Mercury in a Time of War

Fig.1. British sailors towing warships toward the besieged city of Canton
in 1841 during the First Opium War (Credit: Edward Hodges Cree)

Since industrialization, mercury levels in our oceans have tripled. This toxic heavy metal is one of many pollutants that can be seen in environmental records as a testament to human activities in the past. A recent article published in the journal Environmental Science & Technology found a new type of environmental record that measures mercury levels in the seawater through time.

Ruoyu Sun, a geochemist at Trent University, Peterborough, and a team of researchers extracted a core covering the past two centuries from a Porites lutea coral in the South China Sea. Like tree rings, coral’s annual growth bands can be used as a measurement of the organism’s life history. As hard corals grow, they pull in minerals from the surrounding seawater to build calcium carbonate skeletons. Oftentimes, pollutants will also become incorporated into coral skeletons.

Fig.2. Porites lutea off the island La Réunion in the Indian Ocean 
(Credit: Philippe Bourjon/2009)

Sun and his colleagues expected to see a gradual increase in mercury concentrations due to industrial production, similar to patterns seen in ice cores. Instead, they found low and constant levels of mercury in the oldest part of the core, from 1800 to 1830. During the next 170 years, however, the mercury concentrations jumped from around 0.5 pmol/g to as high as 10 times those levels. These spikes coincide with wars in the South China Sea, including the First Opium War (1839-1842), the Second Opium War (1856-1860), World War I (1914-1918), and World War II (1939-1945). The researchers think that elemental mercury released during the detonation of weapons and explosives during conflicts later settled in the sea, only to be taken up by corals.

Questions still remain about the rate at which corals take up mercury, or even if the spikes in concentrations are really due to wars. Nevertheless, a detailed examination of toxic heavy metals in our environment is necessary. Environmental records, such as ice cores, have shown lead pollution due to human activities as far back as ancient Greek and Roman times. More recently, heavy metal pollution has been connected to shell fragments from World War I and possibly even to artillery fire in modern day Syria.

Once in the oceans, these toxins can accumulate in living creatures, from corals to fish, and present a serious problem to ecosystems and food sources. Fortunately, studies on environmental records and metal concentrations reveal much needed information on how human activities affect surrounding land and waters. Sun et al.’s narrow focus on one stretch of water adds an important detail to a long history of industry and conflict, hopefully aiding future efforts to protect our oceans.


References
Lamborg, C. H., et al. (2014). A global ocean inventory of anthropogenic mercury based on water column measurements. Nature, vol. 512: 65-68. doi:10.1038/nature13563

Meerschman, E., et al. (2010). Geostatistical assessment of the impact of World War I on the spatial occurrence of soil heavy metals. Ambio., vol. 40 (4): 417-424. Doi: 10.1007/s13280-010-0104-6/

Monahan, P. (2016, May 31). World War II, Opium Wars recorded in ocean’s corals. Science Magazine. Retrieved from: http://www.sciencemag.org/news/2016/05/world-war-ii-opium-wars-recorded-ocean-s-corals?utm_source=newsfromscience&utm_medium=twitter&utm_campaign=warcoral-4709

Sun, R., Hintelmann, H., Liu, Y., Li, X., & Dimock, B. (2016). Two Centuries of Coral Skeletons from the Northern South China Sea Record Mercury Emissions from Modern Chinese Wars. Environ. Sci. Technol. doi: 10.1021/acs.est.5b05965