Page 29 - Curriculum Visions Dynamic Book

Hydrogen
fungicide: any chemical that is designed to kill fungi and control the spread of fungal spores.
pesticide: any chemical that is designed to control pests (unwanted organisms) that are harmful to plants or animals.
Dioxins
Agent Orange is famous for its use in the Vietnam war. It was sprayed onto Vietnamese rainforests because it quickly caused tree leaves to shrivel and die. By this action the American forces hoped to prevent the Viet Cong guerrillas from hiding in the rainforests. Agent Orange is
a compound based on chlorine (its chemical description is 2,4,5–trichlorophenoxyethanoic acid and esters).
This chemical contained certain impurities, including another compound of chlorine known as dioxin (2,3,7,8–tetrachlorodibenzo-p-dioxin). Dioxin is extremely poisonous, insoluble and clings to the soil, making land unusable for decades.
After Agent Orange was applied in Vietnam, many deformed children were born in the areas that were sprayed. This shows how the dioxin compounds remain active for long periods and find their way up the food chain.
The largest unintentional release of dioxins was in Seveso, Italy, in 1976. Then an escape of dioxins spread out over the area near a chemical plant.
Dioxins were also found in the soil beneath houses in the township of Love Canal, near Niagara Falls, USA. The houses were declared uninhabitable and the citizens forced to move. Dioxins have now been banned.
Paraquat
Paraquat is an organochloride designed as
a weedkiller and is used on many household lawns. However, when it was used on a vast scale to kill weeds in the rubber estates of Thailand (4 million kilogrammes were used!), the chemical got into the river water and killed millions of fish. Not only was this an ecological disaster, but fish are a main source of protein for many rural Thais and so the chemical was passed through the food chain to them, causing pesticide poisoning.
Chlorine
Carbon
PBBs
Another material, this time a compound of bromine (see page 42), polybrominated biphenyl (PBB), is used to prevent materials catching fire. By accident, in 1973, some of it got mixed in with cattle feed in Michigan, USA, and gradually worked its way up the food chain. Many animals had to be put down, and many people became ill.
 A diagrammatic representation of a molecule of DDT.
DDT
DDT (dichlorodiphenyltrichloroethane) is an insecticide based on chlorine that for many years was used to combat mosquitos. Its use has been stopped for fear of its environmental side effects.
 A diagrammatic representation of a molecule of a PCB.
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