Polycyclic aromatic hydrocarbon burden in ambient air in selected Niger Delta communities in Nigeria

Abstract

The Niger Delta area in Nigeria has major oil producing and refining centers that characterized enormous industrial activities, especially in the petroleum sector. These industrial processes release different kinds of atmospheric pollutants, of which there is paucity of information on their levels and health implications. The objective of this study was to determine the ambient levels of polycyclic aromatic hydrocarbons (PAHs) in communities of a local government area (Eleme) where oil wells, petrochemical installations, a refinery, and a fertilizer complex are located. Respirable particulate matter (PM) in air were collected using Anderson high-volume sampler with PM with aerodynamic diameter ≥10 μm (PM₁₀) inlet for collecting filterable, particle-bound PAHs according to standard methods. PAHs were analyzed following standard methods for the 16 World Health Organization (WHO) prioritized components. The results were compared against the levels in another local government area (Ahoada East) with low industrial presence. The average total PAH concentration in Eleme of 9.2 µg/m3 was among the highest in the world; by contrast, the average concentration in Ahoada East was only 0.17 ng/m³. The most prominent PAHs at Eleme were those known to be carcinogenic and included benzo(a)pyrene (1.6 × 10⁴ ng/m³ at bubu), benzo(k)fluoranthene (2.4 × 10⁴ ng/m³ at Akpajo where a petrochemical is located), pyrene (3.1 × 10³ ng/m³ at Ogale), and indeno(1,2,3-cd)pyrene (9.1 × 10³ ng/m³ at Akpajo). Data from this study emphasize the need for a comprehensive source apportionment study and an assessment of the health effects of oil production on local communities of Nigeria where no such information currently exists.

Implications:

This investigation reveals that communities adjoining industrial locations in Nigeria's Delta area are more exposed to higher concentrations of pollutants. This predisposes affected communities to environmentally induced health problems. The scenario requires a review of policy that would compel industrial facilities in the area to improve their pollution control regimes. This should be supported by stringent environmental monitoring by regulatory authorities. Also there is the need for in-depth epidemiological and toxicological studies in order to establish causality between the environmental exposure factors and emerging health problems. The outcome of such studies would be critical for instituting intervention programs in the area.

Introduction

Polycyclic aromatic hydrocarbons (PAHs) could be a common constituent of ambient air in Nigeria. This is expected because of widespread combustion of biomass for energy and waste disposal. The common practice of slash-and-burn cultivation can add to the atmospheric burden of PAH in many parts of the country.

With growing population of motor vehicles, which often are badly maintained, elevated levels of PAH may be expected in urban areas, especially near heavily trafficked roads. Also the upstream and downstream oil industry operations (crude oil extraction and petroleum refining processes) in the Niger Delta could possibly present a significant source of PAH in the country. In spite of the presence of potentially large and varied sources of emissions, little is currently known about the levels of PAH in ambient air in any part of Nigeria.

Interest on airborne PAHs stems from the fact that their toxic effects on human health are well documented in the scientific literature (ATSDR, 1995). Children seem to be particularly at risk to airborne PAH because their respiratory and immune systems are not fully developed; they inhale comparatively more air per kilogram of body weight than adults and generally spend more time outdoors (Schwartz, 2004). Childhood exposure to PAH has been associated with increased risk of asthma and cancer (Crosignani, et al., 2004; Kim et al., 2005 Knox, 2005). Pregnant women are vulnerable to PAH, which can cross the placental barrier. PAHs are regarded as endocrine disruptors and animal studies have associated exposure to these compounds with negative fetal growth and pregnancy outcomes, including fetal death, preterm delivery, malformations, and transplacental carcinogenesis (Singh et al., 2008).

Another underlying reason for concern with exposure to PAH is the fact that some of these compounds may be human carcinogens based on epidemiological studies (Brody et al., 2007; Knox, 2005). The U.S. Environmental Protection Agency (EPA, 2002) has classified benzo[a]anthracene, benzo[b]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, dibenzo[a,h]anthracene, and indeno[1,2,3-c,d]pyrene as probable human carcinogens (group B2). The International Agency for Research on Cancer has recognized benzo[a]anthracene and benzo[a]pyrene as probable human carcinogens, whereas benzo[b]fluoranthene, benzo-[j]fluoranthene, benzo[k]fluoranthene, and indeno[1,2,3-c,d]pyrene are labeled as possible human carcinogens (IARC, 2004).

As an important component of indoor air pollution, generated during household combustion of solid fuels, PAHs have been associated with high incidence of lung cancer risk in developing countries (Straif et al., 2006). Because of their carcinogenic potential in human populations, every effort must be made to minimize the exposure concentration of PAHs in ambient air. A target value of 0.25 ng/m³ for benzo[a]pyrene (BaP) in ambient air (annual average to be achieved by the end of 2010) has been set in the U.K. National Air Quality Strategy (Vardoulakis et al., 2009). The European Community's Fourth Air Quality Daughter Directive (2005/107/EC) has set a target value of 1 ng/m³ for BaP (annual average). The Chinese national ambient air quality standard for PAH is 10 ng/m (Crosignani et al., 2004; Liu et al., 2007).

In view of the potential for emission of large quantities of PAH in Nigeria, there is concern that environmental burdens of these compounds may be posing a health risk to people in some parts of the country. In support of this assumption, high concentrations of PAHs have been reported in soils, sediments, water, and foods in Nigeria (Nganje et al., 2006; Olajire and Brack 2005; olajire et al., 2007) but no information is yet available on PAH levels in the atmosphere, which serves as a medium for dispersing this pollutant locally, regionally or even globally (Sehilia and Lammel, 2007). Here we present the first set of such measurements in Nigeria.

Materials and Methods

The study communities

In Figure 1, the two study areas Eleme and Ahoada East are vividly illustrated. Eleme Local Government Area (ELGA) constitutes 1 of the 24 Local Government Areas (LGAs) of the present Rivers State. It is located about 20 km away from Port Harcourt city, the state capital. Eleme LGA consists of 10 communities made up of two major tribes, viz. Nchia and Odido. This LGA has oil wells at Ebubu, petrochemical operations at Akpajo/Agbonjia, a refinery at Alesa/Okirika, and a fertilizer complex at Onne. As of the time of sampling at Alesa, a major unit of the refinery that is the catalytic cracking unit (CCU) was down, whereas other sections of the plant were in operation. The Eleme area is mostly deltaic with a mixture of rain forest and mangrove/swamp forest. Because of the deltaic nature of the area, the people are mostly fishermen and peasant farmers, whereas a few people engage in public service and industry work. Some of the residents are involved in private business, government service, and industrial operations. Unlike Eleme, the Ahoada East Local Government Area (AELGA) is less industrialized. It has similar geographic characteristics as Eleme, including the rainfall and temperature patterns as well as the vegetation and soil types. The AELGA consists of three major ethnic settlements, namely Upata, Akoh, and Ahoada. It is made up of over 20 communities divided into 13 wards whose people are engaged in farming, fishing, private, and government service.

Figure 1. Map showing communities and sample locations.

Sampling

Particulate bound PAH samples from outdoor ambient air were collected from 14 locations: 7 from Eleme and 7 from Ahoada East communities, respectively (Tables 1A and 1B and Figure 1). Samples were collected during late dry season conditions (February–March). The average meteorological conditions recorded showed temperature range of 28–31 °C, wind speed conditions averaging 2–5 m/sec at the sample locations with no cloud cover, and a low precipitation of about 12–33 mm. The samples were obtained using a 10-µm inlet high-volume sampler according to the Andersen PM₁₀ Hi-Vol sampler system, which is approved by the U.S. Environmental Protection Agency (EPA) with reference method no. RFPS-1287-063. A glass fiber filter paper (catalog no: 1882 866 EPM 2000; Sigma-Aldrich, USA) with dimensions 20.3 cm×25.4 cm was used. Sampling was done cross-sectionally and intermittently for 4 hr in each of the 14 sampling locations between 10 a.m. and 2 p.m. daily to capture peak activity periods.

Table 1A. Description of sample locations at Eleme community

Sample No.	Community	Sample Location	Coordinates
1	Akpajo	5 km from petrochemicals	LAT 4.803, LON 7.109
2	Aleto	Within 10 m radius of petroleum staff quarters	LAT 4.809, LON 7.139
3	Alesa	3 km away from refinery	LAT 4.786, LON 7.119
4	Ogale	Within 5 m radius of local council quarters	LAT 4.778, LON 7.127
5	Ebubu	About 1 km from Ejama flow station	LAT 4.780, LON 7.152
6	Ekporo	Within 10 m radius of local market square	LAT 4.720/ LON 7.211
7	Onne	2 km from air force base	LAT 4.725, LON 7.153

Table 1B. Description of sample locations at Ahoada East community

Sample No.	Community	Sample Location	Coordinates
1	Ulapata	Within 10 m radius of town hall playground	LAT 5.090, LON 6.626
2	Ahoada	About 50 m away from highway	LAT 5.075, LON 6.654
3	Ula Ehuda	Within 5 m radius of community	LAT 5.140, LON 6.615
4	Ihubogu	Within 5 m radius of community playground	LAT 5.169, LON 6.693
5	Ihuoho	100 m away radius of a market square	LAT 5.159, LON 6.663
6	Ikata	Within 10 m radius of a market	LAT 4.985, LON 6.610
7	Odiabidi	Within 10m radius of a school building	LAT 4.950, LON 6.638

Sample preparation

After sampling, the particle-impregnated filter paper was stored under dark and cool conditions prior to further processing. Before solvent extraction, the filter paper was shredded into tiny particles to increase its surface area. The chips were placed in a thimble for solvent extraction based on a modified standard method (Lee et al., 1979). About 150 mL of the extracting solvent was used for the process, which lasted 1 hr. This was repeated and the combined extract recovered for purification and concentration stages. The extract was purified, and concentrated, and analyzed according to standard methods (Lee et al., 1979).

Concentration

The combined extract obtained from above was introduced into a 500-mL K-D flask (Advance Scientific & Chemical, Inc., Fort Lauderdale, FL) equipped with a 10-mL concentrator tube that was also attached to a refluxing column. The K-D apparatus was placed on a steaming hot water bath and after proper adjustments of the apparatus as well as regulation of water temperature, the solution was heated for 30 min so as to reduce the volume of extract to about 20 mL.

Clean-up

In the clean-up stage, use was made of activated silica gel heated overnight at 120 °C and placed inside a 15-mm-diameter chromatography column into which 30 mL of dichloromethane (DCM) was poured in and eluted. About 2 cm of anhydrous sodium sulfate was added to the top of the silica gel bed and the column pre-eluted with 40 mL of pentane and the eluate discarded. The extract was then transferred onto the column with 25 mL each of DCM and pentane used to elute the column and the combined eluate collected into a 500-mL K-D flask equipped with a 10-mL concentrator tube.

Solvent exchange

This stage could also be regarded as the final concentration stage in which the combined clean-up extract placed in the K-D apparatus was subjected to the same conditions previously described above only that at a reduced extract volume of about 5 mL was achieved, after which 10 mL of acetonitrile was added and the exchange of solvent allowed to take place for about 10 min, from which the final extract volume of 5 mL was obtained ready for analysis.

Sample analysis

The analysis of extracts was carried out using a Millipore high-performance liquid chromatography (HPLC) apparatus that consisted of an auto sampler (model: Waters 717; Spectra Lab Scientific Inc., Canada), a pump (model: Waters 610) for both the fluid unit and valve station (Waters 6.00E) for the pump system controller, a photodiode detector (model: Waters IM 996), and a fluorescence detector (model: Waters 470). The software Millennium 32 was used and the method of operation was of the isocratic/gradient type with a combination of acetonitrile and deionized filtered water as the mobile phase and a stationary phase made up of silica gel loaded in 5-µm HPLC column, SUPELCOSIL LC-PAH col:12435-007 (Fisher Scientific, USA) of dimensions 15 cm × 4.6 mm. All the processed field samples were analysed against standards following a method set created using the 16 World Health Organization (WHO) prioritized PAH components. The unknown sample was run against the standard, calibrated, integrated, and the concentration of the PAH components based on the peak sizes of the eluted chromatogram quantitated. The source of PAH standards was EPA 8310 reference standard catalog no. 31841. The methodology used in this study was designed to measure the following 16 compounds in each sample: naphthalene (NAP), acenaphthylene (ACY), acenaphthene (ACE), fluorene (FLO), phenanthrene (PHE), anthracene (ANT), fluoranthene (FLA), pyrene (PYR), benz[a]anthracene (BaA), chrysene (CHR), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), dibenz [a,h]anthracene (DahA), benzo[g,h,i]perylene (BghiP), and indeno[1,2,3-cd]pyrene (IcdP).

Results and Discussion

Tables 2A and 2B show that a number of common PAH homologues, such as naphthalene, acenaphthylene, chrysene, dibenzo(a,h)anthracene, and benzo(g,h,i)perylene, were not detected at all at Eleme and Ahoada East sample locations. The last two compounds are used as atmospheric signatures of coal combustion (Ladji et al., 2009) and hence should not be expected in these communities that do not burn coal.

Primary sources of naphthalene in the atmosphere are petroleum refining and coal tar distillation (Environmental Australia, 2001). The later was not present at all in any of the communities studied; the former being present was only partially functional due to the breakdown of the CCU. Both acenaphthene (detected at very low levels in only two stations) and acenaphthylene are emitted from a variety of incomplete combustion sources such as diesel exhaust and the low concentrations of these homologues suggest that such combustion sources particularly from automobile emissions may have contributed less to the atmospheric burden of PAHs in the two communities.

The profiles of PAH at individual stations show that the highest number of homologues (11), namely, acenaphthene, fluorene, anthracene, phenanthene, fluoranthene, pyrene, benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, and indeno(1,2,3-cd)pyrene, was recorded in Ebubu (Figure 2a, Table 2A). Compared to the other stations, total PAH concentration at Ebubu (2.2 × 10⁴ ng/m³) was the second highest indicating that installations in this town (such as the SPDC oil wells and its proximity to the refinery) are an important source of PAH in this area.

Figure 2. Ambient outdoor total PAH concentration at Eleme (a) and Ahoada East (b).

Table 2A. Concentration of PAH in ambient air at Eleme

Sample ID/ LocationComponents	APE1 Akajo	APE2 Aleto	APE3 Alesa	APE4 Ogale	APE5 Ebubu	APE6 Ekporo	APE7 Onne
Naphthalene	—	—	—	—	—	—	—
Acenaphthalene	—	—	—	—	—	—	—
Acenaphthene	—	—	—	—	5.20 × 10^−4	—	4.43 × 10^−4
Fluorene	—	—	—	2.17 × 10^−4	2.58 × 10^−3	—	7.03 × 10^−3
Anthracene		9.13 × 10^−4		4.48 × 10^−4	2.81 × 10^−1	—	1.12 × 10^1
Phenanthrene		2.53 × 10^−3	1.27 × 10^−3	9.8 × 10^−5	6.20 × 10^−3	—
Fluoranthene	—	—	2.55 × 10^−3	9.10 × 10^−4	8.14 × 10^0	—	2.52 × 10^−1
Pyrene	—	—	—	3.13 × 10^3	3.12 × 10^1	—	1.42 × 10^1
Benzone(a)anthracene	—	—	—	2.61 × 10^1	5.71 × 10^3	—	5.87 × 10^−1
Chrysene	—	—	—	—	—	—	—
Benzo(k)fluoranthene	2.40 × 10^4	—	—		1.35 × 10^0		2.59 × 10^−2
Benzo(a)pyrene	—	3.20 × 10^3	—	1.16 × 10^2	1.59 × 10^4	2.12 × 10^0	1.96 × 10^0
Benzo(b)fluoranthene	—	—	—	—	1.97 × 10^0	—	—
Indenol(1,2,3-c,d)pyrene	9.12 × 10^3	3.41 × 10^−1	1.91 × 10^1	—	1.08 × 10^2	—	2.12 × 10^0
Dibenzo(a,h)anthracene	—	—	—	—	—	—	—
Benzo(g,h,i)perylene	—	—	—	—	—	—	—
∑PAH	3.3 × 10^4	0.34	19.1	3.2 × 10^3	2.2 × 10^4	2.1	28.3
Notes: Results expressed in µg/m^3. Detection limit = 0.001 to 0.1 µg/m^3.

In general, total PAH concentrations tend to decrease with distance from Ebubu with Ekporo which is the furthest town having the smallest number (one) of measurable homologue in the air (Table 2A). However, the lowest total PAH concentration was recorded at Aleto, which was one of the locations with less oil installations.

The highest concentration of total PAHs in the air was recorded in Akpajo (3.3 × 10⁴ ng/m³) and this was made up mostly of benzo(k)fluoranthene (2.4 × 10⁴ ng/m³), a marker of the petrochemical complex located in this town (El Haddad et al., 2011; Robinson et al., 2006). The refinery located in Alesa was partially in operation when the samples were taken, which may have accounted for the low total PAH level in the town. The large number of PAH homologues (nine) at Onne probably reflects the diversity of industries there which includes port complex, chemical fertilizer plant and oil servicing installations.

The average total PAH concentration in the Ahoada LGA was 0.09 ng/m³ (range 2.30 × 10⁻⁵ to 7.40 × 10⁻²), well below the value for Eleme LGA of 8.34 µg/m³ (range 0.34–3.3 × 10⁴ ng/m³). The later was dominated by observed high values at Akpajo and Ebubu. If these two stations were excluded from the analyses, the average value would drop to 649 ng/m³. These average values are comparable to what have been reported around point sources, in tunnels, and toll stations in other parts of the world. (ATSDR, 1995).

For instance, there has been reported total PAH levels of 8.3–12.3 µg/m³ at highway toll stations in Taipei, Taiwan. By contrast, levels in industrial, urban, and rural areas in central region of Taiwan were found to be 1.2–1.6, 0.7–1.7, and 0.610–0.8 µg/m³ respectively (Cheng et al., 2007). Even with the value for Akpajo and Ebubu excluded, the average value for Eleme was still much higher than the typical PAH concentrations found in industrialized and urban areas in many developing countries: 8–29 ng/m³ in downtown Algiers, Algeria (Ladji et al., 2009); 53–371 ng/m³ in Qingdao, China (Guo et al., 2003); 4.7–99 ng/m³ in Guangzhou, South China (Li et al., 2006); 38–53 ng/m³ in Ho Chi Minh City, Vietnam (Hsieh et al., 2007); 3.1–48 ng/m³ in Kuala Lumpur, Malaysia (Omar et al., 2002); and 22–50 ng/m³ in Sarajevo, Bosnia (Čupr et al., 2007).

The absence of detectable amount of BaP in any of the stations does not preclude the fact that such PAH component may still be present in the environment. Interestingly, it could be argued that large portion of particles released by combustion sources such as automobiles and as wood smoke have particle sizes less than 10 µm that are impregnated with PAHs rich in BaP (Anittila et al., 2005; Glasius et al., 2008; Rehwagen et al., 2005; Spezzano et al., 2008).

The concentration ratios of some specific PAHs were evaluated to characterize and identify PAHs emission sources. The calculated diagnostic ratios for the aerodynamic diameter ≤ 10 μm (PM₁₀) fraction of the particulate matter together with some specific ratios related to their sources reported in the literature are presented in Table 3. The evaluated ratios of IcdP/(IcdP + BghiP), FLT/(FLT + PYR), ANT/(ANT + PHE), BaP/BghiP, and BaA/(BaA + CHY) for PM₁₀ fraction indicate a significant contribution from petrogenic sources, in contrast with coal combustion sources as reported in the following references (Mandalakis et al., 2005; Tang et al., 2005; Wu et al., 2007; Zhou et al., 2005).

Table 2B. Concentration of PAH in ambient air at Ahoada East

Sample ID/Location Components	APA1 Ulapata	APA2 Ahoada	APA3 Ula Ehuda	APA4 Ihugbogu	APA5 Ihuoho	APA6 Ikata	APA7 Odiabidi
Naphthalene	—	—	—	—	—	—	—
Acenaphthalene	—	—	—	—	—	—	—
Acenaphthene	—	—	—	—	—	—	—
Fluorene	—	—	—	—	—	—	—
Anthracene		—		3.55 × 10^−4	—	—	—
Phenanthrene	1.61 × 10^−4	—	—	—	—	—	—
Fluoranthene	2.03 × 10^−4	—	—	—	—	—	—
Pyrene	—	—	—	2.16 × 10^−4	—	—	—
Benzone(a)anthracene	—	—	—	2.65 × 10^−3	—	2.65 × 10^−3	—
Chrysene	—	—	—	—	—	—	—
Benzo(k)fluoranthene	—	1.24 × 10^−2	—	2.63 × 10^−3	—	—	—
Benzo(a)pyrene	—	—	—	—	—	—	—
Benzo(b)fluoranthene	—	4.68 × 10^−4	—	—	—	—	—
Indenol(1,2,3-c,d)pyrene	2.79 × 10^−4	6.21 × 10^−2	2.30 × 10^−5	—	2.77 × 10^−4	2.33 × 10^−4	2.51 × 10^−4
Dibenzo(a,h)anthracene	—	—	—	—	—	—	—
Benzo(g,h,i)perylene	—	—	—	—	—	—	—
∑PAH	1.6 × 10^−2	7.4 × 10^−2	2.30 × 10^−5	5.8 × 10^−3	2.8 × 10^−4	2.8 × 10^−3	2.5 × 10^−4
Notes : Results expressed in µg/m^3. Detection limit = 0.001 to 0.1 µg/m^3.

Table 3. Diagnostic ratios of PAHs associated with PM₁₀

	IcdP/(IcdP + BghiP)	FLT/(FLT + PYR)	ANT/(ANT + PHE)	BaP/BghiP	BaA/(BaA + CHY)
Coal combustion*	0.56 ^a	>0.5 ^c,d	>0.1 ^d	0.9–6.6 ^e,f	>0.35 ^d
Vehicular emission*	0.18–0.40 ^a,b	0.4–0.5 ^b,c,d	<0.1 ^d	0.3–0.44 ^f	0.2–0.35 ^d
Wood combustion*	0.62 ^a	>0.5 ^c			0.43 ^g
Coke production*				5.1 ^e
Eleme (PM10)**	1.0	0.003	0.99	0	1.0
Akpajo ^+	1.0	0	0	0	0
Ogale ^+	0	2.9 × 10^−7	0.830	0	1.0
Ebubu ^+	1.0	0.207	0.978	0	1.0
Ekporo ^†	0	0	0	0	0
Ahoada East (PM10)*	1.0	0.48	0.69	0	1.0
Notes: ^a Pio et al., 2001 (Pio et al., 2001); ^b Kavouras et al., 1999 (Kavouras et al., 1999); ^c Zencak et al., 2007 (Zencak et al., 2007); ^d Yunker et al., 2002 (Yunker et al., 2002); ^e Simcik et al., 1999 (Simcik et al., 1999); ^f Wu et al., 2007 (Wu et al., 2007); ^g Mantis et al., 2005 (Mantis et al., 2005). *Information from literature (secondary data). **Information from field work (primary data). ^+Highly polluted areas in Eleme. ^†Least polluted area in Eleme.

It has been reported that FLT/(FLT + PYR) ratios below 0.40 imply the prominence of unburned petroleum (petrogenic sources), ratios from 0.40 to 0.50 suggest the combustion of liquid fossil fuels (vehicle and crude oil), whereas ratios larger than 0.50 are characteristic for grass, wood, or coal combustion (Yunker et al., 2002). The ratios of IcdP/(IcdP + BghiP) obtained in this work for the PM₁₀ fraction were 1.0 for both Eleme and Ahoada East communities, respectively, and this was different from values obtained from closely related studies reported elsewhere (Tang et al., 2005). In this study (see Table 3), the ratio of FLT/(FLT + PYR) of 0.003 for Eleme depict the dominance of PAH from petrogenic sources, whereas that of 0.48 depict PAHs from the combustion of fossil fuels particularly automobiles (Yunker et al., 2002). At Ogale and Ebubu, two of the most polluted communities at Eleme, the ratio of FLT/(FLT + PYR) obtained was 2.9 × 10⁻⁷ and 0.207, respectively, which was less than 0.40 thus implying that the PAHs were mostly from petrogenic sources.

The ratios of ANT/(ANT + PHE) were 0.830 and 0.978 for Ogale and Ebubu communities, both located in Eleme. However, Eleme generally recorded 0.99 and Ahoada East 0.69 and all these ratios were higher than 0.1, thus implying that the PAHs were typically associated with combustion processes (Li et al., 2006; Vasilakas et al., 2007; Yunker et al., 2002). The BaP/BghiP ratios were extremely high for Eleme, whereas no value was recorded for Ahoada East, indicating poor PAH sources from coal combustion, a result found to be different from those previously reported (Liu et al., 2007; Wu et al., 2007). Also, BaA/(BaA + CHY) ratios of 1 for both Eleme and Ahoada East, respectively, did not indicate PAH from coal combustion sources. Incidentally, Ekporo, the least polluted community at Eleme, did not reflect PAHs arising from any of the major sources given the nil ratios recorded.

Conclusions

Since PAHs are suspected to be carcinogenic, an absolutely safe level cannot be established for any of these compounds. The concentrations found in five of the seven sampling stations in Eleme LGA exceeded the Chinese national ambient air quality standard for total PAH of 10 ng/m³ (Liu et al., 2007).

In view of the fact that BaP has high carcinogenic potency and occurs widely in the environment, most assessments of risks associated with PAH uptake via the inhalation route are often based on BaP concentrations in air (Chen and Liao, 2006). BaP is a prominent member of the PAH homologues found in Eleme along with BKF and IcdP, which are also known to be carcinogenic (Figure 2a, Table 2A). The BaP concentrations in four stations in Eleme exceeded the 1.0 ng/m³ guideline established in the European Community's Fourth Air Quality Daughter Directive (2005/107/EC).

We believe that the human health risks associated with exposure concentrations of PAH in Eleme LGA are significant because (a) the BaP concentrations at two stations are several thousand-folds above established ambient air quality guidelines for this carcinogen; (b) concentrations of other PAHs known to be carcinogenic are high at many stations and there thus a strong co-exposure to carcinogenic homologues; and (c) the actual ambient airborne levels of PAHs were probably much higher than reported here considering that only PM₁₀ fractions have been analyzed, excluding the volatile fractions.

Hence this study draws attention to an urgent need to study the health effects of oil industry operations on the health of local communities in Nigeria; to the best of our knowledge, no such assessment has ever been done.

Finally, arising as a limitation of this study, future investigation should explore the use of PUF during PM sampling to be able to capture the volatile and nonparticulate fraction of the PAHs. More importantly, premium attention should be paid on the source apportionment for PAHs in the localities, since this would help in establishing the actual burden of the PAHs from various sources within the study area.

Acknowledgments

The Authors gratefully acknowledge the support of R&D, Nigerian National Petroleum Corporation (NNPC), for providing the facilities used in the conduct of this study. The technical assistance rendered by Prof. J. Nriagu, of the Department of Environmental Health Sciences, University of Michigan, Ann Arbor, Michigan, USA, is highly appreciated.