Global distillation
Encyclopedia
Global distillation or the grasshopper effect is the geochemical
process by which certain chemicals, most notably persistent organic pollutants (POPs), are transported from warmer to colder regions of the Earth, particularly the Poles and mountain tops. Global distillation explains why relatively high concentrations of POPs have been found in the Arctic environment and in the bodies of animals and people who live there, even though most of the chemicals have not been used in the region in appreciable amounts.
s used to make liquor or purify chemicals in a laboratory. In these processes, a substance is vaporized
at a relatively high temperature, and then the vapor travels to an area of lower temperature where it condenses. A similar phenomenon occurs on a global scale for certain chemicals. When these chemicals are released into the environment, some amount evaporates when ambient temperatures are warm, blows around on winds until temperatures are cooler, and then condensation occurs. Drops in temperature large enough to result in deposition can occur when chemicals are blown from warmer to cooler climates, or when seasons change. The net effect is atmospheric transport from low to high latitude
and altitude
. Since global distillation is a relatively slow process that relies on successive evaporation/condensation cycles, it is only effective for semi-volatile
chemicals that break down very slowly in the environment, like DDT
, polychlorinated biphenyls, and lindane
.
, and lindane measure in water, lichens, and tree bark have been shown to be greater in higher latitudes.
The effect is also used to explain why certain pesticides are found in Arctic and high altitude samples even though there is no agricultural activity in these areas, and why indigenous peoples
of the Arctic have some of the highest body burdens of certain POPs ever measured.
Geochemistry
The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks, water, and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and...
process by which certain chemicals, most notably persistent organic pollutants (POPs), are transported from warmer to colder regions of the Earth, particularly the Poles and mountain tops. Global distillation explains why relatively high concentrations of POPs have been found in the Arctic environment and in the bodies of animals and people who live there, even though most of the chemicals have not been used in the region in appreciable amounts.
Mechanism
The global distillation process can be understood using the same principles that explain distillationDistillation
Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
s used to make liquor or purify chemicals in a laboratory. In these processes, a substance is vaporized
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
at a relatively high temperature, and then the vapor travels to an area of lower temperature where it condenses. A similar phenomenon occurs on a global scale for certain chemicals. When these chemicals are released into the environment, some amount evaporates when ambient temperatures are warm, blows around on winds until temperatures are cooler, and then condensation occurs. Drops in temperature large enough to result in deposition can occur when chemicals are blown from warmer to cooler climates, or when seasons change. The net effect is atmospheric transport from low to high latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
and altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
. Since global distillation is a relatively slow process that relies on successive evaporation/condensation cycles, it is only effective for semi-volatile
Volatility (chemistry)
In chemistry and physics, volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance's vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.The term is primarily...
chemicals that break down very slowly in the environment, like DDT
DDT
DDT is one of the most well-known synthetic insecticides. It is a chemical with a long, unique, and controversial history....
, polychlorinated biphenyls, and lindane
Lindane
Lindane, also known as gamma-hexachlorocyclohexane, , gammaxene, Gammallin and erroneously known as benzene hexachloride , is an organochlorine chemical variant of hexachlorocyclohexane that has been used both as an agricultural insecticide and as a pharmaceutical treatment for lice and...
.
Effect of global distillation
Several studies have measured the effect, usually by correlating the concentrations of a certain chemical in air, water, or biological specimens from various parts of the world with the latitude from which the samples were collected. For example, the levels of PCBs, hexachlorobenzeneHexachlorobenzene
Hexachlorobenzene, or perchlorobenzene, is a chlorocarbon with the molecular formula C6Cl6. It is a fungicide formerly used as a seed treatment, especially on wheat to control the fungal disease bunt...
, and lindane measure in water, lichens, and tree bark have been shown to be greater in higher latitudes.
The effect is also used to explain why certain pesticides are found in Arctic and high altitude samples even though there is no agricultural activity in these areas, and why indigenous peoples
Indigenous peoples
Indigenous peoples are ethnic groups that are defined as indigenous according to one of the various definitions of the term, there is no universally accepted definition but most of which carry connotations of being the "original inhabitants" of a territory....
of the Arctic have some of the highest body burdens of certain POPs ever measured.
Further reading
External links
- The Grasshopper Effect and Tracking Hazardous Air Pollutants, Environment Canada.