It is projected that the anthropogenic emission into the atmosphere, for several heavy metals, is one-to-three orders of magnitude higher than natural fluxes [ 17 ].
Heavy metals in the soil from anthropogenic sources tend to be more mobile, hence bioavailable than pedogenic, or lithogenic ones [ 1819 ].
Metal-bearing solids at contaminated sites can originate from a wide variety of anthropogenic sources in the form of metal mine tailings, disposal of high metal wastes in improperly protected landfills, leaded gasoline and lead-based paints, land Heavy metal term paper of fertilizer, animal manures, biosolids sewage sludgecompost, pesticides, coal combustion residues, petrochemicals, and atmospheric deposition [ 1220 ] are discussed hereunder.
Fertilizers Historically, agriculture was the first major human influence on the soil [ 21 ]. To grow and complete the lifecycle, plants must acquire not only macronutrients N, P, K, S, Ca, and Mgbut also essential micronutrients.
Some soils are deficient in the heavy metals such as Co, Cu, Fe, Mn, Mo, Ni, and Zn that are essential for healthy plant growth [ 22 ], and crops may be supplied with these as an addition to the soil or as a foliar spray.
Cereal crops grown on Cu-deficient soils are occasionally treated with Cu as an addition to the soil, and Mn may similarly be supplied to cereal and root crops. Large quantities of fertilizers are regularly added to soils in intensive farming systems to provide adequate N, P, and K for crop growth.
The compounds used to supply these elements contain trace amounts of heavy metals e. Metals, such as Cd and Pb, have no known physiological activity.
Application of certain phosphatic fertilizers inadvertently adds Cd and other potentially toxic elements to the soil, including F, Hg, and Pb [ 24 ].
Pesticides Several common pesticides used fairly extensively in agriculture and horticulture in the past contained substantial concentrations of metals. Examples of such pesticides are copper-containing fungicidal sprays such as Bordeaux mixture copper sulphate and copper oxychloride [ 23 ].
Lead arsenate was used in fruit orchards for many years to control some parasitic insects. Arsenic-containing compounds were also used extensively to control cattle ticks and to control pests in banana in New Zealand and Australia, timbers have been preserved with formulations of Cu, Cr, and As CCAand there are now many derelict sites where soil concentrations of these elements greatly exceed background concentrations.
Such contamination has the potential to cause problems, particularly if sites are redeveloped for other agricultural or nonagricultural purposes. Compared with fertilizers, the use of such materials has been more localized, being restricted to particular sites or crops [ 8 ]. Biosolids and Manures The application of numerous biosolids e.
Certain animal wastes such as poultry, cattle, and pig manures produced in agriculture are commonly applied to crops and pastures either as solids or slurries [ 25 ]. Although most manures are seen as valuable fertilizers, in the pig and poultry industry, the Cu and Zn added to diets as growth promoters and As contained in poultry health products may also have the potential to cause metal contamination of the soil [ 2526 ].
The manures produced from animals on such diets contain high concentrations of As, Cu, and Zn and, if repeatedly applied to restricted areas of land, can cause considerable buildup of these metals in the soil in the long run.
Biosolids sewage sludge are primarily organic solid products, produced by wastewater treatment processes that can be beneficially recycled [ 27 ].
Land application of biosolids materials is a common practice in many countries that allow the reuse of biosolids produced by urban populations [ 28 ].
The term sewage sludge is used in many references because of its wide recognition and its regulatory definition. However, the term biosolids is becoming more common as a replacement for sewage sludge because it is thought to reflect more accurately the beneficial characteristics inherent to sewage sludge [ 29 ].
It is estimated that in the United States, more than half of approximately 5.The major pesticides of the world are glyphosate-based herbicides (GBH), and their toxicity is highly debated. To understand their mode of action, the comparative herbicidal and toxicological effects of glyphosate (G) alone and 14 of its formulations were studied in this work, as a model for pesticides.
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Metal analysis. For heavy metal analysis in seawater, water samples were collected before each water exchange, acidified with nitric acid (Trace SELECT ®, Sigma–Aldrich) and stored until kaja-net.com addition, 50 PS beads and 30 PVC fragments were also sampled from the same units after seawater sampling by using a filtering (nylon mesh) and a metal-free counting unit (paper box).
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This paper is based on a review of the usage of the term heavy metal carried out for Eurometaux by the author. This review is available from Eurometaux.
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