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Distribution of Petroleum Hydrocarbons in Coastal Sediments of Askar,
East of Bahrain
Al-Anoud F. Al-Khatlan, Thamer S. Ali & Asma A. Abahussain
Department of Natural Resources & Environment, College of Graduate Studies, Arabian Gulf
University, Manama, Bahrain
*Corresponding author: [email protected]
Abstract: The coast of Askar is one of the common fishing grounds exposed to
several anthropogenic activities. Twenty-seven monitoring stations have been
selected to assess the total petroleum hydrocarbons (TPHs) in Askar coastal
sediments. The stations are distributed into three sectors; one is associated with
intertidal zone and other two are associated with subtidal zone at 100 m and 350 m
from the coastline. Three control and three checkpoint stations have been adopted.
Multi-dimensional scale (MDS) was applied to find out spatial variations among the
selected stations. Mapping on TPHs distribution was produced using Arc GIS. The
TPH levels were found to be of wide range (3.15-31.51 µg/g) with an average of
6.67 µg/g, 10.11 µg/g and 15.30 µg/g at the intertidal, first and second subtidal
sectors, respectively. Generally, TPHs levels at the subtidal zone are higher than the
control and checkpoint stations, however the levels in the intertidal zone are below
the control and checkpoint stations. The mapping showed two hotspots in the second
subtidal zone with noticeable high concentrations in the area located between
stations 3 and 5. These findings were confirmed by the MDS analysis, where three
main contours are found representing the hotspot areas, moderate and lowest levels.
All levels detected are below the CEFAS standards.
Keywords: Coast, Sediments, GIS, MDS, TPHs, Askar, Bahrain.
Introduction
Globally, huge amounts of oil are being spilled into the coastal and marine areas from
several activities such as production, transporting, explosion, colliding between ships, coastal
refineries and leakage.
Bahrain and the rest of the Arabian Gulf states are supplying ¼ of world`s demand of oil
(Khan, 2002). Therefore, Regional Organization for the Protection of the Marine Environment
(ROPME) Sea Area is considered as one of the most polluted areas in the world due to
various oil and gas installations, tanker loading, terminals and intensive oil transportation. The
oil spill is considered as a chronic environmental problem in this region, where 2 Mbbls of oil
are spilled annually, which mostly resulted from ballast water and from 800 offshore oil and
gas platforms (AFED, 2008).
The marine environment in the Arabian Gulf was heavily affected due to ~11 Mbbls of oil
spilled during the Gulf war in 1991. The bulk of the oil spill was released from 7 abandoned
tankers and Al-Ahmadi terminal near the coast of Kuwait (Tawfiq & Olsen, 1993). Moreover,
~8 Mbbls of oil fallout from smoke plumes as a result of burning 727 oil wells was deposited
in the marine environment of the Arabian Gulf as soot and other particulate matter rich in
petroleum compounds (Literathy, 1993; Al-Ghadban et al., 1999).
In spite of the limited land area of Bahrain, the territorial waters supporting vital coastal
and marine habitats such as seagrass beds, coral reefs, mangroves, mud and sand flats, salt
marshes and offshore islands, which are associated by endangered megafauna species
Vol. 3 (1): 82-92, 2019
Received Dec. 3, 2018, accepted Feb. 4, 2019
83 Al-Khatlan et al.
(dugongs, green turtles and dolphins) and pearl oysters in addition to broad-scale of shellfish
and finfish species (Preen, 2004; Naser et al., 2008; Loughland & Zainal, 2009).
These ecosystems are subjecting to physical and chemical stresses mainly due to oil and
other development discharges. The east coast of Bahrain is exposed to several anthropogenic
pressures originated by petroleum refinery, petrochemical industry, desalination and sewage
outfalls, and sand wash processes as well as noticeable dredging and reclamation activities
where large coastal development projects are constructed. As a result, the coastal and marine
environment may physically and chemically be affected by different types of pollutants
affecting coral, seagrass beds and benthic community (Al-Hassan et al., 2000; Al-Madany &
Al-Sayed, 2001; Naser, 2011).
The aim of the present study is to identify the spatial variation of TPHs hotspot locations
and to which extent the levels may exceed the acceptable limits. At the same time, it will
provide a baseline for sediment quality of vital site on the east coast of Bahrain, to provide
data supporting the national reports on environmental state.
Materials and Methods
Study area
The study area is located at the east of Bahrain along the coast of Askar, extending to
approximately 5 km between the refineries of Bahrain Petroleum Company (BAPCO) at the
north and the National Mariculture Center (NaMaC) at Ras Hayan at the south. The NaMaC
was constructed in 1980 and initiated the production during 1994. A sewage treatment plant
(STP) based on secondary treatment was constructed on the coast in 1985 at 1.5 km to the
north of NaMaC. A total of 46 barrier fishing traps (locally known Hadra) are located at the
intertidal and subtidal zones along Askar coast (Fig. 1). Those fishing gears support the
traditional fisheries of Bahrain.
The population in Askar village is estimated by 1000 capita most of them are fishermen or
interested with fishing. There is a very small island known as “Shaikh Ibrahim” located in
opposite to the new fishing harbor at a distance of ~500 m from the coast. Currently, the
island provides nesting ground for different local and migratory sea bird species.
In 2012, a fishing harbor with a capacity of 150 speed boats was constructed close to the
STP in addition to new housing complex (400 housing units) just behind the STP location.
Regarding the strategic development plan 2030, Askar coast is one of the southern
municipality sites involved in such plan. Recently, construction works have been initiated
along the southern Askar coast including new coastal road parallel to King Hamad highway.
In spite of the potential pressures of industrial and domestic sources along Askar coast, no
attention has been directed to assess the pollution levels in sediments notably post
construction of the new projects mentioned above.
Distribution of petroleum hydrocarbons in coastal sediments of Askar, east of Bahrain 84
Figure 1: Study area showing land based and coastal activities at Askar.
Sampling
The sampling locations were distributed within three sectors (Fig. 2). One represents the
intertidal zone and the two others are associated with the subtidal zone. The first at a distance
of 100 m from the coast and the second at a distance of 350 m. A total of 27 monitoring
stations have been selected, nine at each sector with a distance interval of ~300 m between
each other.
85 Al-Khatlan et al.
Further three monitoring stations have been selected, 3 km south of Askar coast. These are
located within the intertidal and subtidal zone as based for monitoring stations. Another three
checkpoints were selected offshore at approximately 1.5 km from the coast with 500 m
distance interval between each other.
Consequently, 33 sediment samples were collected during November 2013 from surface
sediments (top ~20 cm) using Van Veen grab sampler (0.05 m2). The subsamples used for
grain size analysis were sealed in plastic bags and the other subsamples were preserved in
borosilicate glass jars of 1500 g wrapped with aluminum foil. The containers were stored and
transported in cool box (frozen) to the laboratory of Supreme Council for Environment (SCE)
in the Kingdom of Bahrain for chemical analysis. Samples were kept refrigerated during the
period from collection to analysis in order to reduce metabolic activity of bacteria and infauna
(IAEA, 2003).
Figure 02: Local map of sampling locations at Askar coast.
Distribution of petroleum hydrocarbons in coastal sediments of Askar, east of Bahrain 86
Laboratory Methods
At the SCE laboratory, the sediment samples were analyzed using Shimadzu (RF-540)
spectrofluorometer following to the Manual of the Oceanographic Observations and Pollutant
Analysis Methods (MOOPAM) prepared by ROPME (2010).
The subsamples were dried using freeze dryer (LABCONCO), homogenized, sieved and
the coarse sediments (> 2 mm) were removed. All the analytical measurements were based on
a dry weight and the values were reported in µg/g dry weight. Consequently, the moisture
content was estimated to correct the results for further analysis. Moisture content was
determined after freeze drying and then dried at 105° C for 24 hours. The sample was
reweighted and the loss of weight was considered as equivalent to moisture content.
The TPHs in sediment samples were analyzed using Shimadzu (RF-540) fluorescence
spectrofluorometer where the intensity was recorded at the 360 nm wavelength and the results
were expressed in ROPME crude oil equivalent for quantification (high range).
The quality assurance program was applied according to ACS (1980), UNEP (1990),
UNEP (1995), IAEA (2003) and ROPME (2010). Quality assurance and quality control
measures during the sample preparation ensure that the sample identity and the elemental
distributions in the original sample are maintained until the time of analytical determination.
Mapping
The sampling locations were positioned using GPS. The x and y co-ordinates for each
location were saved as tabular data in Excel spreadsheet. The x and y co-ordinates were
converted to point layer in Arc GIS Software. The results were interpolated spatially using
Inverse Distance Weight (IDW). A contour map was produced covering the locations
surveyed in the present study.
Data analysis
Multivariate analysis was applied using PRIMER v6 (Clarke & Gorley, 2006) to identify
the spatial variations among the monitoring stations based on Multi-Dimensional Scale
(MDS) routine.
Results and Discussion
The concentrations of TPHs in the intertidal zone was ranged between 3.54-15.49 µg/g
with an average of 6.67 µg/g ± 4.01 (Fig. 3). The maximum level was observed at station A8
where tar balls were found associated with sediments (Fig. 4). The minimum concentration
was found at station A5. The mean of concentration in the intertidal zone was below the
relevant control station in which the level was 11.82 µg/g and the check point station (17.23
µg/g) as well.
The TPH levels in the first subtidal sector was varied from 3.15 µg/g at B2 to 13.13 µg/g at
both B1 and B3 stations with an average of 10.11 µg/g ±3.31, which is slightly higher than the
relevant control station (8.83 µg/g), however, it was lower than the concentration of the
checkpoint.
87 Al-Khatlan et al.
Figure 3: Concentrations of TPHs in sediment samples from Askar coast.
Figure 4: Tar balls observed in station A8.
For the second subtidal sector, the maximum level was found at station C3 (31.51 µg/g)
and the minimum at station C6 (7.35 µg/g). The TPHs average in this sector was 15.30 µg/g
±8.52, which is relatively higher than the relevant control station (12.08 µg/g) and still lower
than the checkpoint (Fig. 3).
Consequently, the TPH levels in the intertidal sector were below both control and
checkpoints, however, the levels in the first subtidal sector were lower than in the checkpoints
and higher than the control and on the contrary, the levels in the second subtidal sector are
lower than the checkpoints and higher than the control. The mapping of TPHs distribution
presented in Fig. 5 showed higher levels between station 3 and station 5 particularly in the
subtidal sectors with two hotspots on the second one.
0
5
10
15
20
25
30
35
40
45
50
A1
A2
A3
A4
A5
A6
A8
A9
A10 B
1
B2
B3
B4
B5
B6
B7
B8
B9
B1
0
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
Ch
eck
µg/
g
Stations
Distribution of petroleum hydrocarbons in coastal sediments of Askar, east of Bahrain 88
The coastal area of Askar village is subjected to potential polluted levels of petroleum
hydrocarbon discharging from the BAPCO‘s refinery located at approximately 1.5 km to the
north of Askar village and might be also affected from the Gulf Petrochemical Industries
Company (GPIC), which is located at the north of BAPCO refinery. This area is considered as
one of the TPHs hotspots found in sediments following to de Mora et al. (2010).
The TPHs are a complex mixture of hundreds of hydrocarbons, which are categorized into
a wide range of structures from light compounds characterized by volatile fraction with short
chain of carbon atoms to heavy fraction composed of long chain. The composition varies in
relation to the source of the crude oil and the refining practices design. Although some light
weight components of oil evaporate or dissolve with water, most of the oil residuals settle on
beds. Bahrain, as other Arabian Gulf countries, is subjected to chronic oil-related pollution
from different sources including oil tanker incidents, under water pipe lines, oil terminals,
loading and handling operations, weathered oil and tar balls and illegal dumping of ballast
water (Literathy et al., 2002).
Sediment samples in all stations showed no differences in TPHs content at similarity level
of 70% (Fig. 6), however, at similarity level of 80%, three contours were formed. The first
(C3 and C5) representing high TPHs concentration. The second (B2, A1, A2, A4 and A5) was
characterized by the lowest TPHs, mostly at intertidal sector. Generally, these two contours
represented stations located to the north of the fishing harbor, either at intertidal sector or first
subtidal sector. However, the third contour contained a mixture of rest stations, representing
the moderate TPHs levels.
Figure 5: TPHs distribution in sediment samples at Askar.
89 Al-Khatlan et al.
Figure 6: MDS analysis of TPHs in sediment samples from Askar coast.
The overall mean of TPHs obtained in the present study is lower than the previous records
in Askar in early 1990s (Table 1). These studies were carried out at one station located within
Askar region, which was relatively within the extent of the present study. The variation could
be attributed to the distance differences of sampling locations from BAPCO refinery.
Moreover, all the TPH levels detected throughout the monitoring stations along the three
sectors are below the standard adopted by CEFAS guideline (100 µg/g).
Table 1: Comparison of TPHs (µg/g) in Askar coastal sediments with previous studies.
The TPH levels in Askar’s coastal sediments are considered to be within the minimal
records in the region in comparison with Fowler (1993), Beg et al., (2001), Tolosa et al.
(2005), Al-Saad et al. (2009), de Mora et al. (2010), Al-Enezi (2012) and Mahmoodi et al.
(2012). The higher levels of TPHs in the subtidal sectors indicate that TPHs are dispersed
toward the subtidal zone due to currents movement.
Location Range (µg/g) Mean Reference
Bahrain (1991) 3-14
Fowler (1993)
Askar (1983-1991) 14.0-103
Folwer et al. (1993)
Askar 59 Tolosa et al. (2005)
Bahrain 3-1600
Askar 20 de Mora et al. (2010)
Bahrain 1.45-1850
Present study 0.26-31.51 10.46±6.83
transection
s
Similarit
y
Distribution of petroleum hydrocarbons in coastal sediments of Askar, east of Bahrain 90
It is well known that pollutants are positively correlated with sediment texture, where the
higher levels are associated with fine particle size (mud and clay fractions). The low levels of
TPHs detected in the present study could be attributed to the sediment grain size where the
sediment textures along Askar coast are predominated by sand fraction as indicated by Al-
Khatlan (2015) with very low percentage of fine sediment particle size. However, this is not a
universal phenomenon as there may be further multiple factors controlled the pollutant
adsorption such as type of oil, weathering, depth, velocity as well as direction of currents and
wind and sedimentation rate.
The dense of tar balls observed at station A8 within the intertidal sector is probably due to
the accumulation of hydrocarbons around this location as a result of pocket-like shape coast at
which the station A8 is located, where the currents are relatively stagnant. Although the levels
at this station are within an acceptable limit, potentially such levels may affect the water
quality at the intake of NaMaC.
Moreover, some of the fishing traps are located within the TPHs hotspots indicating potential
bioaccumulation of these pollutants. Accordingly, it is of great importance that common
finfish species particularly rabbitfish, Siganus canaliculatus (locally known Safi) and emperor
fish, Lethrinus nebulosus (locally known Sheari) and shellfish notably crabs caught by fishing
traps at Askar coast to be involved in prospective studies on marine pollution in the eastern
coast of Bahrain.
Acknowledgements
The authors would like to gratefully acknowledge Mr. AbdulAzeez Al-Azmi from Askar
village and Mr. Abdullah Al-Mansori the former member of the Southern Municipality
Consul for their kind assistance in providing the boat during the sampling. The efforts of the
laboratory staff at Supreme Council for Environment are greatly appreciated in coordinating
and processing the chemical analysis.
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