Thanks so much for this Lesson.
what are the main five classes of incesticides.
hay diferentes contaminantes de los suelos, todos dependen de la integración de los suelos, el agua es importante para este proceso.
Soil pollution covers huge areas e.oil spills,coal ash,electronic waste and mining waste.
What is geohydrological contamination?
What are xebiotic waste?
What are organic contaminants?
The persistence of pesticides in the soil is related to how quickly these chemicals degrade in the environment. There are three ways pesticides are degraded in the soil:
• chemical degradation, and
• photochemical degradation.
Microorganism activity plays the predominant role in the biodegradation of pesticides. Water plays an important role in the chemical degradation of pesticides (e.g. some pesticides are hydrolyzed on the surfaces of minerals by water). Exposure to sunlight can also degrade some pesticides (photochemical degradation).
A variety of pesticides are used to control insects, weeds, fungi and mildew in agricultural, garden, and household environments. There are three classes of pesticides:
• insecticides, which kill insects;
• herbicides, which kill plants; and
• fungicides, which kill fungi.
Each of these classes includes different types of chemicals. These chemicals differ in chemical composition, chemical action, toxicity, and persistence (residence time)
in the environment. Some of these pesticides can bioaccumulate (e.g. they concentrate in specific plant and animal tissues and organs).
Pesticides can accumulate in the soil if their structures are not easily broken down in the environment. Besides rendering the soil toxic to other living organisms, these pesticides may leach out into the groundwater, polluting water supplies. The five classes of insecticides are:
• chlorinated hydrocarbons,
• botanicals and
• synthetic botanicals.
Chlorinated hydrocarbons such as DDT, are highly toxic in birds and fishes, but have relatively low toxicity in mammals. They persist in the environment, lasting for many months or years. Because of their toxicity and persistence, their use as insecticides has been somewhat restricted.
Organophosphates, such as Malathion, are more poisonous than other types of insecticides, but have much shorter residence times in the environment. Thus, they do not persist in the environment and cannot bioaccumulate.
Carbamates, such as Sevin, are generally less toxic to mammals than are organophosphates. They also have a relatively low persistence in the environment and usually do not bioaccumulate.
Botanicals, such as camphor, are derived from plant sources. Many of these compounds are toxic to mammals, birds, and aquatic life. Their persistence in the environment is relatively low, and as a result bioaccumulation is not a problem.
Synthetic botanicals, such as Allethrin, generally have a low toxicity for mammals, birds, and aquatic life, but it is unclear how persistent they are and whether or not they bioaccumulate.
The three classes of herbicides are:
• contact chemicals,
• systemic chemicals and
• soil sterilants.
Most herbicides do not persist in the soil for very long.
Contact chemicals are applied directly to plants, and cause rapid cell membrane deterioration. One such herbicide, Paraquat, received notoriety when it was used as a defoliant on marijuana fields. Paraquat is toxic to humans, but does not bioaccumulate.
Soil sterilants such as Diphenamid, render the soil in which the plants lives toxic. These chemicals have a low toxicity in animals, and do not bioaccumulate.
Systemic chemicals, such as Alar, are taken up by the roots and foliage of plants, and are of low to moderate toxicity to mammals and birds. Some systemic herbicides are highly toxic to fishes. These compounds do not have a tendency to bioaccumulate.
Fungicides are used to kill or inhibit the growth of fungi. Fungicides are not very toxic and are moderately persistent in the environment.They can be separated into two categories: protectants and systemics.
Protectant fungicides, such as Captan, protect the plant against infection at the site of application, but do not penetrate into the plant.
System fungicides, such as Sovran, are absorbed through the plant's roots and leaves and prevent disease from developing on parts of the plant away from the site of application.
Soil can absorb vast amount of pollutants besides pesticides every year.
Sulfuric acid rain is converted in soil to sulfates and nitric acid rain produces nitrates in the soil. Both of these can function as plant nutrient pollutants.
Suspended particulate matter from the atmosphere can accumulate in the soil, bringing with it other pollutants such as toxic metals and radioactive materials.
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