This study undertaken at the University of Canberra is a pilot project to investigate mercury cycling in coastal ecosystems of Australia. Mercury (Hg) is a globally important pollutant and is of particular concern because of the potential to both bioaccumulate (accumulate in the tissues of an individual animal over its lifetime) and biomagnify (increase in concentration as it moves up food chains). Assessing the risks to iconic marine mammals, in this instance the Tursiops australis dolphin, from mercury contamination of coastal ecosystems has been a significant driver for this study.
This study enabled early-career research scientist, Dr Olha Furman, to conduct high quality studies on biological processes affecting bioaccumulation of mercury. This project built on skills she developed in a post-doctoral position in the US and the strengths of the University's Institute for Applied Ecology (IAE). As a research training institute, the staff, students and associates within the IAE contribute to understanding and improving the management of species, communities and social-ecological systems.
Aims & objectives
The project examined mechanisms of mercury bioaccumulation and toxicity in coastal food webs. Selenium (Se) plays a major role in detoxifying mercury within organisms. The selenium– mercury molar ratios were determined in liver tissues of aquatic organisms as a measure of potential mercury toxicity. The researchers were awarded beam time at the X-ray Absorption Spectroscopy Beamline at the Australian Synchrotron to examine mercury–selenium complexes and evaluate their toxicity within the tissue.
A field campaign took place between March and May 2016, involving 12 sampling locations in Port Philip Bay, Victoria. Seagrass, seaweed, polychaetes, crustaceans, molluscs and fish were collected, where present, at these sites.
The field sampling involved undergraduate students from the University, and was extended and coordinated in collaboration with Dr Paul Hamer (Fisheries Victoria) and Dr Kate Charleton-Robb (Museum of Victoria and Australian Marine Mammal Conservation Foundation). Total mercury and selenium concentrations were determined in more than one thousand biological samples using an inductively coupled plasma mass spectrometry.
The findings show mercury levels in food sources at the base of the food web and sediments were consistently low and approached the minimum detection limit. However, once mercury entered the food chain it bioaccumulated and biomagnified in carnivores, particularly those which target seabed and sediment living species.
Our results also show that trophic level (including correlated measures of size, length and age) and habitat influenced mercury bioaccumulation and biomagnification in Port Phillip Bay.
Stated plainly, larger species such as dolphins which are long-lived, high trophic-level species, had the highest mercury concentrations, but also had the lowest Se/Hg molar ratios. Through the use of x-ray absorption spectroscopy beamline we have demonstrated the formation of HgSe in dolphin liver tissues. This novel finding suggests the formation of HgSe is an important element in the detoxification pathway in these dolphins.
We have collected and analysed over 1000 samples collected from a variety of sites in the Port Phillip Bay region. The scale of the projects allowed us to demonstrate spatial variability in the concentrations of mercury found in fish muscle tissue. The results of this study indicate an important role for selenium in protecting dolphins from the effects of mercury contaminations.
We will seek further funding to examine metabolic transformation of mercury species in dolphins exposed to different levels of mercury in their natural environment.
Dr Olha Furman, Post-doctoral scientist at the University of Canberra. (Current position: Risk Assessment Scientist, Chemicals and Biotechnology Assessments, Australian Government Department of the Environment.)
'This grant supported Dr Furman and four undergraduate students to examine the Mercury levels of the fish in Port Phillip Bay testing more than 1000 biological samples. Mercury is a globally important environmental pollutant. This high quality research led to some interesting results in terms of the detox properties of Selenium in filtering Mercury in dolphins. We look forward to learning more as the project team explore this finding further.'
Nicole Bortone, Science Program Manager