Abstract
The present work was carried out in the Ria de Aveiro Lagoon (Portugal) to better understand the dynamics driving the bioaccumulation processes in edible bivalves, namely in the Manila clam Ruditapes philippinarum. For the first time, a holistic approach was applied, collecting data on sediment physico-chemical characteristics and its contamination, geochemical speciation and metal(loid) bioaccumulation in clams, from three exploited areas of the lagoon (Costa Nova, Torreira, Ílhavo). The Ria de Aveiro Lagoon is part of the Natura 2000 network, has the designation of Special Protection Area (SPA), contains Sites of Community Importance (SCI), it is protected by the EU Birds Directive (79/109/CEE) and includes a natural reserve in its northern part. Specifically concerning the metal(loid) occurrence, the monitoring and the identification of contaminated sites in protected areas are priorities, to improve the biodiversity conservation efforts and to ensure the correct management of natural resources.Results showed that multiple driving forces interacted together to determine site-specific impacts, resulting in different risks at local scale for the transferring of the metal(loid)s to the trophic chain. Hydrodynamics played a major role driving the occurrence of depositional or ablative sites, influencing the granulometric composition of sediments and their contamination; metal(loid) chemical forms were then determinated by multiple factors like pH, redox potential and organic matter content. The geochemical speciation data showed that the Ílhavo area should be considered the most dangerous in terms of clam consumption, since in case of environmental changes, possible conversion of the elements from the potentially bioavailable forms to the bioavailable ones can occur. Moreover, bioaccumulation processes in Manila clam were observed for Cd, Zn and especially As, the latter representing serious risk for consumer safety throughout clam consumption.
Highlights
Coastal lagoons are considered as highly unpredictable environments, subjected to spatial and temporal bio-geochemical variability (Ferrarin et al, 2010)
Significant correlations were observed among i) fine grained sediments, Total organic matter content (TOM) and metal(loid) content and ii) sandy fraction, pH and Eh. These results indicated that hydrodynamics played a major role in the Ria de Aveiro Lagoon, influencing both the grain-size distribution of particles and the contaminant fluxes (Lopes and Dias, 2007; Martins et al, 2015a)
The results showed a considerable amount of As, Cr, Ni, Zn and Pb associated to the third phase, and especially for Pb, this fraction was comparable to the fraction detected in the second phase
Summary
Coastal lagoons are considered as highly unpredictable environments, subjected to spatial and temporal bio-geochemical variability (Ferrarin et al, 2010). They are among the most productive ecosystems (Covelli, 2012), deeply exploited for human activities. The Ria de Aveiro Lagoon, located in the North-Western Portugal, represents an interesting example of a shallow-water ecosystem. It is formed by several branches and it is characterized by a network of saltmarshes and channels resulting in a very irregular and complex geometry (Martins et al, 2015 a, b). It must be underlined that, in multi-use protected areas, like the Ria de Aveiro Lagoon, it is fundamental to identify the risks related to pollution and transferring of the contaminants among abiotic and biotic compounds, both for biodiversity conservation and human health
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