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: thamersa@agu.edu.bh

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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