The presence of methylmercury in sea ice provide the first empirical evidence that bacteria can convert mercury into a very dangerous chemical. When ingested by birds, fish or even people methylmercury can travel to the brain, causing developmental and physical problems.
The toxin is formed by a chemical process whereby inorganic mercury is converted by the action of microbes that live in aquatic systems. The chemical presents a great risk to the food chain, for it becomes “biomagnified” in aquatic food chains, starting with bacteria, to plankton, through macroinvertebrates, to herbivorous fish and to piscivorous (fish-eating) fish, and then to seabirds The toxin could also end up in human consumed fish.
The new evidence comes from University of Melbourne scientists who have undertaken a series of tests. Here doctoral researcher Ms Gionfriddo spent two months aboard the icebreaker Aurora Australis to collect samples of Antarctic sea ice. The ice was later analyzed for different forms of mercury.
Further testing revealed the presence of bacteria in the sea ice with the genetic ability to convert mercury into the more toxic form. The source mercury comes from volcanoes, bushfires, and from fossil fuel power plants. Human energy production is regarded as a major source and earlier research has shown mercury deposits can extend up to 3,000 kilometers. In a research note, Ms Gionfriddo states: “The deposition of mercury into the sea occurs all year-long but increases during the Antarctic spring, when the sunlight returning causes reactions that boost the amount of mercury that falls onto sea ice and the ocean.”
The findings are published in the journal Nature Microbiology. The research paper is titled “Microbial mercury methylation in Antarctic sea ice.”
