Food and Agriculture : Glossary

There are 46 documents in this section.

  • Subsistence farming

    14 September 2000

    The production of sufficient food and other necessities to meet the requirements of a farm unit, leaving no surplus for sale and little for storage.Source: Many of these definitions have been taken from, or abridged from The Environment Dictionary by David D Kemp (Routledge, London, 1998).

  • Organochlorides

    22 August 2000

    A group of organic compounds that contain chlorine (Cl). They have a variety of forms and uses including aerosol propellants, plasticisers, transformer coolants (PCBs) and food packaging (PCVs), but their greatest use was as pesticides, in the form of DDT, Aldrine and Lindane. However, with time many pests have developed immunity to them and it has also become clear that the characteristics that made them good pesticides - persistence, mobility and high biological activity - also posed dangers for the environment. Organochlorides accumulate in the fatty tissue of animals, and through biomagnification in the food chain may reach toxic levels in predators. Because of side effects such as sterility, birth defects, cancer and damage to the nervous system, they have been banned or had their use severely restricted in most parts of the world.

  • Organophosphoruus compounds

    22 August 2000

    A group of pesticides that work by blocking the central nervous systems of the organisms exposed to them. Malathion and diazonon are the most commonly used organophosphates. They are highly effective against insects, but break down rapidly in the environment and do not bioaccumulate. For these reasons, they are preferred over organochloride pesticides. Although generally considered safer than the organochlorides, they are highly toxic to humans and other mammals and may be carcinogenic.

  • Pesticides

    22 August 2000

    Chemical products designed to kill or restrict the development of pests. They include fungicides, herbicides and insecticides. Pesticides range from relatively simple elements such as sulphur (S) to complex chemical compounds such as chlorinated hydrocarbons and may be broad-spectrum or narrow-spectrum agents. Pesticides also vary in their persistence in the environment, and in general, the longer they remain chemically stable the greater is their potential for environmental damage. The use of pesticides has undoubtedly benefited society, by preventing disease and improving the food supply. At the same time, ignorance of the environmental impact of pesticides, the indiscriminate use of certain products and inadequate control of the production and use of pesticides has created problems for wildlife and natural vegetation and has threatened human health.

  • DDT (Dichlorodiphenyl-trichloroethane)

    21 August 2000

    A chlorinated hydrocarbon once widely used as a broad-spectrum insecticide. Introduced during the Second World War as a delousing agent, it proved very effective against diseases such as malaria, yellow fever and typhus, which were spread by insects. Over the longer term, serious side affects became apparent. Being a broad-spectrum product, it killed beneficial insects as well pests and could accumulate in the environment for perhaps 20 years. Although not soluable in water, it was soluable in fat, which allowed it to migrate up the food chain, where it accumulated in the body tissue of the predators. In birds it caused the thinning of eggshells, seriously reducing the breeding success of some species. By the mid-1960s, DDT was found to be widespread in the fatty tissue of the human population, passed on from mother to child through breast milk. Although the link between DDT concentration and human health was not clear, its potential to cause serious ecological disruption was recognised, and it was eventually banned or had its use severely restricted in the developed world.

  • Ecological balance

    21 August 2000

    Stability in an ecosystem achieved through the development of equilibrium among its various components. This does not imply that the community is static. It is subject to natural variations associated with ecological succession and other influences such as fire, disease and climate change, but the system is normally sufficiently elastic to make the necessary adjustments without major displacement of the balance. Human intervention that includes the introduction or removal of plants and animals, pollution of the environment and destruction of habitat is now a main cause of imbalance in many ecosystems.