RESEARCH NOTE FATE OF MCPP AND ATRAZINE IN AN ANAEROBIC LANDFILL LEACHATE PLUME (GRINDSTED, DENMARK) KIRSTEN RU È GGE*, POUL L. BJERG, HANS MOSBáK and THOMAS H. CHRISTENSEN Department of Environmental Science and Engineering/Groundwater Research Centre, Technical University of Denmark, Building 115, DK-2800 Lyngby, Denmark (First received July 1998; accepted in revised form October 1998) AbstractÐThe fate of the two pesticides MCPP (mecoprop) and atrazine was investigated in an anaero- bic aquifer downgradient from the Grindsted Land®ll, Denmark, by means of a ®eld injection exper- iment, in situ microcosms and laboratory batch experiments. The redox conditions in the experiments were dominated by iron reduction, but also methanogenesis and sulfate reduction occurred closest to the land®ll. No degradation nor sorption was observed for the two pesticides in any of the biologically active experiments. In microbially inhibited laboratory experiments, supplied with sodium azide as a sterilizing agent, a chemical degradation of atrazine occurred. # 1999 Elsevier Science Ltd. All rights reserved Key wordsÐMCPP, mecoprop, atrazine, pesticides, anaerobic groundwater, ®eld injection experiment, in situ microcosms, laboratory batch experiments INTRODUCTION Pesticides are often found in groundwater in con- centrations exceeding the drinking water standards (Barbash and Resek, 1996; GEUS, 1996). Pesticides have also been found in groundwater contaminated by land®ll leachate (Schultz and Kjeldsen, 1986; Gintautas et al., 1992; Lyngkilde and Christensen, 1992), since pesticides often has been disposed o in land®lls. MCPP was for instance found in the groundwater in concentrations of up to 250 mg/l in the anaerobic part of the plume downgradient from the Vejen Land®ll, Denmark (Lyngkilde and Christensen, 1992). The literature is very sparse in studies on anaero- bic degradation of pesticides in aquifers. A few stu- dies concern aerobic aquifer conditions (Agertved et al., 1992; Heron and Christensen, 1992), but most studies are conducted in the top soil and represent high pesticide concentrations (mg/l). Some of the most often found pesticides in groundwater are the phenoxy acids (e.g. MCPP, MCPA and dichlor- prop) and the triazines (e.g. atrazine and simazine) (Barbash and Resek, 1996; GEUS, 1996). In the present study, the anaerobic degradation of MCPP and atrazine was studied at trace levels (mg/l) in a leachate-aected groundwater aquifer downgradient from the Grindsted Land®ll, Denmark. MATERIALS AND METHODS The Grindsted Land®ll site The Grindsted Land®ll covers approximately 10 ha and has an average depth of 5 m. In total, approximately 500000 m 3 of waste, consisting of municipal, demolition and some chemical waste, have been land®lled in the period from 1930 to 1977 (Kjeldsen et al., 1998). The land- ®ll is located on a glacial outwash plain, and the sediments are composed of medium and coarse grained sand and gravel. The average temperature is 108C (Bjerg et al., 1995) and the aquifer material is low in solid organic car- bon (f oc =0.01±0.03%) (Heron et al., 1998). The distribution of speci®c organic compounds in the groundwater downgradient from the land®ll was studied by RuÈgge et al. (1995). More than 15 dierent organic compounds were identi®ed close to the land®ll, with the BTEX compounds dominating: concentrations of 0± 222 mg/l were observed close to the land®ll, with single ob- servations of o-xylene concentrations up to 1550 mg/l. No chlorinated aliphatic compounds were present in this part of the pollution plume. Pesticides were not observed, but compounds which could be degradation products from dierent chlorinated phenoxy acids were observed at trace levels. Experimental set up The fate of the two pesticides MCPP and atrazine was studied under anaerobic conditions using three dierent experimental set-ups: ®eld injection, in situ microcosms, Wat. Res. Vol. 33, No. 10, pp. 2455±2458, 1999 # 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/99/$ - see front matter PII: S0043-1354(98)00444-8 *Author to whom all correspondence should be addressed. [Fax: +45-45-932850, e-mail: kr@imt.dtu.dk]. 2455