Impact of a Sacrificial Anode as Assessed by Zinc Accumulation in Different Organs of the Oyster Crassostrea gigas: Results from Long- and Short-Term Laboratory Tests

Abstract

Sacrificial anodes made of zinc are currently used in marine environments to mitigate marine corrosion as part of CP systems of immerged metallic structures. The aim of this work was to study zinc bioconcentration in the oyster Crassostrea gigas by performing two in vivo tests during different time periods and at different zinc concentrations. The first test was conducted during a period of 10 weeks at a concentration of 0.53 ± 0.04 mg Zn L(-1) to simulate long-term exposure, and a second test was conducted during a 168-hour period at a concentration of 10.2 ± 1.2 mg Zn L(-1) to reproduce short-term exposure. In these experiments, the zinc source was an electrochemical device that included a sacrificial anode to mimic the in situ conditions. During the first 14 days of the long-term experiment, digestive glands of C oysters exhibited bioaccumulation of zinc that varied according to the oysters' reproductive cycle. Both a bioconcentration factor (BCF) of ≤ 13,397 and a zinc accumulation percentage of +297% of zinc occurred in this organ after 10 weeks. The results obtained from the short-term test showed a lower BCF of 405 but a faster bioaccumulation of zinc (starting from the first day) in the same organ. No mortality was observed in long-term assay, but 81.8% of the oysters died at the end of the short-term assay. These results demonstrate the great capacity of C. gigas to accumulate zinc released from the anode, especially when low concentrations are released, as in the case of anode dissolution used as CP. This study confirmed the necessity to monitor this zinc-contamination source in marine environments in relation to the usual oyster consumption by humans (especially in France). No implication for human health of this zinc-contamination source was demonstrated until now, and this was not the purpose of this study; however, zinc remains one of the most abundant nutritionally essential elements in the human body that may affect the human immune system at high-level uptake.

Effect of zinc sacrificial anode degradation on the defence system of the Pacific oyster, Crassostrea gigas: Chronic and acute exposures

“…In contrast, these authors did not observe MT gene induction in Dreissena polymorpha. In the present study, it appeared that MT mRNA expression was correlated with zinc bioaccumulation in tissues, which also appears to be time and dose dependent (Caplat et al, 2012). Correlations between zinc concentrations and MT levels in tissues of some species of bivalves have been reported (Irato et al, 2003;Marie et al, 2006b).…”

“…Correlations between zinc concentrations and MT levels in tissues of some species of bivalves have been reported (Irato et al, 2003;Marie et al, 2006b). However, during chronic exposure, expression of MT mRNA was increased in gills, but not in the digestive gland, whereas the zinc concentration was higher in the digestive gland than in gills (Caplat et al, 2012). It therefore appeared that zinc accumulation in the digestive gland did not lead to MT induction.…”

“…Inversely, when zinc was present in excess, zinc accumulation was too rapid to allow MT to sequester this metal. As a consequence, zinc exposure resulted in a lower zinc concentration in the organs (Caplat et al, 2012), decreases in immune system parameters and high rates of oyster mortality under these conditions.…”

“…We hypothesise that during exposure to a moderate zinc concentration, oysters present an adaptative metabolism leading to induction of MT, which protects organisms from mortality to some degree because no mortality and the highest zinc concentrations in the organs were recorded under these conditions (Caplat et al, 2012). Inversely, when zinc was present in excess, zinc accumulation was too rapid to allow MT to sequester this metal.…”

Effect of chronic exposure to zinc in young spats of the Pacific oyster (Crassostrea gigas)

“…In coastal marine systems, its concentration is influenced by many human activities [2], including the use of antifouling paints and sacrificial anodes [3]. The effects of chronic exposure to zinc on filtering bivalves have been previously investigated by several authors who focused on bioavailability, tissue accumulation, transfer kinetics, and relationships with metallothionein [4][5][6][7][8][9]. Numerous studies have addressed early life stages and toxicity [7,[10][11][12][13][14][15][16][17], most of which involved larvae.…”