Preliminary report on thyroid hormone levels in tissues of stranded cetaceans

Exposure to environmental pollutants is one of most important risks for marine ecosystem and species. Most important contaminants are those which persist for long time in the environment and which can concentrate in animal and lead to subtle but important effects, such as endocrine disruption. Knowing the actual levels of pollutant burden and pathophysiological consequences can better the assessment of risk for ecosystems, endangered populations and human health. In monitoring activities focusing on endangered species like sea mammals and turtles, stranded dead animals are often used, as they are easier to collect with respect to live, free ranging animals. Sampling from these individuals only rarely allows the collection of blood samples or the efficient evaluation of markers of effect, particularly those concerning thyroid activity. The present study aims at the evaluation of the applicability of a thyroid hormone extraction method developed for fish tissues to cetacean tissues, in order to create a new tool for the evaluation of endocrine disruption effects of pollutants in highly protected species and/or endangered local populations. Samples from stranded animals collected along Italian Northern Adriatic Sea and Israeli Mediterranean coasts were used. The applied extraction method proved to be efficient for T3 only, which was always above the limit of detection (LOD), while T4 levels were close to or below LOD. This may be expected because data concerning thyroid hormones concentration in animals' fish tissues indicate about low levels of thyroxine T4 in fish tissues and detectable levels of triiodothyrosine T3. The fact that 14 of 73 samples presented T4 concentrations slightly higher than LOD seems to confirm this hypothesis and the applicability of the method to these types of tissues. Mean values of T3 were higher in kidney of many species, followed by muscle and liver. This makes it possible to consider kidney as marker tissue for T3 quantification. These findings are somewhat unexpected, as metabolism and degradation of thyroid hormones occurs in liver, which could have been considered a storage tissue, presenting highest hormone concentrations. Instead, kidney and muscle, which are usually among the less degraded tissues in dead stranded animals, seems to be the best markers of thyroid functioning. To confirm this hypothesis, additional samples need to be analyzed. No statistical difference was observed between species and tissue considered; however a sampling bias should be considered, linked to the large differences in species and tissues numbers. No other information is available on thyroid hormones tissue concentration in cetaceans or other mammals. Scarce data are available concerning blood levels. To our knowledge, the present data are to be considered as the first report concerning thyroid hormone levels in tissues of cetaceans. Further development of an applied analytical method and its application to a larger number of samples, possibly including tissues from healthy, controlled animals (i.e. those housed in...