An assessment of metal contamination in coastal sediments of the Caspian Sea

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Marine Pollution Bulletin 48 (2004) 61–77

An assessment of metal contamination in coastal sedimentsof the Caspian Sea

Stephen de Mora a,*, Mohammad Reza Sheikholeslami b, Eric Wyse a, Sabine Azemard a,Roberto Cassi a

a Marine Environment Laboratory, International Atomic Energy Agency, 4 quai Antoine 1er, B.P. 800, MC 98012, Monacob Theme for Effective Regional Assessment of Contaminant Levels (ERACL), Department of the Environment (DOE), 187 Nejatollahi Avenue,

P.O. Box 15875-5181, Tehran, Iran

Abstract

An assessment of marine pollution due to metals was made in the Caspian Sea based on coastal sediment collected in Azerbaijan,

Iran, Kazakhstan, Russia and Turkmenistan. Despite the high carbonate content, the distribution of most metals was largely

controlled by terrigenous inputs. Several metals (As, Cr, Ni) exhibited concentrations that exceed sediment quality guidelines. Such

metals have a high natural background but anthropogenic activities, notably mining, may further enhance concentrations. This

would explain hot spots for Cu and Zn in Azerbaijan and Iran, and Cr at the mouth of the Ural River in Kazakhstan. Contam-

ination by Hg was observed to the south of Baku Bay, Azerbaijan. Some anomalously high concentrations of Ba in the central

Caspian are probably from offshore drilling operations, but the elevated U concentrations (up to 11.1 lg g�1) may be natural in

origin. Several metals (Ag, Cd, Pb) have relatively low levels that pose no environmental concerns.

� 2003 Elsevier Ltd. All rights reserved.

Keywords: Caspian Sea; Sediments; Pollution; Metals; Mercury; Barium

1. Introduction

The Caspian Sea, bounded by the five littoral states of

Azerbaijan, Federation of Russia, Islamic Republic of

Iran, Kazakhstan and Turkmenistan, is the largest in-

land body of water in the world (Kosarev and Yab-

lonskaya, 1994). Having a surface area of�436,000 km2,it is 1200 km long and varies in width between 204 and

566 km, with an average of 330 km. There are three

distinct basins. The central and southern basins are quite

deep, with maxima of 788 and 1025 m, respectively.

However, the northern part is shallow with an average

depth of �5 m and a maximum depth of only 20 m. The

sea level is presently �27 m below the level of the world

oceans, following a marked increase of about 2.5 m since1977. The resulting inundation has flooded oil fields,

agricultural lands and toxic waste sites, thereby con-

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

72-76.

E-mail address: [email protected] (S. de Mora).

0025-326X/$ - see front matter � 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/S0025-326X(03)00285-6

tributing to the pollution burden in the land-locked

system (Dumont, 1998; Dahl and Kuralbayeva, 2001).

About 130 rivers of varying size drain into the Cas-

pian Sea providing an annual input in the order of 300

km3. The most important source is the Volga River,

which contributes �80% of the annual flow. The Kura

and Ural Rivers contribute 6% and 5%, respectively.The remainder of the inflow comes mainly from the

numerous rivers in Russia and Iran. Reflecting the fresh

water input, the salinity is �0.1 psu at the mouth of the

Volga and Ural rivers and increases to 12.6–13.5 psu in

middle and southern parts of the Caspian Sea. The sa-

linity generally increases slightly from west to east, and

with depth. The composition of the salt differs from that

of sea water owing to the enrichment of sulphate fromrunoff (Karpinsky, 1992). Thermohaline circulation in

the Caspian Sea ensures that the water remains oxy-

genated to the bottom (Dumont, 1998).

As a land-locked system, pollutants discharged into

the Caspian Sea remain trapped within the basin. The

main sources of pollution are considered to be offshore

oil production and land-based sources, notably from the

mail to: [email protected]

62 S. de Mora et al. / Marine Pollution Bulletin 48 (2004) 61–77

Volga River basin (Karpinsky, 1992). Whereas coastal

towns around the Caspian Sea contribute about 8 km3 of

wastewater, approximately 12 km3 comes from the

Volga Basin. Karpinsky (1992) noted the marked in-crease in the concentration of several metals (e.g., Cd,

Cu, Pb and Zn) in Volga River water. The sedimentary

record in the Volga delta has similarly shown recent in-

creases for As, Cr and Zn (Winkels et al., 1998) and Zn

concentrations in the tissue of Caspian seals increased

during the period 1993–2000 (Anan et al., 2002). The

Kura River is another important source of pollution due

to discharges of Cu and Mo into the upper catchment inArmenia and Georgia (Dumont, 1995). As noted above,

the sea level rise acerbated marine pollution, particularly

from the industrial complex of Sumgait (or Sumgayit)

and the oil fields of Baku, both cities being situated on

the Apsheron Peninsula in Azerbaijan (Dumont, 1995).

The geological characteristics of the Caspian Sea are

quite variable (Krilov, 1987; Kosarev and Yablonskaya,

1994). The sedimentary material is comprised of cal-careous, sub-calcareous and terrigenous material, with

the calcium carbonate having both biogenic and hy-

drogenous origins. Coarse-grained sediments dominate

in the shallow northern Caspian. In the central Caspian,

fine-grained terrigenous material accumulates on the

narrow shelf in the west. Biogenic carbonate sedimen-

Table 1

General characteristics of sediments sampled in the Caspian Sea

Depth (m) TOC (%) Carbonates (%)

Azerbaijan

Mean 43 1.41 9.21

Std Dev 31 0.58 1.81

Min 10 0.37 6.00

Max 102 2.34 13.0

Iran

Mean 34 0.92 13.4

Std Dev 25 0.38 6.33

Min 9 0.30 1.00

Max 100 1.90 28.0

Kazakhstan

Mean 7 0.58 10.8

Std Dev 17 0.66 7.87

Min 2 0.08 1.00

Max 100 2.80 38.0

Russia

Mean 22 0.81 20.3

Std Dev 21 0.65 13.9

Min 3 0.11 5.70

Max 84 2.51 53.9

All data

Mean 25 0.90 13.5

Std Dev 27 0.64 9.50

Min 2 0.08 1.00

Max 102 2.80 53.9

a Sedimentary material <62.1 lm in diameter.

tation occurs on the wider eastern shelf due to the desert

climate and absence of river inflows. Fine-grained ma-

terial, notably calcareous silts, deposits on the shelf in

the southern Caspian. Throughout the Caspian Seathere are regions with very low sedimentation rates, due

to either the intensive hydrodynamic conditions or

slumping. Also, there are numerous submarine mud

volcanoes. Although the major element geochemistry

and the distribution of several trace elements have been

previously described (Krilov, 1987), the data mainly

referred to the deep sediments and there was no infor-

mation for the Iranian sector. One study of metal pol-lution history concentrated on eight priority elements,

but only in the Volga River Delta (Winkels et al., 1998).

Another recent investigation focussing on fish included

measurements of only four metals at four sites in the

northeast Caspian Sea (Moore et al., 2003).

This paper interprets sediment quality in the coastal

zone of the Caspian Sea. Samples were collected in all

littoral states, although only two samples were availablefrom Turkmenistan. A wide range of elements was de-

termined for pollution assessment and to facilitate in-

terpretation of the origins of potential contaminants.

Concurrent studies were conducted on petroleum hy-

drocarbons (Tolosa et al., 2003) and organochlorinated

compounds (de Mora et al., submitted for publication).

Finesa (vol%) Al (mg g�1) Ca (mgg�1)

38.6 69.2

13.0 7.7

24.1 50.0

70.4 81.3

47.2 60.5 102

20.5 11.4 40.1

10.8 37.5 60.7

81.9 77.5 192

11.2 17.1 146

8.0 9.3 84.0

2.3 1.1 21.5

45.2 45.1 344

15.8 18.8

20.3 8.5

1.3 2.6

81.4 38.3

27.6 39.0 126

22.2 25.0 70.3

1.3 1.1 21.5

81.9 81.3 344

Fig. 1. Volume percentage of fine-grained (i.e. <62.1 lm) material in coastal sediments of the Caspian Sea.

S. de Mora et al. / Marine Pollution Bulletin 48 (2004) 61–77 63

2. Methods

2.1. Sample collection

Details of sampling and station locations (Fig. 1 in

Tolosa et al., 2003) have been previously described. In

total 105 samples, 2 more than available for analysis of

organic components, were collected from the coastalzone of the Caspian Sea using a Van Veen grab. Sedi-

ment from the surface (�4 cm) was sub-sampled and

stored in plastic Ziplock bags. All samples were frozen

()18 �C) immediately upon collection and kept frozen

for transport to the laboratory. The 21 samples from the

Russian sector were analysed at the Russian laboratory

‘‘Typhoon’’ Center for Environmental Chemistry. All

other samples were analysed at the International Atomic

Energy Agency Marine Environmental Studies Labo-

ratory in Monaco. The samples were analysed for grain

size distribution, total organic carbon (TOC), carbonatecontent, and the following elements: Ag, Al, As, Ba, Ca,

Cd, Co, Cr, Cu, Fe, Hg, Li, Mg, Mn, Ni, Pb, Sb, Se, Sn,

U, V and Zn.

Fig. 2. The distribution of aluminium (lg g�1) in coastal sediments of the Caspian Sea.


2.2. Metal analyses

Sediment sub-samples were freeze-dried and then

sieved on a 1-mm clean plastic sieve. They were then

transferred to individual clean Ziplock bags and shaken

to obtain a homogeneous powder. All samples were di-

gested using a CEM MARS5 high-pressure microwavedigestion system. Approximately 250 mg of dried sedi-

ment material was weighed and digested in acid-cleaned

Teflon microwave vessels using 5 ml of nitric acid and 2

ml of concentrated hydrofluoric acid (Merck Suprapur in

both cases). Samples were prepared in batches of 12,

which included at least one reagent blank, a representa-

tive standard reference material, e.g., MESS-2 or BCSS-1

(NRCC, marine sediment) and a duplicate sample or

reference material. For digestion, the temperature was

ramped to 200 �C over a 30 min span and then held at

that temperature for 12 min. After cooling for at least 1

h, the sample digests were transferred to a graduated 50-ml plastic test tube containing 0.9 g boric acid for the

dissolution of fluoride precipitates. Following dilution to

50 ml with Milli-Q water, tubes were capped, and placed

in an ultrasonic bath for �1 h to ensure the complete

dissolution of residual solid material.

y = 787.05x + 18317

R2= 0.4799

0

50000

100000

150000

200000

250000

300000

350000

400000

0 10 20 30 40 50 60 70 80 90

Fine-Grained Material In Sediments (%)

Ala

nd

Ca

Co

nte

nt

(µg

g-1)

0

10

20

30

40

50

60

Car

bo

nat

eC

on

ten

t(%

)

Fig. 3. (h) Al (lg g�1), (n) Ca (lg g�1) and (}) carbonate (%) content of Caspian Sea sediments as a function of the volume percent of fine-grained

(i.e. <62.1 lm) material. The solid line shows the linear regression for Al.


Mercury was analysed by cold vapour atomic ab-

sorption spectrometry (CV-AAS) using SnCl2 reduction

with a flow injection vapour generator (VGA-76).Replicate blanks, replicate samples and reference mate-

rial MESS-2 (NRCC, marine sediment) were analysed

for quality control purposes. Precision of measurements,

determined from replicate measurements of the same

digestion varied from 2% to 13% (performed on the

reference material and samples). Analytical precision,

determined from replicate digestions of MESS-2 was

4%. Sample homogeneity was estimated by triplicatedigestions of two samples and varied from 6% to 8%.

All other elements were determined using a Finnigan

Element magnetic sector inductively-coupled plasma

mass spectrometer (ICP-MS) using a micro-concentric

nebulizer (MCN) with a standard double-pass con-

densing spray chamber for sample introduction. Sample

digests were diluted with 2% nitric acid for analysis: 20·for low resolution analysis and 100· for medium reso-lution analysis. An internal standard (2 ngml�1 Be, In

and Th) was also added to the diluted samples to correct

for matrix effects and instrument drift. These elements

were chosen based firstly on their absence in the sam-

ples, and secondly on their representativeness (mass and

chemical properties) of the analytes of interest. Larger

dilutions up to 2000· were necessary for certain analytes

observed at relatively high concentrations (e.g., Fe andAl). Results were quantified via an external calibration

curve, which was generated from the responses obtained

from multiple dilutions of a multi-element calibration

standard prepared from single-element standards (Alfa

Aesar).

2.3. Analyses of other parameters

Grain size analysis involved laser diffractometry usinga Malvern Instruments Mastersizer Micro. Samples

were introduced into the instrument as a slurry, pre-

pared by suspending 300–600 mg of freeze-dried sedi-

ment into 500 ml of distilled water.

Both total carbon (TC) and total organic carbon

(TOC) were determined using an Elementar Vario EL

apparatus. About 30 mg aliquots of freeze-dried sedi-

ment were weighed into small tin vessels. For the de-termination of TC, the samples were analysed directly

without further treatment. TOC was determined fol-

lowing an acidification step that eliminates the inorganic

carbon. The samples were acidified by adding a few

drops of ortho-phosphoric acid (1 M) and then baked at

50 �C for a few hours. The carbonate content was then

inferred by the difference between the TC and the TOC.

3. Results and discussion

3.1. General characteristics

Some general characteristics of the sediments are

shown in Table 1. Most samples were obtained from

shallow sites, usually <50 m, although some samplesfrom �100 m were collected. As the northern Caspian

Sea is quite shallow, most of the samples from Ka-

zakhstan and the Federation of Russia were obtained

from <10 m depth. The samples from the northern

Caspian Sea were quite coarse-grained, having relatively

Fig. 4. Carbonate content (%) in coastal sediments of the Caspian Sea.


low percentages of fine material (Fig. 1). Such obser-

vations agreed with previous studies (Kosarev and

Yablonskaya, 1994) and were further reflected in therelatively low concentration of aluminium (Fig. 2) in

these sediments. Al is a good proxy for terrigenous input

and the Al concentration in sediments increased with the

percentage of fine-grained material present (Fig. 3).

Calcium and carbonate concentrations could be very

high (Table 1) and calcium carbonate occasionally

dominated the sediment composition. The carbonate

content (Fig. 4) was relatively higher in the northernsector than in Azerbaijan and Iran. However, high levels

of carbonate were also observed in the southeast Cas-

pian. Although shell fragments were often found in the

sediments, hydrogenous precipitation of CaCO3 occurs

in the Caspian Sea (Kosarev and Yablonskaya, 1994).

Whereas Ca and carbonate content co-varied and ten-

ded to be present at higher concentrations in the coarse

sediments, they bore no relationship to the amount of

fines in the sediment (Fig. 3). The total organic content

(TOC) in the sediments tended to be higher in the deepsediments (Fig. 5), with elevated levels in Azerbaijan.

Given the diversity of environments sampled, the TOC

in the Russian sector (0.81± 0.65%) agreed reasonably

with the data from Winkels et al. (1998) for just the

Volga delta (1.3 ± 0.7%).

Such sediment characteristics play an important role

in interpreting the distribution of pollutants in the

Caspian Sea sediments. Fine-grained material, with alarger surface to volume (or weight) ratio, has a greater

potential to scavenge both inorganic and organic pol-

lutants from the water column. In general terms, fine

mud/silt/clay sediment with high organic content retain

more contaminants than does relatively coarse sandy

sediment. Thus, sites where fines are deposited are likely

to exhibit an elevated loading of heavy metals. As wind-

Fig. 5. The total organic content (TOC as %) in coastal sediments of the Caspian Sea.


induced mixing in the shallow northern waters winnows

out the fine material (Kosarev and Yablonskaya, 1994),

particularly in the Kazakhstan sector, pollutants dis-charged into this region are not likely to accumulate in

the immediate vicinity and so are exported from the

region.

In the study presented here, 23 elements were deter-

mined in the Caspian Sea sediments. Statistical infor-

mation for each element is shown in Table 2 on a

country basis. Data for Turkmenistan are not included

as only two samples were analysed. With respect to in-terpretation of the results, a pragmatic approach was

taken whereby metal concentrations were compared to

North American sediment quality guidelines (Table 3).

Marine sediment quality guideline values from NOAA�sNational Status and Trends Program (Long et al., 1995)

designate an effects range low (ERL) and an effects

range medium (ERM). The Canadian interim marine

sediment quality guidelines (ISQG) value and the

probable effects level (PEL) are defined by EnvironmentCanada (ISQG, 1995). Several issues remain to be

solved with respect to sediment toxicity guidelines. The

Caspian Sea is a unique system, being essentially a

brackish lake with a salt composition that differs from

that of seawater, for which sediment toxicity guidelines

have yet to be established. Accordingly, the North

American values were applied here with caution as a

first step in assessing pollution in the Caspian Sea. Thereare clearly some problems with trying to apply these

criteria in a mineral-rich region, and as discussed below,

in particular with respect to arsenic.

Elemental associations in the sediments of the Cas-

pian Sea were evaluated using tree diagrams (single

linkage, 1-Pearson r, calculated with Statistica 5.5).

Table 2

Elemental concentrations (lg g�1) in Caspian Sea sediments listed by country

Al Ag As Ba Ca Cd Co Cr Cu Fe Hg Li

Azerbaijan

Mean 69,200 0.07 14.7 643 na 0.14 14.9 85.3 31.9 37,100 0.15 52.6

Std Dev 7690 0.02 4.15 262 na 0.03 1.9 11.3 9.6 3800 0.12 9.5

Min 50,000 0.03 8.87 314 na 0.08 11.5 56.4 14.5 29,300 0.05 27.6

Max 81,300 0.12 22.6 1080 na 0.19 18.1 100 57.6 43,500 0.45 63.6

Iran

Mean 60,500 0.07 12.5 406 102,000 0.16 15.9 85.2 34.7 35,500 0.05 40.0

Std Dev 11,400 0.03 3.04 123 40,100 0.03 4.0 15.3 11.9 5950 0.02 6.6

Min 37,500 0.03 6.97 200 60,700 0.10 6.9 59.6 13.2 22,200 0.02 24.0

Max 77,500 0.17 20.1 679 192,000 0.24 24.2 128 50.9 44,000 0.09 52.5

Kazakhstan

Mean 17,100 0.02 4.13 293 146,000 0.05 3.0 31.4 6.4 6730 0.01 8.2

Std Dev 9250 0.01 3.27 186 84,000 0.04 2.1 19.4 8.3 5130 0.01 6.0

Min 1070 0.00 2.13 75 21,500 0.01 0.7 1.9 1.2 1940 <0.01 1.2

Max 45,100 0.06 20.2 1250 344,000 0.25 12.1 103 49.5 28,000 0.04 32.3

Russia

Mean 18,800 0.02 2.97 272 na 0.06 3.8 32.0 8.3 5520 0.02 13.6

Std Dev 8510 0.01 1.95 140 na 0.02 1.8 19.0 5.4 1840 0.01 7.8

Min 2560 0.01 0.42 70 na 0.02 1.3 2.1 2.5 1600 0.01 3.0

Max 38,300 0.03 6.71 669 na 0.10 7.6 69.3 21.9 9680 0.07 35.3

All data

Mean 39,000 0.04 8.12 396 126,000 0.10 8.8 56.1 19.5 20,000 0.05 26.3

Std Dev 25,000 0.03 5.79 234 70,300 0.06 6.6 31.4 16.0 15,500 0.07 19.3

Min 1070 0.00 0.42 70 21,500 0.01 0.7 1.9 1.2 1600 <0.01 1.2

Max 81,300 0.17 22.6 1250 344,000 0.25 24.2 128 57.6 44,000 0.45 63.6

Mg Mn Ni Pb Sb Se Sn Sr U V Zn

Azerbaijan

Mean na 832 50.1 19.6 0.70 0.30 2.03 487 1.54 114 83.2

Std Dev na 124 8.89 3.88 0.11 0.21 0.40 199 0.60 18.3 13.8

Min na 543 34.5 12.2 0.43 0.10 0.95 269 0.88 73.9 51.1

Max na 971 68.0 28.6 0.88 0.80 2.51 1060 2.96 136 110

Iran

Mean 18,500 815 51.6 18.0 0.74 0.26 2.19 693 2.20 116 85.3

Std Dev 2240 190 11.8 4.17 0.29 0.14 0.86 353 0.55 20.5 17.9

Min 13,900 470 29.4 11.3 0.37 0.10 1.32 362 1.53 76.5 55.9

Max 22,400 1110 67.8 24.6 1.35 0.56 4.78 1710 4.46 145 146

Kazakhstan

Mean 3690 196 10.4 5.75 0.26 –a 0.35 1220 1.13 20.4 11.1

Std Dev 2720 107 10.8 2.36 0.24 –a 0.27 749 1.78 15.9 11.0

Min 701 45 1.80 1.43 0.07 –a 0.01 220 0.32 5.6 1.0

Max 14,500 630 54.8 14.6 1.54 1.67 1.38 3180 11.1 81.2 59.9

Russia

Mean na 200 14.0 4.19 na na na 1970 na 28.7 17.1

Std Dev na 96 7.64 2.15 na na na 1940 na 20.4 12.9

Min na 90 5.42 0.69 <0.01 <0.01 <0.01 356 na 7.3 2.8

Max na 455 34.2 8.03 <0.01 <0.01 <0.01 6240 na 84.5 52.9

All data

Mean 10,400 482 29.8 11.3 0.53 0.32 1.37 1110 1.66 65.7 46.0

Std Dev 7760 338 21.9 7.45 0.33 0.27 1.04 1110 1.39 49.2 37.9

Min 701 45 1.80 0.69 0.07 0.10 0.01 220 0.32 5.6 1.0

Max 22,400 1110 68.0 28.6 1.54 1.67 4.78 6240 11.1 145 146

na¼ not analysed.a Se was determined in only one sample (Station DP-6) from southern Kazakhstan (see Fig. 1 in Tolosa et al., 2003).


Table 3

Sediment quality guidelines (lg g�1––dry) from NOAA (Long et al.,

1995) and Environment Canada (ISQG, 1995)

Element ERLa ERMb ISQGc PELd

As 8.2 70 7.24 41.6

Cd 1.2 9.6 0.7 4.2

Cr 81 370 52.3 160

Cu 34 270 18.7 108

Pb 47 220 30.2 112

Hg 0.15 0.71 0.13 0.7

Ni 21 52

Ag 1 3.7

Zn 124 271

a ERL¼Effect range low (NOAA).b ERM¼Effect range medium (NOAA).c ISQG¼ Interim sediment quality guideline (Environment Can-

ada).d PEL¼Probable effects level (Environment Canada).

Linkage Distance

SRCAR

BA HG AG AS CD CU CR

LI PB MN

NI CO ZN V

FE AL

%_FINES TOC

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

A

Linkage Distance

SR CA

CAR U

BA AG HG SN SB CD AS CU CR PB MN MG

LI CO NI

ZN V

FE AL

%_FINES TOC

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

B

Fig. 6. Tree diagrams (single linkage, 1-Pearson r) illustrating ele-

mental associations in the sediments of the Caspian Sea. (A) 20 vari-

ables from 102 sites; (B) 25 variables, including Ca, Mg, Sb, Sn and U

from only 61 sites.


Ca, Mg and U were not analysed in samples from

Azerbaijan and Russia. Also, Sb and Sn were always

below the limits of detection in the data from Russia (i.e.

<0.30 and <10 lg g�1, respectively). Missing data cre-

ates problems with this analysis and for that reason two

scenarios were assessed. The first case maximises the

number of stations considered by ignoring data for Ca,

Mg, Sb, Sn and U. The analysis was based on 20 vari-ables at 102 stations (Fig. 6A). This diagram illustrates

the notable importance of Al, which influences the dis-

tribution of most of the elements investigated. A cluster

of elements (Al, Fe, V, Zn, Co, Ni, Mn, Cr, Li, Pb, Cu,

Cd, As, Ag) is associated with the fine-grained material

and can be considered as terrigenous in origin. Sr is

associated with carbonate, but otherwise carbonate ex-

erts little affect on elemental composition of the sedi-ments. Similarly, TOC seems not to be a determining

factor of importance. Disparate behaviour is evident for

Hg and Ba, suggesting that these elements are influenced

by sources other than clay minerals and carbonates. The

second scenario maximises the number of analytes taken

into account and consequently 25 variables were con-

sidered but only for 61 sites (Fig. 6B). Ca, not surpris-

ingly, is influenced by the carbonate content. Mg,together with Sb and Sn, behave as terrigenous com-

ponents. However, U displays disparate behaviour, as

noted above for Ba and Hg. Mercury is the only element

that seemingly displays different character in the two

diagrams. In the second scenario, Hg is apparently more

closely associated with the terrigenous elements. How-

ever, this data set has eliminated all data from Azer-

baijan, which includes the most mercury-contaminatedlocations in the Caspian Sea.

3.2. Arsenic, chromium and nickel

Arsenic, chromium and nickel displayed some similar

characteristics in the data reported here. The concen-

trations found reflected terrigenous input (Fig. 6A),

however, the levels of these three elements were often

quite high and exceeded sediment toxicity guideline

values. Arsenic tended to be present at much higher

concentrations in the central and southern regions

compared to the northern Caspian Sea (Table 2). Twosites in the Kazakhstan sector of the northern Caspian

also showed elevated As levels (10.2 and 20.2 lg g�1).

The generally low amounts measured in the Russian

sector (2.97± 1.95 lg g�1) agree well with the mean As

content of only 4.1 lg g�1 for sediments in the Volga

delta (Winkels et al., 1998). Similarly, there is agreement

with As levels in sediments found off California, having

a range of 1.6–13.8 and a mean concentration of 5.1lg g�1 (Schiff and Weisberg, 1999). The ERL value for

As of 8.2 lg g�1 (Long et al., 1995) was exceeded

throughout Iran and Azerbaijan. However, this value

seems to be too low given that uncontaminated coastal

sediments generally have concentrations in the range of

5–15 lg g�1 (Neff, 1997). The elevated concentrations of

As reported here (�20 lg g�1) are comparable to those

observed in the surface sediments of the Gulf of Finland

Fig. 7. The distribution of chromium (lg g�1) in coastal sediments of the Caspian Sea.


(Vallius and Lehto, 1998). For comparison, extremely

As-contaminated sediments in the North Sea off the

English coast have concentrations reaching 137 lg g�1

(Whalley et al., 1999).

Chromium (Fig. 7) exhibited much higher concen-

trations in the central and southern regions compared to

the northern Caspian Sea. The Cr level exceeded the

ERL value of 81 lg g1 (Long et al., 1995) at most lo-

cations in Azerbaijan and Iran. The maximum concen-

tration of 128 lg g�1 was found in Iran. In the north, the

influence of the Ural River as a source of Cr was obvi-ous and a local hot spot of 103 lg g�1 was detected.

Overall, the elevated concentrations of Cr stem from its

high natural background in the region. Concentrations

of Cr >100 lg g�1 have been reported for many parts of

the Caspian Sea (Krilov, 1987). The Caspian region is

mineral-rich and several countries, most notably Ka-

zakhstan, are important producers of chromium. Thus,

mining and mineral processing activities probably ac-

count for the hot spot at the mouth of the Ural River.

Overall, the distribution pattern manifest here demon-strates the influence that grain size has on determining

the metal content. Thus, the elevated Cr concentrations

in Azerbaijan and Iran reflect the deposition of the clay

mineral fractions in the sedimentary material. Cr does

not accumulate in the northern sector, where the sedi-

ments are largely coarse-grained.

The distribution of Ni in the Caspian Sea was similar

to that of Cr, reflecting the high natural background dueto mineralisation. Ni displayed exceptionally high con-

centrations in sediments throughout the central and

southern Caspian Sea. The ERL of 21 lg g�1 was always

exceeded and Ni concentrations were higher than the

ERM value of 52 lg g�1 (Long et al., 1995) at several

sites. These results are broadly in accord with previous

studies reporting concentrations of Ni as high as 100

Fig. 8. The distribution of copper (lg g�1) in coastal sediments of the Caspian Sea.


lg g�1, but rarely <21 lg g�1 (Krilov, 1987). The highest

concentrations of Ni recorded here, 64.8 and 68.0

lg g�1, were found near the mouth of the Kura River,but the Ural River influence was also evident with a

local hot spot of 54.8 lg g1. The elevated Ni levels re-

flected a high natural background, but could be aug-

mented though mining activities as was evident for Cr.

3.3. Copper and zinc

The distribution of copper in the sediments (Fig. 8)was quite similar to that shown for chromium. Although

one hot spot of 49.5 lg g�1 was observed off southern

Kazakhstan, the concentrations were much lower in the

northern Caspian Sea than in the central and southern

parts. The levels found in the north agreed well with

limited data sets for the Volga Delta (Winkels et al.,

1998) and the northeast Caspian Sea (Moore et al.,

2003). In contrast, the Cu content exceeded the ERL

value of 34 lg g�1 (Long et al., 1995) at several locations

in Azerbaijan and Iran. The distribution indicates thatthe Kura River is an important source of Cu locally.

This localised contamination may be derived from

mining activities in the catchment area (Dumont, 1995).

The distribution of zinc was similar to that for fine-

grained material, again reflecting the importance of

terrigenous sources. However, one important hot spot

was obvious in Iran where the concentration of 148

lg g�1 exceeded the Canadian ISQG value of 124 lg g�1

(ISQG, 1995). This site was located near the mouth of

the Sefidrood River, the catchment region of which

contains zinc mines and the zinc smelter at Zanjan. It is

noteworthy that flocculation studies using Iranian river

water and Caspian Sea waters (Karbassi and Nadjaf-

pour, 1996) significantly removed dissolved metals from

solution: Cu (74%), Pb (61%) and Zn (34%).

Fig. 9. The distribution of cadmium (lg g�1) in coastal sediments of the Caspian Sea.


3.4. Cadmium, lead, silver and vanadium

These four elements also have a terrigenous origin(Fig. 6A), which explains the tendency for the metals to

exhibit somewhat higher concentrations in Azerbaijan

and Iran compared with Russia and Kazakhstan. An-

thropogenic inputs have not been sufficiently high to

cause pollution. The cadmium concentration for all sites

in the Caspian Sea is shown in Fig. 9. Although the Cd

levels were higher in the central and southern part of the

Caspian Sea compared to the northern sector, concen-trations never exceeded the ERL value of 1.2 lg g�1

(Long et al., 1995). Similarly, the lead concentrations

were not very high for the sites investigated in the

Caspian Sea. The maximum concentration of 28.6

lg g�1 was found just south of Baku Bay, but the Pb

levels never exceeded the ERL value of 47 lg g�1.

Concentrations of Pb> 40 lg g�1 reported for deep

sediments in the southeast Caspian Sea (Krilov, 1987)

were not observed in the present study that was re-

stricted to much shallower depths.Considering the silver content of sediments, no par-

ticular pattern was obvious and the levels never ex-

ceeded the ERL value of 1 lg g�1 (Long et al., 1995).

The maximum concentration of 0.17 lg g�1 was ob-

served in Iran, near the border with Azerbaijan. Con-

sidering the Azeiri sector, the samples from just south

of Baku Bay appeared to contain a slightly elevated

concentration of Ag. However, the levels were notstatistically different from those at other locations in

Azerbaijan. The distribution of vanadium (data not

shown) in the sediments of the Caspian Sea closely

mimicked that of aluminium. Accordingly, relatively

high concentrations were found along the coast of

Azerbaijan and Iran, where fine-grained material has

been deposited.

y = 0.0053x + 186.52R2 = 0.3215

0

200

400

600

800

1000

1200

1400

0 10000 20000 30000 40000 50000 60000 70000 80000 90000

Al ( g g-1)

Ba (

g g

-1)

µ

µ

Fig. 11. Ba versus Al concentrations (lg g�1) in coastal sediments of the Caspian Sea.

Fig. 10. The distribution of barium (lg g�1) in coastal sediments of the Caspian Sea.


Fig. 12. The distribution of mercury (lg g�1) in coastal sediments of the Caspian Sea.


3.5. Barium, mercury and uranium

Ba, Hg and U are very poorly associated with the Al

concentration and the percentage of fine-grained mate-rial, and even less so with respect to the carbonate

content of the sediments (Fig. 6). Thus, the sources of

these elements must be influenced by contributions other

than the main terrigenous and biogenic inputs.

The distribution of barium in Caspian Sea sediments

is illustrated in Fig. 10. There were several sites in the

central Caspian with anomalously high levels of Ba rel-

ative to other locations. The highest concentrations inKazakhstan (1250 lg g�1) and Turkmenistan (1110

lg g�1) exceeded those found in the coastal region of

Azerbaijan. Overall, the barium content showed no re-

lationship to the percentage of fine-grained material or

the Al concentration (Fig. 2). However, the relationship

of Ba with Al shows some interesting features. Most of

the data for Ba trended reasonably well with the Al

content, but there were several outliers with Ba concen-

trations of two to three times those expected based on the

Al concentration (Fig. 11). Barite is often used in drillingmud (UNEP, 1986; Hartley, 1996) and these elevated

levels may reflect such a source. Enhanced Ba concen-

trations in sediments due to offshore oil drilling activities

have been reported off south-east Brazil (Rezende et al.,

2002). Sub-surface maxima for Ba in Skagerrak sedi-

ments date to the late 1960s, coincident with the start of

oil exploration in the adjacent North Sea (Lepland et al.,

2000). As much as 35,000 km 3 of the shelf of the north-western Black Sea was affected by Romanian and

Ukrainian offshore oil drilling activities and, as observed

in the Caspian Sea, Ba concentrations sometimes ex-

ceeded 1000 lg g�1 (Secrieru and Secrieru, 2002). It is

noted that barium is not an element of concern with re-

spect to environmental toxicity (UNEP, 1986).

Fig. 13. The distribution of uranium (lg g�1) in coastal sediments of the Caspian Sea.


With respect to mercury (Fig. 12), concentrations

were low in the northern Caspian and southeastern

Caspian where sediments were relatively coarse or

composed mostly of carbonates. Mercury levels werenotably high at a number of sites in Azerbaijan, ex-

ceeding the ERL value of 0.15 lg g�1 (Long et al., 1995).

In particular, the sediments from just south of Baku Bay

were affected by anthropogenic inputs, with a maximum

concentration of 0.45 lg g�1 (Table 2). Mercury con-

centrations in other polluted environments can be much

higher. The Gulf of Trieste is exceedingly polluted due

to historic cinnabar mining in the catchment, with totalHg ranging from 0.064 to 30.38 lg g�1 and averaging

5.04 lg g�1 (Covelli et al., 2001). Surface sediments from

the Yatsushiro Sea off Japan had maximum Hg con-

centrations in the range 0.086–3.46 lg g�1, with the

highest values found in Minamata Bay near the Mina-

mata River, the sources of the pollution (Tomiyasu

et al., 2000). Outside Azerbaijan, the mercury concen-

trations found in the Caspian Sea were usually low and

reflected background levels (Table 2). Estimated fromsubsurface concentrations in sediments, baseline Hg

levels in San Francisco Bay were 0.06 ± 0.01 lg g�1

(Hornberger et al., 1999) and 0.059± 0.013 lg g�1 in the

Yatsushiro Sea (Tomiyasu et al., 2000). Mercury was

not detected, i.e. <0.1 lg g�1, in sediments from the

Volga delta (Winkels et al., 1998).

The Caspian Sea sediments generally contained <5

lg g�1 of uranium and many of the sediments had <1lg g�1. Such data are consistent with the crustal abun-

dance of 1.7 lg g�1 (Wedepohl, 1995). The highest

concentrations of uranium, 11.1 and 6.2 lg g�1, were

observed at two deep sites in the central eastern Caspian

(Fig. 13). Kazakhstan has rich resources of uranium and

Table 4

Uranium concentrations and isotope ratios (235U:238U) in some Caspian Sea sediments

Country Samplea Latitude Longitude U (mgkg�1) 235U:238U Standard

deviation

Relative

standard

deviation (%)

Natural U std 7.12E)03 2.39E)05 0.34

Iran C4 37�30.9040 49�55.5550 1.91 7.24E)03 1.63E)05 0.23

Iran IS6-3 36�50.5880 51�03.2060 2.60 7.20E)03 2.38E)05 0.33

Iran D8 36�55.6970 53�13.7490 2.01 7.21E)03 1.76E)05 0.24

Iran DP1A 37�52.9470 49�26.1390 4.46 7.13E)03 3.1E)05 0.44

Kazakhstan IS11-2 45�050360050�3004200

0.742 6.99E)03 7.57E)05 1.08

Kazakhstan 23 46�110240052�1503600

0.626 7.11E)03 6.78E)05 0.95

Kazakhstan 11 46�230180052�3600000

0.707 7.08E)03 4.74E)05 0.67

Kazakhstan 21 46�180240051�4503600

0.966 7.09E)03 2.25E)05 0.32

Kazakhstan 9 46�330060052�1700000

0.975 7.05E)03 1.11E)04 1.58

Kazakhstan 15 46�170180052�3503000

0.896 7.04E)03 6.20E)05 0.88

Kazakhstan 34-A 45�570060051�4805400

0.368 7.04E)03 2.04E)05 0.29

Kazakhstan 34-B 45�570060051�4805400

0.368 7.11E)03 8.97E)05 1.26

Kazakhstan 20 46�210240051�3803000

1.11 7.07E)03 3.52E)05 0.50

Kazakhstan 45 46�520000051�3500000

1.37 7.19E)03 1.05E)04 1.46

Kazakhstan 30 46�000480052�1002400

0.526 7.14E)03 1.17E)04 1.63

Kazakhstan DP-6 42�15.1170 51�47.4230 11.1 7.19E)03 6.5E)05 0.90

Turkmenistan T3 41�08.5670 52�08.3200 6.19 7.19E)03 7.0E)05 0.98

a Station locations are shown in Fig. 1 of Tolosa et al. (2003).


the commensurate environmental problems associated

with mining and processing of the element (Dahl and

Kuralbayeva, 2001). The city of Aktau on the Caspian

Sea in south Kazakhstan was one of the largest uranium

extracting and processing centres in the Soviet Union.

Lake Koshkar-Ata, 5 km from Aktau, has long served

as a uranium waste disposal site and could also be an

anthropogenic source of uranium for the Caspian Sea.Although the highest U concentrations reported here are

to the south of Aktau, the isotopic signature of these hot

spots does not differ from other samples within the

Caspian Sea (Table 4).

4. Conclusions

Calcium carbonate of biogenic and hydrogenous or-

igins is often the main component in Caspian Sea sedi-

ments. However, most metals are strongly associated

with aluminium, a good proxy for terrigenous material.

Notable exceptions to this behaviour are barium, mer-

cury and uranium. Some anomalously high concentra-

tions of barium in the central Caspian are probably

from drilling muds used in offshore oil exploration. Al-though mercury concentrations are generally low in the

Caspian Sea sediments, hot spots occur in Azerbaijan,

with notable mercury pollution evident in the vicinity of

Baku Bay. Uranium levels are generally low (<3 lg g�1),

except for sites in the central eastern Caspian Sea.

Several metals (As, Cr and Ni) exhibit concentrations

that are sufficiently high to exceed sediment quality

guidelines. Such metals undoubtedly have high naturalbackground levels in this mineral-rich region. However,

anthropogenic activities, notably mining, may have

further enhanced the metal burdens in the sediments of

the Caspian Sea. This would explain the high chromium

content at the mouth of the Ural River in Kazakhstan.

Similarly, the hot spots for copper and zinc in Azer-

baijan and Iran are likely to result from mining activities

in the respective catchment regions. Some metals (Ag,

Cd and Pb) have relatively low levels that pose no en-vironmental concerns.

Acknowledgements

The IAEA Marine Environment Laboratory operates

under agreement between the International Atomic

Energy Agency and the Government of the Principalityof Monaco. Sediment samples from the coastal zone of

the Caspian Sea were collected as part of the At Sea

Training Programme from October 2000 to September

2001. We thank the crews of the R/V Mammed Sule-

ymanov, Gidrohimik, Issledovatel Kaspiya and Midiya

for the sample collection. This project was carried out

under the auspices of the Caspian Environment Pro-

gramme (CEP), with financial support from UNOPSand UNDP-GEF. Data from the Russian sector were

provided by the ‘‘Typhoon’’ Center for Environmental

Chemistry under contract to the CEP. We thank our

colleagues, especially Tim Turner and Vladimir Vlady-

myrov, at the CEP Programme Co-ordinating Unit for

their encouragement and support. Finally, we thank Ben

Oregioni for the grain size analyses and Juan-Carlos

Miquel for assistance with measurements of TOC andcarbonate content.


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Documents

An assessment of metal contamination in coastal sediments of the Caspian Sea