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AVAILABILITY OF HEAVY METALS IN SOILS AFTER APPLICATION OF SULFUR PULP AND PHOSPHATE ROCK

Monika Tabak

Abstract

Waste application, beneficial in terms of soil abundance in nutrients, cannot lead to soil contamination. The incubation experiment aimed at assessing the effect of applying sulfur pulp (waste material containing elemental sulfur) and ground phosphate rock on the availability of heavy metals in soils. The experiment was conducted on two soils with different soil category: medium and heavy, both of acid reaction and not contaminated with heavy metals. Doses of sulfur pulp and phosphate rock were set based on soil abundance in sulfur and phosphorus, guidelines on the limit content of these elements in soils, and on the principles of crop fertilization. Doses of 20 and 40 mg S as well as 40 and 80 mg P ? kg-1 DM were added to medium soil; 30 and 60 mg S as well as 60 and 120 mg P ? kg-1 DM were added to heavy soil. The experiment comprised: control soils (without additions), soils with only sulfur addition (in both doses), soils with simultaneous sulfur and phosphorus addition (in both doses). The content of available forms of heavy metals (Zn, Mn, Ni, Cd, Pb) in the soils was determined after 90 days of incubation. The elements were extracted with: 1) a mixture of 0.1 mol ? dm-3 hydroxylammonium chloride and 1 mol ? dm-3 ammonium acetate; 2) 0.01 mol ? dm-3 calcium chloride. The element content in the solutions was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). A higher content of trace elements was recorded after extraction with a mixture of hydroxylammonium chloride and ammonium acetate than after extraction with calcium chloride. Trace content of Cd and Pb was extracted with calcium chloride from both soils. Moreover, trace content of Ni was extracted from the medium soil with both reagents and trace content of Cd was extracted from the heavy soil with the mixture of hydroxylammonium chloride and ammonium acetate. Introduction of sulfur pulp and phosphate increased the content of manganese extracted with calcium chloride (especially from the medium soil). In other cases, no significant effect of the applied materials on the content of the analyzed forms of trace elements in both soils was recorded, or the effect was small and concerned only certain fertilization treatments. The element content in eluates obtained after extraction with calcium chloride was as follows: Mn > Zn > Ni (regardless of soil category). The element content in eluates obtained after extraction with the mixture of hydroxylammonium chloride and ammonium acetate was as follows: Mn > Zn > Pb > Cd > Ni (medium soil) and Mn > Pb > Zn > Ni (heavy soil).

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