organotin speciation in bizerte lagoon (tunisia)

www.elsevier.com/locate/scitotenv

Science of the Total Environm

Organotin speciation in Bizerte lagoon (Tunisia)

N. Mzoughia, G. Lespesb,T, M. Bravob, M. Dachraouic, M. Potin-Gautierb

aInstitut National des Sciences et Technologie de la Mer, Laboratoire Milieu Marin, 28 Rue 2 Mars 1934, 2025 Salammbo, TunisiebLaboratoire de Chimie Analytique, UMR 5034, CNRS, LCABIE, Universite de Pau et des Pays de l’Adour,

BP 1155, 64013 Pau Cedex, FrancecLaboratoire de Chimie Analytique et Electrochimie, Faculte des Sciences de Tunis, Tunisie

Received 20 July 2004; accepted 22 December 2004

Available online 10 March 2005

Abstract

For the first time, organotins have been assessed in samples collected from Bizerte lagoon, in Tunisia, during two seasons

(summer and winter). The organotin distribution was studied in marine sediments and mussels tissues of this lagoon. Butyl-,

phenyl- and octyltins were determined using a rapid speciation analytical method based on one-step ethylation/extraction with

sodium tetraethylborate in aqueous phase. Simultaneously to the ethylation, the extraction was performed by either liquid/liquid

extraction (LLE) or head-space solid phase microextraction (HS-SPME). Gas chromatography with pulsed flame photometric

detection (GC-PFPD) was used to perform quantitative determination. The technique has been validated using biological and

sediment reference materials. The different samples from Bizerte lagoon were found to be moderately contaminated, especially

by butyltins. This pollution was attributed to industrial activities, which are very important in this area. Organotins appeared

accumulated in both sediments and mussels, while significant degradations of triorganotins to monosubstituted ones was

observed in water.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Organotin compounds; Bizerte lagoon; Liquid–liquid extraction; Ethylation; Solid phase microextraction (SPME); Gas

chromatography; Pulsed flame photometric detector (PFPD); Sediment; Mussel tissue

1. Introduction

For more than 20 years, speciation of organo-

metallic compounds in environmental samples is an

analytical and environmental challenge because of the

0048-9697/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.scitotenv.2004.12.067

T Corresponding author.

E-mail address: [email protected] (G. Lespes).

species preservation during their determination and

needs of sensitive and accurate monitoring methods.

Organotin compounds have been used in marine

antifouling paints since the mid-1960s, and have

generated great concerns and interest in their environ-

mental fate because their high toxic effects on non-

target marine organisms (Fent, 1996; Hall and

Pinkney, 1985; Alzieu, 1981). These compounds,

especially the tributyltin (TBT), exhibit broad spec-

ent 349 (2005) 211–222

N. Mzoughi et al. / Science of the Total Environment 349 (2005) 211–222212

trum biocidal properties and so have involved con-

siderable research attention. Hence, it is important to

study the chemical speciation of these compounds

especially in sediments and biological tissues, since

they are stored in sediment and bioaccumulated in

living organisms. Mussels are able to filtrate large

volume of water and bioconcentrate metal such a as

mercury and corresponding organometals in their

tissues (Cossa and Claisse, 1999). High organotin

content was also found in mussels from La Spezia

(Italia) (Montigny et al., 1998). For this reason, they

are considered as good bio-indicator organisms to

monitor contamination of the coastal marine environ-

ment (i.e. bmussel watchQ).The analytical method currently used for the

determination of the organotins are based on chroma-

tographic separation coupled to various detection

techniques (Carlier-Pinasseau et al., 1996a,b; Cassi

et al., 2002; Aguerre et al., 2001a). Prior the gas

chromatographic separation, the organometallic spe-

cies must be either sufficiently volatile or, in the case

of ionic organometallic species, make volatile by

derivatisation. The technique commonly used for

derivatisation procedure directly applied to the aque-

ous phase is based on sodium tetraethylborate

(NaBEt4) (Carlier-Pinasseau et al., 1996a).

Simultaneously to the ethylation, extraction is

performed using either liquid–liquid extraction

(LLE) or solid phase microextraction (SPME). This

last technique is simple, solventless and allows the

rapid pre-concentration of trace compounds onto a

fibre from liquid samples or extracts (Flores Menen-

dez et al., 2000; Le Gac et al., 2003; Aguerre et al.,

2003). The SPME device can be used either in direct

(contact with fibre and aqueous medium) or head-

space (HS) mode, allowing a quasi on-line process

from the sample preparation to the analysis. HS-

SPME is well-adapted for the analysis of biological

specimens as interference from high-molecular-mass

components (e.g. proteins) in the matrix is reduced,

yielding cleaner extracts.

The direct SPME procedure followed by GC

with specific detection has been developed in

previous works (Aguerre et al., 2000; Lespes et

al., 1998) for the speciation of butyl- and phenyltins

in various environmental samples. More recently,

HS-SPME has been proposed as a potentially

interesting alternative to direct mode, but was only

applied to a restricted number of samples (Le Gac

et al., 2003).

In the present paper, HS-SPME and LLE have

been compared and applied to environmental analy-

sis, in order to validate the SPME-based method for

organotin monitoring. This work concerns especially

butyl- and phenyltins in sediments and mussel tissue,

which have never been determined by such a method

in such matrices before. The coastal zones are

important considering the ecological and economical

point of view. However, the determination of

organotin compounds in microtidal lagoons is still

less studied. Thus, in this work, the first data

concerning butyl-, phenyl- and octyltin concentra-

tions in surface sediments and mussel tissues from a

microtidal lagoon (Bizerte, Tunisia) are reported.

This lagoon is one of the most economically

important areas in Tunisia. It is subject to intensive

industrial activities. There are four main zones of

anthropogenic influence (Fig. 1): In zone A are

situated oil refineries, food and ceramic industries. In

zone B are located cements, treatment of metals

(copercraft, asbestos) and sprinkling beverage facto-

ries. In zone C are ceramic and metallurgy activities.

In zone D are present metallurgy activities (Fe, Zn,

Cd, Sn, Hg), naval constructions and tire produc-

tions. A previous study has shown that a moderate

but significant contamination by organic compounds

exits (Mzoughi, 2003). Thus, polycyclic aromatic

hydrocarbures (PAH) were found in the sediments of

the northwest of the lagoon (along the channel

connecting it to the sea). The corresponding concen-

tration levels ranged over 0.01–2.5 Ag g�1, lower

than the environmental standard (45 Ag g�1). The

mussels sampled in the north and south of the lagoon

appeared contaminated by various hydrocarbons (n-

alcans, olefins or PAH), with concentrations gener-

ally under 70 Ag g�1 dry tissue. This contamination

was attributed to the oil coming from boats (leading

to the presence of various aromatic and alkylated

compounds) as well as both natural (forest fires) and

anthropogenic combustion (industrial activities).

These different results enhance the significant con-

tribution of the anthropogenic activities on the

general quality of the lagoon. So, the present study

allows the environmental data concerning the Bizerte

lagoon be completed. In order to reach this goal,

attention is given to the possible anthropogenic

LAGOON OF BIZERTE

Mediterranean seaMussel

Sediment

1

2

3

4

5

6

7 8

9

10

11

1213

14

MA

MJ

Water flow

N

W E

S

AB

C

D

D

B zerte

Zarzouna

Menzel A.ErrahmenMenzel Djemil

Tinja

Menzel Bourguiba

F.M.B

Fig. 1. Map of the lagoon of Bizerte with location of the sampling stations and different types of industrial areas (A, B, C and D).

N. Mzoughi et al. / Science of the Total Environment 349 (2005) 211–222 213

sources to the lagoon and seasonal variations of

organotin concentrations.

2. Materials and methods

2.1. Study area

The lagoon of Bizerte is the second largest lagoon in

Tunisia (Fig. 1). The surface area is 128 km2 and the sea

depth is between 3 and 12 m. The lagoon is connected

to the Mediterranean Sea and to the Lake Ichkeul by

straight channels. The exchanges of water between

the Mediterranean and the lake determine the salinity

of the lagoon, which varies between 32.5 and 38.5.

The water temperature is between 10 8C during winter

(wet season) and 29 8C during summer (dry season).

2.2. Sampling and storage

Oxic surface sediments and mussels (Mytilus

galloprovincialis) were collected during two sampling

campaigns (August 1999 and January 2000). Sedi-

ments were sampled in 14 different points (numbered 1

to 14 on the Fig. 1). The first 10–20 cm of surface

sediments (about 1–2 kg) were sampled by using a

grab. These sediments are made up of 100–500 Amsize-ranged sand. Mussels were taken in three stations

(mussel farming, called MA, MJ and FMB) where they

are kept and grow usually. All these samples (sedi-

ments andmussels) were frozen in situ. As soon as their

arrival in the laboratory, the samples were freeze-dried

for 48 h, ground and stored at �20 8C until analysis.

2.3. Experimental

All organotin concentrations reported in this paper

are expressed as the mass of tin (Sn) per mass or

volume unit.

2.3.1. Apparatus

Organotins were determined using a varian 3800 gas

chromatograph (Walnut Creek, CA, USA) equipped

with a pulsed flame photometric detector (PFPD) and a


varian 1079 split/splitless injector temperature pro-

grammable. The separation was carried out on a capil-

lary column (30 m�0.25 mm i.d.) coated with methyl-

silicone (0.25 Am film thickness) (Quadrex, New

Haven, USA). Nitrogen was used as carrier gas. The

following temperature program was necessary to allow

separation of organotin compounds: the column tem-

perature was held at 80 8C for the first minute increased

to 180 8C at the rate of 30 8C/min and then to 270 8C at

10 8C/min. These operating conditions have been

previously validated for a suitable analysis (Carlier-

Pinasseau et al., 1996b; Bancon-Montigny, 2001).

2.3.2. Characteristic of PFPD operation

The PFPD is based on an air/hydrogen flame which

ignites two to four times per second (Amirav and Jing,

1995a,b; Jiang et al., 1996; Amirav and Jing, 1998).

Thus, the time emission profiles are characteristic of

the species involved (Quevauviller et al., 1994). Then,

by adjusting the start and the duration of the detection

according to the profile of the species studied, the

highest selectivity as possible can be obtained. These

particular operating conditions also allow a large-

passband filter can be used at the both wavelengths

(390 and 610 nm, respectively, corresponding to Sn–C

and Sn–H emissions), instead of an interferential filter.

This is particularly interesting considering that the 390

nm wavelength corresponds at once to the most

important Sn–C emission and the main-interfering

sulphur species.

In this work, the detector was operated with 390

and 610 nm optical interchangeable filters (Schott,

Clichy, France) in order to at once check the peak

assignation and obtain satisfactory sensitivity.

2.3.3. Reagents and standards

Methanol and sodium ethanoate were purchased

from Prolabo. Hydrochloric, nitric and ethanoic acids

were obtained from Merck, and isooctane from Fluka.

The deionised water used was 18 MV (Millipore

system).

Sodium tetraethylborate (NaBEt4) was obtained

from Strem Chemicals. The working solution was

made daily by dissolving 0.02 g in 1 ml of deionised

water and stored at +4 8C in the dark.

Glassware was rinsed with deionised water, decon-

taminated overnight in 10% (v/v) nitric acid solution

and then rinsed again.

Organotin standards stock solutions (1000 mg l�1

as tin) monobutyltin trichloride (MBT, 95%), dibu-

tyltin dichloride (DBT, 97%), tributyltin chloride

(TBT, 96%), monophenyltin trichloride (MPhT,

98%), diphenyltin dichloride (DPhT, 96%), triphenyl-

tin chloride (TPhT, 95%), monooctyltin trichloride

(MOcT, z90%), dioctyltin dichloride (DOcT, z90%)

and trioctyltin chloride (TOcT, 100%) were purchased

from Aldrich (Milwaukee, WI, USA). Tripropyltin

chloride (TPrT, 98%) was obtained from Strem

Chemicals. Stock solutions stored at +4 8C in the

dark are stable for 1 year (Lespes et al., 1996).

Working standards were obtained by dilution in

water (weekly for 10 mg l�1 and daily for 100 Ag l�1).

They were also stored in the dark at +4 8C.

2.3.4. Reference material and samples

The validation of the method was performed using

a certified reference material: the BCR 646, sediment

from the Institute for Reference Materials and

Measurements (IRMM-Geel, Belgium) certified for

its butyltin and phenyltin content. Another material,

the T38 Oyster tissue from the European Community,

contains MBT, DBT and TBT. It was used during an

intercomparison exercise. Its contents (results from

the Group of Analytical Chemistry, Universite de Pau

et des Pays de l’Adour) were considered as a

laboratory reference for checking and validating our

present results.

2.4. Analytical procedure

The method used for organotin determination was

adapted according to Bancon-Montigny (2001).

2.4.1. Extraction from the sample

Extraction was performed as follows:

– 1 g of freeze-dried mussels was extracted in 2.5 ml

methanol+12.5 ml 0.1 M HCl in methanol by

ultrasonic stirring for 1 h.

– 0.5 to 2 g sample of freeze-dried sediment were

extracted in 20 ml of glacial ethanoic acid by

mechanical stirring for 12 h.

2.4.2. Derivatisation and analysis

Simultaneously to the ethylation, the extraction

was performed using either classical liquid/liquid


extraction (LLE) or solid phase microextraction

(SPME).

In case of LLE, 0.5 ml to 1 ml of raw extract was

directly introduced into the derivatisation reactor,

ethylation was carried out using NaBEt4 in sodium

ethanoate/ethanoic acid buffer (100 ml, pH=4.8) and

0.5 ml of isooctane. The mixture was shaken at 420

rpm for about 30 min in order to ensure efficient

transport of the ethylated analytes from the solution to

the organic solvent. After a decanting step, 1 Al ofisooctane extract was directly injected into the GC-

PFPD.

In case of SPME, a manual SPME device from

Supelco (Supelco, Saint Quentin Fallavier, France)

was used, with a fibre coated by an apolar carboxen-

polydimethylsiloxane (Carboxen-PDMS) phase of 70

Am thickness. The device was fixed to the top of the

flask such that the fibre can be used either in direct

mode (i.e. continuously into the buffered aqueous

medium) or in headspace (i.e. above the buffered

medium) (Aguerre et al., 2000). The solution was then

shaken horizontally on an elliptic table (420 rpm, 40

min) in order to ensure efficient transport of the

analytes from the solution to the fibre. Measurement

was performed immediately after the sorption process.

The optimised conditions have been determined and

precisely described elsewhere (Lespes et al., 1998;

Aguerre et al., 2001b; Mayer et al., 2000).

2.4.3. Quantitation

Tripropyltin was used as internal standard. The

TPrT-relative chromatographic responses of butyl-,

phenyl- and octyltin were calculated from standard

solutions prepared in deionised water. The internal

standard procedure was then applied to 0.5 to 2 ml of

acidic extract of sediment or biological tissues.

3. Results and discussion

Considering the number of sampling points and

analysed samples, a lot of data concerning each

organotin species were obtained. In order to decrease

this number and enhance the main environmental

tendencies, data were regrouped. Thus, to evaluate the

origin and risk according to the (RnSn(4�n)) toxicity of

organotins, their distribution according to the nature

of the organic group R and degree n of substitution

was considered and evaluated as it follows (Bancon-

Montigny, 2001):

– the sum of all the organotin concentrations (butyl-,

phenyl- and octyltins) noted as the total organotin

concentration (TOC)X

TOC ¼ MBT½ �þ DBT½ �þ TBT½ �þ TeBT½ �ð Þfþ MPhT½ � þ DPhT½ � þ TPhT½ �ð Þþ MOcT½ � þ DOcT½ � þ TOcT½ �ð Þg

– the sum of the concentrations of the compounds

with the same substitution group R:

XR ¼ MRTþ DRTþ TRTþ TeRTð Þ; with R

¼ B;Ph or Oc

This sum allows to get an indication on the

organotin origins (Bancon-Montigny, 2001).

– the sum of the concentrations of the organotins

with the same degree of substitution n:

Xn ¼ BnTþ PhnTþ OcnTð Þ; with n

¼ mono�; di�; tri� or tetraorganotinsThis sum allows to give an indication on the level of

contamination since the toxicity increases with the

degree n of substitution (Bancon-Montigny, 2001).

3.1. Selectivity

The two main potentially interfering elements of

tin in flame photometry are sulphur and phosphorus

(Hill and Smith, 2000). PFPD is presented as more

selective than conventional FPD. Moreover, the

possible use of two different wavelengths associated

with gate delay and gate width of detection was

expected to significantly decrease the potential risk of

interference.

The selectivity was first tested by qualitatively

analysing sediments (reference and from Bizerte

lagoon) with LLE-GC-PFPD, since it is now well-

known that sediment may content sulphur species

(Montigny et al., 1998).

Figs. 2 and 3 (A and B) show the actual possibility

to decrease interferences especially observed in the

samples from Bizerte lagoon, according to the

A

B

2.5 5.0 7.5 10.0 12.5 15.0Minutes

0.0

2.5

5.0

7.5

mVolts

mVolts

MB

TT

PT

MP

hT

TeB

T

DP

hT

TP

hT

DB

T2.5 5.0 7.5 10.0 12.5 15.0

Minutes

0.00

0.25

0.50

0.75

1.00

MB

TT

PT

D

BT

MP

hT

TP

hT

7.5 10.0

U2 : 9.052 minU1 : 4.592 min

U1 : 4.592 min

TeB

T

DP

hT

Fig. 2. Typical chromatograms of a sediment sample (station 2) using: (A) Sn–C filter and (B) Sn–H filter, after LLE.


wavelength used. When Sn–C filter is used (Figs. 2A

and 3A), an unknown peak (U2) occurs at 9.052

min, while this peak is significantly decreased by

using Sn–H filter (see Figs. 2B and 3B). However,

the Sn–H filter does not allow this interference

disappears. But its presence is not a problem since

its retention time is not similar to those of the

organotins of interest.

Another unknown peak (U1) appears at 4.592 min

retention time, very close to DBT one. When the less

selective Sn–C filter is used and U1 is present in

important concentration, the corresponding peak is

particularly high, leading to a significant overlapping

between U1 and DBT peaks, as it can be noticed on

Figs. 2A and 3A. Then, it is a real drawback for the

DBT determination.

These two unknown peaks can be attributed to

sulphur species, as some authors already observed

similar peaks (Amirav and Jing, 1995a,b, 1998; Jiang

et al., 1996; Montigny et al., 1998). Other studies

made in our laboratory (Bravo, personal communica-

tion, 2004) confirm this hypothesis. Elemental sulphur

submitted to acidic extraction and NaBEt4 ethylation

can give ethylated polysulphur compounds, able to be

extracted simultaneously to organotins. Although

sulphur-relative PFPD sensitivity is limited in com-

parison to organotin one, the important amounts of

elemental sulphur present in some environmental

samples such as sediments induce possible interfering

peaks during organotin determination. The present

two examples illustrate this phenomenon and show

the limitations of the PFPD selectivity.

MB

T T

PT

DB

T

MP

hT

TeB

T

DP

hT

TP

hT

U2 : 9.052 min

2.5 5.0 7.5 10.0 12.5 15.0

TB

T

U1 : 4.592 min

MB

TT

PT

DB

T

MP

hT

DP

hT

TP

hT

U2 : 9.052 minU1 : 4.592 min

DP

hT

TeB

T

TB

TM

PhT

TP

TD

BT

MB

T

Minutes

TP

hT

U1 : 4.592 min

A

B

C

TB

TT

eBT

Fig. 3. Typical chromatograms from a sediment sample (station 8) obtained using: (A) LLE and Sn–C filter (B) LLE and Sn–H filter (C) Head

Space SPME and Sn–C filter.


3.2. Efficiency of SPME

Because selectivity is a crucial point in environ-

mental analysis and in order to overcome the

problems due to sulphur interference, the idea was

to increase the selectivity over the whole analytical

method (i.e. from derivatisation to detection). So,

SPME was investigated.

Indeed, the high preconcentration power of this

technique and the quantitative extraction of the

organotins of the fibre used in direct mode lead to

obtain very low limits of detection (LOD), ranged

over 7–500 pg (Sn) L�1 (Aguerre et al., 2000; Lespes

et al., 1998). Unfortunately, strong matrix effects

occur when samples rich in organic matter (OM) as

sediment or biomass are analysed (Aguerre et al.,

2003). They are due to competitive co-extraction

between OM and organotins, involving the organotin

extraction yields decrease dramatically. Quite similar

effects can be noticed when LLE is used (Montigny et

al., 1998).

A recent study has shown the interest of headspace

mode (HS), when applied to the determination of

volatile methyl- and butyltins, and even less volatile

octyl- and phenyltins (Le Gac et al., 2003). However,

it was only applied to some waters and a fish tissue. In

order to evaluate this SPME mode for sediment

analysis, the chromatograms obtained after HS-SPME

and LLE are comparatively presented on Fig. 3A and

C. For the both chromatograms, the least-selective

Sn–C filter was used. As it was noticed previously,

two unknown peaks are present after LLE. However,


by using HS-SPME, it can be observed that the U2

peak disappears, while the resolution between U1 and

DBT peaks is improved, leading to a satisfactory

quantitative analysis. So, it seems that HS-SPME can

ensure a relative selectivity since less-volatile sulphur

species present in aqueous phase can not be trans-

ferred to the SPME fibre. In case of organotins, the

ethylated species remain sufficiently volatile to be

sorbed onto the fibre, as demonstrated previously (Le

Gac, 2003). In the same time, the organotin extraction

yields seem less affected by the co-extracted products

originally present after acidic extraction from solid

sample.

3.3. Applications

3.3.1. Reference materials

As a quality insurance procedure, reference materi-

als BCR 646 (certified in butyl- and phenyltins) and

T38 were firstly analysed by GC-PFPD using at once

LLE and HS-SPME. Organotin concentrations

obtained are presented in Table 1.

Concerning butyl- and phenyltins, the certified and

determined concentrations presented in Table 1 are in

good agreement, considering the experimental errors

(standard deviations), even for the least-volatile DPhT

and TPhT. For butyltins in mussel tissue (Table 1), the

whole values (reference and found) correlate as well.

Because octyltins were also preliminary detected in

samples, sediments were spiked in these compounds

in order to check the analytical reliability. The results

obtained show a satisfactory correlation between

spiked and determined values.

These results confirm the interest and possibility of

HS-SPME for environmental analysis, especially in

Table 1

Concentrations (Ag (Sn) kg�1) of organotins found in (A) BCR 646 and (B

and Sn–H filters

Compounds (A) BCR 646

LLE

(Sn–C)

LLE

(Sn–H)

HS-SPME

(Sn–C)

Certified

values

MBT 392F45 378F38 438F54 411F81

DBT 375F30 366F44 385F40 392F46

TBT 207F13 200F24 204F22 196F33

MPhT 48F2 40F6 38F4 42F11

DPhT 13F4 14F3 9F3 16F3

TPhT 9F3 8F2 6F2 10F4

case of samples containing any potentially interfering

compounds such as hydrocarbonated or sulfur species

(Montigny et al., 1998).

3.3.2. Organotins in surface sediments

The different organotin concentrations obtained

after seasonal samplings are presented in Fig. 4.

The spatial distribution profiles in figures A, B and

C appears similar during summer (a) and winter (b).

This fact is due to important MBT concentrations

comparatively to those of the other species. It can

express at once significant degradations occurring in

the lagoon and direct rejects from urban and industrial

waste waters. In addition, mono- and dibutyl and

octyltins are also detected, coming probably from PVC

tube leaching. However, this contribution remains

limited whatever the season considered, octyltin

concentrations being low, as shown in Fig. 4B. The

trisubstituted organotin concentrations appear gener-

ally significantly higher in winter, remaining however

lower than 40 Ag (Sn) kg�1. Even if these values can

appear relatively low, they are preoccupying consid-

ering the high toxicity of these species for aquatic

ecosystem (WHO, 1990). Moreover, the Bizerte

lagoon is a quite wide open system with large diffusion

and some possible areas of accumulation. Butyltins are

generally mainly preponderant, except in points 4, 9

and 12, in summer and 1 and 7 in winter, where the

three phenyltins are also found. The corresponding

concentrations can be over 50 Ag (Sn) kg�1. These

stations are located in the North West and South of the

lagoon, where cultivated fields are connected to the

lagoon by straight channels. During storms, they drain

rainwater, which can transport agricultural TPhT-based

biocides after soil leaching.

) T 38 after LLE-GC-PFPD and HS-SPME-GC-PFPD, using Sn–C

(B) T 38

LLE

(Sn–C)

LLE

(Sn–H)

HS-SPME

(Sn–C)

Laboratory

reference values

195F21 209F11 220F15 226F22

32F5 29F4 27F4 25F2

252F7 240F8 227F10 223F2

– – – –

– – – –

– – – –

(a) (b)

0

50

100

150

200

Stations

Con

cent

rati

ons

Total ButyltinsTotal PhényltinsTotal Octyltins

0

50

100

150

200

250

1 2 3 4 5 6 7 8 9 10 11 12 13 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 2 3 4 5 6 7 8 9 10 11 12 13 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14Stations

Con

cent

rati

ons

0

50

100

150

200

250

Stations

Con

cent

rati

ons

0

50

100

150

200

Stations

Con

cent

rati

ons

Total Butyltins

total Phényltins

Total Octyltins

0

40

80

120

160

1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 2 3 4 5 6 7 8 9 10 11 12 13 14Stations

Con

cent

rati

ons

mono -di-tri -

0

40

80

120

160

Stations

Con

cent

rati

ons

mono -di-tri -

A

B

C

Fig. 4. Concentrations of organotins (in Ag (Sn) kg�1) in sediments sampled in (a) summer and (b) winter, respectively: (A) total organotin

concentrations, (B) total butyl-, total phenyl- and total octyltins, (C) total mono-, total di- and total tri- (butyl-, phenyl- and octyltins).


In summer, the stations 5, 6 and 7 appear as the

most contaminated, with total organotin concentra-

tions around 200 Ag (Sn) kg�1. Due to the location of

these four sampling points, the contamination can be

connected to naval activities of area D, where usually

antifouling paints are used. In these points, TBT is

mainly present, confirming the origin of the contam-

ination. Considering the water flow, it is interesting to

notice the organotin diffusion to stations 8, 9, 10 and

11, where a concentration gradient appears. In point 8

especially, quite high concentrations of MBT and TBT

were found. It seems that, in this precise location,

butyltins can be accumulated with slower biodegra-

dation effects, even in summer.

Quite high contamination also appears in a second

group of sampling points (stations 12, 13 and 14).

With regard to the water flow, this contamination can

be connected to activities from areas C and possibly

D. Relatively high trisubstituted concentrations were

also found in point 14.

The Bizerte sediments can be generally considered

as moderately polluted compared to harbour ones

(Moore et al., 1992; Carlier-Pinasseau, 1996). The

comparison of these results with other ones from


similar microtidal lagoons is difficult, due to the lack

of data. The butyltin concentrations are comparable to

those found in a Rhine lagoon in Germany (150 Ag(Sn) kg�1) (Schebek and Andreae, 1991). They are

much lower than those reported from other areas in

Swiss (Geneva), Canada (Ontario) or United King-

dom (Hamble), where concentrations are respectively

1500, 800 and 4300 Ag (Sn) kg�1 (WHO, 1990;

Becker et al., 1992).

3.3.3. Organotins in mussel tissues

Bivalve molluscs, including mussels, are known to

be the best organisms indicator of pollution since they

are (1) filter-feeders and therefore exposed to large

volumes of seawater; (2) immobile and therefore ex-

posed to local contamination only. So they have been

used in many national and international programs.

Among these organisms, mussels are world-wide

used as sentinel to rapidly assess the level of the

contamination of the marine environment for a large

number of pollutants.

Fig. 5(a) and (b) show the organotin concentrations

(Ag (Sn) kg�1 in dry weight) found in the mussels in

summer and winter, respectively.

0

20

40

60

MA MJ FMBStations

Con

cent

rati

ons

MBTDBTTBT

0

20

40

60

Con

cent

rati

ons

0

20

40

60

80

100

120

140

MA MJ FMB

Stations

Con

cent

rati

ons

0

20

40

60

80

100

120

140

Con

cent

rati

ons

(a)A

B

Fig. 5. Organotin concentration (in Ag (Sn) kg�1 dry weight) in mussels in

TBT).

The mean concentrations of total organotin com-

pounds are highly variable, ranging from 55F7 to

122F12 Ag (Sn) kg�1 during the two seasons. The

highest winter values (over 100 Ag (Sn) kg�1) were

found in stations MA (North) and FMB (South) and

the lowest one was obtained in FMB station during

summer.

Butyltins were systematically and mainly found.

MPhT was also detected in mussels from stations MA

(during summer and winter) and MJ (in summer

only). However, the corresponding concentrations

remain very low (below 13 Ag (Sn) kg�1). Octyltins

were never detected in any station. The examination

of the butyltin speciation shows that MBT is

predominant in all the sampling points, especially

during summer, while MBT and TBT concentrations

are very close during winter in stations MJ and FMB.

DBT remains in low concentration compared to MBT

and TBT ones, which it was already noticed by other

authors (Carlier-Pinasseau et al., 1996a; Carlier-

Pinasseau, 1996) and attributed to a rapid degradation

kinetics of DBT to MBT by microorganisms. The

successive desalkylations induced were also reported

previously (Ceulemans et al., 1994). Considering all

MA MJ FMBStations

MBTDBTTBT

MA MJ FMB

Stations

(b)

(a) summer and (b) winter, (A) total, (B) butyltins (MBT, DBT and


these data, and also the fact that total organotin

concentrations were significantly higher during win-

ter, it is probable that degradations occur mainly in

water, mussels simply accumulating the organotins.

The mussel contamination by organotins can be

connected to anthropogenic (industrial areas C and D)

and geographic factors again. Thus, the highest

concentrations were found mainly in the Northwest

and Southwest of the lagoon, near sediment sampling

points 13–14 and 8–9, respectively, point 8 being

previously identified as an area where MBT and TBT

are accumulated. Agriculture seems to have very

limited effects on mussel contamination probably

because of low rainfall level and strong organotin

sorption onto soil particles (IPCS, 1999a,b; May et al.,

1993; Inaba et al., 1995; Morabito, 1995; Keijzer and

Loch, 1994).

The mussel contamination level appears rather low

compared to those found in other coastal living

organisms, in other places. Especially in two Euro-

pean sites, La Spezzia (Italia) and Zurich (Swiss),

butyl- and phenyltins in mussels were found to be

over 2500–11,890 and 1600–1930 Ag (Sn) kg�1,

respectively (Carlier-Pinasseau et al., 1996b). How-

ever, the comparison between these data remains

critical since weather conditions and human activities

are completely different.

4. Conclusion

For the first time, the level of contamination of the

Bizerte lagoon has been assessed, by using both LLE

and HS-SPME coupled to GC-PFPD. Even if some

matrix effects can remain, partly due to some lack of

selectivity of the PFPD, the speciation analytical

method based on these coupled tools has been

validated and appears suitable for environmental

monitoring, especially the HS-SPME.

In Bizerte lagoon, Tunisian area economically

very important, sediments and mussels appear

moderately polluted, mainly by butyltins. These

species come from industrial activities partly con-

nected to antifouling paints. Octyl- and phenyltins

were also found, these last species coming probably

from agricultural products. The most toxic trisub-

stituted compounds appear significantly degraded

into monosubstituted species, probably mainly in

water. However, the biodegradation seems relatively

slow and organotin can be accumulated in oxic

surface sediment (especially in the South of the

lagoon) and in mussels.

Because Tunisia has a long Mediterranean coast of

crucial economical interest, it is obvious that a larger

spatio-temporal organotin monitoring has to be

planned, including harbour areas. This is the condition

to have an evaluation of the actual organotin

contamination of the Tunisian marine environment.

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