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Agency for Toxic Substances and Disease Registry's
HerbicideLast Updated on 2014-10-26 16:45:24A herbicide is any of a number of chemical substances intended to kill vegetation. Since the vast majority of herbicides are non-selective in their lethal action, there may be widespread adverse ecological consequences from their use. These outcomes include not only organism death, but may involve mutagenic, developmental and carcinogenic effects to animals and plants.
Herbicides are in broad use for agriculture, golf courses, utility corridors, residential and other land uses. The earliest herbicides were inorganic chemical substances, although modern herbicides are dominated by organic compounds. Presently, there is massive application of chemical herbicides; in the USA alone 480 million kilograms are applied annually.
Widespread herbicide use beginning in the 1940s is responsible for numerous species extinctions, including birds, amphibians, fish and arthropods. In many cases,... More »
FluorineLast Updated on 2014-09-13 19:14:38Fluorine is a highly reactive chemical element with atomic symbol F. Having the atomic number nine, fluorine is the lightest halogen. Fluorine is a yellow-green gas which does not occur as a free, unreacted element in the natural environment. Under conditions of standard temperature and pressure, elemental fluorine forms a diatomic molecule with chemical formula F2. Chemically, fluorine is one of the strongest known oxidizing agents, and even more reactive and hazardous than chlorine. Its very high electron affinity causes fluorine to react directly with almost all other elements except for several of the Noble gases.
Previous Element: Oxygen
Next Element: Neon
Phase at Room Temp.
Density... More »
Calvin, MelvinLast Updated on 2014-06-30 16:18:37
Melvin Calvin (1911-1997), American biochemist who first described the photosynthetic process, now known as the Calvin Cycle. Calvin determined the process by tracking radioactive carbon dioxide through its transformation into carbohydrates. He allowed carbon-14 to be absorbed by plants, then mashed up the cells and separated the contents using paper chromatography. He discovered intermediate reaction products of photosynthesis and worked out the reaction scheme. He also discovered that photosynthesis proceeds in the absence of light. Calvin later confirmed which primary elements had formed the atmosphere from which primitive life developed. He received the Nobel Prize in Chemistry in 1961.
Melvin Calvin - Biography (The Nobel Foundation)
Calvin Photosynthesis Group Subject of History Project (Lawrence Berkeley National Laboratory)
Kamen, Martin DavidLast Updated on 2014-06-30 16:09:31Martin David Kamen, (1913–2002), a Canadian-born American biochemist who discovered carbon-14, the radioactive isotope of carbon used to trace biochemical pathways and mechanisms and to date archeological and anthropological objects. He also carried out extensive research in photosynthesis. Kamen used the isotope oxygen-18 to trace the chemical's role in the process, confirming that that the oxygen created during photosynthesis comes only from the water molecules. Unfortunately, much of his energy at this time was diverted to non-scientific matters; a successful but protracted libel suit against the Chicago Tribune, which falsely accused him of being a communist, as well as a successful, 7-year battle to recover his passport, which had been rescinded by the U.S. government.
Martin Kamen, Who Discovered Carbon-14, Wins Fermi Award (U. S. Department of Energy,... More »
Successional Soils: How edaphic conditions change within aggrading forests in a case study of the North Carolina PiedmontLast Updated on 2014-06-30 15:03:45
Soil composition—its abiotic physical and chemical properties—changes under an aggrading forest. Through "space for time studies" in the Piedmont of North Carolina, researchers have examined changes in soil composition and processes among three successional stages of old fields. Differences in nitrification rates, nutrient concentration, and acidity indicate that soil nutrient availability decreases during the course of forest succession.
The characteristics of forest change are highly interconnected with changes in soil conditions through time. A positive relationship exists between species richness and soil nutrient availability. Organisms can change the chemical composition of the soil, which in turn influences the forest composition. For example, some species of trees and other plants decrease soil pH while others increase nitrogen availability. Much... More »
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