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Pol. J. Environ. Stud. Vol. 21, No. 6 (2012), 1603-1611 Original Research Mobility of Heavy Metals in Municipal Sewage Sludge from Different Throughput Sewage Treatment Plants Jarosław Gawdzik1*, Barbara Gawdzik2** 1Faculty of Civil and Environmental Engineering, Kielce University of Technology, Division of Waste Management, Al. 1000-lecia Państwa Polskiego 7, 25-314 Kielce, Poland 2Institute of Chemistry, Faculty of Mathematics and Science, Jan Kochanowski University of Humanities and Sciences, Świętokrzyska 15, 25-406 Kielce, Poland Received: 27 June 2011 Accepted: 11 May 2012 Abstract Sewage sludge heavy metals can be dissolved, precipitated, co-precipitated with metal oxides, and adsorbed or associated on the particles in biological debris. Heavy metals are found in the form of oxides, hydroxides, sulphides, sulphates, phosphates, silicates, organic bindings forming complexes with humic com- pounds, and complex sugars. Polish regulations specifying the maximum levels of heavy metals in municipal sewage sludge used for agricultural purposes refer to the total content of lead, cadmium, mercury, nickel, zinc, copper, and chromium. The aim of our study was to evaluate the mobility of heavy metals in sewage sludge from wastewater treatment plants in Świętokrzyskie Province. Stabilized sewage sludge from wastewater treatment was ana- lyzed in accordance with the extraction method proposed by the Community Bureau of Reference (BCR). Zinc, cadmium, lead, and nickel were determined by means of the standard addition with the use of a Perkin-Elmer 3100-BG FAAS atomic absorption spectrophotometer. Chromium and copper were tested using the FAAS technique. The sequence analysis revealed the presence of heavy metals in all fractions (F-I, F-II, F-III, F-IV). It should be strongly emphasized that organometallics and aluminosilicates constitute the most prevalent forms of metals under consideration. Those, according to BCR, make fraction III and fraction IV, respectively. The results for stabilized sewage sludge confirmed a trend being observed in heavy metals concentrations in the immobile fractions, here in combination with aluminosilicates. On the basis of the investigations, it can be con- cluded that the dominant forms of heavy metals are immobile. It was shown that the total content of heavy metals in the sewage sludge does not provide an objective criterion for environmental risk evaluation. Bearing that in mind, however, it should be noted that heavy metals immobilized in the fraction F-III, may pose a potential hazard to soil in the aeration zone. Keywords: heavy metals, BCR, sewage sludge, metal speciation *e-mail: [email protected] **e-mail: [email protected] 1604 Gawdzik J., Gawdzik B. Introduction Plants, animals, and humans differ in their reactions to various HMs [1]. The mechanisms of the harmful action of Heavy metals (HMs) are elements that have density HMs are diversified. They can inactivate enzyme systems, greater than 4.5 g/cm3 and which in chemical reactions tend thus leading to physiological changes which, in the most to give away electrons, forming simple cations. In the solid extreme cases, can cause tissue and cell necrosis. For and liquid states they are characterized by good thermal and instance, inhibited nitrate reductase can result in the accu- electrical conductivity; they are shiny and opaque. They mulation of nitrates in plants, which is particularly danger- have high melting and boiling points. They are malleable ous for humans and animals. The natural content of HMs in and ductile, their vapors are most frequently monatomic. soils generally does not pose a hazard to plants, animals, or They have reduction properties [1]. people [4]. Due to the results of investigations, however, HMs comprise the following: Cu, Co, Cr, Cd, Fe, Zn, alarming voices of research can be heard that industrializa- Pb, Sn, Hg, Mn, Ni, Mo, V, and W, plus non-metal Se. The tion and heightened standards of living makes the acreage group includes both the elements that are indispensable for of soils having the natural HM concentrations shrink con- living organisms and those whose role in the physiology of stantly. The lack of information on the natural content of plants, animals, and humans is still unexplained [2]. HMs in the environment leads to a gross simplification in HMs constitute very important components of the the evaluation and interpretation of the causes of HM pol- earth’s crust and are considered to be non-renewable natur- lution. al resources. Also, HMs play an important role in microor- The total content of HMs in sewage sludge does not ganism metabolic processes, e.g. those in bacteria, by tak- provide information on what amount is accessible to plants, ing part in the control of biochemical process, in cell struc- thus on what amount will enter the biological cycle. It is ture stabilization, or in enzyme reaction catalysis [3]. HM only the sequence analysis that makes it possible to esti- pollution constitutes a major problem in all water-related mate the percentages of metals in their mobile form that are environmental issues. The environmental problem HMs accessible to plants. In the hydrosphere, heavy metals are pose is complex in character. On one hand their ores get found in the form of suspensions or they are dissolved. The depleted, on the other, heavy metal concentration both in analysis of metals in a complex environmental matrix living organisms (plants, animals, humans) and also in the requires mineralization. This stage decides on metals being habitats of those organisms tends to increase continuously converted into their ionic forms [1]. In accordance with the [1]. guidelines for the regulation [6], it is recommended to use Dynamically developing industries and transport unrea- the analytical method, applied after sample mineralization sonably apply crop protection chemicals in agriculture, with aqua regia (or with concentrated acids), in which an sewage sludge, and wastes used to deacidify soils. All con- AAS spectrophotometer is employed. tribute to the excessive accumulation of trace elements in Many wet and dry mineralization methods with differ- plant soils, which poses a health hazard for animals and ent oxidation agents are known [4]. humans [4]. One of the effects produced by the growth of urbanization and industrialization involves a constant Occurrence of HMs in Sewage increase in HM content in the natural environment, which and Sewage Sludge continues to adversely affect the operation of ecosystems. The accumulation of HMs in soil is particularly dangerous Industrial sewage, which through the municipal sewage due to the fact that soil constitutes the most crucial link in system is brought to sewage treatment plants, provides a the element cycle in nature. HMs migrating to the environ- relevant source of HMs in the environment. Surface flows ment produce an impact on all components of the food constitute an additional source of HMs in sewage [7-8]. chain. They affect micro-organisms, plants, animals and, Although HMs found in sewage cannot disturb biolog- finally, humans. Plants that people and animals eat are a nat- ical purification processes, they accumulate in sludge, ural source of heavy metals, therefore the latter constitute a which affects its treatment and determines its final compo- substantial health risk due to the dietary quality of food sition. Sewage sludge can be used for remediation of crops. Those elements accumulate both in soft and hard tis- degraded areas, provided that the requirements specified in sues in animals and people. On the basis of their toxicity, the regulations are satisfied [6, 9-14]. two groups of HMs are differentiated. The first one includes cadmium, mercury, and lead, which are highly toxic for humans and animals and less harmful for plants. The other Forms of HM Occurrence in Sewage group comprises copper, zinc, and nickel, which when pre- and Sewage Sludge sent at excessive levels, are more damaging to plants than to animal and human organisms [5]. The level of pollution with HMs is determined by the Increased content of HMs can lead to ground water con- amount of metal ions dissolved in sewage and sludge liquid tamination, produce an adverse effect for soil biological phase, floating in suspension and precipitated with the sludge. properties, be toxic for plants, and also alter the food chain. Ions of HMs can be naturally bound in them through [15]: Above the admissible level, toxic metals significantly - Cation exchange and adsorption binding on the surface reduce soil fertility. They also inhibit enzyme activity in the of fine particles (e.g. clayey particles, iron and man- soil and alter soil acidity. ganese oxides and hydroxides, and organic substances). Mobility of Heavy Metals in Municipal... 1605 - Organic binding – especially with humic acids, which Metals that occur in bindings that are water-soluble and are insoluble in water and which are characterized by a metals bound to carbonates are considered to be the most high ability to exchange cations. They cause the forma- mobile ones. Metals bound to iron and manganese oxides tion of chelates, from which HM ions do not return to and to organic matter also are dangerous, yet their disen- the solution. gagement usually proceeds slowly. Metals bound to alumi- - Inorganic binding, which is a main means of binding nosilicates are thought to be inaccessible. In order to deter- HM ions. mine bindings, in which heavy metals occur, thus their - co-precipitation with oxides or hydroxides of iron and bioaccessibility, so-called speciation analysis is performed manganese, which allows HM ions binding with the [20, 23, 24]. sludge. The speciation analysis determines forms, defined in In the presence of ammonia, some HMs in sewage and a different manner, of a given element in a sample [22, sludge form soluble complex compounds [7]. 25]. Speciation analysis employs analytical techniques and HM Mobility in Sewage Sludge sample preparation for tests that do not affect the original balance of the sample.

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