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Hydrobiologia

, Volume 714, Issue 1, pp 13–24 | Cite as

Imposex and butyltin burden in Bolinus brandaris (Mollusca, Gastropoda) and sediment from the Tunisian coast

  • Sami Abidli
  • Youssef Lahbib
  • Pablo Rodríguez González
  • José Ignacio García Alonso
  • Najoua Trigui El Menif
Primary Research Paper

Abstract

The present study aimed at analyzing the imposex incidence and the presence of butyltins namely tributyltin (TBT) with its di- and mono-substituted metabolites in Bolinus brandaris whole tissues and in surface sediments at seven sites from the Tunisian coast during one campaign in May 2010. Butyltin levels were evaluated using isotope dilution GC–MS. Except the population collected from Zarat site, imposex was found in snails from the remained six sites with a maximal incidence and sterility (closure of the vaginal opening) registered in Carrier bay. Both imposex indices VDSI and RPLI showed a positive correlation with tissue concentrations of TBT. Total butyltin concentrations in sediments were higher in sites located in the vicinity of shipping areas with levels of TBT high enough to cause environmental concern if there is no legislative restriction and enforcement for the sale and use of these chemicals in Tunisia. These results further confirmed that B. brandaris is a good bioindicator of butyltin pollution in the studied areas. In addition, this study provided recent and new data on sediment butyltin concentrations that could serve for long-term monitoring of TBT pollution in Tunisia and the Mediterranean Sea.

Keywords

Organotins Bolinus brandaris Imposex Bioindicators Sediments Tunisia 

Introduction

Tin is one of the most important metals necessary for humans and animals to maintain life functions. Its toxicity toward live organisms is low, however, the majority of organic compounds of tin are poisonous (Kimbrough, 1976; Hoch, 2001). Organotins, like tributyltin (TBT) and its derivatives, have been widely used for several purposes, such as polyvinyl chloride (PVC) stabilizers, wood preserving agents, fungicides in agricultural activities, catalysts in the production of polyurethane foams and as antifouling agents in ship and aquaculture facilities paints (Fent, 1996; Terlizzi et al., 2001). TBT is environmentally degraded by debutylation to form dibutyltin (DBT), monobutyltin (MBT), and ultimately inorganic tin. The rate of debutylation in sediments is dependent upon microbial activity (Lee et al., 1989). The half-life of TBT in sediments has been shown to range from 6 months to 8.7 years (Maguire & Katz, 1985; Stang & Seligman, 1986; Smith, 1996). The debutylation of TBT in marine gastropods is mediated by cytochrome P450 enzymes (Fent, 1996). However, Gooding & LeBlanc (2001) showed that P450-mediated detoxification/elimination reactions appear to be restricted in molluscs resulting in limited biotransformation of TBT (Bryan et al., 1993) and increased accumulation which may contribute to the high sensitivity of gastropods to TBT toxicity. In fact, TBT is known to cause genital disorder in female marine prosobranch snails at a concentration of just a few nanograms per liter (Gibbs & Bryan, 1986; Abidli et al., 2009a, b). This phenomenon was called imposex (Smith, 1971) as an abbreviation of imposed sexual organs, because male genital organs, such as penis and vas deferens, are imposed upon female individuals. This irreversible syndrome was first reported by Blaber (1970) in British population of the dogwhelk Nucella lapillus. One year later, Smith (1971) noted similar abnormalities in the gastropod Ilyanassa obsoleta collected on the American coast. By the late 1970s, imposex had been recognized in at least 34 marine gastropod species (Jenner, 1979). One decade later, at least 100 species were known to exhibit imposex (Fioroni et al., 1991). Currently, approximately 260 gastropod species are known to be affected by imposex worldwide (Sternberg et al., 2010; Titley-O’Neal et al., 2011) distributed by 28 families and largely dominated by species belonging to Muricidae (76 species) (Shi et al., 2005). In extreme cases, this abnormality caused the disappearance of some populations following female sterility by closure of the vaginal opening or by the fissure of the capsule gland (Trigui El Menif et al., 2006), which leads to population decline or to its local extinction (Bryan et al., 1987). Imposex studies in the Mediterranean Sea have been mainly restricted to populations of the banded murex Hexaplex trunculus (Martoja & Bouquegneau, 1988; Axiak et al., 1995, 2003; El Hamdani et al., 1998; Terlizzi et al., 1998, 1999; Trigui El Menif et al., 2006; Lahbib et al., 2007, 2008a, b, 2009, 2010, 2011a, b; Abidli et al., 2009a). However, in Bolinus brandaris, which has a wide distribution in the Mediterranean Sea and on the adjacent Atlantic coast, from Morocco to Portugal (Poppe & Goto, 1991; Vasconcelos et al., 2008, 2010a, b), studies are limited to few surveys of Oehlmann (1994), Solé et al. (1998), Ramón & Amor (2001) and Chiavarini et al. (2003) in the northern Mediteranean Sea. In the southern Mediterranean Sea, only the studies of Lemghich & Benajiba (2007) in Moroccan coast and Abidli et al. (2009b, 2011, 2012a, b) in northern Tunisian coast were made in this species. Many countries worldwide have banned the application of TBT based paints to small vessels (<25 m) and various studies worldwide have shown a slow decline on TBT contamination (Hoch, 2001; Castro et al., 2012a). However, evidence of recent use of TBT is been reported in areas without any specific restriction on TBT use (Castro & Fillmann, 2012). Díez et al. (2002) showed that present and future restrictions will not immediately remove the TBT and its degradation products (DBT and MBT) from the marine environment since these compounds are persistently retained in the sediments. For this reason, the aims of this study are: (a) monitoring imposex degree in B. brandaris, (b) assessing the level of organotin compounds in sediments and in the soft body of this neogastropod, (c) investigating the relationship between organotin compound concentrations in tissues of B. brandaris and the level of imposex development. This study could be used as baseline data for further biomonitoring studies in these areas and for comparison with other Mediterranean locations.

Materials and methods

Sampling

Surface sediments and specimens of B. brandaris (n ~ 30/site) were sampled in May 2010 from seven sites (old harbor of Tabarka, Carrier Bay, Menzel Abderrahmane, South Lake of Tunis, Tunis Bay, Radès channel, Zarat) along the Tunisian coast at 0.5–20 m depth using fishing nets for gastropods and by scuba diving for the sediment using a manual core (Fig. 1). The stations were mainly differed by the intensity and type of ship traffic and by the percentage of total organic carbon (TOC) (Table 1). At each site, the following parameters were recorded: depth, type of sediments, shipping density, and percentage of total organic carbon (Table 1).
Fig. 1

Map of Tunisia showing the sampling sites of Bolinus brandaris: 1. Old harbor of Tabarka, 2. Carrier Bay, 3. Menzel Abderrahmane, 4. Tunis Bay, 5. Radès Channel, 6. South Lake of Tunis, 7. Zarat

Table 1

Number and type of boats in the studied sites and the percentage of total organic carbon (% TOC) in the sediment

Sampling stations

Old harbor of Tabarka

Carrier Bay

Menzel Abderrahmane

Tunis Bay

Radès Channel

South Lake of Tunis

Zarat

Depth (m)

4

8

7

20

1

0.5

0.5

Type of sediment

Sandy-muddy

Sandy-muddy

Sandy-muddy

Sandy-muddy

Muddy

Sandy-muddy

Sandy-muddy

TOC (%)

nd

0.75–1a

1.5–1.75a

0.8b

2.4c

2.47c

nd

Boats/year

139

492

150

1276

127

125

81

Type of boats

Costal fishing boats, trawlers, sardine boats, Coral boats

Artisanal fishing boats, passenger liners, merchant ships, ferry boats, army boats.

Artisanal fishing boats

Artisanal fishing boats, passenger liners, merchant ships, ferry boats

Coastal fishing boats, trawlers

Fishing boats (trawlers, sardine boats, tuna boats, small artisanal boats)

Small artisanal fishing boats

nd Data not found

aEssid (2008)

bAdded et al. (2003)

cOuertani et al. (2006)

Biological analyses

In the laboratory, individuals were placed in different aquaria for 48 h to allow depuration from adhering particles and gut contents. After thawing, the shell length (SL), including the siphonal canal, was measured to the nearest 0.1 mm using a Vernier caliper, the shell was broken, and the animals were carefully removed and observed under a stereomicroscope. Sexual identification was based on the presence or absence of the vagina and capsule gland. The color of the gonad was also used as a criterion for sexual identification, because the female gonad is pinkish while that of the male is yellowish. In females, the imposex severity was determined under a stereomicroscope using a calibrated eyepiece, through the examination of the area between the penis and the vagina. Imposex development was assessed by calculating the following indices:
  • Imposex incidence or Frequency (I%) = percentage of imposex-affected females in the sample,

  • Female penis average length (FPL),

  • Male penis average length (MPL),

  • Vas deferens sequence index (VDSI) = sum of imposex stages of all females/total number of females in the sample, following Gibbs et al. (1987). VDS stages were determined according to the general scheme proposed by Stroben et al. (1992), as partially modified by Axiak et al. (1995) and Lahbib et al. (2007).

  • Relative penis length index (RPLI) = average length of female penises × 100/average length of male penises, according to Stewart et al. (1992).

Butyltin analyses

Butyltin analyses were performed, following the method of Rodríguez-González et al. (2004, 2005) in sediments and using five males and five females selected from each sampling site after removing the operculum. The upper 2 cm of sediment were recovered and placed in acid-cleaned glass containers, then homogenized in mortar porcelain (100–500 μm size-ranged sand) and stored at −20°C in the dark until analysis. The soft body of each specimen was freeze-dried, grinded, and maintained at −20°C in the dark until analysis. Approximately 150 mg of sample (two replicates) were spiked with a diluted solution of the 119Sn-enriched spike of MBT, DBT, and TBT and 4 ml of a mixture of acetic acid and methanol (3:1) (g/g) were immediately added in 7 ml glass vials with screw cap (Supelco, Bellefonte, PA, USA) for biological tissue and added in centrifuge tubes for sediments. The vials were introduced in a thermostatic bath at 37°C for at least 2 h under mechanical shaking while centrifuge tubes were introduced in a Microwave (Explorer Hybrid, CEM, USA). During the derivatization, 2 ml of acetate buffer to adjust the pH to 5.4, 2 ml of hexane and 300 μl of a 2% w/v sodium tetraethyl borate in 0.2 M NaOH were added to 1 ml of the extract for the ethylation of the organotin compounds. Then, the vials were centrifuged at 3,000 rpm for 5 min to allow a better phase separation. The organic layer was transferred to a 2 ml chromatographic vial with a Pasteur pipette. The hexane phase was evaporated under a gentle stream of argon until nearly dry (a few microliters). Finally, 2 μl of this final volume were injected into the GC–MS system. The analytic instrument was an Agilent Model 6890 N gas chromatograph (Agilent Technologies, Waldbronn, Germany) fitted with a splitless injector and a HP-5MS column (30 m × 250 mm i.d. × 0.25 mm) and equipped with an Agilent Model 5973 Network MSD mass spectrometric detector (Agilent Technologies, Tokyo, Japan). The detection limits in solid matrix (sediment samples, three replicates) were 0.09 ng Sn/g for MBT, 0.03 ng Sn/g for DBT and 0.06 ng Sn/g for TBT. Analysis of a certified reference material (mussel tissue BCR 477, three replicates) using this procedure resulted in the following recoveries: 116.17 ± 2.65% for MBT, 98.13 ± 1.76% for DBT, and 91.43 ± 1.57% for TBT, being in agreement with the certified range. In order to ascertain the chronology of organotin contamination, the butyltin degradation index (BDI) was calculated as follows: BDI = (MBT + DBT)/TBT (Díez et al., 2002).

Statistical analysis

Imposex frequency was compared among samples using the χ 2 test in the software R. Analysis of variance (ANOVA) was performed using the software Statistica 8.0. After testing ANOVA assumptions, statistical significance was evaluated through one way ANOVA. Whenever ANOVA detected significant differences, post-hoc comparisons were made using the Newman–Keuls test. Data that did not fit ANOVA assumptions were tested through the Kruskal–Wallis nonparametric ANOVA. In all statistical analyses, significance level was considered at α = 0.05.

Results

Imposex analysis

The imposex frequency, mean female and male penis lengths, VDSI and RPLI in each sample of gastropods collected in the seven stations are listed in Table 2. Except Zarat where no imposex was found, all the remained stations showed this deformity with different level and degree. The highest imposex indices were found in Carrier bay with 4.54% of females with closure of the vaginal opening (sterility) (Table 2; Fig. 2). Females from the channel of Radès are in the second range but without showing any sign of sterility. In Menzel Abderrahmane and Tunis bay imposex was moderate and similar (χ 2 = 0.00, df = 1, P = 1 for I%), (SNK: df = 1, F = 0.05, P = 0.82 for FPL), (SNK: df = 1, F = 0.12, P = 0.72 for VDL), (Kruskal–Wallis: df = 1, H = 2.38, P = 0.12 for VDSI) and (Kruskal–Wallis: df = 1, H = 0.23, P = 0.62 for RPLI). The least affected populations came from south lake of Tunis and old harbor of Tabarka with respectively an I (%) of 45 and 16.66, a VDSI of 1.25 and 0.32 and RPLI of 2.15 and 0.00.
Table 2

Imposex parameters in each sampling station

Sampling stations

Old harbor of Tabarka

Carrier Bay

Menzel Abderrahmane

Tunis Bay

Radès Channel

South Lake of Tunis

Zarat

No. of ind.

28

30

30

28

28

28

32

No. females

18

23

22

18

18

20

23

I (%)

16.66

100.00

77.27

72.22

88.88

45.00

0.00

FPL (mm)

0.00

3.62 (1.50)

1.75 (1.37)

1.28

2.06 (1.44)

0.28 (0.49)

0.00

MPL (mm)

12.78 (1.22)

15.12 (4.52)

12.24 (2.11)

13.71 (2.32)

13.53 (1.04)

13.21 (1.90)

12.06 (1.26)

VDSI

0.32

4.12

2.86

2.27

3.33

1.25

0.00

RPLI

0.00

25.51

9.59

9.36

15.27

2.15

0.00

Sterility (%)

0

4.54

0

0

0

0

0

Fig. 2

Bolinus brandaris in stage 5 of imposex. CG capsule gland, OT ocular tentacle, OVO closure vaginal opening, P penis, VD vas deferens. Scale bar: 2 mm

Butyltins analyses in B. brandaris

TBT and its degradation products (DBT and MBT) were present in the whole tissues of B. brandaris collected from seven sampling sites (Fig. 3). Data clearly show that contamination detected by chemical analyses parallels the levels of imposex. TBT concentrations were higher in B. brandaris from the Carrier bay (18.77 ± 0.35 ng Sn g−1 dw in female and 9.90 ± 2.49 ng Sn g−1 dw in male) and Radès channel (21.60 ± 0.00 ng Sn g−1 dw in female and 22.7 ± 0.00 ng Sn g−1 dw in male). Both sites are located in areas with intense shipping traffic. In Menzel Abderrahmane station and Tunis bay, no significant differences in TBT concentration were recorded (10.70 ± 2.33/11.10 ± 1.74 ng Sn g−1 dw in female (SNK: df = 1, F = 0.05, P = 0.82) and 13.60 ± 3.53/10.53 ± 3.76 ng Sn g−1 dw in male (SNK: df = 1, F = 1.05, P = 0.36). In old harbor of Tabarka and south lake of Tunis stations, TBT concentrations were lower with, respectively, 4.3 ± 0.14/4.50 ± 0.71 ng Sn g−1 dw in female and 2.55 ± 0.77/6.23 ± 1.06 ng Sn g−1 dw in male. In Zarat station TBT concentration was below detection limit (<DL). Considering the gender, TBT concentrations in tissues of B. brandaris were quite close in both sexes (Fig. 4). TBT in males and females was highly correlated after log transformation, with r coefficient of 0.95 (P < 0.05).
Fig. 3

Butyltin concentrations (ng Sn g−1 dw) (n = 5) in the tissues of female (A) and male (B) B. brandaris

Fig. 4

Plot of tributyltin (TBT, ng Sn g−1 dw) in Bolinus brandaris, males versus females; the broken line reflects equal concentrations

Considering the evolution of TBT concentration in females according to VDSI and RPLI, a positive correlation was found for both indices (r = 0.93, P < 0.05 for VDSI; r = 0.89, P < 0.05 for RPLI, Fig. 5).
Fig. 5

Correlations between vas deferens sequence index (VDSI) and relative penis length index (RPLI) and body burden of tributyltin (TBT)

Butyltins analyses in sediments

Butyltins in sediments were determined in seven sampling sites. The concentrations varied widely depending on the location. Results are shown in Fig. 6. The higher levels were found in Radès channel and in Menzel Abderrahmane sites (Fig. 6) with average levels of 13.95 ng Sn g−1 for MBT, 11.65 ng Sn g−1 DBT, and 9.85 ng Sn g−1 for TBT in the first site and 22.05 ng Sn g−1 for MBT, 10.85 ng Sn g−1 DBT, and 8.40 ng Sn g−1 for TBT in the second site. The lowest concentrations of butyltins were recorded in Zarat and Carrier Bay with respectively values <DL and 1.2 ng Sn g−1 for MBT, <DL and 1.65 ng Sn g−1 for DBT, and <DL and 2.1 ng Sn g−1 for TBT.
Fig. 6

Butyltin concentrations (ng Sn g−1 dw) (n = 5) in the sediment of sampling sites

Discussions

Tunisia occupies a strategic position in the Mediterranean Sea since it opens on the Eastern and Western basins with 1,300 km coastline. Given the high intensity of vessel traffic in local waters, one would expect butyltins contamination to be serious if there is no legislative restriction and enforcement for the sale and use of these chemicals. The current study showed that all areas under the influence of ship or boat traffic presented imposex. Only Zarat population does not show any imposex anomaly in the studied species. However, in the remaining stations, imposex was found at varied levels and degrees. The greater imposex levels were found in the population collected from Carrier bay with imposex frequency of 100% and a sterility of 4.54%. Similar to these results, Lahbib et al. (2009) recorded in H. trunculus collected from Bizerta channel a high imposex frequency of 100% and a sterility of 14.3%. In fact, Carrier bay has a high shipping traffic (492 artisanal fishing boats, passenger liners, merchant ships, ferry boats, army boats) and it is a station situated in the channel of Bizerta which is characterized by a high shipping traffic [505 fishing boats/year (trawlers, sardine boats, crawfish boats, small artisanal boats) and 557 commercial boats, oil tankers, gas tankers, passengers, containers] and navy boats/year (Lahbib et al., 2009).

The relationship between TBT concentration and the intensity of imposex (VDSI and RPLI) was correlated across stations. Similar correlations have been also reported for this species collected from six stations along the Catalan coast. In fact, Solé et al. (1998) showed that FPL and RPLI fluctuated similarly and a correlation between these markers and TBT body burden was noticed in B. brandaris. In other gastropod species, significant positive correlations between imposex indices (VDSI and RPLI) and TBT concentrations in females of Hinia reticulata and H. trunculus were reported (Stroben et al., 1992; Barreiro et al., 2001; Lahbib et al., 2009). These field correlations provide further evidence of the cause-effect relationship established from laboratory experiments. In fact imposex in B. brandaris is caused by TBT, after exposure (Santos et al., 2006; Abidli et al., 2012b).

Present results confirm also the findings by Bryan et al. (1993), Couceiro et al. (2009) and Abidli et al. (2011) on the absence of TBT significant bioaccumulation differences between sexes in gastropods as N. reticulatus and B. brandaris. However, Lahbib et al. (2009) showed that most females of H. trunculus collected along the Tunisian coast have higher TBT concentration than males. According to Bryan et al. (1987), TBT accumulation in females changes according to the physiological state of the organism, namely with the accumulation of body lipids related to the spawning season.

The comparison of imposex data and TBT concentration for B. brandaris from the Tunis bay and Menzel Abderrahmane stations with previous data reported in the same species and stations, showed that imposex incidence and TBT contamination did not change significantly between 2007 (TBT: 12.65 ± 1.48 ng Sn g−1 dw in female and 15.21 ± 1.13 ng Sn g−1 dw in male in Menzel Abderrahmane station and: 10.71 ± 1.26 ng Sn g−1 dw in female and 11.65 ± 1.63 ng Sn g−1 dw in male in Tunis bay station; Abidli et al., 2011) and 2010. This result is possibly explained by the slow rhythm of degradation of TBT in B. brandaris or by the continuous use of TBT in antifouling paints covering local boats.

To get an idea on the sensitivity of B. brandaris to organotins pollution, the comparison of the present data with those revealed by Lahbib et al. (2011a) in H. trunculus showed that H. trunculus is more sensitive to organotin pollution than B. brandaris. Indeed, in the Bizerta channel and Menzel Abderrahmane stations and in the same period, imposex indices were higher in H. trunculus except for I (%), which were similar (100%) (Lahbib et al., 2011a). This result was also shown by Abidli et al. (2009b) following an annual survey of the imposex incidence in H. trunculus and B. brandaris collected from the bay of Tunis. Regarding TBT accumulation, the comparison of our results with those of Lahbib et al. (2011a) showed that B. brandaris accumulates more TBT than H. trunculus collected from Bizerta channel (6.1 ± 0.3 ng Sn g−1 dw in female H. trunculus and 18.77 ± 0.35 ng Sn g−1 dw in female B. brandaris). From these results, we suggest that H. trunculus is likely to be more sensitive to TBT exposure than B. brandaris.

Legislation to ban TBT in ships’ antifouling paints was agreed by the adoption of International Convention on the Control of Harmful Anti-Fouling Systems on Ships at International Maritime Organisation in 2001 (the AFS Convention). Under this convention, the last date for the application of organotin paints on ships was 1 January 2003. The total phase-out of organotin antifouling coatings have been completed by 1 January 2008. The AFS convention entered into force on 17 September 2008. Many countries have signed this convention but Tunisia does not appear in the list and when the restrictions on the use of TBT are not exist, this has continuing implications for local and global marine fauna including food resources, particularly in nations where economies are developing as Tunisia.

Butyltin concentrations in sediments found in this study show that, with the exception of Carrier bay, higher levels were observed in areas of dense shipping traffic and imposex severity. Nevertheless, factors other than shipping and stratification of the water column, may affect the accumulation of butyltins in sediments. For instance, the level of organotins in sediments collected from Menzel Abderrahmane were higher than those found in the other high shipping density areas sampled in this study such as Tunis bay and Carrier bay. Some reasons can be cited to explain this fact, such as the strong upwelling currents in Carrier bay and Tunis bay (during the sampling period) that can reduce the butyltins accumulation in the sediment of this area and also, we registered that TBT levels in sediments have been shown to be related to the organic content. In fact, the percentage of total organic carbon was lower in these two sites and it’s known that TBT adsorbs to organic material (Fent, 1996). In the same context, Kim et al. (2011) showed that water exchange rate and sedimentation process in the study area, and particle size and organic carbon contents in sediment may also influence the accumulation of TBT in sediment. It has been reported that TBT is highly adsorbed to fine textured sediment with abundant organic carbon (Burton et al., 2004) thus minimizing the bioavailable fraction amenable to degradation. The correlation between % TOC and TBT concentration in some sites of the present study is not significant (P > 0.05). In the same context, Shim et al. (1999) and Castro et al. (2012b) demonstrated little or no correlations for these parameters in surface sediments from an enclosed bay system in Korea and along the Ecuadorian coastal shore. Contradictory results have been reported between % TOC and BT by Pinochet et al. (2009) in marine sediments from San Vicente bay (Chile). These contradictory results can be explained by the physicochemical sediment complexity, such as different composition of organic matter, relative adsorbability on inorganic particles, and the existence of biological activity in the sediment layers (Castro et al., 2012b).

An organotin monitoring has been done in sediments of Bizerta Lagoon, during summer 1999 and winter 2000, showed a TBT concentration varying between 4 ng Sn g−1 dw in Carrier bay and 14 ng Sn g−1 dw in Menzel Abderrahmane (Mzoughi et al., 2005). The comparison of the TBT levels in sediment from the present study to that of Mzoughi et al. (2005) revealed low decrease in this pollutant in sediment. Compared with other Mediterranean sites, Tunisian coast can be considered lowly contaminated by butyltins if compared with TBT levels that can reach up to 4,702 ng Sn g−1 dw in sediments from Barcelona harbor (Spain) (Díez et al., 2006), and 820 ng Sn g−1 in Theoule harbor (France) (Wafo et al., 2004). On contrary, along the North-Western Sicilian coasts (Italy), Chiavarini et al. (2003) showed that TBT concentrations were lower than the detection limit of the used analytical method (1 ng Sn g−1 dw). Compared with Pacific Ocean sites, Tunisian coast is lowly polluted by TBT if compared with values registered in surface sediment of Ecuador coast (TBT concentrations varied between 12.7 and 99.5 ng Sn g−1 dw; Castro et al., 2012b).

In order to predict if the butyltin contamination is recent or old in the sediment, it is useful to calculate the butyltin degradation index. An estimation of their fate could be obtained by considering all the butyltins involved in the degradation process, thus by calculating the ratio between the two main degradation products (DBT and MBT) over the tri-substituted parent compound (TBT). Results for BDI showed that butyltin contamination in all studied sites is old being more recent in Carrier Bay site without excluding some factors that may influence TBT degradation.

In Tunisia, there are no sediment quality guidelines for TBT contaminations. However, in order to determine the potential ecological toxic effects, we used sediment quality guideline from other countries for comparison. Spanish port authorities have proposed sediment quality guidelines of 10 and 200 ng Sn g−1 dw for low and high trigger values (Rodríguez et al., 2010). All the sampled stations had TBT levels lower than the low trigger value. However, except Zarat station, the observed levels of TBT compounds at all the areas sampled are higher than those known to induce imposex in marine Gastropods (Peña et al., 1988; Abidli et al., 2012b).

Conclusion

The combined results for imposex levels and chemical analysis presented in this study show the importance of this association to understand the intensity of butyltins contamination. Relatively high TBT contamination was found at locations close to large shipyards as in Menzel Abderrahmane station and Radès channel. The results can be used as baseline for future monitoring studies to determine whether the contamination in the Tunisian marine water is diminishing or not.

Notes

Acknowledgments

The present study was partially funded by a scholarship attributed to Sami Abidli by the Ministry of High Education and Scientific Research in Tunisia. This work is a result of collaboration between Faculty of sciences of Bizerta (Tunisia) and Faculty of Chemistry (Oviedo, Spain). Authors are grateful to the staff of the Department of Physical and Analytical Chemistry (Oviedo) for their help in butyltins analysis and to the staff of the laboratory of Molecular Genetic, Immunology and Biotechnology (Faculty of Sciences of Tunis) for the lyophilization of biological samples. Finally, we acknowledge the Editor and two anonymous referees for valuable comments and suggestions that greatly improved the manuscript.

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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  • Sami Abidli
    • 1
  • Youssef Lahbib
    • 1
  • Pablo Rodríguez González
    • 2
  • José Ignacio García Alonso
    • 2
  • Najoua Trigui El Menif
    • 1
  1. 1.Laboratory of Environment Biomonitoring, Faculty of Sciences of Bizerta (FSB)University of CarthageZarzouna, BizertaTunisia
  2. 2.Department of Physical and Analytical Chemistry, Faculty of ChemistryUniversity of OviedoOviedoSpain

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