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Marine Pollution Bulletin 49 (2004) 410–424

Distribution of heavy metals in marine bivalves, fish andcoastal sediments in the Gulf and Gulf of Oman

Stephen de Mora *, Scott W. Fowler, Eric Wyse, Sabine Azemard

Marine Environment Laboratory, International Atomic Energy Agency, 4 Quai Antoine 1er, B.P. 800, MC 98012,

Principality of Monaco, Monaco 98012, Monaco

Abstract

An assessment of marine contamination due to heavy metals was made in the Gulf and Gulf of Oman based on marine biota (fish

and various bivalves) and coastal sediment collected in Bahrain, Oman, Qatar, and the United Arab Emirates (UAE) during 2000–

2001. Sediment metal loadings were generally not remarkable, although hot spots were noted in Bahrain (Cu, Hg, Pb, Zn) and on

the east coast of the UAE (As, Co, Cr, Ni). Concentrations of As and Hg were typically low in sediments and the total Hg levels in

top predator fish commonly consumed in the region were <0.5 lg g�1 and posed no threat to public health. Very high Cd con-centrations (up to 195 lg g�1) in the liver of some fish from southern Oman may result from food-chain bioaccumulation of elevated

Cd levels brought into the productive surface waters by upwelling in the region. Very high As concentrations (up to 156 lg g�1) weremeasured in certain bivalve species from the region. Although not certain, the As is probably derived from natural origins rather

than anthropogenic contamination.

� 2004 Elsevier Ltd. All rights reserved.

Keywords: Trace metals; Oyster; Sediments; Pollution; Cadmium; Arsenic; Gulf

1. Introduction

Pollution studies in the Gulf and Gulf of Oman,

collectively known as the ROPME Sea Area (RSA), are

extremely important. The Gulf comprises a relatively

shallow, semi-enclosed sea with very high evaporation

rates and poor flushing characteristics (Sheppard, 1993).

As a result, contaminant inputs undergo more limiteddilution and slower dispersion than would occur in open

marine systems. The ecosystem is relatively fragile,

experiencing elevated temperatures, salinity and UV

exposure. Many species function close to physiological

limits (Sheppard, 1993), and thus, added stress imposed

by pollutants is likely to have severe consequences.

Maintaining good marine environmental quality is cru-

cial for several socio-economic reasons. The seafood,notably fish and shrimp, is of value for both local con-

sumption and export revenue. Moreover, the region

relies heavily upon the sea water itself as a source of

fresh water through desalination (Price et al., 1993).

* Corresponding author. Tel.: +377-97-97-72-72; fax: +377-97-97-

72-76.

E-mail address: s.de_mora@iaea.org (S. de Mora).

0025-326X/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.marpolbul.2004.02.029

The RSA has experienced several impacts in recent

years that have contributed to pollution burdens in the

region. The waterways are heavily utilised, especially

with respect to oil tanker traffic, with the consequential

discharges related to shipping activities. There are some

key industrial developments, especially in Bahrain, that

act as localised sources of organic and inorganic pollu-

tion. Ongoing industrial development in the region, al-beit geographically variable, continues to cause concern

with respect to marine environmental quality. Unfor-

tunately, the regional database with respect to many

metals is not uniform (Fowler, 2002b). Agriculture,

mostly located in the northern zone, is expanding in the

region, with the threatened increase of emissions of

pesticides and other agrochemicals, including metal-

based formulations. However, the current database foragrochemical residues in the Gulf is rather limited

(Fowler, 2002a), and even more so with respect to the

Gulf of Oman.

Superimposed on trends related to changing land

uses, there has been the environmental impact of three

wars in the past two decades. Considering metals in the

marine environment, some initial consequences were

described relatively soon after the 1991 Gulf War. Clam

Fig. 1. Location of all sampling sites for sediments (O), fish (X), and

bivalves (+) in Bahrain, Qatar, UAE, and Oman.

S. de Mora et al. / Marine Pollution Bulletin 49 (2004) 410–424 411

samples collected near Kuwait contained higher levels of

several metals (Cd, Cu, Ni, Pb, and V) in 1991 compared

to 1985 (Kureishy, 1993). Concentrations of oil-related

metals, Ni and V, exhibited slightly elevated concen-trations along the oil-impacted coastline of Saudi Ara-

bia relative to other locations in the Gulf in 1991

(Fowler et al., 1993). The effects did not extend as far as

Qatar, where there was no observable increase in the

concentrations of Hg, Cd, Pb, Cu, Co, and Ni in benthic

and semi-pelagic marine organisms (Sadiq and McCain,

1993). A post war assessment of several potential con-

taminants, including metals, was conducted along thecoast of United Arab Emirates (Banat et al., 1998).

Moreover, the potential long-term effects have contin-

ued to be explored. Various tissues of the blue crab,

Portunus pelagicus, collected in Kuwait were analyzed to

assess the bioaccumulation of several metals associated

with petroleum input a decade after the 1991 Gulf War

oil spillage (Al-Mohanna and Subrahmanyam, 2001).

The concentrations of trace metals in seawater andparticulate matter were determined during 1993 and

1994 in order to assess the environmental consequence

of the massive oil spill off the Kuwait Coast during the

Iraqi invasion (Bu-Olayan et al., 1998). The interpreta-

tion of successive war-induced impacts relies on good

environmental data based on reliable techniques dem-

onstrating good quality control.

Under the ROPME-IAEA contaminant screeningprojects, surveys of heavy metals and organic contami-

nants have taken place in the Gulf and Gulf of Oman

since the early 1980s (Burns et al., 1982; Fowler, 1988;

Fowler et al., 1984). Such pre-war studies have proved

invaluable for the identification of pollution hot spots

and assessing the consequences of the 1991 Gulf War

(Fowler et al., 1993). This paper firstly evaluates marine

pollution of metals in the coastal zone of the easternGulf and Gulf of Oman based on sediment quality.

Sediment samples were collected from several coastal

locations in Bahrain, Oman, Qatar, and the UAE during

2000–2001. A wide range of elements was determined

for pollution assessment and to facilitate interpretation

of the origins of potential contaminants. Secondly, the

paper examines the quality of local seafood with respect

to metal contamination. The focus was on two fishspecies of commercial importance, namely the orange

spotted grouper (Epinephelus coioides, known locally as

hamoor) and the spangled emperor (Lethrinus nebulosus,

known locally as sha’ri, shaeri or sheiry), together with

various bivalves, notably oysters. Overall, the results for

sediments and biota contribute to the regional database

for the RSA, most notably for Oman given the paucity

of such information. Concurrent studies of organotincompounds have been presented elsewhere (de Mora

et al., 2003) and similar assessments are under prepa-

ration for petroleum hydrocarbons and organochlori-

nated compounds.

2. Methods

2.1. Sample collection

Marine samples were collected in the Gulf and Gulf

of Oman during 2000–2001. In general, all sampling

procedures were carried out according to internationally

recognized guidelines (UNEP, 1991). All sampling

locations in Bahrain, Oman, Qatar, and the United

Arab Emirates are shown in Fig. 1. Exact coordinates

and dates for sediment sampling are shown in Table 1.

Similarly, locations for the collection of fish and bivalvesare given in Table 2. Surface sediments were collected

directly into pre-cleaned Teflon containers. To obtain a

suitable mass of material for analysis, soft parts from

1 to 18 individual bivalves were dissected, then drained

of excess liquid and stored in plastic bottles. For fish,

100–300 g of dorsal muscle from a single individual was

dissected for the sample. Fish liver tissue was also re-

moved and prepared for analysis in some cases. Allsamples were frozen ()18 �C) for return to the labora-tory in Monaco.

2.2. Sample treatment

All sediment samples were freeze-dried and sievedthrough a 1 mm clean plastic sieve to remove shell

fragments. In some cases where sample size was small,

the sieved sediments were ground in an agate mortar.

The sieved and/or powdered sediments were then

Table 1

Location of sediment samples from Qatar, UAE, Bahrain, and Oman

Country Station Site no. Date Location

Qatar Umm Said 1 28/3/00 24�56.3980N, 51�37.7090EDukhan 2 29/3/00 25�21.0690N, 50�45.7180EDoha 3 29/3/00 25�20.2570N, 51�34.4560ERas Laffan 4 30/3/00 25�47.0000N, 51�35.7750ERas Al Nouf 5 30/3/00 25�37.4270N, 51�32.8890E

UAE Jebel Ali 6 1/4/00 25�06.9910N, 55�09.1150EAbu Dhabi 7 1/4/00 24�27.9570N, 54�18.2940EAl Marfa 8 2/4/00 24�06.2000N, 53�29.2070EAlRuweis (Al Dhannah) 9 2/4/00 24�09.8420N, 52�38.8870EAkkah Head, ‘‘Three Rocks’’ north of Bidya 10 4/4/00 25�28.9770N, 56�21.9400EAkkah Beach, South of ‘‘Three Rocks’’ 11 4/4/00 25�28.7210N, 56�21.7700E

Bahrain Askar 12 23/11/00 26�03.1020N, 50�37.9590EOff BAPCO Refinery 13 23/11/00 26�06.1380N, 50�37.7730EJasra 14 25/11/00 26�11.0980N, 50�26.5230ENorth of Meridien Hotel 15 25/11/00 26�16.0560N, 50�31.4230E

Oman Mina Al Fahal (PDO Beach) 16 27/7/01 23�37.9780N, 58�30.6930ERas Al Yei (Masirah east coast) 18 28/7/01 20�31.3480N, 58�57.0740EHilf (Masirah west coast) 19 29/7/01 20�38.1030N, 58�51.8130EMughsayl (beach) 20 30/7/01 16�52.9560N, 53�47.6050ERaysut Port Area (east beach) 21 31/7/01 16�59.00N, 54�01.00EAl Sawadi 23 01/8/01 23�47.2600N, 57�47.6330E

Table 2

Location for the collection of biota

Country Site Site no. Coordinates Species Species

Fish

Bahrain Badaiya 24 26�120N, 50�240E Epinephelus coioides Orange spotted grouper

Bahrain Fasht Al Adham 25 26�030N, 50�430E Epinephelus coioides Orange spotted grouper

Oman Quriyat 26 23�200N, 59�060E Epinephelus coioides Orange spotted grouper

Qatar Al Khawr 27 25�400N, 51�380E Epinephelus coioides Orange spotted grouper

Qatar Doha 3 25�20.2570N, 51�34.4560E Epinephelus coioides Orange spotted grouper

Qatar Umm Said 1 24�56.3980N, 51�37.7090E Epinephelus coioides Orange spotted grouper

UAE Al Marfa 8 24�06.2000N, 53�29.2070E Epinephelus coioides Orange spotted grouper

UAE Dhannah 28 24�120N, 52�390E Epinephelus coioides Orange spotted grouper

Oman Raysut Port Area 21 16�59.00N, 54�01.00E Lethrinus nebulosus Spangled emperor

Oman Sagar 29 16�320N, 53�430E Lethrinus nebulosus Spangled emperor

Qatar Al Dakhira 30 25�450N, 51�400E Lethrinus nebulosus Spangled emperor

Bivalves

Qatar Ras Al Nouf 5 25�37.4270N, 51�32.8890E Circentia callipyga Venus clams

Bahrain North of Meridien Hotel 15 26�16.0560N, 50�31.4230E Pinctada radiata Pearl Oysters

Bahrain Off BAPCO refinery 13 26�06.1380N, 50�37.7730E Pinctada radiata Pearl Oysters

UAE Abu Dhabi 7 24�27.9570N, 54�18.2940E Pinctada radiata Pearl Oysters

UAE Akkah Head 10 25�28.9770N, 56�21.9400E Pinctada radiata Pearl Oysters

UAE Jebel Ali 6 25�06.9910N, 55�09.1150E Pinctada radiata Pearl Oysters

UAE Jebel Ali 6 25�06.9910N, 55�09.1150E Pinna muricata Pen Shells

Oman Al Sawadi 23 23�47.2600N, 57�47.6330E Saccostrea cucullata Rock Oysters

Oman Hilf 19 20�38.1030N, 58�51.8130E Saccostrea cucullata Rock Oysters

Oman Mirbat 22 16�58.500N, 54�41.500E Saccostrea cucullata Rock Oysters

Oman Ras Al Hamra 17 23�38.3630N, 58�29.4950E Saccostrea cucullata Rock Oysters

Oman Ras Al Yei 18 20�31.3480N, 58�57.0740E Saccostrea cucullata Rock Oysters

UAE Akkah Beach 11 25�28.7210N, 56�21.7700E Saccostrea cucullata Rock Oysters

UAE Abu Dhabi 31 24�29.9170N, 54�21.6680E Spondylus sp. Rock Scallops

412 S. de Mora et al. / Marine Pollution Bulletin 49 (2004) 410–424

transferred to clean zip-lock bags and shaken to obtain a

fine homogeneous powder. Between 150 and 300 mg of

dried sediment material were weighed for digestion.

Samples were digested in acid-cleaned Teflon microwave

vessels with 5 ml of ultrapure nitric acid and 2 ml

ultrapure concentrated hydrofluoric acid. A Milestone

S. de Mora et al. / Marine Pollution Bulletin 49 (2004) 410–424 413

MLS 1200 Mega system was used for samples from

Qatar and UAE and a CEM MARS5 system was em-

ployed for samples from Bahrain and Oman. Each

digestion batch included at least one reagent blank and arepresentative standard reference material, e.g., MESS-2

or BCSS1 (NRCC, Marine sediment), and generally a

sample replicate to check homogeneity and process

efficacy. Samples were digested typically for 30–40 min

at 200 �C. After allowing at least 1 h for cooling, thevessels were opened and 0.9 g boric acid was added to

dissolve the fluoride precipitates. The vessels were then

resealed and put back in the microwave digestion systemfor an additional 20–30 min. Following cooling for at

least 1 h, the digested sample was transferred to a

graduated plastic test tube with an additional 0.5 ml HF

and brought up to volume (either 15 or 50 ml) with

Milli-Q water.

Biota samples were freeze-dried and then ground on

an agate mortar to obtain a fine homogeneous powder.

Separate sub-samples were oven dried (105 �C for 24 h)to determine residual water content. Between 150 and

300 mg of dried sample material were weighed and then

digested in acid-cleaned Teflon microwave vessels with

5 ml of ultrapure nitric acid. Each digestion batch in-

cluded at least one reagent blank and a representative

standard reference material, e.g., DORM-2 or DOLT-2

(NRCC, Dogfish muscle and liver, respectively) and

usually a sample replicate as a check for homogeneityand process efficacy. Microwave digestion typical took

30–40 min at a target digestion temperature of 200 �C.After allowing at least 1 h for cooling, the digested

sample was quantitatively transferred to a graduated

plastic test tube and brought up to volume (either 15 or

50 ml) with Milli-Q water.

Samples were analysed for metals other than Hg

using a Finnigan Element magnetic sector inductivelycoupled plasma mass spectrometer (ICP-MS) with a

microconcentric nebulizer (MCN) and a standard dou-

ble-pass condensing spray chamber for sample intro-

duction. Sample digestates were typically diluted 20· foranalysis with 2% nitric acid. Larger dilutions up to

10,000· were necessary for certain analytes observed atrelatively high concentrations in sediment digestates

(e.g., Fe and Al). An internal standard (1–10 lg l�1 Be,In, and Th) was also added to the diluted samples to

correct for matrix effects and instrument drift. Results

were quantified via an external calibration curve gener-

ated from the responses obtained from multiple dilu-

tions of a multi-element calibration standard that was

prepared from single-element standards (Alfa Aesar).

Analytical quality control included analysis of a 2%

ultrapure nitric acid blank and a drinking water refer-ence material (TMDW1, acquired from High Purity),

together with the procedural blank, a reference material

of similar matrix, and a sample duplicate from the

microwave digestion.

2.3. Analysis of mercury

In the case of Qatar and UAE sediments, approxi-

mately 1 g of sample was digested in a closed Teflon vialwith 4 ml of nitric acid (Merck Suprapur) for 3 h on a

hot plate at 90 �C. Following the addition of 1 ml 10%w/v K2Cr2O7 solution as a preservative, the samples were

diluted to 50 ml with Milli-Q water. For sediment from

Bahrain and Oman, the same aliquots prepared for ICP-

MS analysis were used for the determination of Hg. In

addition, a preservative solution (200 ll of 10%w/vK2Cr2O7) was added to a 10 ml aliquot of the digestatewithin 24 h of preparation. The digested samples were

analysed by cold vapour atomic fluorescence spectro-

metry (CV-AFS) using SnCl2 reduction with a flow

injection vapour generator (VGA-77). Replicate blanks

and the reference material MESS-2 (NRCC, marine

sediment) were analysed for quality control purposes.

Precision of the measurements, determined on replicate

digestions of MESS-2 ranged between 1.2% and 12%.For the analysis of biota, �0.5 g of sample was di-

gested in a closed Teflon vial with 4 ml of nitric acid

(Merck Suprapur) and 2 ml of sulphuric acid (Merck

Suprapur) for 3 h on a hot plate at 90 �C. Following theaddition of 1 ml 10%w/v K2Cr2O7 solution as a pre-

servative, the samples were diluted to 50 ml with Milli-Q

water. Samples from Qatar, UAE, and Bahrain were

analysed by cold vapour atomic absorption spectro-metry (CV-AAS) using SnCl2 reduction on a Varian

SpectrAA-220FS with a flow injection vapour generator

(VGA-77). The concentration of Hg in some samples

was confirmed by CV-AFS due to the very low Hg

content. Replicate blanks and the reference materials

IAEA142 (mussel homogenate), SRM-2976 (NIST,

mussel), and DOLT-2 (NRCC, fish liver) were used for

quality control purposes. Precision of the measurementsbased on replicate digestions was between 0.5% and

3.8% (mean 1.3%). In the case of the samples from

Oman, Hg was analysed only by ICP-MS.

3. Results and discussion

3.1. Sediments

Concentrations, expressed on a dry weight basis, for a

wide range of elements in the coastal sediments from the

RSA are presented in Table 3. Only two locations stand

out in terms of their elevated levels of trace elements in

sediments: off the BAPCO (Bahrain Petroleum Com-

pany) refinery in Bahrain and at Akkah Beach on the

east coast of UAE (Fig. 2). As outlined below, elevatedlevels at the BAPCO site signals localised anthropogenic

inputs, whereas the Akkah Beach location may reflect

the metal-rich mineralogy of the region. Concentrations

of trace elements at locations other than these hot spots

Table 3

Trace element concentrations (lg g�1 dry weight) in near shore sediments from Qatar, UAE, Bahrain, and Oman

Location No. Al V Cr Mn Fe Co Ni Cu Zn As Ag Cd Sb Hg Pb

Qatar

Umm Said 1 5870 24.7 31.9 84.9 4790 1.96 17.1 8.17 – 5.2 0.30 0.09 0.17 0.0114 3.00

Dukhan 2 18000 20.1 34.0 127 4160 1.73 12.2 3.03 – 6.3 0.39 0.07 0.12 0.0034 3.88

Doha 3 9120 32.1 40.8 88.0 5680 2.20 20.8 8.02 – 5.0 0.30 0.08 0.22 0.0167 3.16

Ras Laffan 4 484 2.7 11.5 13.2 305 0.10 0.74 1.22 – 1.0 0.47 0.03 0.01 0.0007 0.43

Ras Al Nouf 5 2410 9.0 17.2 37.6 1480 0.61 5.31 1.41 – 3.9 0.42 0.08 0.07 0.0015 1.63

UAE

Jebel Ali 6 8530 10.4 31.7 96.6 2740 1.16 8.3 1.92 – 1.9 0.33 0.05 0.09 0.0022 2.10

Abu Dhabi 7 2570 4.6 17.6 32.9 874 0.34 2.0 1.99 – 1.3 0.58 0.02 0.04 0.001 0.78

Al Marfa 8 21000 23.1 37.6 225 5820 2.61 15.5 3.58 – 2.7 0.14 0.11 0.21 0.0015 2.93

Al Ruweis 9 26000 35.5 171 358 8940 2.40 8.6 2.62 – 2.2 0.20 0.11 0.29 0.0013 5.88

Akkah Head 10 534 4.5 83.5 60.3 4020 6.13 139 0.64 – 0.7 0.47 0.05 0.04 0.0006 0.69

Akkah Beach 11 2680 18.2 303 360 29600 45.2 1010 3.31 – 9.6 0.23 0.09 0.22 0.0009 1.30

Bahrain

Askar 12 1595 5.94 11.8 22.6 1091 0.307 3.79 3.12 8.92 3.16 0.014 0.046 0.055 0.0107 13.2

BAPCO refinery 13 8954 28.4 41.8 84.3 6475 2.43 23.2 48.3 52.2 4.96 0.161 0.182 0.123 0.2202 99.0

Jasra 14 6155 11.3 14.2 42.2 1945 0.683 6.63 2.74 18.4 6.88 0.012 0.061 0.129 0.0032 2.49

North of Meri-

dien Hotel

15 601 3.47 3.36 26.9 471 0.172 2.46 2.38 6.12 5.00 <0.01 0.040 0.046 0.0025 0.673

Oman

Mina Al Fahal 16 3850 18.6 119 133 5540 2.91 43.4 2.03 6.48 5.01 0.010 0.16 0.162 <0.0001 1.59

Ras Al Yei 18 18300 44.1 133 209 10700 6.92 77.8 6.66 11.4 1.72 0.006 0.14 0.086 <0.0001 0.449

Hilf 19 14800 34.9 39.9 265 11600 5.75 48.8 4.91 8.12 2.25 0.017 0.15 0.12 0.0112 1.82

Mughsayl 20 632 4.70 6.46 27.8 334 0.125 1.84 0.602 1.61 0.740 0.009 0.21 0.025 <0.0001 0.253

Raysut Port

Area

21 2100 5.02 31.2 29.1 905 0.276 2.49 0.827 1.57 1.09 0.002 0.20 0.025 0.0019 0.729

Al Sawadi 23 2750 12.8 96.2 70.4 3500 2.45 50.9 1.60 4.92 4.22 0.002 0.10 0.124 0.0002 1.82

414

S.deMora

etal./Marin

ePollu

tionBulletin

49(2004)410–424

Fig. 2. Concentrations of selected heavy metals in sediments of the ROPME Sea Area. Data are arranged in order along the coast from western

Bahrain to southern Oman. Concentrations on a dry weight basis are given in lg g�1 for all metals, except Hg, which are presented as ng g�1.

S. de Mora et al. / Marine Pollution Bulletin 49 (2004) 410–424 415

were for the most part substantially lower, and fell

within the ranges reported previously for these elements

in the RSA (Fowler et al., 1993).

Akkah Beach in the Gulf of Oman represents anoteworthy hot spot for several metals (Fig. 2), and also

hydrocarbon contaminants (IAEA, unpublished data).

The extremely elevated Ni concentration, 1010 lg g�1, isby far the highest level of Ni reported for RSA sedi-

ments (Fowler, 2002b; ROPME, 1999). Other maximum

concentrations measured at this site included 303 lg g�1

Cr and 45 lg g�1 Co. Whereas most sediments in thisstudy exhibited Fe:Al concentration ratios <1, the sed-iments at Akkah Beach and Akkah Head were unusual

in having very high ratios, namely 11.0 and 7.5,

respectively. Regarding this particular eastern region of

UAE, very high concentrations of Cr (506 lg g�1), Ni(187 lg g�1), and Co (36 lg g�1) were found in sedimentsfrom Bidya approximately 4 km south of Akkah Beach

in June 1994 (IAEA, unpublished data).

There is no major industrial activity or high popula-tion centre near Akkah Beach, which is a fairly remote

area. It is unlikely that these high levels were related to

the March 1994 oil spill off Bidya (Shriadah, 1998), as

the corresponding concentration of V, a metal some-

times used as a marker for oil, was not particularly

elevated compared to the level present in other sedi-

ments from the region (Fowler, 2002b). Moreover, the

V:Ni ratio was relatively low owing to the extremely

high Ni content. Thus, it is difficult to ascribe anthro-

pogenic causes to the apparent metal enrichment. These

sediments were especially rich in Ni and Cr, but alsocontained high levels of Fe, Mn, and As. The geology of

Oman and eastern UAE is rich in ophiolites and me-

talliferrous sediments of marine origin. The Oman

ophiolites contain chromite and various nickel sulfide

minerals (Leblanc and Ceuleneer, 1991; Lorand and

Ceuleneer, 1989). Thus, the high metal concentrations

are most likely due to the local mineralogy, and are

natural, rather than pollution.In the case of the sediments collected off the BAPCO

refinery complex in Bahrain, maximum levels were

measured for several metals: 99 lg g�1 Pb, 48.3 lg g�1

Cu, 52.2 lg g�1 Zn, and 0.220 lg g�1 Hg (Fig. 2). Thecontamination likely emanates from the industrial and

refinery complex around the aluminium plant situated

just shoreward of the sampling site. Relatively high

concentrations of certain metals were also observednearby at Askar, supporting the hypothesis of a point

source of contamination at the BAPCO site for Cu, Hg,

Pb, and Cd, the effects of which diminish with distance

from the source. This spatial decrease is most notable

for Pb and Hg (Table 3). Very high metal concentrations

in sediments from near this site have been reported since

the early 1980s; for example, in 1983–1984 Hg levels in

Fig. 3. Map showing the concentrations (in lg g�1 dry) of Cd (a) andAg (b) in sediments from the ROPME Sea Area. The mid-point of the

concentration bar represents the sampling location.

416 S. de Mora et al. / Marine Pollution Bulletin 49 (2004) 410–424

sediments off Askar ranged from 0.106 to 0.286 lg g�1

(Fowler, 1988). Considering that the Hg content in the

present survey was only 0.0107 lg g�1 (Table 3), theorder of magnitude decrease over 17 years may reflect anactual reduction in Hg inputs in this area during that

time.

With respect to Oman, maximum concentrations for

most of the trace elements were found in sediments from

Masirah Island, particularly those from Ras Al Yei on

the east coast. As the population density is very low and

there are no major industrial activities on the island, the

trace metal concentrations in coastal sediments are mostlikely natural and reflect the local mineralogy. Thus, the

relatively elevated concentrations of V, Co, and Ni are

probably related to the high Fe and Mn content in these

sediments, given that Masirah Island largely comprises

an ophiolite with associated hydrothermal activity

(Abbotts, 1979). The only notable acceptation was Cd,

which exhibited somewhat higher concentrations in

sediments from the Raysut Port area and Mughsayl inthe south. Cadmium concentrations at pristine sites

in the Gulf of Oman were high compared to locations in

the Gulf, and were comparable to the polluted site off

the BAPCO refinery in Bahrain (Fig. 3a). Although

there are few data from Oman for comparison, the levels

of Cu, Pb, and V were similar to previously reported

concentrations (Fowler, 1988; Fowler et al., 1993). The

trend in enhanced Cd levels towards the south wasconsistent with data from earlier surveys that indicated

elevated sediment Cd concentrations around Salalah

compared to other areas in Oman (Fowler et al., 1993).

In contrast to the trend for Cd in sediments, Ag

exhibited very low concentrations in Oman (Fig. 3b).

Silver is often considered a good tracer for sewage dis-

charges (Papakostidis et al., 1975; Ravizza and Bothner,

1996). Thus, the maximum concentration, 0.58 lg g�1,observed at Abu Dhabi likely indicates an anthropo-

genic input. Apart from Abu Dhabi and Akkah Head,

the Ag content of sediments in Qatar was higher than

elsewhere in the RSA.

Considering Hg in more detail, the concentrations in

sediments were quite low, ranging from <0.001 to 0.0167

lg g�1, apart from the one hot spot at the BAPCO site

(0.220 lg g�1). For comparison within the region, Hglevels were seen to vary between 0.19 and 2.34 lg g�1

in coastal sediments from Doha, Qatar (Al-Madfa

et al., 1994) and the Hg content in surface sediments

throughout the Gulf was found to range from 0.032 to

0.27 lg g�1 (Kureishy and Ahmed, 1994), and from

0.042 to 0.375 lg g�1 (Al-Majed and Rajab, 1998).

Furthermore, the levels in near-shore sediments were

reported to vary from <0.02 to 0.613 lg g�1, with thehighest Hg concentrations found in Kuwait and the

United Arab Emirates (Fowler, 2002b). The low Hg

content reported here agrees favourably with some

baseline measurements that have been reported for other

regions (Fowler, 1990). Hg levels were found to be quite

low (<0.09 lg g�1) through most of the Caspian Sea

(de Mora et al., 2004). Estimated from subsurface con-

centrations in sediments, baseline Hg levels in San

Francisco Bay were observed to be 0.06 ± 0.01 lg g�1

(Hornberger et al., 1999) and 0.059 ± 0.013 lg g�1 in theYatsushiro Sea (Tomiyasu et al., 2000). Thus, Hg con-

centrations in coastal sediments of the Gulf and Gulf ofOman are generally quite low by international stan-

dards.

Although the hot spot near the BAPCO refinery did

exceed the sediment quality guideline value of 0.15

lg g�1 (Long et al., 1995), much higher concentrationshave been reported at polluted sites world-wide. In

Azerbaijan, the sediments in Baku Bay and adjacent

S. de Mora et al. / Marine Pollution Bulletin 49 (2004) 410–424 417

areas to the south were contaminated, with Hg con-

centrations up to 0.45 lg g�1 (de Mora et al., 2004). TheGulf of Trieste is exceedingly polluted due to historic

cinnabar mining in the catchment region, with total Hgranging from 0.064 to 30.38 lg g�1 and averaging 5.04lg g�1 (Covelli et al., 2001). Surface sediments from the

Yatsushiro Sea off Japan had maximum Hg concentra-

tions in the range of 0.086–3.46 lg g1 with the highestvalues found in Minamata Bay near the Minamata

River, the sources of the pollution (Tomiyasu et al.,

2000).

Arsenic is another element that has previously at-tracted much attention in the RSA, but often with re-

spect to biota rather than sediments. Concentrations in

coastal sediments found here vary from 0.7 to 9.6 lg g�1.Only the highest value, found at Akkah Beach in the

Gulf of Oman, exceeded the sediment quality guideline

value for As, 8.2 lg g�1 (Long et al., 1995). There arefew data from the RSA for comparison; however, our

results are much lower than those (7.13–35.2 lg g�1)previously reported for the region (Fowler et al., 1993).

Uncontaminated coastal sediments normally have con-

centrations in the range 5–15 lg g�1 (Neff, 1997). SimilarAs contents were reported in the North Caspian Sea,

commonly <5 lg g�1, (de Mora et al., 2004; Winkelset al., 1998) and off California, having a range of 1.6–

13.8 lg g�1 and a mean concentration of 5.1 lg g�1

(Schiff and Weisberg, 1999). More elevated concentra-tions, �20 lg g�1, were observed in surface sediments

from the South Caspian Sea (de Mora et al., 2004) and

the Gulf of Finland (Vallius and Lehto, 1998). Ex-

tremely As-contaminated sediments in the North Sea off

the English coast have concentrations reaching 137

lg g�1 (Whalley et al., 1999). Clearly, the As levels re-ported here are quite low by global standards, and

generally not of environmental concern.

3.2. Fish

Two economically important species in the RSA were

investigated, namely the orange spotted grouper (Epi-

nephelus coioides, hamoor) and the spangled emperor

(Lethrinus nebulosus, sheiry). Although both species are

demersal carnivores, hamoor feed preferentially on fishand crustaceans whereas sheiry tend to eat echinoderms,

worms molluscs and crustaceans (Carpenter et al.,

1997). Data for a suite of trace elements in fish muscle

and liver are set out in Table 4, in all cases expressed on

a dry weight basis.

Mercury concentrations in the muscle and liver of

grouper varied in the ranges 0.50–2.35 and 0.287–4.65

lg g�1, respectively. Mercury is known to bioaccumulatein fish, and thus relatively high concentrations can be

attained in top predators, such as hamoor. Furthermore,

the total Hg concentrations generally increase with age,

and thus size, of the fish. The Hg content in both the

liver and the muscle depended upon the size (wet weight)

of the fish (Fig. 4). This has been shown previously only

for Hg in grouper muscle as a function of fish length (Al-

Majed and Preston, 2000b; Kureishy, 1993; Sadiq et al.,2002). The highest concentration of Hg (2.35 lg g�1 dryor 0.49 lg g�1 wet) in muscle was measured in a 4.7 kggrouper from Al Marfa in UAE, and only just ap-

proached 0.5 lg g�1 wet, a level considered by many

countries to be the upper acceptable limit for consum-

able fish, including for instance Saudi Arabia (Sadiq

et al., 2002). Despite the difficulties in comparison,

particularly due to the size of fish, the Hg levels ingrouper fell within the range reported in other recent

surveys within the RSA (Al-Majed and Preston, 2000a;

Al-Majed and Rajab, 1998; Sadiq et al., 2002). Some

earlier observations (Fowler, 1988) were lower, namely

0.17–0.40 lg g�1, but based on 5 fish averaging <2 kg.For the spangled emperor, mercury concentrations in

the muscle and liver varied in the ranges 0.34–0.52 and

0.33–1.02 lg g�1, respectively. The Hg content in musclefrom the spangled emperor was comparable to previous

measurements, 0.29–0.33 in Bahrain and UAE (Fowler

et al., 1993), but somewhat lower than has been ob-

served in Kuwait, 0.76–0.88 lg g�1 (Al-Hashami andAl-Zorba, 1991), and Saudi Arabia, 0.65–1.35 lg g�1

(Fowler et al., 1993).

The As concentrations in the muscle of grouper and

spangled emperor ranged 0.83–14.4 and 2.5–10 lg g�1,respectively. There was no size dependence of the As

content in either the liver nor the muscle in grouper, in

agreement with previous general observations in the

marine environment (Phillips, 1990). The highest con-

centration of As in grouper muscle was found in the

smallest fish, which was from Fasht Al Adham, Bahrain.

For comparison, pervious measurements of As in mus-

cle of grouper have been reported in the ranges <0.25–0.49 lg g�1 wet (Attar et al., 1992) and 0.7–53 lg g�1 dry(Fowler et al., 1993). Regarding spangled emperor, the

maximum As level in both muscle and liver samples was

from a fish caught in Al Dakhira, Qatar. The As content

in muscle of spangled emperor has previously been re-

ported in the ranges 1.03–3.58 lg g�1 wet (Attar et al.,1992) and 1.3–27 lg g�1 dry (Fowler et al., 1993). Al-though dependent upon the species considered, the fewother data that have been reported for the RSA have

suggested that the As levels in RSA fish are amongst the

highest reported in the literature (Attar et al., 1992;

Fowler et al., 1993; Madany et al., 1996). In contrast,

the As concentrations in RSA fish reported here are

generally lower than those previously observed, and also

seem to be relatively low by global standards (see Attar

et al., 1992; Francesconi and Edmonds, 1993). This isclearly a topic of regional interest that merits further

investigation.

The most unusual findings here relate to Cd mea-

surements. Cd concentrations in muscle for both species

Table 4

Trace element concentrations (lg g�1 dry weight) in fish from Qatar, UAE, Bahrain, and Oman

Location Species Weight

(kg)

Tissue V Cr Mn Fe Co Ni Cu Zn As Se Ag Cd Sb Hg Pb U

Qatar

Al Khawr O.S.G.a 1.7 Muscle 0.03 0.03 0.19 21.7 <0.005 0.03 0.56 8.2 3.1 2.20 0.003 0.013 <0.001 1.04 0.113 0.007

Liver 0.25 <0.01 3.63 801 0.324 <0.01 38.4 143 3.0 6.23 0.300 0.787 <0.001 0.930 0.103 0.012

Umm Said O.S.G. 2.2 Muscle 0.03 <0.01 0.29 2.4 <0.005 0.09 0.49 5.8 2.4 2.82 0.002 0.001 <0.001 0.970 0.551 0.005

Liver 0.17 0.01 2.40 1070 0.402 0.05 80.6 356 2.8 8.54 0.298 0.109 <0.001 1.13 0.108 0.008

Doha O.S.G. 1.7 Muscle 0.04 0.05 0.35 3.3 0.013 0.09 0.54 67.3 2.2 2.09 0.005 0.003 <0.001 0.987 0.209 0.006

Liver 0.26 <0.01 3.87 1210 0.517 0.08 90.9 317 2.4 7.29 0.437 0.417 <0.001 1.28 0.074 0.010

Al Dakhira S.E.b 1.7 Muscle 0.03 <0.01 0.18 4.0 <0.005 0.03 0.59 6.5 10.0 4.68 0.005 0.005 <0.001 0.343 0.108 0.009

Liver 0.31 0.08 4.20 1570 0.583 <0.01 33.7 228 22.4 – 0.196 1.46 <0.001 0.333 0.276 0.046

UAE

Al Marfa O.S.G. 4.7 Muscle <0.01 <0.01 0.063 25.1 0.014 <0.01 0.37 13.5 4.1 2.35 <0.001 <0.001 <0.001 2.35 0.025 0.035

Liver 0.29 0.03 3.21 478 0.164 0.05 36.2 184 2.6 7.09 0.281 0.594 <0.001 4.65 0.085 0.011

Al Marfa S.E. 1.7 Muscle 0.04 <0.01 0.12 203 <0.005 <0.01 0.71 1.82 5.0 2.71 0.002 0.001 <0.001 0.452 0.119 0.007

Liver 1.00 0.05 5.19 1350 0.163 0.08 39.0 2400 19.2 12.2 0.675 7.19 <0.001 0.587 0.385 0.023

Dhannah S.E. 1.7 Muscle <0.01 0.03 0.06 23.3 0.012 <0.01 0.88 11.5 2.5 3.14 <0.001 <0.001 <0.001 0.509 <0.01 0.027

Liver 1.04 0.02 4.09 1900 0.228 <0.01 9.25 1160 9.2 22.6 0.248 9.9 4 <0.001 1.02 0.308 0.069

Dhannah O.S.G. 2.8 Muscle <0.01 0.05 0.14 24.3 0.012 <0.01 19.5 23.3 1.9 2.37 <0.001 <0.001 <0.001 1.62 – 0.033

Liver 0.40 <0.01 5.05 481 0.185 0.07 18.6 380 1.5 5.46 0.277 0.108 <0.001 2.30 0.092 0.009

Bahrain

Badaiya O.S.G. 1.6 Muscle <0.01 0.013 0.297 3.10 <0.01 <0.01 0.235 15.9 1.23 3.27 0.002 0.001 <0.001 0.740 0.028 <0.001

Liver 0.238 0.019 3.88 1024 0.395 0.063 170 379 2.15 6.01 0.186 0.499 <0.001 1.31 <0.001 0.003

Badaiya O.S.G. 1.15 Muscle <0.01 0.020 0.256 13.9 <0.01 <0.01 0.294 17.9 1.38 2.73 <0.001 <0.001 <0.001 0.820 0.005 <0.001

Liver 2.67 0.028 5.31 2866 0.423 0.085 159 295 2.62 5.80 0.747 0.369 0.002 2.10 0.012 0.011

Fasht Al

Adham

O.S.G. 1.26 Muscle <0.01 0.075 0.677 9.09 <0.01 0.05 0.593 27.1 4.66 2.18 <0.001 0.002 <0.001 0.705 0.020 <0.001

Liver 0.201 0.047 3.28 2150 0.410 0.061 276 421 2.23 5.67 1.29 2.14 0.002 0.725 0.017 0.002

Fasht Al

Adham

O.S.G. 1.03 Muscle <0.01 0.024 0.406 3.88 <0.01 <0.01 0.389 25.8 14.4 2.37 <0.001 0.001 <0.001 0.669 0.028 <0.001

Liver 0.030 0.023 2.81 822 0.162 0.039 75.5 183 2.81 4.23 0.253 1.05 <0.001 0.287 0.001 0.001

Oman

Quriyat O.S.G. 1 1.8 Muscle <0.05 0.072 0.204 8.46 <0.05 <0.05 0.513 13.4 0.834 2.21 <0.005 <0.005 <0.005 0.517 0.025 <0.005

Liver 0.771 0.062 3.63 1499 0.377 0.100 104 1714 2.61 17.5 0.248 11.4 <0.005 1.3 0.107 0.022

Quriyat O.S.G. 2 1.8 Muscle <0.05 0.054 0.182 10.6 <0.05 <0.05 0.511 12.8 1.35 2.16 <0.005 0.005 <0.005 0.498 0.011 <0.005

Liver 0.422 0.060 1.85 520 0.224 <0.05 164 1335 2.84 8.27 0.516 11.2 <0.005 0.985 0.076 0.009

Raysut

Port Area

S.E. Muscle <0.05 <0.05 0.114 5.20 <0.05 <0.05 0.519 11.1 2.07 1.24 <0.005 0.011 0.012 0.522 0.014 <0.005

Liver 1.09 <0.05 4.12 1207 0.256 <0.05 98.8 1627 11.6 5.22 0.339 109 <0.005 0.398 0.175 0.008

Sagar S.E. Muscle <0.05 0.077 0.087 8.13 <0.05 0.111 0.58 10.47 2.88 1.30 <0.005 0.014 <0.005 0.435 0.011 <0.005

Liver 1.937 <0.05 4.788 1302 0.253 <0.05 38.6 1484 11.9 8.05 0.222 195 <0.005 0.480 0.426 0.005

– Not analysed.aOrange spotted grouper.b Spangled emperor.

418

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Fig. 4. The concentration (in lg g�1 dry) of Hg in both liver and muscle of orange spotted grouper (hamoor or Epinephelus coioides) as a function ofthe wet weight of the fish. The lines show the linear regression for the two sets of data.

S. de Mora et al. / Marine Pollution Bulletin 49 (2004) 410–424 419

were quite low, <0.014 lg g�1, and less than previousmeasurements of up to 0.23 lg g�1 that have been ob-served in the RSA (Fowler et al., 1993). The concen-

trations are typical of levels that have been found in

various fish species from pristine areas (Hellou et al.,

1996; Rom�eo et al., 1999; Zauke et al., 1999). However,the Cd content in liver, especially for spangled emperor,

was much higher than observed in the muscle. For

example, Cd levels in the liver of spangled emperor from

Dhannah (9.94 lg g�1) and Al Marfa (7.19 lg g�1) wererelatively high, but of particular note were the extremely

high concentrations (109 and 195 lg g�1) in fish liver

from southern Oman. These levels were an order of

magnitude higher than those in the same species from

UAE (Table 4). To our knowledge, such high Cd

concentrations in fish liver have not been reported pre-

viously. Many species of fish exhibit higher Cd con-

centrations in liver relative to muscle, but levels havegenerally been reported to be <10 lg g�1 (Hellou et al.,1996; Zauke et al., 1999). Relatively high content of Cd

in liver, found to vary from 4.67 to 51.0 lg g�1, wasobserved in five species of fish caught off the Maurita-

nian coast (Rom�eo et al., 1999).The source of this Cd enrichment in fish from

southern Oman is conjectural. Anthropogenic contam-

ination cannot be ruled out, but is unlikely given theopen water conditions, together with the limited popu-

lation and industry in the region. The apparent

enhancement is more likely due to food chain transfer of

high levels of Cd brought into the surface waters

through the strong upwelling of nutrient-rich waters

that was occurring during the sampling period. This

mechanism also has been suggested to account for the137Cs levels noted in seaweeds along the southern coastof Oman (Jupp and Goddard, 2001). Cadmium, which

has been shown to maintain a one to one relationship

with phosphorus in upwelled waters (Bruland, 1983),could be readily bioaccumulated in the lower portion of

the food chain and passed along and eventually bio-

concentrated to high levels in the liver of top predator

fish, much as is Hg. Indeed, such a pathway has been

implied to explain the elevated Cd in liver from fish in

Mauritania (Rom�eo et al., 1999). It is interesting to notethat the limited data for Cd in liver of commercial deep-

sea fish were not particularly elevated (Mormede andDavies, 2001).

3.3. Bivalves

Several composite samples of oysters were obtained

in the Gulf and Gulf of Oman, comprising five samples

of pearl oysters (Pinctada radiata) and six samples of

rock oysters (Saccostrea cucullata). Composite samplesof rock scallops (Spondylus sp.), Venus clams (Circentia

callipyga), and pen shells (Pinna muricata) were ob-

tained from single sites. The concentrations, expressed

on a dry weight basis, of trace elements in different

bivalves are shown in Table 5. The pen shells from Jebel

Ali, UAE, had relatively high concentrations of Co (12.9

lg g�1) and Ni (35.8 lg g�1). They also had an excep-tionally high Mn content (1110 lg g�1). No comparabledata from the RSA are available for this species. Rock

scallops have been analysed in past surveys in UAE and

Bahrain. The specimens collected at Abu Dhabi con-

tained considerably lower concentrations of V, Pb, Ag,

Co, Cr, and Ni than in scallops analysed in earlier years

(Fowler et al., 1993). Only Zn levels (1150 lg g�1) werehigher in the sample from Abu Dhabi (Table 5). Apart

from As, metal concentrations in the one clam samplefrom Ras Al Nouf, Qatar, are comparable to or lower

Table 5

Trace element concentrations (lg g�1 dry weight) in bivalves from Qatar, UAE, Bahrain, and Oman

Location Species V Cr Mn Fe Co Ni Cu Zn As Se Ag Cd Sb Hg Pb U

Qatar

Ras Al Nouf Clams 0.76 0.97 17.7 517 4.45 23.9 8.35 69.1 156 7.15 3.03 1.17 0.027 0.315 1.45 0.390

UAE

Jebel Ali Pen Shells 2.05 3.41 1110 501 12.9 35.8 19.4 1830 153 12.8 1.92 10.7 0.007 0.207 1.23 0.498

Pearl Oysters 0.95 0.34 12.9 180 0.181 0.54 4.61 1430 37.7 5.45 0.430 9.97 <0.001 0.0371 0.389 0.149

Abu Dhabi Rock Scallops 0.43 <0.01 5.36 131 0.117 0.07 7.65 1150 40.0 5.71 0.017 6.78 <0.001 <0.147 0.098 0.010

Pearl Oysters 3.23 2.36 8.40 320 1.86 7.02 17.3 159 30.6 5.71 0.540 2.73 0.013 0.0987 2.29 0.381

Akkah Head Pearl Oysters 0.44 0.29 25.0 106 0.313 0.93 5.10 306 21.0 3.92 0.235 7.82 <0.001 0.0087 0.147 0.119

Akkah Beach Rock Oysters 0.28 0.49 12.0 89.9 0.227 1.12 63.8 425 16.2 2.69 1.17 6.15 <0.001 0.0280 0.250 0.094

Bahrain

Off BAPCO refinery Pearl Oysters 7.30 0.794 4.31 271 0.150 0.884 4.46 4290 24.9 4.89 0.011 3.68 0.019 0.112 3.92 0.218

North of Meridien

Hotel

Pearl Oysters 4.48 0.672 6.16 214 0.168 0.709 3.13 1825 45.7 5.10 0.047 3.79 0.011 0.035 0.396 0.169

Oman

Al Sawadi Rock Oysters 0.272 0.929 7.11 164 0.640 1.46 130 745 11.1 2.42 1.76 19.9 <0.005 0.147 0.673 0.174

Ras Al Hamra Rock Oysters 0.40 0.88 2.77 142 0.310 1.07 210 1614 15.3 2.46 3.23 9.83 <0.005 0.153 0.550 0.199

Ras Al Yei Rock Oysters 1.05 3.76 6.50 406 0.360 3.14 121 391 17.2 1.87 2.11 21.9 <0.005 0.050 0.384 0.288

Hilf Rock Oysters 0.44 1.05 4.46 137 0.325 1.39 276 1596 14.9 2.07 2.33 10.6 <0.007 0.153 0.447 0.246

Mirbat Rock Oysters 0.730 0.494 3.44 150 0.184 0.796 60.9 1074 14.8 2.17 2.59 8.99 <0.005 0.079 0.501 0.143

420

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S. de Mora et al. / Marine Pollution Bulletin 49 (2004) 410–424 421

than previous limited measurements of clams, Meretrix

meretrix and Tapes sulcarius, from Saudi Arabia

(Fowler et al., 1993).

All pearl oysters were collected in the Gulf, except forthe sample from Akkah Head. Very high concentrations

of Zn (4290 lg g�1), V (7.3 lg g�1), and Pb (3.92 lg g�1)were found in pearl oysters near the BAPCO site in

Bahrain. Local contamination of the sediments with

respect to both Pb and Zn was previously discussed. The

pearl oysters from Abu Dhabi contained relatively high

concentrations of Cr, Fe, Co, Ni, Cu, and Ag (Table 5).

Whereas the Ag content in sediments from Abu Dhabiwas the maximum observed in this study (Table 3), the

concentrations of the other elements in these sediments

were not especially noteworthy. Similarly, the maximum

Cd concentration in the sample from Jebel Ali, UAE,

was not reflected in the local sediments. The pearl oyster

sample from Akkah Head, the only one collected in the

Gulf of Oman, actually contained the lowest levels

measured for several elements, namely V, Cr, Fe, As,Hg, and Pb. Table 6 compares concentrations of Cd,

Cu, Ni, Pb, and Zn in pearl oysters from various loca-

tions in the RSA. In general, the metal contents agree

well with previous studies, but the high Zn level found

near the BAPCO refinery was exceptional.

All rock oysters were collected in the Gulf of Oman.

Although relatively few studies of rock oysters in the

RSA are available for comparison (Table 6), the contentof several metals are comparable to previous observa-

tions. Moreover, the concentrations of most elements

were comparable to those in the pearl oysters. Whereas

markedly lower As was found in the rock oysters, Cd,

Cu, and Ag were notably more enriched in the rock

Table 6

Metal concentrations (lg g�1 dry weight) in pearl oysters (Pinctada radiata) a

Location Species Cd Cu Ni

Bahrain Pinctada radiata 0.25–3.8 0.4–3.4 0.2–8.

Bahrain Pinctada radiata 3.3–17.9 1.8–6.9 0.44–1

Bahrain Pinctada radiata 3.3–3.8 3.9–6.9

Bahrain Pinctada radiata 3.68–3.79 3.13–4.46 0.709–

Kuwait, 1990 Pinctada radiata 0.82–0.94 0.79–0

Kuwait, 1992 Pinctada radiata 7.70± 2.8 3.67± 0.9 4.33±

Kuwait, 1994 Pinctada radiata 160–174 1.42–1

UAE Pinctada radiata 2.6–20.8 1.9–23.6 1.64

UAE Pinctada radiata 2.6–34.2 3.0–9.7

UAEa Pinctada radiata 2.73–9.97 4.61–17.3 0.54–7

Oman Saccostrea cucullata 2.8–34.8 20–235 0.41–1

Oman Saccostrea cucullata 6.2–19.3 46–265

Oman Saccostrea cucullata 8.99–21.9 60.9–276 0.80–3

UAEb Saccostrea cucullata 6.15 63.8 1.12

a From the Gulf coast.b From the Gulf of Oman.

oysters. As noted above for pearl oysters from Akkah

Head, it is of particular interest that concentrations in

the rock oysters from Akkah Beach were not enhanced

in the same trace metals (notably As, Co, Cr, and Ni)that were greatly elevated in the local sediments. This

observation suggests that the metals associated with the

local sediments are not readily bioavailable to the local

filter-feeding bivalves. The rock oysters from Ras Al Yei

on the seaward side of Masirah Island, Oman, contained

the highest levels of many of the trace elements analysed

(Table 5). In particular, Cd, a nutrient-type element

associated with upwelled waters has always exhibitedhigh concentrations in oysters from this location (16–35

lg g�1), especially during the southwest monsoon season(Fowler et al., 1993). During the monsoon months,

many of these trace metals are possibly enhanced in the

water and the filterable suspended particulates when

upwelling and rough sea conditions are predominant.

Arsenic in bivalves from the RSA deserves particular

consideration, and Table 7 compares As content inoyster species from various locations. Of the bivalves

examined in this study, clams and pen shells contained

the highest levels of As with 156 and 153 lg g�1,respectively. The highest As concentrations reported

previously for bivalves from the RSA were approxi-

mately 100 lg g�1 in clams collected from Ras Al

Tanajib in Saudi Arabia in 1991 (Fowler et al., 1993)

and 1998 (IAEA, unpublished data). If As data for allthe bivalves sampled in the present and previous surveys

are examined, it is clear that on average clams typically

contain higher As concentrations than the other bivalve

species. For example, the average As concentration for

clams collected in these surveys since 1991 is 67.4 ± 42.6

nd rock oysters (Saccostrea cucullata) from the Gulf and Gulf of Oman

Pb Zn Reference

95 1.25–14.0 159–1532 Al-Sayed et al. (1994)

.24 0.32–3.9 898–1607 Fowler et al. (1993)

1.0–1.1 Fowler (1988)

0.884 0.396–3.92 1825–4290 This study

.92 0.40–0.62 50.6–509 Bu-Olayan and Subrahmanyam

(1997)

3.17 45.4± 19.5 Bou-Olayan et al. (1995)

.62 0.40–0.52 554–561 Bu-Olayan and Subrahmanyam

(1997)

0.14–3.0 1261 Fowler et al. (1993)

0.39–0.9 Fowler (1988)

.02 0.147–2.29 159–1430 This study

.69 0.06–2.2 152–1073 Fowler et al. (1993)

0.27–3.8 Fowler (1988)

.14 0.384–0.673 391–1610 This study

0.250 425 This study

Table 7

Worldwide As concentrations in oysters (lg g�1 dry weight dw or wet weight ww)

Location Species As Reference

Bahrain and UAE Pinctada radiata 4.5–73 dw Fowler et al. (1993)

Oman Saccostrea cucullata 14–23 dw Fowler et al. (1993)

North and South Carolina, USA 9.2a dw Lauenstein et al. (2002)

Maryland, USA Crassostrea virginica 16.3± 2.9 dw Riedel and Valette-Silver (2002)

South Carolina, USA Crassostrea virginica 15.6± 3.8 dw Riedel and Valette-Silver (2002)

Florida, USA Crassostrea virginica 23.6± 5.5 dw Valette-Silver et al. (1999)

Southeast USA Crassostrea virginica 25.4± 10.4 dw Valette-Silver et al. (1999)

Southwest Spain Crassostrea angulata 1.67–3.58 ww Suner et al. (1999)

Bahrain and UAE Pinctada radiata 21.0–45.7 dw This study

Oman and UAE Saccostrea cucullata 11.1–17.2 dw This study

aMedian of 281 mussel (Mytilus edulis) and oyster (Crassostrea virginica) samples.

422 S. de Mora et al. / Marine Pollution Bulletin 49 (2004) 410–424

lg g�1 (range 19–156 lg g�1, n ¼ 11). It is noteworthythat this average concentration is six times higher than

the national median (9.2 lg g�1 dry) in bivalves, prin-cipally oysters (Crassostrea virginica) and mussels (My-

tilus edulis), collected during 1986–1997 for the USA

National Status and Trends Mussel Watch project

(Lauenstein et al., 2002). Several related studies (Riedel

and Valette-Silver, 2002; Valette-Silver et al., 1999) have

focused on the southeast coast of the USA owing to therelatively elevated As content (25.4 ± 10.4 lg g�1) inoysters, which averaged more than double the national

average and had maximum values reaching 66 lg g�1.The elevated concentrations of these oysters were

attributed to higher inputs of As to the southeastern

region of the USA from natural phosphate deposits and

soil pesticide residues. In surveys dating from 1991, As

concentrations in pearl oysters and rock oysters fromthe RSA averaged 32.6 ± 17.4 (n ¼ 15, range 4.5–73

lg g�1) and 16.7 ± 4.8 lg g�1 (n ¼ 15, range 11.1–29.7

lg g�1), respectively. As evident in Table 7, the levels arecomparable to those in oysters from the southeastern

coast of USA and should accordingly be considered of

concern. Aside from these data, virtually no other

published information is available on As levels in biv-

alves from the RSA. Given these observations, it wouldbe worthwhile to examine in more detail what factors

might contribute to enhanced As concentrations in

many biota from the RSA.

4. Conclusions

Several heavy metals and trace elements were deter-mined in coastal sediments and marine biota (fish and

bivalves) from Bahrain, Oman, Qatar and the United

Arab Emirates. Sediment in the Gulf of Oman off the

east coast of UAE contained extremely high levels of

some heavy metals, especially Ni. In contrast, metal

levels in oysters from Akkah Head and Akkah Beach

(UAE) were not particularly enhanced. The metals in

the sediments are probably derived from Oman ophio-

lites and are present in mineralogical phases that aregenerally not bioavailable to the local organisms. The

metals in the region are thus interpreted to be natural in

origin, rather than the result of contamination.

The origins of high trace metal levels in rock oysters

from certain locations on Masirah Island, Oman, are

not evident, but may be due to natural geochemical and

oceanographic processes. Likewise, the very high Cd

concentrations in the livers of some fish from southernOman may result from food-chain bioaccumulation of

elevated Cd levels brought into the productive surface

waters by prominent upwelling in the region.

Hg concentrations are generally very low in sediments

and the total Hg levels in top predator fish commonly

consumed in the RSA were found to be below the 0.5

lg g�1 wet threshold safety value set by many countries.Hg content was similar to levels measured in the samespecies during earlier years.

Most interesting, and as yet unexplainable, is the

observation of very high arsenic concentrations in cer-

tain bivalve species from the RSA when compared to

those from other regions in the world. Again, it is not

clear whether this is related to point sources of con-

tamination (unlikely) or to natural biogeochemical

processes in the region (more likely). It is evident that tointerpret sources of possible metal contamination

properly, it is imperative to understand the natural

bioaccumulation potential and natural background

levels of elements like As in the species under study since

content and ratios of heavy metals vary greatly among

the bioindicator species (particularly bivalves) used in

the RSA.

Acknowledgements

This was a collaborative project between the IAEA

and ROPME, financially supported by both organiza-

tions. The IAEA Marine Environment Laboratory

operates under agreement between the International

Atomic Energy Agency and the Government of the

S. de Mora et al. / Marine Pollution Bulletin 49 (2004) 410–424 423

Principality of Monaco. We acknowledge with gratitude

the logistic support received in each country: in Bahrain

from the Ministry of Housing, Municipalities & Envi-

ronment; in Oman from the Ministry of RegionalMunicipalities and Environment; in Qatar from the

Ministry of Municipal Affairs and Agriculture; and in

the UAE from the Federal Environment Agency. We

thank Dr. Nahida Al-Majed from ROPME for assis-

tance organising the field studies and with sample col-

lection in Bahrain and Oman.

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