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Evaluation of the potential of translocated common cockle for ecological risk assessment studies: bioaccumulation and biomarkers test
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Sediment–bound contamination is a major concern factor in estuaries and other confined coastal water bodies, frequently subjected to anthropogenic sources of pollution. In order to investigate the effects and responses of the common cockle (Cerastoderma edule, L. 1558, Bivalvia: Cardiidae) to sediment contaminants and to assess the species’ potential as an
indicator organism, the bivalve was subjected to a laboratorial translocation assay with sediments collected from distinct sites of the Sado Estuary (Portugal). Cockles were collected from a mariculture site of the Sado estuary (Portugal), herewith identified as site A, and exposed through 28–day, semi–static laboratorial essays, to sediments collected from three
other sites (B, C and D) of the estuary that revealed different levels of metals, organic
contaminants and physico–chemical properties and that ranged from globally unimpacted to
moderately impacted levels when compared to available sediment quality guidelines. The
animals were surveyed for bioaccumulation of metals (Ni, Cu, Zn, As, Cd and Pb) and
organic contaminants (PAHs, PCBs and DDTs). Two sets of potential biomarkers were
employed to assess toxicity: whole–body metallothionein (MT) induction and digestive gland histopathology. The bioaccumulation factor (BAF) and the biota-to-soil accumulation factor(BSAF) were estimated as ecological indices of exposure to metals and organic compounds.
Significant positive correlations between BSAF and MT were found for PHAs, and between
each factor (BSAF and BAF) and MT were found for Cd. Histopathological alterations were
found in cockles exposed to all sediments where they were translocated. The digestive gland integrity was found to be especially compromised in cockles from sediment B and C and at day 28 from sediment A. Results allowed concluding that C. edule responds to sediment–bound contamination and is capable to regulate and eliminate both types of contaminants and might, therefore, be suitable for biomonitoring. Still, the sediment contamination levels do not
explain the variation in bioaccumulation and MT levels, which may result from the moderate
contaminant concentrations found in sediments and, more importantly, from yet unexplained xenobiotic interaction effects.
Descrição
Thesis submitted to the Faculdade de Ciências e Tecnologia to obtain the Master’s degree in Environmental Engineering, profile in Ecological Engineering