Evaluation of chemical and ecotoxicological characteristics of biodegradable organic residues for application to agricultural land P. Alvarenga a, ⁎ , P. Palma a , A.P. Gonçalves a , R.M. Fernandes a , A.C. Cunha-Queda b , E. Duarte b , G. Vallini c a Departamento de Ciências do Ambiente, Escola Superior Agrária de Beja, Rua Pedro Soares, Apartado 158, 7801-902 Beja, Portugal b Departamento de Química Agrícola e Ambiental, Instituto Superior de Agronomia, Technical University of Lisbon (TULisbon), Tapada da Ajuda, 1349-017 Lisboa, Portugal c Dipartimento Scientifico e Tecnologico, Università degli Studi di Verona, Ca' Vignal 2, Strada Le Grazie 15, 37134 Verona, Italy Abstract The use of organic waste and compost as a source of organic matter and nutrients is a common practice to improve soil physico-chemical properties, meanwhile reducing the need for inorganic fertilisers. Official guidelines to assess sewage sludge and compost quality are mostly based on total metal content of these residues. Measurement of the total concentrationof metals may be useful as a general index of contamination, but provides inadequate or little information about their bioavailability, mobility or toxicity when the organic residue is applied to the soil. However, ecotoxicity tests provide an integrated measure of bioavailability and detrimental effects of contaminants in the ecosystem. In the present study, three different types of biodegradable organic residues (BORs) have been considered: sewage sludge from municipal wastewater treatment (SS), compost from the organic fraction of unsorted municipal solid waste (MSWC), and garden waste compost (GWC). The BORs were subjected to chemical characterisation and total metal quantification (Cd, Cr, Cu, Ni, Pb and Zn), in order to verify their suitability for land application. Water leachability was determined through the DIN 38414-S4 method, while the modified BCR sequential extraction procedure was used for metal speciation. Ecotoxicity of the BORs was studied by direct and indirect bioassays. Direct toxicity bioassays were: plant growth tests with cress (Lepidium sativum L.) and barley (Hordeum vulgare L.), and earthworm (Eisenia fetida) mortality. On the other hand, indirect exposure bioassays, with leachate from the residues, took into account: luminescent bacteria (Vibrio fischeri), seed germination (L. sativum and H. vulgare) and Daphnia magna immobilization. As far as total metal concentration is concerned, with particular reference to Zn, SS resulted neither suitable for the use in agriculture nor compatible to be disposed of as an inert material into landfill, according to the Directive 1999/31/EC. Zinc in SS was mainly present in exchangeable form (28.5%), appearing as highly bioavailable. As a consequence, SS exhibited either high ecotoxicity effects with the indirect exposure bioassays or significant mortality with the earthworm bioassay. Total content of metals in MSWC allowed its classification as “stabilised biowaste”, according to 2nd draft [DG Env.A.2. Working document of Biological treatment of biowaste — 2nd draft. Directorate- General Environment, Brussels, 12th February; 2001. accessed in:http://europa.eu.int/comm/environment/waste/facts_en.htm, at 10/09/2002] while leachate, on the basis of the concentration of these contaminants, could be classified as “inert waste”. This residue showed significant ecotoxicity effects with direct exposure bioassays as well as with the luminescent bacteria bioassay. However, it resulted less toxic than SS. Finally, GWC could be classified as a Class 2 compost, with no detectable toxic effects on the organisms used in the bioassays, except for the luminescent bacteria. In this case, an EC 50 of 73.0% was observed. Considering the results, the use of a battery of toxicity test in conjunction with chemical analysis should be suggested, in order to correctly assess possible environmental risks deriving from disposal or land application of biodegradable organic residues. © 2006 Elsevier Ltd. All rights reserved. Keywords: Biodegradable organic residues; Sewage sludge; Compost; Metals; Sequential extraction; Ecotoxicity assays 1. Introduction Generation of biodegradable organic residues (BORs) is increasing worldwide and strategies for its environmentally sound use must be developed and optimised. Due to the high content of organic matter and nutrients of these residues, they Environment International xx (2006) xxx – xxx + MODEL EI-01553; No of Pages 9 www.elsevier.com/locate/envint ⁎ Corresponding author. Tel.: +351 284 314 300; fax: +351 284 388 207. E-mail address: paula.alvarenga@esab.ipbeja.pt (P. Alvarenga). 0160-4120/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.envint.2006.11.006 ARTICLE IN PRESS Please cite this article as: Alvarenga P et al. Evaluation of chemical and ecotoxicological characteristics of biodegradable organic residues for application to agricultural land. Environ Int (2006), doi:10.1016/j.envint.2006.11.006