Ž . Applied Clay Science 18 2001 309–326 www.elsevier.nlrlocaterclay Organo-clay formulations of pesticides: reduced leaching and photodegradation Yasser El-Nahhal a,b , Tomas Undabeytia a,c , Tamara Polubesova a , Yael Golda Mishael a , Shlomo Nir a, ) , Baruch Rubin a a Seagram Center for Soil and Water Sciences and Department of Field Crops, Vegetables and Genetics, Faculty of Agricultural, Food and EnÕironmental Quality Sciences, Hebrew UniÕersity of Jerusalem, POB 12, RehoÕot 76100, Israel b ( ) ( ) EnÕironmental Protection and Research Institute EPRI , Gaza, Palestinian National Authority PNA , Palestine c Instituto de Recursos Naturales y Agrobiologia, CSCI, Apdo 1052, SeÕille 41080, Spain Received 14 March 2000; received in revised form 11 September 2000; accepted 30 January 2001 Abstract Adsorption of organic cations on several clay minerals is reviewed with an emphasis on the effect of ionic strength and modeling. The clay exchanged with suitable organic cations forms a basis for ecologically acceptable formulations of herbicides with reduced leaching, ground water contamination and enhanced weed control efficacy. Incomplete neutraliza- tion of the clay surface charge by an organic cation may be advantageous in achieving maximal adsorption of hydrophobic herbicides. One conclusion from these studies is that optimization of clay-based herbicide formulations requires a selection of structurally compatible organic cations preadsorbed on the clay at optimal coverage. New experimental results are presented for alachlor formulations, which significantly reduce herbicide leaching under conditions of heavy irrigation. We were able to demonstrate that organo-clay formulations of alachlor and metolachlor can increase crop yields in a 1-year field experiment. The photostabilization of pesticides is reviewed and improved organo-clay formulations of the herbicides trifluralin and norflurazon are described. A pillared clay, nanocomposite micro- andror meso porous material, was effective in reducing leaching and in conferring photostabilization, without added organic cations. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Alachlor; Metolachlor; Norflurazon; Trifluralin; Organic cations; Herbicide leaching; Photostabilization; Organo-clay formula- tion 1. Introduction Herbicide run-off and leaching down the soil profile have become a serious environmental prob- ) Corresponding author. Tel.: q 972-8-948-9172; fax: q 972-8- 947-5181. Ž . E-mail address: NIR1@agri.huji.ac.il S. Nir . lem and a primary source for polluting surface- and Ž . groundwater Carter, 2000 . Widely used herbicides such as atrazine, isoproturon, diuron and mecoprop are the main herbicides found in groundwater in the UK, whereas atrazine, alachlor and metolachlor were detected in ground water in other European countries Ž . and the US El-Nahhal et al., 1997, 1999a . Herbi- cide movement in the soil profile is highly dependent 0169-1317r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-1317 01 00028-X