Evaluation of the potential of translocated common cockle for ecological risk assessment studies: bioaccumulation and biomarkers test

Thesis submitted to the Faculdade de Ciências e Tecnologia to obtain the Master’s degree in Environmental Engineering, profile in Ecological Engineering

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.