Elemental and isotopic fingerprints during the life cycle of the manila clams Ruditapes philippinarum in the Goro Lagoon (north Adriatic Sea): tools

In Italy, the production of manila clams (Ruditapes philippinarum, Adams and Reeve, 1850) is mainly localized in northern Adriatic lagoons of the Po River delta, where shellfish farming provides important economic revenue (Giani et al., 2012). However, the seafood market is threated by fraudulent activities in which agri-food products, whose provenance is not certified, are sold posing a risk to consumers health. Multiisotope ratios and elemental analyses are commonly used to trace the provenance of food products in different countries, included seafood and to assess their safety. However, the variability of geochemical fingerprints during the life-cycle of the manila clams where never investigated. In this study, the elemental concentrations and isotopic ratios in seeded manila clams (both shells and tissue) were monitored during mollusks growth at two sites of the Goro Lagoon (Emilia-Romagna). Tissues of juvenile (< 1.6 cm) and old (> 1.6 cm) organisms were analyzed with an elemental analyzer coupled with an isotopic ratio mass spectrometer (EA-IRMS) for total carbon, organic carbon, nitrogen, and sulphur elemental contents and the relative isotopic ratios (d13CTC, d13COC, d15N, d34S). Shells of the same organisms were analyzed with a head-space analyzer coupled with an IRMS for carbon and oxygen isotopic fingerprints (d13C, d18O) and with an inductively coupled plasma mass spectrometer (ICP-MS) for the trace elemental compositions. Total Hg concentrations in manila clam tissues were also determined with a Direct Mercury Analyser (DMA-80, Milestone) according to EPA Method 7473 in order to assess contamination levels and potential risk for human consumption. The environmental conditions of the Goro Lagoon during shellfish sampling were also monitored through the in-situ measure of pH, temperature and electrical conductivity of the water. Anions and cations of water samples were measured with ion-chromatography. Finally, also sediment samples from the two sites were collected during the different sampling seasons and CaCO3 content measurements, grain size and geochemical (isotopes and elemental concentrations) analyses were performed. The obtained results complement earlier works on tracing the provenance of manila clams in the northern Adriatic lagoons (Bianchini et al., 2021; Brombin et al., 2022) by adding physico-chemical, elemental and isotopic parameters during the entire life-cycle of the mollusks. This will allow to test the reliability of the food traceability geochemical techniques. Finally, the outcomes of this work might help to monitor the resilience of these organisms to the effects of anthropogenic and natural factors (e.g. pollution, water circulation, nutrient supply, climate changes) occurring in the Goro Lagoon.