Cadmium And Sewage Sludge Term paper
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Cadmium and sewage sludge
This essay concentrates on the heavy metal cadmium, and its occurrence in the environment, its pathways into and out of the human body and its movement into and out of Sewage sludge. Firstly, I will provide a clear definition of the Heavy Metal Cadmium.
What is Cadmium?
Cadmium is a naturally occurring element in the earth s crust. Pure cadmium is a soft silver-white metal, but this form is not common in the environment. Rather, cadmium is most often encountered in combination with other elements such as oxygen (cadmium oxide), chlorine (cadmium chloride), or sulphur (cadmium sulphide). These compounds are all stable solids that do not evaporate, although cadmium oxide is often found as part of small particles present in air.
Most cadmium is obtained as a by-product from the smelting of zinc, lead or copper ores. Cadmium has a number of industrial applications, but it is used mostly in metal plating, pigments, batteries, and plastics.
Cadmium in the Environment
Small quantities of cadmium occur naturally in air, water, soil and food. For most people, food is the primary source of cadmium exposure, since food materials tend to take up and retain cadmium. For example, plants take up cadmium from soil; fish take up cadmium from water, and so on.
It is introduced into the environment from mining and smelting operations. Other cadmium emissions are from fossil fuel use, fertilizer application, sewage sludge disposal or galvanized pie corrosion. The largest source of these cadmium releases into the general environment is the burning of fossil fuels (such as coal or oil) or the incineration of waste materials. Cadmium may also escape into the air from zinc, lead or copper smelters. Working in or living close to a major source of airborne emissions such as these may result in higher than average exposure.
Pathways into the human body
Food and Drink
Cadmium can enter the blood by absorption from the stomach or intestines after ingestion of food or water. The amount of Cadmium ingested by an individual within a population can differ greatly due to dietary habits. For example, an individual who consumes a large amount of brown crabmeat or vegetables grown on land which is fertilised with sewage sludge are likely to have intakes of cadmium significantly above the average population level.
Only a small percentage of cadmium ingested with the food intake is absorbed, approximately 6%. However there are many factors, which can affect this figure, namely, physiological, such as age and the content of the diet.
Smoking
Smoking is another important source of cadmium. Like most pants, tobacco contains cadmium, some of which is inhaled in cigarette smoke. Most people who smoke have about twice as much cadmium in their bodies as do non-smokers. Unlike other methods of cadmium uptake, much of the cadmium present in tobacco is absorbed.
Respiration
Very little cadmium enters the body through the skin. Usually only about 1 to 5% of what is taken in by mouth is absorbed into the blood, while about 30-50% of that which is inhaled is taken up into the blood. Cadmium may escape into the air from the burning of fossil fuels or the incineration of waste. Inhalation of cadmium through airborne dusts can occur, but concentrations of cadmium are relatively low and therefore insignificant when compared to food ingestion. However, working or living close to a major source of airborne emissions may result in a higher than average exposure and build up. Once cadmium enters the body, it is very strongly retained; therefore even low doses may build up significant cadmium levels in the body if exposure continues for a long time.
Other Sources of Intake
Children are very vulnerable to cadmium poisoning due to their habitual chewing and licking of toys, pencils and other items. Toys made of vinyl, PVC or painted articles...
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