Direct and Indirect Effects of the Fungicide Carbendazim in Tropical Freshwater Microcosms Michiel A. Daam Æ Kriengkrai Satapornvanit Æ Paul J. Van den Brink Æ Anto ´nio J. A. Nogueira Received: 13 December 2008 / Accepted: 13 July 2009 / Published online: 29 July 2009 Ó Springer Science+Business Media, LLC 2009 Abstract Direct and indirect effects of the fungicide carbendazim on ecosystem structure and functioning were studied B8 weeks after application (nominal concentra- tions: 0, 3.3, 33, 100, and 1000 lg/L) to outdoor micro- cosms in Thailand. Direct effects on macroinvertebrates are discussed in detail in a separate article. The present article presents the effects on other end points and discusses the hypothesized ecologic effect chain. Negative treatment effects on the zooplankton community were only recorded for the highest carbendazim treatment (NOEC commu- nity = 100 lg/L). The rotifer Keratella tropica, cladocer- ans (Moina micrura, Ceriodaphnia cornuta, and Diaphanosoma sp.), and cyclopoid copepods were decreased or even eliminated at this treatment level. The decrease in zooplankton and macroinvertebrate abundances was accompanied by an increase in numbers of several tolerant invertebrates, presumably caused by a release from competition and predation. The death of sensitive inverte- brates probably also led to an overall decreased grazing pressure because increased levels of chlorophyll-a and bloom of the floating macrophyte Wolffia sp. were noted. The increase in primary producers is discussed to be the probable cause of changes in physicochemical water con- ditions, eventually resulting in an anoxic water layer during the last 3 weeks of the experiment. This is likely to have resulted in decreased invertebrate abundances noted in that period. Furthermore, the decreased decomposition of Musa (banana) leaves observed 8 weeks after application is considered to be the indirect effect of a decreased micro- bial activity resulting from these anoxic water conditions, rather than a direct toxic effect of carbendazim. As a result of a shift from traditional subsistence farming toward intensive-crop farming, pesticide use in Thailand has increased considerably since the Green Revolution in the late 1960s (Pingali 1997; Thapintha and Hudak 2000; Satapornvanit et al. 2004). Furthermore, decreasing prices for rice and a production restructuring program by the Thai Ministry of Agriculture in 1994 led to a conversion of land used to cultivate rice, cassava, coffee, and pepper into more pesticide intensive crops of fruits and vegetables (Jungb- luth 2000). Because fungicides are mainly used for the cultivation of fruit and vegetables, fungicide imports dou- bled between 1991 (2,087 tons) and 1996 (4,446 tons), after which fungicide imports increased gradually to 6,732 tons in 2003 (Jungbluth 2000; Chunyanuwat 2005). Like in many other tropical countries, few studies into the fate and environmental side effects of pesticides have been conducted in Thailand (Bourdeau et al. 1989; M. A. Daam Á A. J. A. Nogueira CESAM and Department of Biology, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal M. A. Daam (&) Instituto Superior de Agronomia, Technical University of Lisbon, Tapada da Ajuda, 1349-017 Lisbon, Portugal e-mail: mdaam@isa.utl.pt K. Satapornvanit Department of Fishery Biology, Faculty of Fisheries, Kasetsart University, Chatujak, Bangkok 10900, Thailand P. J. Van den Brink Alterra, Wageningen University and Research Centre, P.O. Box 47, 6700 AA Wageningen, The Netherlands P. J. Van den Brink Department of Aquatic Ecology and Water Quality Management, Wageningen University and Research Centre, Wageningen University, P.O. Box 8080, 6700 DD Wageningen, The Netherlands 123 Arch Environ Contam Toxicol (2010) 58:315–324 DOI 10.1007/s00244-009-9367-y