Mercury and selenium levels in lemon sharks (Negaprion brevirostris) in relation to a harmful red tide event

Abstract

Tissue levels of mercury (Hg; total, organic) and selenium (Se) were assessed in juvenile lemon sharks (Negaprion brevirostris) from Florida nearshore waters collected during a harmful algal bloom (HAB, brevetoxin) event and compared with sharks not exposed to HABs. In all sharks studied, total Hg levels in the muscle were generally present in a molar excess over Se (which may protect against Hg toxicity) and mean muscle Hg levels (0.34 microg/g) exceed safe human consumption guidelines. While there was generally no difference in tissue Hg and Se levels following exposure of sharks to HABs, hepatic Hg levels were significantly lower (56% reduction) in the HAB-exposed sharks compared to controls. As Hg and HABs are globally increasing in scope and magnitude, further work is warranted to assess their interactions and biotic impacts within aquatic ecosystems, especially for a species such as the lemon shark that is classified as a near-threatened species by the International Union for the Conservation of Nature.

Cyanobacterial Neurotoxin BMAA and Mercury in Sharks

“…In addition, MeHg was measured in a subset of sharks with concentrations ranging from 0.05 to 1.95 ng/mg and a mean concentration of 0.42 ± 0.11 ng/mg (Table 4). THg and MeHg concentration in shark samples tested were highly correlated (Spearman correlations r = 0.94, p < 0.0001; n = 18) in our shark cohort as expected [33,34,35]. …”

“…Shark samples were analyzed for BMAA using high performance liquid chromatography with fluorescence detection (HPLC-FD) and Hg concentrations were quantified by cold vapor atomic fluorescence spectrometry (CVAFS). Since the total Hg (THg) that is measured in shark muscle and fin is mostly in the form of MeHg+, measures of total Hg are generally equivalent to MeHg+ [33,34,35] Here, THg concentrations in fin and muscle samples were measured and compared to MeHg+ for confirmation of levels in select samples. Our results demonstrated that all 10 shark species tested positive for both BMAA and Hg.…”

Mercury and Selenium in Muscle and Target Organs of Scalloped Hammerhead Sharks Sphyrna lewini of the SE Gulf of California: Dietary Intake, Molar Ratios, Loads, and Human Health Risks

“…5b). Hg is likely sequestered by metallothioneins and other protective proteins, such as selenium proteins (Nam et al 2011). From in vivo assay studies, proposed Hg and Se toxicokinetics when fishes are exposed to MeHg and Se, accumulation is much lower in all organs than when fishes are exposed solely to MeHg, this may result from (Yang et al 2008;Branco et al 2012): (i) excess Se induce an increased production of selenoprotein, with the selenocysteine in this protein acting as a trap for MeHg keeping it in circulation and preventing its entry to the different organs; (ii) selenium preventing MeHg interactions with proteins by competing for the binding sites (SeH and SH groups); and (iii) Se binding MeHg during coexposure enhancing its excretion.…”

Heavy Metal Concentrations of Two Highly Migratory Sharks (Prionace Glauca and Isurus Oxyrinchus) in the Southeastern Pacific Waters: Comments on Public Health and Conservation

“…Large size individuals of P. glauca had greater mercury and lead concentrations than small individuals. This is a well-documented process [12,13,20,[25][26][27][28][29][30][31][32][33][34] known as bioaccumulation [25,28,35]. The bioaccumulation process can take different pathways, one of which is through the diet (biomagnification).…”