Browsing by Author "Langston, W. J."
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- Cadmium and metallothionein turnover in different tissues of the gastropod Littorina littoreaPublication . Bebianno, Maria João; Langston, W. J.This paper attempts to link the kinetics of Cd and metallothionein turnover in the intertidal marine snail Littorina littorea. The results demonstrate that the turnover of metallothionein is tissue dependent. Metallothionein has an estimated half-life of 69 and 160 days in the gills and kidney, respectively. The half-life could not be calculated for metallothionein in the digestive gland and is probably much longer than the other two tissues. Cadmium elimination from the gill and kidney is considerably slower than the respective metallothioneins (half-life in excess of 300 days) indicating closed cycling of the metal in these tissues. In contrast, cadmium levels in the digestive gland continue to increase during the detoxification period reflecting some remobilization from other tissues, Metallothionein turnover is extremely slow in Littorina when compared with mammals and other bivalve molluscs: even though metallothionein degradation is measurable in some gastropod tissues, the released cadmium may induce de novo metallothionein synthesis to which cadmium becomes resequestered. The stow metallothionein turnover rates and the lack of significant cadmium excretion testify to the relatively stable nature of the cadmium-metallothionein complex in this invertebrate.
- Effect of TBT on Ruditapes decussatus juvenilesPublication . Coelho, M. R.; Langston, W. J.; Bebianno, Maria JoãoThe effects of sublethal concentrations of tributyltin (TBT) on growth of juvenile clams Ruditapes decussatus were determined during exposure to TBT concentrations of 50, 100 and 250 ng l(-1) (as Sn) for a period up to two years. Length and weight of clams increased continuously in all treatments throughout the experimental period, and, overall, rates were not significantly influenced by TBT exposure, although final length and weight were inversely related to increasing TBT concentration. Juvenile R. decussatus therefore appear to be less sensitive to TBT than larval stages. Some juveniles exposed to TBT developed abnormal shell growth, laterally, changing the typical flattened shape of clams into a more "rounded" form. This characteristic was more visible in the anterior margins of valves than posteriorly, and mainly observed in clams exposed to TBT at 50 ng l(-1) (as Sn).
- Metallothionein induction inMytilus edulis exposed to cadmiumPublication . Bebianno, Maria João; Langston, W. J.The exposure of mussels,Mytilus edulis, collected from Whitsand Bay, southwest England, in August 1988, to sublethal concentrations of cadmium (400µg l−1) for 65 d resulted in the induction of metallothionein (MT) synthesis in the soft tissues. In cadmium-exposed mussels, metallothionein concentrations, measured by differential pulse polarography, increased by a factor of three, from 2 to 3 mg g−1 to a maximum of 9 mg g−1 after 30 d. No significant changes could be detected in controls. Cadmium accumulated in the soft tissues of mussels correlated significantly with metallothionein concentrations and can be described by the relationship: MT (mg g−1)=0.045 Cd (µg g−1)+3.03 (r=0.803,P<0.001). Gel chromatography of heat-treated cytosolic extracts showed that the accumulated cadmium is bound principally to the newly formed metallothioneins. Copper and zinc were also analysed in the whole soft-tissues and in subcellular fractions of cadmium-exposed mussels. Although copper concentrations were not affected by cadmium-exposure, zinc levels were significantly reduced. The results demonstrate that the induction of metallothioneins inM. edulis is a quantifiable biological response to sublethal levels of cadmium exposure.
- Organotin levels in the Ria Formosa lagoon, PortugalPublication . Coelho, Márcio; Bebianno, Maria João; Langston, W. J.Organotin concentrations were measured in water, sediments and clams (Ruditapes decussatus) from 11 sites in the Ria Formosa lagoon, Portugal, in 1992-93. Results showed a marked spatial pattern of tributyltin (TBT) and dibutyltin concentrations. The highest organotin concentrations were observed at Olhao (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 Olhao (site 5), were the major source of organotin contamination to the lagoon. No significant seasonal trend was observed, suggesting a continuous input of organotin compounds throughout the year. In several areas of the lagoon the TBT burdens in R. decussatus could have deleterious developmental effects
- Routes of TBT uptake in the clam Ruditapes decussatus. I. Water and sediments as vectors of TBT uptakePublication . Coelho, Márcio; Bebianno, Maria João; Langston, W. J.This study assesses the relative importance of water and sediments as vectors of TBT uptake in the sediment-dwelling suspension feeder, Ruditapes decussatus. Accumulation of TBT was determined in R, decussatus exposed for 60 days to moderately high but environmentally realistic levels of TBT in water (100 ng Snl(-1)) and sediments (0.8 mug Sn g(-1) 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 site for accumulation of TBT from water. irrespective of whether contaminated sediments are present or not.
- Turnover rate of metallothionein and cadmium in Mytilus edulisPublication . Bebianno, Maria João; Langston, W. J.The results demonstrate the first attempt to determine metallothionein turnover in the whole soft tissues of mussels Mytilus edulis exposed to cadmium. Half-lives for metallothionein and cadmium are 25 and 300 days, respectively. As metallothionein degrades the released cadmium induces further synthesis of the protein, to which the metal becomes resequestered. The slow metallothionein turnover rates (compared with mammals) and the lack of significant cadmium excretion testify to the relatively stable nature of the cadmium-metallothionein complex in these invertebrates and supports the view of a detoxifying role for metallothionein in the mussels.