Heavy metals mobility in soils amended with sewage sludge

Author(s)

Edna Ivani Bertoncini

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 1997-10-29
• Advisor: Maria Emília Mattiazzo

Abstract

A greenhouse experiment was conducted in leaching tubes using soils classified as Typic Quartzipsament (AQ), Typic Hapludox (LV) and Rhodic Typic (LE). The sewage sludge was periodically added and incorporated to the soils in a total amount corresponding to 156,0 Mg ha-1 (dry weight basis), in an experimental period of 310 days. After the incubation period a high amount of salt was perceived on the soil surface and the sampling was performed for the total content determination of metals by the HNO3+HClO4 extractant. The extraction was unsuccessful for the digestion was shown turbulent with material loss. The extractants HCl 0,1 mol L-1 Mehlich 3 and DTPA to soluble contents and HNO3+HClO4; HCl dry via; HNO3+HClO4+HF and EPA-SW-846-3051 to total contents were tested. The extractant HCl 0,1 L-1 was effective on extraction of metal solúvel contents in all treatments. For the total content, the extractants HNO3+HClO4+HF and HCl dry via showed to be more effective, except to Cr, because the EPA-3051 method extracted a higher quantity of this metal in every treatment. In the leaching pots the soils were treated with water and with the following salt solutions: 0,9 mol L-1 KCl; 0,9 mol L-1 KNO3; 0,3 mol L-1 K2SO4 and 0,3 mol L-1 Ca(NO3)2. The water and salt solutions were added in amount corresponding to 4 times the water retention capacity of the soils. The leachate material was analyzed for: pH, electrical conductivity, Cd, Cr, Cu, Ni and Zn. The results showed no presence of any metals in soils without sludge. The presence of Cu was observed in all leached materials, including with water, coming from all sewage sludge amended soils, with the exception of LE soil+sludge. The presence of Zn was not observed in any leaching material and the presence of Ni was observed with the use of all salty solutions in the sandy soil (AQ) plus sludge treatment. With the addition of the KCl solution it was detected the presence of Cd in the treatments in LV and LE amended with sludge. This salt also allow the leaching of Cr in the treatment using AQ soil plus sludge. The presence of Ca2+ and Mg2+ was great in the leachate material resulting from water passing through the soils. Other experiments were performed in order to evaluate metal availability in rice plants, cultivar IAC-165, through Neubauer & Schneider method (1923) modified by Catani & Bergamin (1961). One of them was conducted before the water leaching and another after it. This was to verify if salt carrying would happen during the water passage. The application of sludge increased nutrient contents, pH and CTC of the soils, but it caused salinity and absorption difficulty of water by rice plants. The determination of heavy metals in them was not carried out due to lack of vegetal material. There was a reduction of 70% in the electrical conductivity in very treatments after soil leaching with water. However the dry matter production of rice did not increase. (AU)