Abstract
Since the environmental levels of selenium (Se) can moderate the bioaccumulation and toxicity of mercury (Hg) in marine organisms, their interactions were studied in seawater, sediments, plankton and the benthic (Bull ray Pteromylaeus bovinus, Eagle ray Myliobatis aquila) and the pelagic (Pelagic stingray Dasyiatis violacea) rays, as apex predators in the Gulf of Trieste (Northern Adriatic Sea). Male and female rays showed no difference in the Se contents in muscle tissue. Pelagic species contained higher Se levels in muscle but slightly lower levels in the livers of both genders. The Hg/Se ratios in seawater dissolved and colloidal fractions, plankton and sediment were <0.5, while those in particulate matter were <1.3. In benthic ray species, a parallel increase in Se and Hg in muscle was observed, so that an increased in Hg (MeHg) bioaccumulation results in Se coaccumulation. The Hg/Se ratios (molar) in muscle and liver of pelagic and benthic rays were <1.4 and <0.7, respectively. The low levels of Hg in muscle and liver in all the ray species corresponded to low Hg/Se ratios and increases in muscle and liver to 1 at 7 µg/g, dry weight (dw) and 5 µg/g dw, respectively, i.e., about 1.6 µg/g wet weight (ww).
Highlights
It was proposed that selenium (Se) moderates the bioaccumulation and toxicity of inorganic and organic mercury (Hg) in marine organisms [1,2,3,4,5] and in a wide variety of animal species [6,7,8]
A simple Se/Hg molar ratio can be a useful indicator for assessing Hg toxicity [3]
We studied the interactions between Se and Hg in seawater, plankton and sediment, and in benthic (Bull ray Pteromylaeus bovinus, Eagle ray Myliobatis aquila and Common stingray Dasyiatis pastinaca) and pelagic (Pelagic stingray Dasyiatis violacea) rays in the Gulf of Nutrients 2018, 10, 278; doi:10.3390/nu10030278
Summary
It was proposed that selenium (Se) moderates the bioaccumulation and toxicity of inorganic and organic mercury (Hg) in marine organisms [1,2,3,4,5] and in a wide variety of animal species [6,7,8].Irreversible inhibition of essential selenoenzyme activities appears to be the primary mechanism of Hg toxicity [9,10,11]. The antagonistic effects in fish is complex and thought to be based on the formation of biologically inert Me–Hg-selenol complexes [13], and selenoneine [14] that could promote the excretion and demethylation of methyl mercury (MeHg). The animal intake of Se is crucial when the Se/Hg molar ratio in animal’s diet or tissues approach or exceed 1 [7]. In this context, a Se/Hg molar ratio of 1 can play an important role and serve as an indicator of susceptibility to Hg exposure where a more detailed Se and Hg speciation analyses is unavailable [4]. A simple Se/Hg (or Hg/Se) molar ratio can be a useful indicator for assessing Hg toxicity [3]
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