KoestnerWhy+Worry

=Why Worry About Environmental Sustainability? think mercury.... by Dan Koestner=

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Introduction:
Mercury (Hg) is a very unique transition metal. It is the only one that remains liquid at room temperature. This makes Hg very volatile and more reactive than most transition metals. Hg is a known neurotoxin. It can enter the blood through various mechanisms, but I am only going to discuss the ingestion of Methylmercury (MeHg). MeHg is an organic molecule that incorporates Hg. Because it is organic, it can easily be stored and moved within biologic organisms. The toxicity of MeHg is very high. The current EPA reference dose is 0.1 µg/kg body weight/day without any recognized adverse affects. Exposure to Hg doses over this can damage the human nervous system, which can have detrimental effects on the heart, brain, kidneys, lungs and immune system.

Where does it come from?
Hg is a naturally occurring element. Hg is released into our environment through anthropogenic and natural events. The natural Hg emissions are generally from surface and underwater magma extrusions. The anthropogenic Hg emissions are primarily from the burning of coal. Mercury Sulfides are prevalent in coal, and when burnt, the Hg can be released in its elemental form. In its elemental form, Hg can travel in the atmosphere for up to one year and can even travel glo bally. When Hg enters the atmosphere, it can be deposited by wet or dry deposition. In soil and water sources, Hg undergoes reactions that convert its elemental form into its dangerous organic version, MeHg. That is when it can be bioaccumulated and biomagnified because of its ability to bind to fats. This is where Hg differs from many other pollutants. EPA estimates that annual Hg emissions (natural and anthropogenic) are on the order of 4800-8300 tons per year. The U.S. anthropogenic releases only account for about 3% of the total global emissions. Since Hg has a relatively long atmospheric life span, estimates suggest that less than half of all Hg deposition in the U.S comes from internal sources. Because of this, most Hg problems in waterways are from non-point polluting sources and so it is very difficult to regulate and collaborate clean-up techniques.

Current Regulation:
As of August 2005, there is no regulation of Hg emissions from coal power plants in the U.S. This could be because the numbers involved are very low or that there is no available technology to remove Hg from smoke stacks. However, as noted before, this is a non-point pollution problem. Regulatory actions would have to be made world wide to have any effect on most areas, especially the Adirondack region, or other mountainous regions.

Bioaccumulation and Biomagnification of Methlymercury:
A recent study measured the average concentrations of three different types of gaseous Hg at Huntington Forest in the Adirondacks. The concentrations from June 2006 to May 2007 for gaseous elemental Hg was 1.4 +/- .4 ng m-3, for integrated reactive gaseous Hg was 1.8 +/- 2.2 pg m-3, and for particulate Hg was 3.2 +/- 3.7 pg m-3. These quantities are all relatively small on the scale of this planet. However, as noted before, once Hg is deposited in the soil or water, it is converted to MeHg by sulfate reducing bacteria, which can and will be accumulated by biologic organisms in the region. The bacteria that convert the Hg need an anaerobic environment and the presence of sulfates. Generally, microorganisms are the first to ingest the MeHg. Then, a larger organism that eats the microorganisms eats several of the smaller organisms. From this one step, the MeHg concentration can increase several orders of magnitude. As larger organisms ingest the contaminated organisms, the concentrations can far exceed what is considered safe by the top or near the top of the food chain. Biomagnification factors of up to 10 million have been noticed in largemouth bass in the Florida Everglades.

Eating Fish:
In the US, consumption of ocean fish and shellfish account for over 90 percent of human MeHg exposure, and tuna harvested in the Pacific Ocean account for 40 percent of this total exposure. The US EPA and the Department of Health advises that fish containing Hg with .5 ppm or less are safe for unlimited consumption. However, fish containing levels of Hg in excess of 1.5 ppm should not be eaten, especially by children and woman of childbearing age. The EPA has very intensive lists of the types of fish, locations, and quantities that are recommended to avoid. Some lakes, rivers and watersheds have explicit warnings that no fish should be consumed that are caught there. For example, in the L-67A Canal in the Everglades in Florida, fish have anywhere from 3.2 – 4.36 ppm. There are also more vulnerable areas of the fish itself that are more concentrated with Hg and so there are techniques to try and avoid poisoning from sport fish. The U.S. FDA regulates the sale of commercial fish, but Hg concentrations can vary greatly between fish and so the U.S. FDA advises pregnant women, women who may become pregnant, nursing mothers and young children to not eat shark, swordfish, king mackerel or tilefish. Clearly this does not represent the global stock of high tropic level fish and mammals. In many parts of the world it is not uncommon to eat whale or dolphin meat. Whales and dolphins exhibit some of the highest levels of Hg. They also suggest that women and children under 50 only eat up to 12 ounces of other types of commercial fish a week.

Why worry?
In the North Atlantic Ocean there are a group of islands called the Faroe Islands. Their culture has remained fairly unchanged throughout history. However, the major source of food for many of the islanders is Pilot Whales. Being so high on the food chain, Pilot Whales can have extremely high Hg concentrations, as well as other toxins like PCBs. Sadly, due to the continued ingestion of these toxins over the years, many of the natives have shown that Hg can cause long lasing damage. Research on the islanders have shown damage to fetal neural development, high blood pressure, impaired immunity in children, increased rates of Parkinson’s disease, circulatory problems, and possible infertility in adults. The worst part of all is that they contribute absolutely no Hg to their environment. The Hg that has accumulated in these whales has some of its roots in natural sources but the increased anthropogenic release of Hg could very well be the tipping point that may cause the consumption of many fish to be banned. For example, the primary source of food for Pilot Whales is squid. If Pilot Whales have such high toxin concentrations, it is likely that squids do too. The Hg problem in our fish stock is no single party’s fault but a combination of industrialized nations who are burning high quantities of coal with little regard for pollution control. Sadly for the Faroese people, they may be the subjects of one of the largest Hg exposure experiments without knowing it.

Works Cited:
Atmospheric Mercury (Hg) in the Adirondacks: Concentrations and Sources Hyun-Deok Choi, Thomas M. Holsen, Philip K. Hopke Environmental Science & Technology 2008 42 (15), 5644-5653

Budtz-Jørgensen, E; Grandjean, P; Keiding, N; et al. (2000) Benchmark dose calculations of methylmercury-associated neurobehavioral deficits. Toxicol Lett 112-113:193-199.

South Florida Restoration Science, Mercury Toxicity in the Food Chain. Sept 11, 2010. http://sofia.usgs.gov/sfrsf/rooms/mercury/food_chain/

Response of a Macrotidal Estuary to Changes in Anthropogenic Mercury Loading between 1850 and 2000. Elsie M. Sunderland, John Dalziel, Andrew Heyes, Brian A. Branfireun, David P. Krabbenhoft, Frank A.P.C. Gobas Environmental Science & Technology 2010 44 (5), 1698-1704

Sunderland EM 2007. Mercury Exposure from Domestic and Imported Estuarine and Marine Fish in the U.S. Seafood Market. Environ Health Perspect 115:235-242. doi:10.1289/ehp.9377 Driscoll, Charles 2005. Mercury Deposition Monitoring Network: Adirondacks and Catskills Update. Environmental Monitoring, Evaluation, and Protection Program.

Articles:
Faroe Island New Scientist Article: http://www.newscientist.com/article/dn16159-faroe-islanders-told-to-stop-eating-toxic-whales.html

Everglades Mercury Evaluation: http://sofia.usgs.gov/sfrsf/rooms/mercury/food_chain/

New York State Fish Advisories: http://www.health.state.ny.us/environmental/outdoors/fish/fish.htm#adirondack

Paper on Mercury Cycling in an estuary in Canada : http://pubs.acs.org/doi/abs/10.1021/es9032524

A New Source of Methylmercury Entering the Pacific Ocean: http://toxics.usgs.gov/highlights/pacific_mercury.html