and Delta state out of the nine states in the Niger Delta region of the country was done because these three states arguably have the highest level of oil exploration activities in the Niger Delta. Secondly, simple random sampling of one LGA per selected state from a sampling frame of all LGAs involved in oil exploration activities including gas flaring. Finally, purposive sampling of two communities in each selected LGA was done based on the presence or absence of oil exploration and gas flaring sites, minimal security risk and geographical accessibility. A total of six communities, Sampou and Nedugo in Bayelsa State, Ibada-Elume and Oton-Yasere in Delta state, and Omerelu and Mbodo-Aluu in Rivers State, were selected. Sampou, Ibada-Elume and Omerelu are communities without any oil exploration or gas flaring activities, while Nedugo, Oton-Yasere and Mbodo-Aluu are communities which have been host to oil exploration and gas flaring activities for the past 10 years.

Sources of water samples
The required permission to obtain water samples for hydrochemical analysis was sought from the community leadership during community entry activities. Water was sampled from a minimum of two of the most frequently patronized sources of drinking water for each community as reported by the community leadership. One sample per source of drinking water was collected. A total of 13 samples were collected from the six communities. Water samples were collected for physical, chemical and bacteriological assessments. For physical and chemical analyses, water samples were collected in polysterene bottles. Each bottle was washed and rinsed out several times with water and finally with distilled water before sample collection. Bottle sizes ranged from 0.5 to 1.5 litres. Samples for bacteriological analysis were collected into 200 ml sterilized containers and transported to the laboratory within 72 hours. In the laboratory physical, chemical and bacteriological assessments were carried out as follows: colour, odour, electrical conductivity, pH, taste and turbidity for physical properties; alkalinity, hardness, total dissolved solids (TDS), chromium, arsenic, chlorides, sulphate, nitrates, fluorides, sodium, potassium, calcium, magnesium, bicarbonate, iron, ammonia, phosphate, oil and grease for chemical and hydro-chemical properties and Coliform and Escherichia coli populations for biological properties.

Testing procedures
Various laboratory testing procedures were used. Total dissolved solids (TDS) was analysed using the TDS meter (APHA -209C method). Tests for ammonia (APHA 4500-NH 3 C method), sulphate (APHA 4500 SO 4 2-E method), bicarbonate (APHA 2320B method), phosphate (APHA 4500P-E method), chloride (APHA 4500B method), nitrates (APHA 4500E method) were also done. Hardness of water samples (calcium and magnesium contents) were tested using the Titrimetric method. (Deshpande, 2012) This method is based on the principle that ethylene diamine-tetra-acetic acid and its sodium salt (abbreviated EDTA) form a chelated soluble complex when added to a solution of certain metal cations. The concentration (in mg/l) of metals in the water samples was determined using an atomic absorption spectrophotometer. The metals were analyzed using the direct air-acetylene flame method (APHA 3111-B). Oil and grease content was analysed using a spectrophotometric method (AP1 -RP 45, APHA 5520B, EPA 1664). TPH assessment was done using a calibrated HP 5890 gas chromatograph equipped with a capillary column. Commercially available TPH Standard, C8-C40 (Hydrocarbon window defining standards, AccuStandard DRH 0085) was used for the calibration of the Gas Chromatograph. Total coliform count was assessed by most probable number (MPN) presumptive test using the APHA 9221B method, while for faecal coliform MPN confirmatory test using the APHA 9221B method and faecal coliform MPN complete test were done. All QA/QC procedures were strictly adhered to during each process. (Deshpande, 2012)

Statistical analysis
The results of the analysis for each water sample was entered into IBM Statistical Package for Social Sciences version 23 and analysed. Descriptive statistics included frequency distribution, median and range of the various parameters. The Mann-Whitney U-test was used to ascertain significant differences between values from gas flaring and non-gas flaring communities for each characteristic of drinking water, with the alpha value set at 0.05. Values were also compared the national standards for drinking water. (Standards Organization of Nigeria, 2007)

Review of water samples
A total of 13 samples of drinking water was collected with seven samples (53.9%) obtained from gas flaring communities. Sample collection occurred mostly under sunny/dry weather conditions (10; 76.9%). Boreholes were the drinking water source in 6 out of 13 samples obtained (46.2%). Algae was observed in 11 out of 13 samples (84.6%) ( Table 1).
The median levels of temperature, turbidity, and chlorine in all the states studied, were all above the national standards for drinking water, while values for total dissolved solids, chloride and conductivity were far above national standards. However, pH of all samples was within acceptable limits (Table 2).
A review of the chemical characteristics of drinking water obtained from the three states surveyed showed fluoride, nitrate and sulphate levels to be lower than the National standards. The same observation was made for all cations measured, with the exception of magnesium (Table 3).
Assessment of microbiological and hydrocarbon characteristics of drinking water obtained from the three different states   surveyed showed that the total coliform, faecal coliform and hydrocarbon levels of these samples where higher than the national standards (Table 4).
All Underlying data described above are available from Open Science Framework (Maduka & Ephraim, 2019) Comparison of water samples from gas flaring and nongas flaring communities Review of the atmospheric and physical characteristics of drinking water samples from gas flaring and non-gas flaring communities in the three surveyed states showed that there was no statistically significant difference in these characteristics when compared for both the gas flaring and non-gas flaring communities ( Table 5).
Review of the chemical characteristics of drinking water samples from gas flaring and non-gas flaring communities in the three surveyed states showed that there was no statistically significant difference in these characteristics when comparing the gas flaring and non-gas flaring communities ( Table 6).
Review of the microbiological and hydro-chemical characteristics of drinking water samples from gas flaring and non-gas flaring communities in the three surveyed states showed that there was no statistically significant difference in these characteristics when compared for both the gas flaring and non-gas flaring communities (Table 7).

Discussion
The first major finding from this study is that various components of drinking water exceed or are below the required safe standards for drinking water in Nigeria. (Standards Organization of Nigeria, 2007) Temperature, turbidity, chlorine, dissolved oxygen, magnesium, total coliform, fecal coliform, oil/grease and TPH values were all found to be higher than the national drinking water standard. This finding is corroborated by the research findings of Braide et al. (2016) and Ugwoha et al. (2017); who reported elevated temperatures in surface and groundwater water samples that were tested. Egwurugwu et al. (2013) also reported elevated temperature, dissolved oxygen as well as magnesium levels in water samples obtained from gas flaring areas. The increases in temperature was associated with pollution of the tested samples, which they concluded was probably a result of gas flaring activities. Another study identified distortions in water samples gotten from these gas flaring areas as a direct consequences of the flaring activities which are capable of distorting the chemical and biological composition of the drinking water in affected areas. (Ugwoha & Omenogor, 2017) Also notable in this study was that the pH (of some samples), bicarbonate, iron, fluoride and sulphate values of the tested water samples were found to be lower than the national drinking water standards. These findings are similar to the findings of Dami et al. (2012) who reported reduced levels of the above stated parameters. who reported reduced levels of the above stated parameters. These distortions are indicative of the adverse effects of acid rain (which is associated with gas flaring activity) deposition into the water sources from which the samples were gotten and thus increasing the acidity levels of the water beyond the acceptable normal standard for drinking water. (Idah Seiyaboh, 2018;Ubani & Onyejekwe, 2013) The need for the availability and consumption of safe drinking water cannot be over-emphasized due to the immense benefits this provides, including elimination of diseases, optimal growth and development, provision of essential biochemical requirements of the body, ensuring public health and safety etc. (Duggal et al., 2015). Crude oil exploration in Nigeria which has been incessantly plagued with oil spills mainly as a result of technical errors, pipeline vandalism etc., together with harmful activities such as gas flaring, has adversely affected the health of the populace as well as the biological, economic and socio-cultural elements of the oil-bearing communities of Nigeria (Efeke et al., 2015;Ugwoha & Omenogor, 2017). The activities of crude oil exploration, exploitation and production, including the activity of gas flaring, have been widely reported to negatively impact the normal indices of safe drinking water in these oil-bearing communities as a result of the evaporation, dissolution, oxidization and crystallization of the various components of crude oil whenever an oil spill occurs (Ekpenyong & Udofia, 2015;Ugwoha & Omenogor, 2017;Yakubu, 2017b) The findings of this study are suggestive of the negative effects that gas flaring and oil exploration has on the drinking water quality of oil-bearing communities. It is, however, disturbing to note that the differences in the various physical, chemical and biological constituents of tested water samples gotten from gas flaring areas and those from non-gas flaring areas were not significant. This finding is not corroborated by the findings of various studies that reported that the contaminants in the tested     water samples were high in the immediate gas flaring areas and reduced in concentration further away from the gas flaring stations. (Amadi, 2014; Ubani & Onyejekwe, 2013) Our findings may be attributable to the weather conditions experienced, especially during the rainy season, which has the capability of influencing the spread of the oil exploration (including gas flaring) contaminants through rain, surface and ground water from gas flaring areas to non-gas flaring areas. It can also be attributable to the spread of these adverse consequences through the dynamic nature of surface and groundwater, especially during the rainy season when rain water levels are increased. (Nkereuwem & Udeme, 2015;Nwankwo & Ogagarue, 2011;Ugwoha & Omenogor, 2017).
In conclusion, the deviation from national standards of drinking water for physico-chemical parameters, as well as hydrocarbon and faecal contamination of drinking water, remain major challenges to the availability of potable drinking water to oil-bearing communities in the Niger Delta region of Nigeria. This calls for urgent interventions to improve the availability of potable drinking water in these oil-bearing communities, such as stricter regulation of gas flaring activities to ensure the health of residents of communities in the Niger Delta region of Nigeria. Sheet "Water_Quality_Assessment" contains the raw data measured from each sampling area.

Data availability
Data are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).

Grant information
This research was supported by the African Academy of Sciences and the Association of Commonwealth Universities through a Climate Impact Research Capacity and Leadership Enhancement (CIRCLE) programme grant. CIRCLE is funded by Department for International Development (DfID) of the UK government.
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.