Mercury and heavy metal pollutionPresentation Transcript
Mercury and other heavy metals VCE Environmental Science: Unit 4 Area of Study 1: Pollution
Definition of Heavy Metals Noun (Music) “Very loud, brash rock music, often with shouted, violent lyrics.” ;) "Heavy metals" is an inexact term used to describe more than a dozen elements that are metals or metalloids. Examples of heavy metals include chromium, arsenic, cadmium, lead, mercury and manganese. A metal of relatively high density, or of high relative atomic weight.
Sources of heavy metals Heavy metals occur naturally in the ecosystem with large variations in concentration. The primary anthropogenic sources of heavy metals are point sources such as mines, foundries, smelters, and coal-burning power plants, as well as diffuse sources such as combustion by-products and vehicle emissions. Waste-derived fuels are especially prone to contain heavy metals, so heavy metals are a concern in consideration of waste as fuel. Electronic waste is also a significant source of heavy metal contaminants.
Persistence Because they cannot be degraded or destroyed, heavy metals are persistent in all parts of the environment. Human activity affects the natural geological and biological redistribution of heavy metals through pollution of the air, water, and soil. Humans also affect the natural geological and biological redistribution of heavy metals by altering the chemical form of heavy metals released to the environment. Such alterations often affect a heavy metal's toxicity by allowing it to bioaccumulate in plants and animals, biomagnify in the food chain, or attack specific organs of the body. They are often stored as fat-soluble compounds in the body.
Exposure Heavy metals are associated with myriad adverse health effects, including allergic reactions (e.g., beryllium, chromium), neurotoxicity – affects nervous system(e.g., lead), nephrotoxicity – affects kidneys(e.g., mercuric chloride, cadmium chloride), and cancer (e.g., arsenic, hexavalent chromium). Humans are often exposed to heavy metals in various ways—mainly through the inhalation of metals in the workplace or polluted air, or through the ingestion of food (particularly seafood) that contains high levels of heavy metals or paint chips that contain lead.
Toxicity of heavy metals Living organisms require varying amounts of "heavy metals." Iron, cobalt, copper, manganese, molybdenum and zinc are required by humans. Excessive levels can be damaging to the organism.
Toxicity of Heavy Metals Other heavy metals such as mercury, plutonium, and lead are toxic metals that have no known vital or beneficial effect on organisms, and their accumulation over time in the bodies of animals can cause serious illness. Certain elements that are normally toxic are, for certain organisms or under certain conditions, beneficial. Examples include vanadium, tungsten, and even cadmium.
Example: Cadmium Cadmium has many commercial applications, including electroplating and the manufacture of batteries. Exposure to cadmium can occur in the workplace or from contaminated foodstuffs and can result in emphysema, renal failure, cardiovascular disease, and perhaps cancer.
Example: Lead Humans discovered lead more than 8,500 years ago, and over time have used lead in artwork, plumbing, gasoline, batteries, and paint. Modern-day exposure to lead occurs in the workplace or through the ingestion of lead-contaminated items such as paint chips. The primary adverse health effect from exposure to lead is permanent neurological impairment (particularly in children). Other adverse health effects associated with lead include sterility in males and nephrotoxicity.
Case Study: Mercury Mercury, or quicksilver, was known in ancient times as hydrargyros, hence it’s chemical symbol ‘Hg’. Mercury is the only metal that is liquid at room temperature and pressure. Mercury is an extremely rare element, but occurs in deposits throughout the world mostly as cinnabar (or mercuric sulphide).
More about Mercury Like water, mercury can evaporate and become airborne. Because it is an element, mercury does not break down into less toxic substances. Once mercury escapes to the environment, it circulates in and out of the atmosphere until it ends up in the bottoms of lakes and oceans. Mercury can be found as the elemental metal or in a wide variety of organic and inorganic compounds. Depending on its chemical form, mercury may travel long distances before it falls to earth with precipitation or dust.
Uses of Mercury Felting and Hat-making Fluorescent lamps Mercury batteries Thermometers and thermostats Vacuum pumps, Barometers, Electric rectifiers and switches Printer and photocopy toners. Mercury-vapor lamps (for sterilizing water and instead of steam in boilers of some turbine engines.) Amalgamation (to dissolve silver or gold to form an amalgam, as in tooth fillings) This process has been largely supplanted by the cyanide process, in which gold or silver is dissolved in solutions of sodium or potassium cyanide.
Sources of Mercury Non-ferrous metal manufacturing, mining and alumina production are the largest sources of mercury emissions in Australia. Precious metal mining (which can emit mercury to water or land), Cement manufacturing (which may emit mercury into the air) and Chemical manufacturing, which can emit of mercury to land and into water. Fossil fuel power plants may also emit mercury into the air by burning fuels such as coal, oil, and petrol. Our landfills and sewage also contribute to mercury being released into our soil and water. Small amounts of mercury can be released into the air in the exhaust fumes of cars, buses and motorbikes.
Transport of Mercury Mercury chloride will act as a particle, following wind patterns, and being deposited by rain. Elemental mercury may be a gas in the atmosphere. Emissions of mercury and or mercury compounds can produce elevated, but still low-level concentrations in the atmosphere around the source. Elemental mercury can evaporate from both soil and water into the atmosphere.
Sinks for Mercury When mercury enters the environment from emissions in the air, water or soil, it oxidises into other compounds of mercury. These other forms of mercury form methyl mercury, through either chemical or biological (bacteria) processes. Methyl mercury builds up in the tissues of fish and shellfish. In areas of mercury contamination, larger and older fish tend to have higher levels of mercury.
Exposure to Mercury Eating fish or shellfish which have been exposed to mercury. Drinking water or eating foods that contain traces of mercury. Being exposed to mercury from dental work and medical treatments. Breathing contaminated air. Working at, or living near, factories where mercury is produced or used, such as fossil fuel plants or cement manufacturers.
Effects on Humans Depending on its chemical form (elemental, inorganic or organic) mercury is able to cause a myriad of adverse health effects including : neurotoxicity (elemental mercury, methyl-mercury), nephrotoxicity (elemental mercury, mercuric salts such as mercuric chloride), teratogenicity(methyl-mercury) – abnormalities in physiological development, including birth defects death (elemental mercury, methyl-mercury).
Environmental Health Effects Aquatic life — the fish, shellfish and other creatures in our rivers, lakes and oceans — are likely to be exposed to mercury as it is often found in water. It can make them very sick, and may even kill them. Mercury can build up in the tissues of fish and shellfish and be harmful to people and to other animals that eat them. Once mercury is released into the environment it will remain there for many years.
References Encyclopaedia of Public Health http://www.npi.gov.au/students/mercury.html http://www.npi.gov.au/substances/mercury/index.html http://en.wikipedia.org/wiki/Mercury_(element) http://www.mercuryinschools.uwex.edu/curriculum/hg_in_env.htm