Mercury, organic-mercury and selenium in small cetaceans in Taiwanese waters

Total Hg (sigmaHg), organic-Hg (O-Hg) and Se bioaccumulations in small cetaceans distributed in Taiwanese waters of the Taiwan Strait and the southwestern Pacific have been investigated for the first time. The results could represent the baseline metal concentrations of marine mammals in the southwestern Pacific, where volcanic activities are possibly the major source of mercury to the environments. Muscle samples of four species of small cetaceans were collected from animals accidentally caught by tuna-longline fisheries from 1994 through 1995. In total, 53 pantropical spotted dolphins, Stenella attenuata, nine spinner dolphins, S. longirostris, five bottlenose dolphins, Turiops truncatus and four Risso's dolphins, Grampus giseus were analyzed. In addition, two stranded pantropical spotted dolphins were investigated. Cold vapour AAS and ICP-MS were used in the analysis of Hg and Se, respectively. Significant species difference was found in the four species of small cetaceans. Among them, the pantropical spotted dolphin showed the highest mean concentration (mg/kg wet wt.) of both sigmaHg (3.64 +/- 2.19) and O-Hg (2.79 +/- 1.23), whereas the Risso's dolphin had the highest mean concentrations of Se (1.77 +/- 1.29). There was no significant sex difference with respect to metal bioaccumulation in the samples of S. attenuata. Significant correlations between body length (BL) and sigmaHg, as well as O-Hg concentrations were observed in pantropical spotted (Sa) and spinner dolphins (Sl). The linear relationships were Sa: sigmaHg = -8.290 + 0.066BL, r = 0.421; Sl: sigmaHg = -2.735 + 0.025BL, r = 0.875; Sa: O-Hg = -3.723 + 0.036BL, r = 0.408; and Sl: O-Hg = -3.017 + 0.025BL, r = 0.870. However, a demethylation phenomenon that decreasing the percentage of O-Hg coupled with increasing levels of Se was observed when the sigmaHg concentrations in the muscle tissues of dolphins reached 4 mg/kg wet wt.