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Keywords:

  • Imposex;
  • Reduction;
  • Southern Brazil;
  • Organotin;
  • Temporal trend

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

The imposex incidence was appraised in South American gastropods, considering the scenario before and after the global ban of tributyltin (TBT). A statistically significant reduction in imposex indexes was observed in Stramonita haemastoma collected in 2006 and 2010 from areas under the influence of four coastal harbors from southern Brazil. This reduction may be because of the effectiveness of the global ban issued by the International Maritime Organization, although the restrictions on TBT-based antifouling paints in Brazil might also have helped. Even so, a residual organotin contamination was still detected in female tissues (levels ranged from 7.6 to 164.9 ng Sn/g for TBT; from <2 to 214.5 ng Sn/g for dibutyltin; from <3.5 to 178.8 ng Sn/g for monobutyltin; and from <1.5 to 53 ng Sn/g for triphenyltin). Thus, although a reduction in imposex and environmental levels of organotins is expected in every ocean worldwide soon after the implementation of national and international restriction regulations, this will depend on the effectiveness of the global TBT ban; the effectiveness of local restrictions on producing, selling, and using TBT-based antifouling paints; and specific characteristics of local sediments, because metabolization rates and sorption/desorption of TBT previously deposited might affect its environmental bioavailability. Therefore, the reduction trend detected in the present study cannot be extrapolated to other Brazilian or South American coastal areas. Environ. Toxicol. Chem. 2012; 31: 947–954. © 2012 SETAC


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Imposex was first reported as a sexual aberration in the early 1970s. Blaber 1 described it for Nucella lapillus from Plymouth, United Kingdom, and Smith 2 for Ilyanassa obsoleta from Southport and Westport, Connecticut, USA. However, its cause–effect relationship with exposure to organotins (OTs) was discovered only in 1981 3. Thereafter, imposex has been used as a powerful biomarker to map coastal areas impacted by OTs 4. Currently, imposex is a widespread problem, affecting more than 200 worldwide species of Caenogastropoda 5–7.

Tributyltin (TBT)-based antifouling paints have been used since the 1970s in solid surfaces directly exposed to sea water (ship hulls, aquaculture nets, offshore structures, buoys, and ducts) to avoid an undesirable accumulation of marine organisms (fouling) 8, 9. Meanwhile, several deleterious environmental effects have been related to their application, such as malformation in oysters 10, immunosuppression in dolphins 11, immuntoxicity in fish 12, imposex, decline of gastropod populations 13, and metabolic disruption in fish 14. Hence, in the early 1980s, many countries started to adopt restrictive regulations on the use of TBT-based marine coatings on boats less than 25 m long. However, because shipping is a worldwide activity, controls on antifouling systems by individual countries were not effective enough to prevent contamination, even in their own territorial sea. Therefore, a global prohibition on TBT-based antifouling paints was proposed by the International Maritime Organization, entering into force definitively in September 2008 15.

Recovery of gastropod populations previously affected by imposex had been reported following the restrictive regulation of TBT use in marine protective coatings. For example, a significant imposex reduction was verified for populations of N. lapillus16 and Nassarius reticulatus17 after the European legislation had banned the use of TBT-based antifouling paints. In Africa, imposex recovery was detected between 2004 and 2007 in Hexaplex trunculus from the Tunisian coast 18, and a reinspection of the imposex incidence 10 years after local restrictions on TBT use showed a decrease in Thais orbita from Australia 19. With regard to OT environmental concentrations, many studies have also recently detected a reduction of levels in Asia 20, Europe 21, and North America 22. However, no information regarding the effectiveness of the TBT global ban in South America is available in the literature.

For this reason, areas under the influence of four of the main harbors from the southern coast of Brazil were assessed in 2010 for imposex occurrence and OT levels in Stramonita haemastoma and were compared with a previous study that reported imposex for the same species and areas before the TBT global ban 23. The harbor terminals of Paranaguá (Paraná state), São Francisco do Sul (Santa Catarina state), Itajaí (Santa Catarina state), and Rio Grande (Rio Grande do Sul state) are among the largest and busiest on the southern Brazilian coast.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Sampling

Up to 30 adult specimens of S. haemastoma were caught (either manually or by free diving) in February 2010, in 17 sampling sites located in areas under the influence of four main harbors of southern Brazil (Paranaguá Harbor in Paranaguá Bay, São Francisco do Sul Harbor in Babitonga Bay, Itajaí Harbor in the Itajaí Acú River estuary, and Rio Grande Harbor in the Patos Lagoon estuary; Fig. 1). These sites were exactly the same as those previously measured in February 2006 by Castro and coworkers 23.

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Figure 1. Sampling sites in southern Brazilian harbors. PR1 = Galheta Island; PR2 = Mel Island; PR3 = Ponta do Poço; PR4 = Guará Island; PR5 = Gereres Island; SF1 = Paulas Beach; SF2 = Ingleses Beach; SF3 = Northeastern Harbor; SF4 = Touristic Harbor; IT1 = Brava's Beach; IT2 = Cabeçudas Beach; IT3 = outside of south jetty; IT4 = outside of north jetty; RG1 = shipwreck 16 km south of west jetty; RG2 = outside base of west jetty; RG3 = outside end of east jetty; RG4 = outside base of east jetty.

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Imposex determination

The organisms were narcotized with a 3.5% MgCl2 solution for a period of 2 h before the analysis. Shells were measured with a digital caliper (0.01 mm) from the apex to the lip of the siphonal canal. Thus, shells were removed for analysis of the soft tissues. Gender identification was based on the presence or absence of sexual accessory glands (albumen, capsule, and seminal receptacle). The penis length and the presence of a vas deferens in females and males were recorded at the same time.

The imposex levels were accessed using the following indices: percentage of imposex in females (I%); female penis length index (FPLI; mean penis length of all females in the population, including the zero values); relative penis length index (RPLI; mean penis length in females/mean penis length in males × 100) 24; and vas deferens sequence index (VDSI), which is based on the development of male sexual characteristics (particularly the vas deferens) by females and was calculated according to Fernandez et al. 25.

Female OTs body burdens

Chemical analyses were performed in whole visceral coil tissues pooled from seven to 15 females collected from each site in 2010. Soft tissues were freeze dried after imposex determinations, ground into powder, and kept at –20°C under dark conditions. Organotin (TBT, dibutyltin [DBT], monobutyltin [MBT], and triphenyltin [TPT]) levels were analyzed following the procedure described by Castro et al. 26. Briefly, a given amount (∼1 g) of freeze-dried tissue was placed into 40-ml vials, spiked with 100 ng tripropyltin (TPrT) as surrogate standard. Afterward, OTs were extracted with 15 ml 0.05% tropolone solution (w/v) in methanol and 1 ml concentrated HCl (37%) in an ultrasonic bath for 10 min. The extract volume was reduced to approximately 2 ml and derivatized with 2 ml pentylmagnesium bromide in dietylether solution (2 M). The excess of Grignard reagent was destroyed by adding 15 ml ultrapure water and 1 ml HCl (37%), both previously refrigerated to 4°C. After derivatization, the pentylated butyltins were recovered by a liquid–liquid extraction with 3 × 5 ml hexane. Those extracts were evaporated, transferred on top of a silica-gel column, and eluted with a 15 ml hexane/toluene (1:1) mixture. Finally, the solution was concentrated to 0.9 ml under gentle nitrogen flow, and 100 µl tetrabutyltin solution (1,000 ng Sn/ml) was added as internal standard. Extracts were analyzed in a PerkinElmer Clarus 500MS gas chromatograph equipped with a mass spectrometer detector. The gas chromatograph was equipped with an Elite-5MS (5% diphenyl dimethilpolisiloxane) capillary column (30 m × 0.25 mm inside diameter, 0.25 µm film thickness).

The quality assurance and quality control were based on regular analyses of blanks and spiked matrices. The sample recoveries were between 70 and 109% and relative standard deviations below 20% 27. All concentrations were reported as ng Sn/g (dry wt), and quantification limits were 1.0, 2.0, 3.5, and 1.5 ng Sn/g for TBT, DBT, MBT, and TPT, respectively.

Statistical analysis

Normality and homogeneity of shell lengths, imposex parameters, and butyltin (BT) concentration data were verified by Shapiro–Wilks and Levene tests, respectively. A multiple linear regression was performed to verify whether male shell lengths have a significant effect on male penis lengths. Afterward, the differences between shell length measured in males and females during 2006 and 2010 were evaluated by the Mann–Whitney U test.

Three different statistical approaches were used to assess the changes of imposex levels between 2006 and 2010. First, a combined analysis using the nonparametric Wilcoxon signed rank test was performed, pooling all 17 sites together to verify temporal differences in VDSI and FPL. In the second and third approaches, the Mann–Whitney U test was applied to assess differences between VDS and FPL individual values at each site and by sampling area, respectively.

Spearman nonparametric correlation analysis was used to investigate the relationship between TBT concentrations in female soft tissues and imposex levels (RPLI, FPLI, and VDSI) during the campaign in 2010. All statistical analyses were performed in Statistica software (Ver 6.0; Statsoft) with a significance level of 0.05.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Imposex determination

The imposex parameters, mainly RPLI, are frequently influenced by animal size, even when the sample is composed only by adult animals 28. For males of S. haemastoma, the multiple linear regressions showed that shell size was significantly related to the square root of penis length (t = 6.568, p < 0.0001). Although the range seemed similar between the two sampling campaigns (23.1–48.3 mm in 2006 and 23.5–46.5 mm in 2010; Table 1), 11 of 17 sites showed statistically different male shell lengths (Fig. 2A). For these reasons, the significance in the reduction of RPLI results observed for 13 studied sites was not statistically tested (Table 1). In females, the shell lengths were significantly smaller at four sites only (PR1, PR3, PR5, and RG4; Fig. 2B). In this case, smaller female shells (probably indicating younger organisms) could be responsible for an underestimation of VDSI, FPL (Fig. 3), and I% (Table 1).

Table 1. Mean (± standard deviation) shell length (mm) and imposex levels obtained for Stramonita haemastoma in 2006 and 2010
SiteShell length ♂ (mm) ± sd (n)Shell length ♀ (mm) ± sd (n)I %VDSI ± sdFPL ± sdRPLI
200620102006201020062010200620102006201020062010
  1. sd = standard deviation; n = number of analyzed specimens; I% = imposex frequency; VDSI = vas deferens sequence index; FPL = average of female penis length; RPLI = relative penis length index; see Figure 1 for site abbreviations.

PR143.7 ± 5.2 (14)33.9 ± 2.2 (16)44.1 ± 5.7 (16)32.5 ± 2.4 (14)35.742.80.36 ± 0.050.45 ± 0.050.37 ± 0.040.43 ± 0.110.520.62
PR234.3 ± 3.7 (15)36.6 ± 3.7 (15)35.1 ± 3.2 (15)36.1 ± 4.8 (15)100.073.31.00 ± 0.000.73 ± 0.500.10 ± 0.030.07 ± 0.030.980.93
PR337.8 ± 3.4 (12)28.2 ± 6.1 (15)41.7 ± 8.2 (12)32.1 ± 7.5 (12)100.093.31.92 ± 0.800.93 ± 0.320.93 ± 0.800.09 ± 0.0212.811.57
PR429.3 ± 2.4 (7)27.7 ± 4.1 (8)29.4 ± 1.7 (16)27.3 ± 2.2 (7)85.337.51.14 ± 0.700.37 ± 0.500.34 ± 0.500.04 ± 0.1316.930.65
PR532.6 ± 3.5 (14)23.5 ± 2.4 (12)36.7 ± 4.3 (16)24.2 ± 1.9 (14)87.783.30.86 ± 0.400.83 ± 0.400.86 ± 0.040.08 ± 0.001.441.44
SF146.0 ± 4.9 (21)40.0 ± 5.0 (16)46.0 ± 6.9 (8)41.4 ± 5.1 (14)100.0100.03.44 ± 0.401.00 ± 0.003.10 ± 1.600.10 ± 0.0325.920.88
SF248.3 ± 4.5 (12)42.4 ± 4.1 (13)48.8 ± 5.7 (10)46.2 ± 4.4 (17)100.094.04.85 ± 0.701.31 ± 0.415.70 ± 1.001.03 ± 0.4065.002.99
SF340.2 ± 2.3 (19)41.5 ± 3.6 (10)42.0 ± 7.1 (11)42.3 ± 5.6 (20)100.081.22.41 ± 0.400.81 ± 0.501.70 ± 1.000.12 ± 0.2117.370.49
SF436.9 ± 6.0 (13)46.1 ± 5.0 (14)40.1 ± 5.5 (17)44.6 ± 6.3 (9)100.0100.04.17 ± 0.701.00 ± 0.504.50 ± 1.100.08 ± 0.0254.520.65
IT128.5 ± 5.1 (12)32.1 ± 3.4 (13)30.1 ± 4.5 (18)32.0 ± 2.3 (17)0.00.00.00 ± 0.000.00 ± 0.000.00 ± 0.000.00 ± 0.000.000.00
IT226.0 ± 5.3 (15)29.8 ± 3.0 (16)29.3 ± 4.1 (15)29.2 ± 1.5 (14)0.00.00.00 ± 0.000.00 ± 0.000.00 ± 0.000.00 ± 0.000.000.00
IT326.7 ± 2.3 (10)32.5 ± 3.5 (10)27.4 ± 4.0 (14)35.1 ± 3.6 (20)100.00.01.00 ± 0.000.00 ± 0.000.30 ± 0.040.00 ± 0.003.800.00
IT423.1 ± 2.5 (14)28.8 ± 2.4 (15)24.1 ± 2.2 (16)28.2 ± 2.7 (15)100.00.01.14 ± 0.400.00 ± 0.000.10 ± 0.020.00 ± 0.001.800.00
RG147.0 ± 6.4 (17)42.5 ± 4.8 (14)46.1 ± 9.4 (11)44.7 ± 5.7 (16)18.20.00.20 ± 0.400.00 ± 0.000.02 ± 0.010.00 ± 0.000.150.00
RG244.1 ± 7.3 (18)45.1 ± 6.2 (13)40.5 ± 4.2 (12)39.8 ± 4.3 (17)58.30.00.60 ± 0.500.00 ± 0.000.06 ± 0.030.00 ± 0.000.640.00
RG341.4 ± 5.8 (11)46.5 ± 6.4 (15)43.5 ± 5.7 (19)41.4 ± 4.6 (15)15.80.00.15 ± 0.500.00 ± 0.000.03 ± 0.030.00 ± 0.000.110.00
RG445.8 ± 4.7 (11)41.0 ± 5.7 (13)47.1 ± 4.3 (19)39.5 ± 4.1 (16)53.10.00.63 ± 0.400.00 ± 0.000.01 ± 0.020.00 ± 0.000.580.00
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Figure 2. Comparison of mean (± standard deviation) shells length (mm) for males (A) and females (B) collected in 2006 and 2010. Significant differences are marked (*p < 0.05, **p < 0.01, and ***p < 0.001).

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Figure 3. Comparisons of mean (± standard deviation) vas deferens sequence index (VDSI; A) and female penis length (FPL; B) values obtained for 2006 and 2010. Significant differences are marked (*p < 0.05, **p < 0.01, and ***p < 0.001).

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In considering the whole trend (all sites together), the reduction in VDSI and FPL values (Table 1) was statistically significant according to the Wilcoxon signed rank test (w = –120, p = 0.0006 and w = –109, p = 0.001, respectively). In assessing by locality, VDSI and FPL decreases were extremely significant at São Francisco do Sul Bay, Itajaí Harbor area, and Rio Grande Harbor area (p < 0.0001), whereas no significant differences were observed for VDSI at Paranaguá Bay. Only three sites (PR1, PR2, and PR5) previously impacted by imposex did not show any reduction in the VDSI values. Stations IT1 and IT2 (Itajaí Harbor area) did not show any imposex in either the 2006 or the 2010 campaign (Table 1). In fact, the stations SF1, SF2, SF3, SF4, IT3, and IT4 showed a more pronounced decrease (Mann–Whitney U test, p < 0.001), although the sites PR3, RG2, and RG3 (p < 0.01) and PR4, RG1, and RG4 (p < 0.05) have also shown significant reductions in VDSI values (Fig. 3a). Similarly, a pronounced reduction in FPL values was seen for the same sites (Fig. 3b). However, VDSI and FPL values might have been underestimated at PR3 and RG4 in 2010, because females at these sites were significantly smaller than in 2006. Sterile females (identified by vulva blockage) were observed for stations SF3 (80%) and SF4 (17.6%) in 2006 but were no longer found in the sampling campaign of 2010. Although I% was not statistically compared because of the existence of a single value per site, a decrease trend in 12 of 17 studied sites was in accordance with the reductions detected for VDSI and FPL.

Female OTs body burdens

Organotin compounds were detected in all tissue samples from 2010 (Table 2). Tributyltin was the predominant OT at almost all sites (except for ≤20% of ΣOTs for PR2, SF4, IT2, and RG1), ranging from 7.6 to 164.9 ng Sn/g. The DBT levels ranged between <2.0 and 214.5 ng Sn/g, whereas MBT residues ranged between <3.5 and 178.8 ng Sn/g. Triphenyltin was also detected with concentrations ranging between <1.0 and 53.0 ng Sn/g.

Table 2. Concentrations (ng Sn/g dry wt) and percentage of organotin compounds in S. haemastoma female tissues collected in 2010
SiteSite codeTBTDBTMBTTPTBDIΣOTsPercentage
TBTDBTMBTTPT
  1. <LOD = below limit of detection; TBT = tributyltin; DBT = dibutyltin; MBT = monobutyltin; TPT = triphenyltin; BDI = butyltin degradation index; ΣOTs = total organotins; see Figure 1 for site abbreviations.

Paranaguá BayPR162.323.06.00.00.591.368.225.26.60.0
 PR252.6214.5<LOD4.64.1271.719.478.90.01.7
 PR349.2<LOD<LOD9.50.058.783.80.00.016.2
 PR449.0<LOD8.4<LOD0.257.485.40.014.60.0
 PR558.550.1<LOD6.50.9115.150.843.50.05.6
Babitonga BaySF164.252.628.210.81.3155.841.233.818.16.9
 SF2164.945.883.519.40.8313.652.614.626.66.2
 SF351.238.418.117.91.1125.640.830.614.414.3
 SF430.583.519.410.33.4143.721.258.113.57.2
Itajaí HarborIT110.42.6<LOD<LOD0.313.080.020.00.00.0
 IT215.66.912.553.01.288.017.77.814.260.2
 IT332.5<LOD6.8<LOD0.239.382.70.017.30.0
 IT430.4<LOD<LOD<LOD0.030.4100.00.00.00.0
Rio Grande HarborRG154.669.2178.86.44.5309.017.722.457.92.1
 RG212.56.85.78.51.033.537.320.317.025.4
 RG39.77.3<LOD4.60.821.644.933.80.021.3
 RG47.65.2<LOD3.10.715.947.832.70.019.5

The butyltin degradation index (BDI = [DBT + MBT]/TBT) was calculated following Díez et al. 29. Although this index was first developed for sediments, it has been used recently for mollusk tissues to predict exposition time (BDI <1 corresponds to recent BT contamination) 17, 21. Butytltin degradation index values varied between 0 and 4.1 (mean, 1.1) for Paranaguá Bay, between 0.8 and 3.4 (mean, 1.6) for Babitonga Bay, between 0 and 1.2 (mean, 0.4) for the Itajaí Harbor area, and between 0.7 and 4.5 (mean, 1.7) for the Rio Grande Harbor area.

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Reductions in imposex levels have been reported worldwide 16, 17. However, temporal studies of imposex parameters are frequently affected by animal biometric variations 16, 30. Thus, some precautions were taken to minimize misinterpretations in the trends of imposex levels in the present study. First, the sampling was conducted in the same month to avoid seasonal variability in penis length, which is regulated by the reproductive cycle of S. haemastoma. This problem was previously reported in Bolinus brandaris and may affect FPL and VDSI values 31. In addition, only adult animals (>20 mm) were collected, and the same method was used for imposex determination allowing consistent data interpretation. Second, RPLI is an imposex parameter that roughly balances the sizes of males and females in each sample, so it is less affected by interindividual variabilities than VDSI and FPL 32. Nevertheless, given that high variations in animal sizes were observed in the present study (mainly for males), the use of RPLI might introduce additional bias in the trend analysis. A similar situation was observed for Hidrobia ulvae during a temporal trend study at Rio Aveiro, Portugal 28. In this case, the RPLI data was not used in the statistical analyses.

Even with these limitations in the interpretation, the results have clearly demonstrated a reduction in the imposex data for all areas under the influence of the four main harbors from southern Brazil. In addition, the highest OT concentrations and imposex levels were detected in coastal areas under the influence of São Francisco do Sul (SF1, SF2, SF3, and SF4) and Paranaguá (PR1, PR2, PR3, PR4, and PR5) Harbors, whereas OTs were proportionally lower in sites with low imposex incidence. Therefore, significant correlations were found between TBT concentrations in female tissues and VDSI (r = 0.70, p = 0.001), FPL (r = 0.80, p = 0.0002), and RPLI (r = 0.73, p = 0.001). These relationships were seen previously for other gastropod species such as N. reticulatus17, Hexaplex truculus18, and N. lapillus33. Although TPT can also induce imposex in S. haemastoma under laboratory conditions 34, the low detected concentrations usually recorded in the environment and in the present study probably play only a negligible role in promoting the development of imposex in natural populations 35.

Among the four studied areas, Paranaguá Bay, located in the Paranaguá estuarine complex, has two large commercial harbors (Paranaguá and Antonina) and several marinas. At all of its sites, a significant VDSI reduction was seen in Paranaguá Bay between 2006 and 2010. Even so, the TBT levels and BDI values in S. haemastoma tissues indicated a fresh exposure to OT, because TBT predominated in most of those samples. However, levels were not as high as those at the heavily contaminated site 17, 36. Stramonita haemastoma feed on filter feeder organisms, so its levels might reflect an accumulation from the water column (dissolved plus suspended matter). These results agree with those of Santos et al. 37 and Santos (D.M. Santos, University of São Paulo, São Paulo, Brazil, personal communication), who detected high but reduced levels of OTs in sediment samples collected from Paranaguá Bay in 2006 and 2009. Levels of MBT and DBT in these studies predominated over TBT in almost all sites, suggesting a reduction in recent TBT inputs or a fast environmental degradation rate. These results corroborate a reduction trend in imposex found in the present study, because DBT and MBT have less or no potential to induce imposex 38.

The most impressive imposex reduction occurred in the areas under the influence of São Francisco do Sul Harbor, because all stations in Babitonga Bay showed highly significant decreases of imposex parameters. Although TBT levels ranged between 30 and 165 ng Sn/g, BDI values (≥1) indicated some reduction in fresh inputs. Oliveira et al. 39 also detected OTs in four of five sediment samples collected inside Babitonga Bay in October 2007. Despite the TBT levels, some BDI values also indicated a reduction in fresh inputs. Therefore, the observed imposex reductions are in accordance with the relative predominance of OTs in sediments obtained by Oliveira et al. 39, indicating that attenuation is contributing to environmental remediation in Babitonga Bay.

Itajaí Harbor is located inside the Itajaí-Açu River, a predominantly mesohalinic environment. Thus, the biological monitoring was carried out in the adjacent coastal areas, because S. haemastoma does not occur near the harbor. Although two of four sites have not shown imposex on either occasion (IT1 and IT2), it was possible to detect a statistically significant imposex reduction in two sites (IT3 and IT4). Despite that, the obtained BDI mean in S. haemastoma tissues from Itajaí Harbor suggested that fresh TBT inputs or exposition (although low) were still occurring in these areas. However, Oliveira et al. 39 have reported high TBT levels, with BDI values also indicating fresh TBT inputs, for several sediment samples collected inside the estuarine area in July 2008. The only site located in the coastal area (the nearest from biological monitoring) showed much lower BT contamination and BDI values >>1.

Similarly, biomonitoring of the Rio Grande Harbor area was conducted with samples collected in the adjacent coastal areas, because no gastropods were found inside the Patos Lagoon estuary (low salinities). Although VDSI and FPL obtained for site RG4 in 2010 may be affected by female shell length, results showed a significant reduction in the imposex levels for all stations. However, BDI values suggested some fresh (although low) inputs of TBT to S. haemastoma from Patos Lagoon-adjacent coastal areas. On the other hand, relatively low BT levels and high BDI values were found for sediments from the Rio Grande Harbor area (I.B. Castro, Rio Grande Federal University, Rio Grande, Rio Grande do Sul, Brazil, personal communication), which supports the hypothesis that inputs of TBT have gradually been reduced in the area.

Despite this clear trend of reduction in imposex for these areas, a residual OT contamination was detected in mollusks from these areas, and a predominance of TBT was still evident. Previous studies in sediments from these areas indicated a possible reduction in fresh BT inputs (metabolites predominated over parental BT) 37, 39, so a limited metabolic ability of S. haemastoma to degrade TBT could explain its predominance. However, new inputs of TBT either from sediment desorption or from direct use cannot be ruled out. Stramonita haemastoma is a carnivorous muricid inhabitant of hard substrates 40 that probably accumulates TBT preferentially via food (mainly mussels and barnacles) and also from water. The OT metabolism and bioaccumulation factors in S. haemastoma are still unknown. However, bioconcentration factors for phylogenically related muricid species, such as Thais clavigera and N. lapillus, were about 5,000 to 10,000 and 29,000, respectively 41, 42. In addition, the TBT biological half-life was estimated at 22 d for T. clavigera41. Assuming a similar OT behavior for all muricid species, it is likely that TBT levels detected in S. haemastoma in the present study could be because of recent (although most of the time low) environmental TBT exposition or limited degradation capacity. Ruiz and coworkers 43 revealed a transient distortion of baseline butyltin bioaccumulation in gastropods from Europe. These field observations are consistent with BT desorption from sediments, a natural phenomenon that is expected in developing countries recently subject to the global TBT ban. Although there are no time series for BT contamination in these areas, this could be an explanation for the BT levels found in the present study.

Relevant TBT levels were also found in nonimposexed females from Itajaí and Rio Grande. This could be because of differential sensibility among analyzed populations, in that they were geographically isolated from each other or the presence of estrogenic compounds from sewage 44. Similar situations have been reported for Thais distinguenda from Phuket Island, Thailand 45, and Nucella lapillus in experimental conditions. Additionally, an unpublished experimental study with S. haemastoma (M. Rossato, Rio Grande Federal University, Rio Grande, Rio Grande do Sul, Brazil, unpublished results) showed that exposure (water and injection) to high TBT concentrations was not able to induce imposex in organisms collected from RG1. Thus, further investigation is needed to elucidate possible differences in sensitivity among distinct populations of S. haemastoma previously exposed to impacted areas in comparison with those from clean areas.

The use of OT-based antifouling paints was forbidden in Brazil in November 2007, by means of NORMAN-23/DPC 46. This regulation established inspections and registration standards for all antifouling systems, as well as management of their residues 46. In addition, although the global prohibition of these products entered into force in September 2008, local legislation also imposed restrictions (e.g., in European countries 17). Thus, a reduction in imposex and OT environmental levels is expected in every ocean around the world soon after the implementation of national and international restriction regulations. However, the speed and effectiveness of this reduction trend will depend on the effectiveness of the global TBT ban, which affects all regions evenly. This is the case because it is related directly to international marine traffic and the effectiveness of local restrictions on producing, selling, and using TBT-based antifouling paints, which may differ among countries and regions inside each country. Even with the use of TBT forbidden, many countries (such as Brazil) do not regulate production and sales and have feeble control over its use. Finally, the effectiveness of the global TBT ban will also depend on specific characteristics of local sediments, because degradation rates and sorption and desorption of TBT previously deposited might affect its environmental bioavailability. Therefore, it is difficult to predict when and where such a reduction will effectively take place. Although the current detected decline of imposex incidence in S. haemastoma from southern Brazilian harbors is the first report of imposex recovery in South America, a comparative study performed in 2001 and 2008 at Arraial do Cabo, Rio de Janeiro state (southeastern Brazil), showed a spatial increase in imposex occurrence 47. Thus, because of the scarcity of special and temporal trend studies and the lack of legislation and use control, the reduction trend detected in the present study cannot be extrapolated for other Brazilian or South American coastal areas, because the local oceanographic characteristics and local use of TBT-based antifouling paints are probably more relevant than international restrictions on their use.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

I.B. de Castro (PhD grant 141550/2007) and G. Fillmann (PQ 311459/2006-4 and 314335/2009-9) were sponsored by CNPq (Brazilian National Research Council). The authors are also grateful to Centro de Estudos do Mar (Federal University of Paraná) for help during sampling.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES
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