“Antarctic sea ice may be a source of mercury in southern ocean fish and birds”

Mercury is found both as a naturally-occurring and introduced contaminant. Its toxic effect depends on its chemical form and the exposure route, with methylmercury (CH₃Hg) being the most toxic form¹. Exposure to methylmercury is almost entirely through ingesting contaminated fish, and since this particular chemical form is absorbed more readily and processed more slowly than other forms, it can have significant effects on the immune system, nervous system, and genetic processes. Developing embryos are especially susceptible to the dangers of methylmercury, since they are five to ten times more sensitive to exposure than adults¹. Sources of mercury include coal combustion, metal mining/processing, medical/industrial waste, geologic deposits, ocean volatilization, and volcanoes. However, atmospheric deposition is the main source of mercury in most environments. Its ability to circulate widely and persist in the atmosphere accounts for its wide-spread distribution, and explains its concentrations in Antarctic. Once deposited, inorganic mercury can undergo methylation by anaerobic bacteria, and subsequently get transformed into methylmercury².

Phys.org is an online science, research, and technology news source. An article published on August 1, 2016 entitled “Antarctic sea ice may be a source of mercury in southern ocean birds”³ outlined the findings of a study conducted by researchers at the University of Melbourne. It started off by stating the main results of the study; that sea-ice bacteria are converting mercury into methylmercury, and that it’s making its way into fish and birds. It then briefly explains the methods of the study; the investigators spent two months collecting sea ice samples from the Antarctic, later analyzing them for four different forms of mercury and microorganism protein and DNA. Throughout the article, there were snippets of background information and implications, mostly through short quotes from the investigators. At the end of the article, the writer identified the main finding and implication of the study. Nitrospina is the genus of Antarctic sea-ice bacteria that is responsible for the methylation of mercury. Is it also responsible for the methylmercury found in other regions? What’s going to happen once seafood companies start harvesting closer the Antarctic?

The purpose of the study was to uncover methylation and volatilization pathways in polar marine environments⁴. Prior to this study, the identity of a mercury-methylating microorganism (defined as those with the hgc genes) in the polar regions was unknown. Researchers at University of Melbourne collaborated with scientists from the U.S. Geological Survey and Lawrence Livermore National Laboratory. They spent two months collecting snow, ice, brine, and sea water from five pack-ice stations during an expedition conducted by the Australian Antarctic Division. Back at the lab, they used metagenomic sequencing and bioinformatic analysis of the microbial DNA extracted from the ice and brine samples to identify the genus responsible for mercury methylation. The researchers were specifically looking for the functional genes hgcA and hgcB, which give rise to mercury methylation capabilities. They identified Nitrospina as the bacterial genus, and concluded that sea ice had higher concentrations of inorganic mercury and methyl-mercury compared to deep sea water, indicative of atmospheric deposition. Along with the ones highlighted in the Phys.org article, the discovery of mercury methylation in well-oxygenated polar surface waters in other studies also holds important implications. How much does polar mercury methylation contribute to global mercury methylation? How will this concentration change with global warming and melting ice caps?
          Overall, for the purposes of Phys.org, I think this article did its job. The writer did a good job of inserting relevant quotes from the researchers throughout the article to provide background. Where there was a lack of relevant quote, the author added a quick sentence clarifying some concepts. However, the article failed to mention one of the most important findings of the article – that, although most known mercury methylation is attributed to strict anaerobes, mercury methylators have now been found in the well-oxygenated polar waters.

Since a lot of criticism from previous blog posts lies with click-bait article titles, I was curious to see how this type of outlet would fare. From its “About Me” page, it specifically states that “Phys.org stories go beyond mere catchy jargon…Our job is to find the interesting science and technology stories, uncover the details, and give our readers a daily dose of news”⁶. With that in consideration, I give this article a 9/10.

References:

1. https://www2.usgs.gov/themes/factsheet/146-00/
2. https://www.ncbi.nlm.nih.gov/pubmed/23393089
3. http://phys.org/news/2016-08-antarctic-sea-ice-source-mercury.html
4. http://www.nature.com/articles/nmicrobiol2016127.epdf?referrer_access_token=I43SLNaw3rtHycvs5QZZ19RgN0jAjWel9jnR3ZoTv0MUGiEHcCbkW0uWqU-Z8_VoE3JlpnhngGCs9ufP8CnBwgqhXISGljmc2vN-iDcoMY3gKaAyaz33Atew6XhQS3yjyFJdqfTWZWudNI2Dh3yyOKDtUHQUeYFeHdnmZHEpfADcN9iP55GYkf_C-BhYC3h5v72kdXj8dMtq0w5AvFjpIjKcMIp6XTOpZy-umWaMa4WzNJGe4QpqroJCiC_Ed5La&tracking_referrer=www.popsci.com
5. http://phys.org/help/about-us/