Direct and Indirect Effects of the Fungicide Carbendazim in Tropical Freshwater Microcosms

Abstract

Direct and indirect effects of the fungicide carbendazim on ecosystem structure and functioning were studied B8 weeks after application (nominal concentrations: 0, 3.3, 33, 100, and 1000 lg/L) to outdoor microcosms 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 community = 100 lg/L). The rotifer Keratella tropica, cladocerans (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 invertebrates 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 conditions, 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 microbial activity resulting from these anoxic water conditions, rather than a direct toxic effect of carbendazim.

Fungicides: An Overlooked Pesticide Class?

“…For microorganisms, an indirect effect reported by a few studies is an increase in phytoplankton abundance or biofilm biomass due to fungicide exposure. This effect was observed for fungicides covering a range of MoAs, including azoxystrobin, 111 carbendazim, 120 , 147 chlorothalonil, 125 , 126 fluazinam (i.e., 2,6-dinitro-aniline), 148 organochlorine fungicides (2,4,6-trichlorophenol and pentachlorophenol), 149 , 150 and thiram. 151 The pattern was linked to a reduced grazing pressure by affected invertebrate consumers or, as hypothesized by Staley et al, 152 by microorganisms benefiting from the metabolization of fungicides or organic material set free by dying organisms.…”

Endocrine disrupting effects, at different temperatures, on Moina micrura (Cladocera: Crustacea) induced by carbendazim, a fungicide

“…Likewise, this work has a worldwide interest since this species, besides living in temperate ecosystems, is also abundant in the tropics and carbendazim has been extensively used as a fungicide in tropical agriculture and its effects on tropical freshwater zooplankton have been considered, such as studies of whole communities in mesocosms (Daam et al, 2010).…”

Imazethapyr and imazapic, bispyribac-sodium and penoxsulam: Zooplankton and dissipation in subtropical rice paddy water

“…and Bosmina longirostris and calanoid copepodites and cyclopoid nauplii increased in abundance in the treated ponds (Mohr et al, 2008). Daam et al (2010) pointed out that, apparently, the genus Keratella includes the most susceptible representatives of rotifers to fungicides. Other results regarding rotifers showed that Brachionus sp.…”