Saturday, 15 July 2006
170-23

Zn and Pb Sobility in Soil at Various Ameliorants Applying.

Tatiana Minkina, Alexei Samokhin, and Saglara Mandzhieva. Rostov State Univ, B.Sadovaya 105, Rostov-on-Don, Russia

There are no known ameliorants produced in Russia specifically for weak-alkaline polluted with heavy metals soils which are typical to the Rostov Region. The objective of our research is to investigate Zn and Pb mobility in soil under chalk, glauconite, manure applying and their combinations. Chernozem with pH 7.5 which contains clay 58%, was the object of the research. In the fall Zn and Pb were introduced into the plough-layer (0-20 cm) separately as dry acetate salts and were thoroughly intermixed with soil. The dose introduced was collocated with 3 Maximum Concentration Limits (MCLs) in gross forms: Zn: 300 mg/kg, Pb: 96 mg/kg of soil. The choice of these elements as subjects of inquiry was due to the fact that from out of 10 potential toxicants (Hg, Cd, Pb, Zn, Cu, Cr, As, Mn, Ni, V) in the Rostov Region only Pb, Zn and Cu contents exceed the MCLs in both the soil and the agricultural products. The area of the experimental plot was 50 ì2. There were 3 replicates. The field experiment was carried out from 1999 to 2004 years. After artificial soil contamination chalk (2.5 kg/m2 and 5 kg/m2), glauconite (2 kg/m2) and semi-fire-fanged cattle manure (5 kg/m2), as well as their combinations, were applied as ameliorants. The studied crop was spring barley (Hordeum sativum distichum). The crop samples were collected during the completed ripeness phase together with soil samples (0 to 20 cm). The mobile forms of heavy metals were extracted from soil by ammonium acetate buffer solution NH4OAc (exchangeable forms), pH 4.8; 1% EDTA in ammonium acetate buffer solution (complex-bound forms) and 1N HCl (acid-soluble forms). The amount of complex-bound forms was calculated as a difference between the metal contents in the extracts of EDTA in NH4OAc and NH4OAc. The heavy metals concentrations in plants were determined by dry method. Analysis of the metals in extracts from the soil and plants was made using an AAS. In case of calcareous chernozem, transformation of heavy metals introduced as soluble salts resulted as their redistribution into various forms. The general regularity of Zn and Pb distribution by combination forms in the check soil, under contamination and ameliorant variants is as follows: complex-bound forms < exchangeable forms < acid soluble forms. During the initial investigating year contaminated soil shows a noticeable increase of Zn mobile combination forms of up to 33 mg/kg, which exceeds the MCL (MCL=23 mg/kg). The amount of Pb is 13 mg/kg, which exceeds at almost twice the level of the MCL of 6 mg/kg. With the 3 years of time the concentration of the investigated HMs mobile forms in the contamination variants reduced: Zn by 20% and Pb by 25% within 3 years. With the passage of time there is a further redistribution of absorbed heavy metals between those soil components which possess the big affinity to metal cations. The concentration of Zn acid-soluble forms and Pb complex-bound forms increases under the decreases their mobile forms. Meanwhile there was no exchangeable metal forms reduction to the MCL level. The results indicated significant differences between chalk, manure and glauconite in the level of their impact upon the heavy metals state in soil and intensity of their entrance into crops. The content of exchangeable, most crop-accessible Zn and Pb combination forms during the initial investigating year goes down to the MCL level and is less in the carbonate-containing variants, especially with manure. Glauconite showed better results in combination with manure but weaker than carbonates. It has been stated that Zn and Pb mobility reduced under soil remediation during 3 years. The results are supported with correlation between Zn (r=0.83±0.21) and Pb (r=0.96±0.11) exchangeable forms and the heavy metals contents in the barley grain and straw. The heavy metals contents got lower than MCL under chalk and manure combination applying: lower 50.0mg/kg for Zn and 0.5mg/kg for Pb. Applying glauconite and especially chalk separately or together with manure reduced Zn and Pb mobility in chernozem. The positive effect from the ameliorants applied once left during all investigation period. Acknowledgements: The work was supported by the Russian Foundation for Basic Research (project # 04-04-96804) and the Ministry of Education and Science of Russian Federation.

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