Mercury in 16 demersal sharks from southeast Australia: Biotic and abiotic sources of variation and consumer health implications

Heidi Pethybridge , Daniel Cossa , Edward C.V. Butler

Total mercury (THg) and monomethylmercury (MMHg) concentrations were determined in the tissues of demersal shark (Order Squaliformes and the Families: Scyliorhinidae, Hexanchidae) and chimaera species (Families: Chimaeridae and Rhinochimaeridae) from continental shelf and slope waters off southeast Australia, including embryos, juveniles and adults. The distribution of THg in various tissues (muscle, liver, kidney, and skin), examined in ten species, shows higher levels in the muscle tissue (1.49 ± 0.47 mg kg, ww), which accounted for between 59 – 82% of the total body burden of mercury and in the kidney (0.93 ± 0.14 mg kg, ww) and liver (0.61 ± 0.25 mg kg, ww) with lower levels observed in the skin (0.12 ± 0.06 mg kg, ww). Additional THg determinations were performed in the muscle tissue of five other species allowing geographical and interspecific comparisons. Speciation analysis demonstrated that more than 90% mercury was bound in muscle tissue as MMHg with higher percentages (>95%) observed in sharks species occupying deeper environments. Species differences were observed. Highest THg levels in the muscle tissue (up to 6.64 mg kgwet weight, ww) were recorded in and (mean values; 4.47 ± 1.20 and 3.52 ± 0.07 mg kg, ww, respectively). Consistent with the ongoing paradigm on mercury bioaccumulation, we systematically observed THg concentrations increasing with animal size from the embryos to the larger sharks. Embryos of and had average levels 0.28 and 0.06 mg kg (ww), while adult specimens reached 3.3 and 2.3 mg kg (ww), respectively. THg concentrations in Australian sharks were compared with the same genus collected in other world regions. Levels were closer to data reported for East Atlantic than for the epicontinental Mediterranean margins. At a smaller geographical scale, the habitat effect on mercury concentration in sharks seems less clear. Squalid sharks occupying shelf waters showed higher mean mercury levels relative to their size (body weight, bw) than mid-slope species (0.4 – 6.7 mg kg bw and 0.3 – 2.2 mg kg bw, respectively). However, local regional differences (East and South Tasmania Victoria) in Hg levels were not detected for the majority of taxa examined. All species, with the exception of showed values greater than 0.5 mg kg (ww) and all but four were above many international regulatory thresholds (1.0 mg kg, ww).

Mots clés: Mercury; methylmercury; deep-sea; body distribution; maternal transfer; Squaliformes; Chimaeriformes; Carcharhiniformes

Heidi Pethybridge, Daniel Cossa, Edward C.V. Butler. Mercury in 16 demersal sharks from southeast Australia: Biotic and abiotic sources of variation and consumer health implications. Marine Environmental Research, 2009, 69 (1), pp.18. ⟨10.1016/j.marenvres.2009.07.006⟩. ⟨hal-00563093⟩