Monday, December 5, 2011

Why Study Mercury Contamination in Antarctica?

Global mercury deposition has steadily risen throughout the 20th century due to increased anthropogenic emissions that are transported and deposited around the world, including in remote polar ecosystems. Due to its remoteness the Antarctic has historically been considered “pristine” and unpolluted; however, the Antarctic region has recently become a place of interest for investigations into the global mercury cycle.  With no known point sources of mercury, the Antarctic may provide the opportunity to investigate natural, or “background” fluctuations as well as the impact of increasing anthropogenic inputs into the global mercury cycle.

Mercury is one of the most common and most toxic contaminants present in marine environments today.  While there are natural sources of mercury emissions, such as volcanic eruptions and wildfires, human activities have added significantly to global mercury emissions since the beginning of the industrial age.  Today, coal burning accounts for approximately 45% of all human-related mercury emissions.  Mercury is released into the atmosphere when fossil fuels are burned and it is easily transported around the globe to even the most remote environments, such as the Antarctic. 

Mercury biomagnifies up the food chain;
species, such as krill, at low trophic positions
most often have lower mercury levels than
top predators.
Biomagnification of mercury in the Antarctic marine food web
Mercury from the atmosphere is deposited into the ocean where it bioaccumulates and biomagnifies through the food web.  Biomagnifcation is the process through which mercury concentrations increase with each step up in the food web—organisms that feed at the highest trophic positions are likely at the highest risk of mercury toxicity. 

At high levels mercury is a neurotoxin in both humans and birds (such as penguins); it can cause developmental abnormalities, impair feeding and breeding behavior, and even cause mortality.  However, reproduction is the most sensitive endpoint of mercury contamination and even very small quantities can lead to decreased egg production and hatching success in birds.  At this point, we do not know how much mercury is tolerated by penguins before they start to show signs of mercury toxicity.  My preliminary data suggests that the current level of mercury in brush-tailed penguins is likely too low to cause reproductive impairment or decreased survival.  However, as the brush-tailed penguins in the Antarctic Peninsula are currently experiencing significant impacts of global climate change, any additional stressor such as mercury (even at low levels) may ultimately impact the viability of their populations.

Michael in Mrs. Winder's class at Troy High School in Troy, Kansas has asked: How do you tell how much mercury is in the feathers and eggshells?  I use a piece of equipment called a Direct Mercury Analyzer, DMA-80.  I load a piece of eggshell membrane or feather into a small sample tray in the DMA-80.  Then the sample goes through a combustion furnace where any mercury trapped in the tissue turns into a gas.  The mercury gas then gets analyzed through a process called atomic absorbance spectrophotometry and the machine tells me how much mercury was in the sample.

Penguin feathers loaded into the

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