Direct land application of cement kiln dust- and lime-sanitized biosolids:extractability of trace metals and organic matter quality

Direct-land application of biosolids can affect soil organic matter (SOM) q uality and be a source of trace metals (TMs) which may then be exported out side soil systems by plants, animals, and surface and subsurface waters. Or ganic matter (OM) quality and the chemical distribution of Cu, Zn, Cr, Ni, Pb, Co, and As were evaluated in soil amended with cement kiln dust-(CDB) a nd lime-treated (LSB) biosolids. Forms of these metals were classified by s equential extractions as easily extractable and exchangeable, potentially e xtractable, and non-extractable. SOM quality was assessed by extraction wit h diethyl ether (DEE) and chloroform (CHCl3). Soils amended with CDB and LS B contained more TMs than did the control soil. Sequential extractions show ed that, after one growing season, easily extractable and exchangeable meta ls accounted for 1.8% and 0.9% of total metals in CDB-and LSB-amended soils , respectively. On the other hand, potentially extractable and exchangeable metals constituted 53.4% and 59.5% of total TMs in the two soils, whereas non-extractable and non-exchangeable metals made up 44.8% and 39.6% of tota l TMs in the same sails, respectively. Direct-land application of CDB- and LSB-treated biosolids led to strong modifications of SOM duality as indicat ed by DEE/CHCl3 ratios (indicative of the biodegradability of SOM), respect ively, although the C and N contents did not change. The results also indic ate that the dynamics of TMs are related to the degree of stabilization of the OM. (C) 2000 Elsevier Science B.V. All rights reserved.