Iris Cáceres-Saez

The skin of Commerson’s dolphins (Cephalorhynchus commersonii) as a biomonitor of mercury and selenium in Subantarctic waters

The skin of bycaught Commersons dolphins was tested for mercury (Hg) and selenium (Se) biomonitoring in Subantarctic environments. The correlation of levels detected in the skin with those found in internal tissues - lung, liver, kidney and muscle - was assessed to evaluate how skin represents internal Hg and Se distribution for monitoring purposes. Mercury in skin had a concentration range of 0.68-3.11 μg g(-1) dry weight (DW), while Se had a higher concentration range of 74.3-124.5 μg g(-1) DW. There was no significant correlation between selenium levels in any of the analyzed tissues. Thus, the skin selenium concentration did not reflect the tissular Se levels and did not provide information for biomonitoring. The lack of correlation is explained by the biological role of Se, provided that each tissue regulates Se levels according to physiological needs. However, the skin Hg level had significant positive correlation with the levels in internal tissues (ANOVA p<0.05), particularly with that of muscle (R(2)=0.79; ANOVA p=0.0008). Thus, this correlation permits the estimation of Hg content in muscle based on the multiplication of skin biopsy levels by a factor of 1.85. Mercury bioindication using skin biopsies is a non-lethal approach that allows screening of a large number of specimens with little disturbance and makes possible an adequate sampling strategy that produces statistically valid results in populations and study areas. The correlation between Hg levels in the skin and internal tissues supports the use of the epidermis of Commersons dolphins for Hg biomonitoring in the waters of the Subantarctic, which is a poorly studied region regarding Hg levels, sources and processes.

High status of mercury and selenium in false killer whales (Pseudorca crassidens, Owen 1846) stranded on Southern South America: A possible toxicological concern?

The study was carried out to determine Hg and Se concentrations in false killer whales stranded on the Estrecho de Magallanes, Chile, South America. Tissue samples of five mature specimens were analyzed (two females and three males). Mean Hg concentration in liver 1068 (234) μg g-1 dry weight (DW) (standard deviation in parenthesis) was markedly higher than those in kidney 272 (152) μg g-1 DW, lung 423 (325) μg g-1 DW, spleen 725 (696) μg g-1 DW, muscle 118 (94) μg g-1 DW and testicle 18.0 (2.8) μg g-1 DW. Mean Se concentration in liver, 398 (75) μg g-1 DW, was higher than those in kidney 162 (69) μg g-1 DW, lung 128 (84) μg g-1 DW, spleen 268 (245) μg g-1 DW, muscle 47 (38) μg g-1 DW and testicle 25.4 (2.1) μg g-1 DW. Positive correlations were found between Hg and Se molar concentrations in muscle, lung, spleen and kidney. Molar ratio of Se/Hg in liver, lung and muscle were <1, but those in kidney and testicle were markedly >1 suggesting a Se protection against Hg toxicity. In all the examined specimens Hg values exceeded the toxic thresholds defined for hepatic damage in marine mammals, with Se/Hg molar ratios below 1 implying limited protective action of Se. Generally, our results showed that individuals are carrying a significant burden, reflecting a high exposure to this toxic metal. This constitutes the first report on Hg and Se levels for a large subantarctic odontocete in South America region, providing insights into their contamination status and with information to the understanding of possible impacts on wild populations.

Elemental concentrations in skin and internal tissues of Commerson’s dolphins (Cephalorhynchus commersonii) from subantarctic waters

The skin of cetaceans is the most accessible tissue, and its sampling has been proposed as a noninvasive method to evaluate trace element concentrations in free-ranging populations. In the present work, concentrations of essential (Cl, Na, K, Mg, Fe, Zn, Mn and Co), nonessential (As and Ag), and of unknown essentiality (Br, Rb and Cs) elements were determined in the skin from nine by-caught Commerson’s dolphins (Cephalorhynchus commersonii) from Tierra del Fuego, Argentina. Skin correlations with internal tissues—lung, liver, kidney and muscle—were assessed to evaluate how the skin represents internal element concentration for monitoring purposes. Elemental contents were analyzed by instrumental neutron activation analysis (INAA). Regarding tissue distribution, skin had the highest concentration of Zn being two orders of magnitude higher than internal tissues, while other elements such as Co and Rb had similar concentrations among tissues. High mean concentrations of Cl, Na, Mg, Br and Mn were observed in the lung and liver. Our results support the use of skin to evaluate Fe, Br and Rb concentrations in internal tissues for biomonitoring purposes; however, other elements did not show significant skin-to-tissue correlations. Overall, toxic element levels were far below concentrations found to cause harm in marine vertebrates. This study provided baseline data on elemental concentrations in tissues of Commerson’s dolphins in subantarctic waters from the South Atlantic Ocean.

Mineral and essential element measurements in dolphin bones using two analytical approaches

ABSTRACT We explored the potential of using energy-dispersive X-ray analysis (EDX), a non-destructive technique, to assess elemental contents in dolphin bones. Specimens were deposited in museum collections, and prepared by different methodologies. Fifty eight Commerson’s dolphins (Cephalorhynchus c. commersonii) chevron bones and 24 Franciscana dolphins (Pontoporia blainvillei) were analysed. The EDX allowed us to detect the following elements: Ca, P, Na, Mg, Fe, K, Zn, S, Cl and Al; and quantify their proportion (weight percent of element). Principal components analysis differentiates two groups according to the cleaning procedures applied, supporting that cleaning methods could influence the chemical integrity of bone. No significant age-dependent increase was found for elements analysed in species, and no significant differences were found between sex and physical maturity stages. Alternative assessment was made through atomic absorption spectrophotometry, providing quantitative information on the principal elements in bones (Ca, P, Mg, Na, Fe and Zn) and allowing comparisons with other studies. A standard protocol for bone cleaning and conditioning is needed to exclude any effect on the mineral integrity of calcified tissue. This would enable future comparative studies on the bone mineral matrix over time housed in natural history museums or other scientific collections.