Bioaccumulation and effects of TBT on molluscs from southern Portugal

Tese de dout. Ciências e Tecnologias do Ambiente, Faculdade de Ciências do Mar e do Ambiente, Univ. do Algarve, 2004

The present work intended to study the impact of the highly toxic compound tributyltin (TBT) in one of the most important mollusc species in southern Portugal, the ciam Ruditapes decussatus. The first Chapter provides a general overview of the TBT problem in the marine environment. A summary of the analytical methods employed to analyse organotins in water, sediments and biological tissues is presented in Chapter 2. The effects of sublethal tributyltin concentrations on the growth and development of R. decussatus larvae were studied (Chapter 3). Veliger larvae of Ruditapes decussatus were exposed to TBT nominal concentrations of 25, 50, 75 and 100 ngL"1 Sn in the water for a period up to 13 d. Larval growth and development were chosen as endpoints for evaluation of TBT toxicity. Growth of R. decussatus larvae was severely affected by TBT concentrations (25-100 ngL'1 Sn). A 3- to 5-fold reduction in growth was observed in these early larval stages. Furthermore, R. decussatus larvae exposed to TBT did not develop further than Dlarvae while larvae from control cultures reached the umbonated stage. The effects of sublethal concentrations of tributyltin (TBT) on growth of ciam juveniles, R. decussatus, were determined in clams exposed to nominal TBT concentrations of 50, 100 and 250 ng L^Sn in sea water, for a period up to 2 years (Chapter4). R. decussatus iuvenWes increased regularly in length and weight over the whole experimental period. Final length and weight were affected by TBT exposure. Flowever, growth rates (in length and weight) were not significantly different amongst treatments, after 2 years of TBT exposure. Thus, under the deschbed experimental conditions, although a decrease in growth (length and weight) of R. decussatus juveniles was observed with increasing TBT concentrations, it was not significantly affected by TBT exposure. The relative importance of water, sediments and food as vectors of TBT uptake was assessed for the infaunal, suspension-feeding bivalve, Ruditapes decussatus (Chapter 5). Accumulation of TBT was determined in R. decussatus exposed for 60 days to, moderately high, but environmentally realistic, leveis of TBT dissolved in water (100 ngL"1 Sn) and sediments (0.8 pgg"1 Sn dw), separately or in combination, using constant-flow systems. The results indicate that this species accumulates TBT predominantly from water. Although some accumulation from sediments does occur, the processing of large amounts of water needed to sustain the filter-feeding habits of this species is a prime determinant of TBT uptake. The route of exposure is reflected in tissue distributions of TBT in R. decussatus. However, gills are the most important sites for accumulation of TBT from water, irrespective of whether contaminated sediments are present or not. In addition, the relative importance of phytoplankton as a vector of TBT uptake was assessed in the same species. Accumulation of TBT via the algal diet was determined by experimental exposure of R. decussatus to 14CTBT labelled phytoplankton Isochrisis galbana, for a period up to 60 days. Ruditapes decussatus exhibited increasing TBT burdens during a period up to 40 days, after which an apparent steady state was achieved. Within the body, the digestive tract of these clams initially accumulated TBT. After a few weeks of exposure, internai remobilization resulted in a more widespread partitioning of TBT amongst tissues. From the results of these experiments (Chapter 5), in which R. decussatus were exposed to TBT in water, sediments and food partitioned realistically, it seems clear that this species accumulates TBT predominantly from water. Although some accumulation from sediments and food does occur, the contribution from these phases was negligible when compared to water, at least under the conditions and concentrations used in this experiment. In a filed survey (Chapter 6), organotin concentrations were measured in water, sediments and clams {Ruditapes decussatus) from eleven sites in the Ria Formosa lagoon, Portugal, in 1992-1993. Results showed a marked spatial pattern of tributyltin (TBT) and dibutyltin (DBT) concentrations. Highest organotin concentrations were observed at Olhão (site 5), where the most important fishing harbour of the Southern coast of Portugal is located. Results indicated that fishing vessels, moored in the harbour at Olhão (site 5), were the major source of organotin contamination to the lagoon. No significant seasonal trend was observed, sIn order to assess the incidence of imposex in neogastropods (Chapter 7), a field survey was carried out in Algarve between Vila Real de Santo António, at the eastern border, and Zavial, near Sagres, at the westem end. The degree of imposex was determined in six neogastropod species: Ocenebra erinacea, Hexaplex trunculus, Murex brandaris, Conus venthcosus, Nassarius reticulatus and Nucella lapillus, using the two índices RPLI and VDSI. Imposex was observed in females from ali the sampled sites in Algarve, except in Zavial (13), where ali females Nucella lapillus were unaffected by imposex. The final discussion is presented in the last Chapter (8). It emphasizes that results from this work constitute a further step to confirm that TBT is among the most toxic chemicals introduced in the marine environment. Its potential for negative impact on the benthic community is evident. In the particular case of R. decussatus cultured in Ria Formosa and other important mariculture sites, a continued input of organotins will probably cause serious damage to shellfish species, particularly to its early life-stages. According to the World Health Organisation (WHO, 1990), recommendations for protecting human and environmental health against the damaging effects of TBT include (1) the establishment of restrictions on the use of TBT compounds; (2) evaluation of organotins inputs to the environment from sources other than antifouling paints; (3) improvement of methods for the safe application removal and disposal of organotins. Furthermore, future research needs comprise improvement of detection and analysis of organotins and better knowledge of toxicity, namely immunological effects, mechanisms of toxicity, endocrine effects and mammalian toxicity including studies on potential carcinogenic effects. Human intake of TBT should also be carefully studied; specific consumption recommendations should eventually be published and maximum residue leveis (MRL) for TBT, and other organotin compounds, in seafood products should be set to minimize human risks. Attention should also be given to the search for other sensitive bioindicator species, including freshwater organisms and finally more information is required on butyltin residues in fish and shellfish for human consumption.uggesting a continuous input of organotin compounds throughout the year.