pubs.acs.org/JAFC Published on Web 07/28/2010 © 2010 American Chemical Society J. Agric. Food Chem. 2010, 58, 9147–9156 9147 DOI:10.1021/jf1011853 Degradation and Adsorption of Pesticides in Compost-Based Biomixtures as Potential Substrates for Biobeds in Southern Europe EVANGELOS KARANASIOS, † NIKOLAOS G. TSIROPOULOS,* ,† DIMITRIOS G. KARPOUZAS,* ,‡ AND CONSTANTINOS EHALIOTIS § † Department of Agriculture, Crop Production and Rural Environment, University of Thessaly, Fytokou Street, Nea Ionia-Volos 38446, Greece, ‡ Department of Biochemistry and Biotechnology, University of Thessaly, Ploutonos 26 and Aiolou Street, Larissa 41221, Greece, and § Department of Natural Resources and Agricultural Engineering, Agricultural University of Athens, 75 Iera Odos Street, Athens 11855, Greece Biobeds have been used in northern Europe for minimizing point source contamination of water resources by pesticides. However, little is known regarding their use in southern Europe where edaphoclimatic conditions and agriculture practices significantly differ. A first step toward their adaptation in southern Europe is the use of low-cost and easily available substrates as biomixture components. This study investigated the possibility of replacing peat with agricultural composts in the biomixture. Five composts from local substrates including olive leaves, cotton crop residues, cotton seeds, spent mushroom substrate, and commercial sea wrack were mixed with topsoil and straw (1:1:2). Degradation of a mixture of pesticides (dimethoate, indoxacarb, buprofezin, terbuthylazine, metribuzin, metalaxyl-M, iprodione, azoxystrobin) at two dose rates was tested in the compost biomixtures (BX), in corresponding peat biomixtures (OBX), and in soil. Adsorption-desorption of selected pesticides were also studied. Pesticide residues were determined by gas chromatography with nitrogen-phosphorus detector, except indoxacarb, which was determined with a microelectron capture detector. Overall, BX degraded the studied pesticides at rates markedly higher than those observed in soil and OBX, in which the slowest degradation rates were evident. Overall, the olive leaf compost biomixture showed the highest degradation capacity. Adsorption studies showed that OBX and BX had higher adsorption affinity compared to soil. Desorption experiments revealed that pesticide adsorption in biomixtures was not entirely reversible. The results suggest that substitution of peat with local composts will lead to optimization of the biobed system for use in Mediterranean countries. KEYWORDS: Pesticide degradation; adsorption; biobeds; biomixtures; compost; peat INTRODUCTION Point source pollution has been identified as a major factor contributing to the contamination of groundwater (GW) re- sources with pesticides ( 1 -3 ). This is usually caused by pesticide mishandling such as inadequate control of spray leftovers, accidental spillage or leakage during pesticide loading, or spray tank washdown after application or as an accident during pesticide storage ( 4 ). In these cases, high pesticide loads are released into restricted areas with the potential to leach to GW. Therefore, in an effort to minimize the risk for point source contamination, biofiltration systems were developed ( 5 ). The most commonly used on-farm pesticide biofiltration system is called a biobed. It is a simple to operate and cost- effective multilayered construction in the ground in the form of a pit filled with a mixture of bioorganic substrates ( 6 , 7 ). Their efficacy is based on their increasing capacity to adsorb pesticides or stimulate their rapid biodegradation by offering favorable physicochemical and biological conditions for maximum micro- bial activity. Biobeds were first proposed by Torstensson and Castillo in 1993, and now more than 1500 biobeds are currently operative in Sweden. Studies on full-scale systems showed that they manage to dissipate from 95 to 99% of the applied pesticides ( 8 ). Over the years there have been several modifications of the original design to adapt to the specific climatic conditions and requirements of other countries including the United Kingdom ( 9 -11 ), Italy ( 12 , 13 ), Belgium ( 14 ), and Denmark ( 15 ). The main component of a biobed, the biomixture, has been identified as a major factor controlling the efficacy of the biobed ( 4 ). An efficient biomixture favors pesticide sorption and supports an active microbial community able to degrade pesti- cides at high concentrations. In its typical form the biomixture consists of peat, straw, and topsoil at volumetric proportions of 1:2:1. Each of these components has a key role in biobed *Address correspondence to either author [(N.G.T.) e-mail: ntsirop@uth.gr, phone þ30 24210 93193, fax þ302421093144; (D.G.K.) e-mail dkarpouzas@bio.uth.gr, phone þ302410 565294, fax þ302410 565290].