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1 year ago

2007_6_Nr6_EEMJ

Draghici et al.

Draghici et al. /Environmental Engineering and Management Journal 6 (2007), 6, 497-503 waste tended to be concentrated in the metal wastes, batteries and electronic equipment and tended to have elevated concentrations of cadmium compared to the other fractions in plastics (Burnley, 2007). Heavy metals or trace metals is the term applied to a large group of trace metals which are both industrially biologically important. Agricultural productivity can be limited by deficiencies of essential trace elements such as Cu, Mn and Zn in crops and Co, Cu, Mn and Zn in livestock. However, when are presented in excessive concentrations, certain heavy metals give rise to concern with regard to human health and agriculture (Dobra and Viman, 2006; Statescu and Cotiusca-Zauca, 2006) and their accurate analytical determination remains a challenge for chemists (Anderson, 1999; Baiulescu et al., 1990; Crompton, 2001; Draghici et al., 2003). The purpose of this paper is to present original results concerning concentrations of eight metals in soils adjacent to Eforie Sud and Techirghiol improperly built municipal waste deposits located in Constanta County, Romania, in April-October 2006. 2. Experimental Total Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn concentrations in soils using flame atomic absorption spectrometry (FAAS) have been determined. Adjacent soils of two improperly built landfills located in Constanta County, Romania have been analysed: Eforie Sud waste deposit, corresponding to 8650 people and Techirghiol waste deposit which corresponds to 7150 people. In order to determine metals concentration from soils, five samples were collected using a special device from the surface and depth of 20-40 cm from each location at 1 – 2.5 m distance of the landfill boundary between April and October 2006 (Chirila, 2004). Mean samples from surface and depth have been obtained each month by the appropriate omogenization of collected samples, previously dried for 16 hours at room temperature. To obtain soil solutions, 3 grams of soil sample has been extracted with aqua regia in 250 mL volumetric flask (ISO 11466). The supernatant, the filtrate and the washing solution have been collected in 100 mL calibrated flask (Chirila and Draghici, 2003). The spectrometric measurements have been done using a flame atomic absorption spectrometer Spectr AA220, provided by Varian Company. Analyses have been done in triplicate and the mean values are reported. For the background correction, the zero calibration solution was done using aqua regia and deionised water (for Cd, Co, Cu, Ni, Pb and Zn); for Cr and Mn, the zero calibration solution was prepared by adding of 3.7 mg/L La, using a lantanum chloride solution. All used reagents were of spectral purity grade. 3. Results and discussions Heavy metals existence in the soil can be explained by the natural concentration of (that depends on the soil type and its composition) and by soil contamination with heavy metals, provided by human activity. Soil pollution with heavy metals can be available from infiltration of highly contaminated storm water. The studies were performed in order to observe the heavy metal concentration evolution in adjacent soils to solid waste deposits. Once metals are introduced and contaminate the environment, they will remain. Metals neither are nor degraded like carbon-based (organic) molecules. The measured concentrations have been compared with the Romanian regulations (Table 2). Table 2. Regulatory limits for heavy metals in soils (after 756/1997 – Romanian regulation of environment pollution evaluation) Metal Concentration, mg/kg dry weight Normal Alert limit Intervention limit value S NS S NS Cd 1 3 5 5 10 Co 15 30 100 50 250 Cr 30 100 300 300 600 Cu 20 100 250 200 500 Mn 900 1500 2000 2500 4000 Ni 20 75 200 150 500 Pb 20 50 250 100 1000 Zn 100 300 700 600 1500 S- sensible utilization, NS non-sensible Cadmium concentration in soil depends on the geological origin of the parent material, texture, intensity of weathering processes, organic matter and other factors. Cadmium enters the soil in smaller quantities than lead and it reach the soil through air. It is derived from incinerator exhaust gases and from phosphate fertilizers. Generally, in acidic soils with pH

Metals concentration in soils adjacent to waste deposits environment are soil, dust, seawater, volcanic eruptions and forest fires. All soil contains some amount of cobalt. The average concentration of cobalt in soils around the world is 8 mg/kg dry weight. Toxic effects on plants are unlikely to occur below soil cobalt concentrations of 40 ppm. One of the most important soil properties is soil acidity. The more acidic the soil, the greater are the potential for cobalt toxicity, at any concentration. Co conc., mg/kg d.w. 16 14 12 10 8 6 4 2 0 a) Apr Iun Aug Oct month surface depth b) Co conc., mg/kg d.w. 14 12 10 8 6 4 2 0 Apr Iun Aug Oct month surface depth Fig. 2. Cobalt concentration evolution in soil adjacent to waste deposits in April-October 2006 (mean values, mg/kg dry weight); a) Eforie Sud; b) Techirghiol Fig. 1. Cadmium concentration evolution in soil adjacent to waste deposits in April-October 2006 (mean values, mg/kg dry weight); a) Eforie Sud; b) Techirghiol The cobalt concentration evolution in studied soil samples are presented in the Fig. 2. All founded values are lower than 15 mg/kg dry weight, the normal Co concentrations in soil. Chromium is a trace component in the earth’s crust (0.02%), a unique element in soil, because of essentiality to human and animal life and nonessentiality for the vegetable kingdom and its possible presence in two main oxidation forms, trivalent and hexavalent which show opposite properties. The reported mean total chromium concentration in lithosphere is 69 mg/kg dry weight. The two forms have completely different effects on living organisms: the first Cr(III) is apparently useful or harmless at reasonable concentrations, while the second Cr(VI) is extremely toxic. In addition, Cr(III) is not mobile in soil, therefore the risks of leaching are negligible, while Cr(VI), mainly present in the forms of chromates (CrO 4 2− ) and dichromates (Cr 2 O 7 2− ), is generally mobile and often is part of crystalline minerals. Conversion of Cr(III) to Cr(VI) has been shown in some particular soils: rich in manganese oxides, poor in organic matter and high redox potential. On the contrary, the reverse transformation of Cr(VI) to Cr(III) is very common and easier, so that it is difficult to find hexavalent chromium forms in soil solution or in leaching waters. The problem of Cr enrichment in soil has been often discussed not only in relation to the discharge of tannery wastes, but also to the possibility of Cr presence in soil amendments, mainly organics, and to the existence of excellent organic fertilizers produced from leather residues or wastes. Fig. 3 presents the mean total chromium concentration in studied soil samples. In Eforie Sud soil samples Cr concentration ranged between 3.24 – 28.72 mg/kg dry weight in surface samples and 7.25 – 30.06 mg/kg dry weight in depth samples. Soil samples from Techirghiol registered similar Cr concentrations (7.50 – 28.55 mg/kg dry weight in surface samples and 8.40 – 19.32 mg/kg dry weight in depth samples). All determined Cr concentrations were below the normal limit in soil. Copper is also a trace element in the earth’s crust (0.007%); Cu is among the trace elements essential for life, in the case of plants toxic effects occur at 20 or more mg/kg dry weight. In the past, the 499

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