Effects of persistent organic compounds on vitamin and hormone balance in Greenland sharks from the Kongsfjorden ecosystem, Svalbard.
The Greenland shark (Somniosus microcephalus) is the only non-lamnid shark known to inhabit polar waters. The species is present in the Northern hemisphere in the Atlantic Ocean and the Arctic Ocean. Greenland sharks occupy a broad trophic level, feeding on benthic and pelagic fishes and marine mammals, and it has been shown that Greenland shark in the Canadian Arctic feed at the same trophic level as turbot and ringed seals, and at a higher trophic level than harp seals.
Persistent organic pollutants (POPs) are biomagnified in marine food webs, and there are several reports showing that these compounds may affect reproduction and health of marine top predators, such as seals and polar bears. Greenland sharks are long-lived animals with a lipid-rich liver, and this may result in bioaccumulation of significant amounts of lipophilic anthropogenic compounds. Indeed, mean liver concentrations of PCBs in Greenland sharks from the Canadian Arctic have been reported to be relatively high (3400 ng/g lipid. In Greenland sharks caught off the coast of Iceland, liver concentrations have been reported to be even higher, 4400 ng/g lipid. These concentrations are approximately 50% of the concentrations reported in female polar bears (1995-1998), and within the concentration range that have been reported to cause endocrine effects in fish, seals and polar bears.
With respect to effects of POPs on the endocrine system of animals, there are special concerns about the effects of contaminants such as PCBs and their hydroxylated metabolites (PCB-OHs), brominated flame retardants and perfluorinated compounds on the thyroid and the retinoid system (Vitamin A). In many animals the effects on the thyroid and retinol system of these compounds are linked to a common mode-of-action. In plasma, thyroxin (T4) and retinol are transported by a thyroid-binding-protein (transthyrethin, TTR)- retinol-binding-protein (RBP) complex. Due to their structural similarities, PCBs and in particular PCB-OHs, bind to TTR and causes a structural disruption of TTR which prevents the formation of a TTR-RBP-complex. Thus, the transport of both T4 and retinol in the blood is disrupted, and this may lead to serious health problems which eventually affect development, growth, reproduction and survival. TTR has been identified in elasmobranchs.
The aim of the present study, which is my MSc research project in Environmental toxicology at the Department of Biology, Norwegian University of Science and Technology (NTNU), is to examine the possible effects of thyroid and retinol disruptive anthropogenic in Greenland sharks in the Kongsfjorden ecosystem, Svalbard. Since there is no scientific information on basal levels of thyroid hormones and retinoids for this species, and few studies on endocrine systems of elasmobranches generally, this study will also provide basic insight into the endocrine systems of this group of fishes. Furthermore, by using multivariate statistics, it is possible to identify the contaminants (single and/or mixtures) that have most impact on the endocrine variables, and to identify compounds that act synergistic and/or antagonistic.
Since both these endocrine systems are linked to reproduction and general health, effects caused by contaminants are likely to be of ecological significance, and the results will be important input in ecological risk assessment of POPs in Arctic marine ecosystems.
The specific aims are: 1. Determine associations between persistent organic contaminants and plasma/liver concentrations of thyroid hormones (total and free thyroxin, and total and free triiodothyronine). 2. Determine associations between persistent organic contaminants and plasma/liver concentrations of retinoids (retinol and retinylpalmitate).3. Identify the particular contaminants, or mixture of contaminants, that have largest impact on the endocrine variables.4 Provide basal information on the thyroid and retinol system of the Greenland shark.