Biogeochemical dynamics and bioaccumulation processes in Manila clam: Implications for biodiversity and ecosystem services in the Ria de Aveiro Lagoon

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.