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By David Batcheller.  Heavy, silvery metal  Only metal to exist as liquid at room temperature  Elemental state, Hg 0, found in waters and atmosphere.

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Presentation on theme: "By David Batcheller.  Heavy, silvery metal  Only metal to exist as liquid at room temperature  Elemental state, Hg 0, found in waters and atmosphere."— Presentation transcript:

1 By David Batcheller

2  Heavy, silvery metal  Only metal to exist as liquid at room temperature  Elemental state, Hg 0, found in waters and atmosphere  Exists in two main oxidation states  Mercury (I)  Mercury (II) – most common

3  Toxic at high doses  Organic compounds of mercury are more toxic than inorganic compounds  Hg(II) and Methylmercury are the two most common toxic forms of mercury in the marine environment

4  Natural (accounts for 1/3 of mercury):  Volcanic Activity  Forest fires  Erosion  Anthropogenic (accounts for 2/3 of mercury):  Metal production  Chlor-alkali and pulp industries  Waste handling and treatment  Coal, peat, and wood burning

5 Natural waters supersaturated with Hg 0 compared to atmosphere  Flux from water to atmosphere Hg 0 oxidized to Hg(II) in atmosphere  Returns to Earth’s surface  Global spread  Residence time Over time, Hg(II) is reduced back to Hg 0 and returns to the atmosphere

6  Most toxic form of mercury  Organic  Insoluble  Bioaccumulates  Mercury methylated by sulfate-reducing bacteria to form MeHg  Limited amount produced from anthropogenic sources

7  MeHg is not easily or quickly excreted from marine organisms  All the MeHg that remains in an organism upon being consumed is transferred to the predatory species  Higher trophic levels feed more often and thus accumulate more MeHg at a faster rate

8  Biomagnification continues up the food chain until the highest trophic levels where mercury levels can exist at toxic levels  The more trophic levels, the more mercury accumulated at the top  Mercury concentrations can range from under.001ppm in plankton to over 1.0ppm in large fish and mammals

9  Entry of mercury into the aquatic food chain  Mercury first travels across the lipid membrane of unicellular organisms  At high concentrations, Hg(II) transported into the cell via specialized MerT transport protein  At low concentrations, lipid soluble mercury complexes diffuse across membrane

10  Mercury taken up is then methylated by the bacteria creating methylmercury  Methylmercury is either retained in the bacteria and travels up the food chain or is released by the bacteria to be absorbed by phytoplankton to proceed up the food chain

11  MeHg is retained in the fatty and muscle tissues of higher trophic level animals due to its lipid solubility  Fish still uptake MeHg from the water but majority taken from food  Hg(II) is absorbed at the microvilli interface  Low uptake rate  MeHg proportion over total Hg increases from 10% in the water column to 15% in phytoplankton, 30% in zooplankton, and 95% in fish

12  The affect of high mercury levels on fish has not been well researched  Some studies have found high mercury levels to decrease fecundity and in some cases increase homosexuality in fish

13  Marine mammals are at the top of the marine food chain yet don’t seem to exhibit effects of mercury poisoning  Majority of mercury concentrated in liver  Only a small amount as MeHg  Avoid effects of mercury toxicity due to abundant amount of selenium in liver and kidney  Selenium in marine mammals is positively correlated to mercury in liver and kidney

14  Mercury in birds is concentrated in the liver and kidneys  Marine and fish-eating birds have higher mercury levels than land-dwelling birds  Causes reproductive impairment, reduced hatchability, and deformations during development  Mercury levels in eggs have been found up to 3ppm

15  High levels of mercury in humans can harm the development of the nervous system in unborn babies and young children  In extreme cases, high levels of mercury can lead to mercury poisoning

16  Extremely high levels of mercury in humans can cause severe damage to brain, kidneys, and lungs  Diseases associated with mercury poisoning are acrodynia, Hunter-Russell syndrome, and Minamata disease  Symptoms of mercury poisoning can include:  Itching or burning of skin  Sensory impairment  Muscle weakness and paralysis  Mental instability  Death Minamata Disease

17  Due to rising concerns about mercury in seafood, many restaurants have started testing their food  Many restaurants were found to be selling fish above 1ppm in mercury which is the FDA’s “action level”  Now more restaurants are disposing of fish with levels higher than the “action level” and have quit buying from companies in other countries that sell fish above this level

18  One study found that cage-rearing fish could be a step towards reducing mercury levels in fish  The study tested the mercury levels of 4 kinds of carnivorous and 1 kind of herbivorous caged fish from 5 different sites  These fish were on exclusive diets of either dried pellet feed or fresh fish forage fish or fish viscera feed  Results showed decreased Hg and MeHg levels in fish on the dried pellet feed diet


20  Cut back on anthropogenic sources of mercury through cleaner and more efficient industrial factories  Cage-rear more of the fish we eat, as shown in the study

21  Avoid eating too much fish from higher trophic levels such as shark, swordfish, king mackerel, or tilefish  Eat up to 12 ounces per week of fish that are lower in mercury such as shrimp, canned light tuna, salmon, pollock, and catfish  Make sure the fish you eat has a mercury concentration under the FDA’s “action level” of 1ppm  Inquire as to the mercury levels of fish at your local restaurants  Ask local advisors about the safety of fish caught in your area

22  cury.html?_r=2&fta=y cury.html?_r=2&fta=y  e/article/pii/S0045653599002830 e/article/pii/S0045653599002830  ull/10.1146/annurev.ecolsys.29.1.543 ull/10.1146/annurev.ecolsys.29.1.543  e/article/pii/S0304389411013872 e/article/pii/S0304389411013872   95/ llfish/outreach/advice_index.cfm 95/ llfish/outreach/advice_index.cfm  s.asp s.asp

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