Mercury in the Environment Flashcards
How does mercury get into the environment?
- Mercury is an element that can be found in small concentrations in many rocks and is the main component of mineral cinnabar (HgS). Natural background lvls can be detected in soils, air, and water around the world
- Present in gases emitted by volcanoes. Mining and industrial applications for the metal have increased significantly since the industrial revolution.
- Base metal smelting and gold mining both create mercury vapor, which is a potential hazard. Mercury mines pose an environmental concern.
In 1990, 3 industry sector made up ~2/3 of total US mercury emissions:
medical waste incinerators, municipal waste combustors, and coal-fired power plants. The 1st 2 of these sectors have been subject to emissions standards for years and as a result have reduced their mercury emissions
Coal- and oil-fired power plants emit harmful pollutants, including
mercury, metallic toxins, and acid gases
In 2011 during Obama admin, US EPA introduced legislation to:
○ Prevent 90% of mercury in coal burned power plants from being emitted into the air
○ Reduce 88% of acid gas emissions from acid gas emission power plants
○ Reduce 41% of sulfur dioxide emissions from power plants
Forms of Mercury
- Elemental: liquid metal
- Inorganic: mercuric chloride and mercuric sulfide (cinnabar)
- Organic: methyl, ethyl, dimethyl mercury, and phenyl organic groups
Mercury in Aquatic Spp
- Mercury is converted to methylmercury by bacteria in sediments. It biomagnifies in aquatic animals, and the concentrations can increase by a million fold in animals at the top of the food chain
- Methylmercury is 100% absorbed through the GI tract and distributed through the body
- Formula: [H3CHg]+ and is major source of organic mercury for all humans
Health Effects of Mercury
- As a reproductive toxin and a potent neurotoxin, mercury affects the brain and CNS
- Pregnant women, women of childbearing age, and small children are at the greatest risk. Mercury can cross the placenta and cause irreparable neurological dmg to fetus
- In March 2001, a study by CDC found that 1/10 women in the US have mercury lvls high enough to cause neurological dmg in their children - ~400k babies/yr
Mercury Poisoning Symptoms
- Deteriorated NS
- Impaired hearing, speech, vision and gait
- Involuntary muscle movements
- Corrodes skin and mucous membranes
- Causes chewing and swallowing to become difficult
Case Study: 1971 Iraq poison grain disaster
- A mass methylmercury poisoning incident that began in late 1971.
- Grain treated with a methylmercury fungicide and never intended for human consumption was imported into Iraq as seed grain from Mexico and USA.
- Due to a number of factors, including foreign-language labeling and late distribution within the growing cycle, this toxic grain was consumed as food by Iraqi residents in rural areas
- People suffered from paresthesia (numbness of skin), ataxia (lack of coordination of muscle movements), and vision loss. Recorded death toll was 459 ppl.
Case Study: Minamata, Japan
- Minamata disease is a neurological syndrome caused by severe mercury poisoning. Symptoms include ataxia, numbness in hands and feet, general muscle weakness, loss of peripheral vision, and dmg to hearing and speech.
- Caused by release of methylmercury in industrial wastewater from the Chisso Corporation’s chemical factory, which continued from 1932-1968
- Highly toxic chemical accumulated in shellfish and fish in Minamata Bay, which, when eaten by local pop, resulted in mercury poisoning.
- As of March 2001, 2265 victims had been officially recognized (1784 of whom had died)
Case Study: First Nations ppl in Ontario
- Ontario Minamata disease is a neurological syndrome caused by severe mercury poisoning
- Severely affected 2 First Nation communities (Grassy Narrows and Whitedog) in NW Ontario following consumption of local fish contaminated with mercury, and one First Nation in Southern Ontario due to illegal disposal of industrial chemical waste
- In the 1960s and 70s, Dryden Chemical Company dumped over 9000kg of mercury into the Wabigoon-English river system. This mercury was transformed to methylmercury by bacteria in the river
- Japanese researchers found more than 90% of the pops show signs of poisoning
- 28% of adults in Grassy Narrows have attempted suicide, more than double the rate of other First Nations
Mercury and Dental Amalgam
- Dental amalgam is a dental filling material used to fill cavities caused by tooth decay. Been used for more than 150yrs in hundreds of millions of patients around the world
- Dental amalgam is a mixture of metals, consisting of liquid mercury and a powdered alloy composed of silver, tin, and copper. Approx 50% of dental amalgam is mercury by weight. Chemical properties of elemental mercury allow it to react with and bind together the silver/copper/tin alloy particles to form an amalgam
- Dental amalgam fillings are also known as “sliver fillings” b/c of their silver-like appearance. Despite the name, they do contain mercury
How do dentists make dental amalgam?
- When placing the dental amalgam, the dentist first drills the tooth to remove the decay and then shapes the tooth cavity for placement of the amalgam filling.
- Next, under appropriate safety conditions, the dentist mixes the powdered alloy with liquid mercury to form an amalgam putty. This softened amalgam putty is placed and shaped in the prepared cavity, where it rapidly hardens into a solid filling
Is mercury in dental amalgam the same as mercury in some types of fish?
No.
Form of mercury associated with dental amalgam is elemental mercury, which can slowly release mercury vapor. Form of mercury in fish is methylmercury, a type of organic mercury.
- Mercury vapor is mainly absorbed by the lungs
- Methylmercury is mainly absorbed through the digestive tract
- The body processes these forms of mercury differently and has different lvls of tolerance for mercury vapor and methylmercury
What should you know before getting a dental amalgam filling?
- What filling material to use to treat dental decay is a choice that must be made by you and your dentist
- Benefits: strong and long-lasting, so they are less likely to break than some other types of fillings. Least expensive type.
- Risks: contains elemental mercury which releases low lvls of mercury in form of vapor that can be inhaled and absorbed by lungs. High lvls of mercury vapor exposure are associated with adverse effects in the brain
