Dynamics of Dietary Mercury Determined by Mercury Speciation and Isotopic Composition in Dicentrarchus labrax

Abstract

Seafood has a great ecological and nutritional value for human and wildlife communities. However, accumulation of mercury (Hg) in fish is a concern to animal and human health. There is a crucial need to understand Hg speciation in marine organisms through controlled feeding experiments. This study represents a first assessment of the biological processes that may influence Hg bioaccumulation and dynamics in a marine predatory fish. We conducted a feeding experiment to investigate the dynamics of MeHg and iHg, as well as Hg isotopes in the liver and muscles of captive juvenile seabass (Dicentrarchus labrax). Three groups of juvenile seabass were fed in captivity during 3 weeks of acclimatization and 6 weeks of experiment. Each group was fed with pellets containing environmentally relevant MeHg concentrations (Control, 200 and 500 ng g−1 dw). We monitored the evolution of MeHg and iHg concentrations as well as Hg isotopic values in liver and muscle. We determined Hg dynamics with respect to the contamination level in the fish diet. Muscle δ202Hg and Δ199Hg turnover rates ranged between 33 and 14 days (Low diet) to 5 and 9 days (Mod diet). Liver δ202Hg and Δ199Hg turnover rates ranged between 3 and 7 days (Low diet) to 3 and 2 days (Mod diet), respectively. Hg species concentrations and δ202Hg varied over time between diet groups and tissues, showing the occurrence of internal mass-dependent fractionation (MDF). No significant intra-tissue and temporal Hg mass-independent fractionation (MIF) was observed. The results of our experiment are strongly in favor of the existence of MeHg demethylation in a coastal predatory fish exposed to low to moderate concentrations of environmental Hg. The decrease over time of δ202Hg in muscle of seabass from the most contaminated diet was accompanied by a temporal increase in iHg, pointing to possible Hg detoxification processes occurring in this tissue when dietary Hg exposure is high. The absence of Hg MDF and different turnover between muscle and liver in seabass exposed to 500 ng Hg g−1 confirmed that Hg speciation and bioaccumulation in juvenile fish are controlled by Hg levels and speciation in their diet.

Bioaccumulation of inorganic and organic mercury in the cuttlefish Sepia officinalis: Influence of ocean acidification and food type

“…Other factors, not investigated here, such as tissular and subcellular distribution driving metal bioaccessibility could also play a key role on trace element assimilation (Ni et al, 2000;Pouil et al, 2016). Moreover, differences in trophic transfer of iHg and MeHg has been previously seen in copepods, in mussels and in fish (Trudel and Rasmussen, 1997;Wang and Wong, 2003;Feng et al, 2015;Lee and Fisher, 2017;Pinzone et al, 2022), especially with respect to the lower excretion rates of organomercurial species when compared to the iHg observed in fish (Trudel and Rasmussen, 1997;Feng et al, 2015). Thus, our results strongly suggest that the more abundant iHg contained in the shrimp is rapidly eliminated contributing to the lower Tb1/2 of the total assimilated 203 Hg when compared to the long Hg retention in fish-fed cuttlefish.…”

The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark

“…This onshore fasting implies that MeHg in all seal tissues may come from the same offshore dietary sources . Moreover, as MeHg isotope ratios are similar between different tissues of seals fed a constant diet, and MeHg fraction is high in seal hair, Δ 199 Hg and δ 202 Hg values of THg in NES hair represent a relevant proxy for the MeHg isotopic signature in other tissues (e.g., blubber and muscle) …”

“…Total Hg (THg) is known to be predominantly in the MeHg form in the dermis and muscle of various shark species, ,− aquatic and marine mammal hair, − as well as in pelagic fish muscle and squid mantle. , THg was thus used as a proxy for MeHg concentrations in all the species studied here. Moreover, THg isotope ratios in sharks and seals analyzed in this work, or obtained in pelagic organisms from previous studies, , mainly reflect the isotopic signature of MeHg.…”