Responses of Planktonic Microorganisms from Tropical Reservoirs to Paraquat and Deltamethrin Exposure

Abstract

This study focused on the effects of two pesticides, paraquat (herbicide) and deltamethrin (insecticide), which are two common molecules used intensively in Burkina Faso. Natural bacterial populations, phytoplankton cultures (one cyanobacterium, Cylindrospermopsis raciborskii, and one chlorophycea, Monoraphidium sp.), and two species of zooplankton (Diaphanosoma excisum and Moina micrura) were isolated from aquatic communities and were used as biological targets in the experimental protocols. Paraquat was moderately toxic to bacteria and phytoplankton, whereas deltamethrin was significantly toxic only to the zooplankton species. Paradoxically, the chlorophycea Monoraphidium sp. exhibited a significant increase of in vitro fluorescence after 48 h at the highest doses. Preliminary tests were also performed from natural water extract of the main drinking water supply of the country (Loumbila Reservoir) by using solid-phase extraction. Obviously, the natural extract proved to be toxic to the same biological targets. Despite the absence of any determination of pesticides in the natural extract, the question of contamination and toxicity of these waters affects concerns about the safety of water supply and the effect of human pressure on the dynamics of planktonic communities of freshwater reservoirs in arid regions of western Africa.

Inhibitory effects of paraquat on photosynthesis and the response to oxidative stress in Chlorella vulgaris

“…In freshwater ecosystems, bacteria, phytoplankton, and zooplankton have fast growth rates and, therefore, can be meaningful and quantifiable indicators of ecological change on short timescales (Leboulanger et al 2009;Paerl et al 2003). Moreover, these organisms can respond to low levels of pollutants such as pesticides, which constitute a major anthropogenic stress on natural communities (Relyea 2005).…”

Comparison of the structure and composition of bacterial communities from temperate and tropical freshwater ecosystems

“…All sites except Bagré appeared to be well mixed systems, primarily because of their shallowness. A more complete description of the sites is proposed in Leboulanger and colleagues (2009).…”

Implications of differences between temperate and tropical freshwater ecosystems for the ecological risk assessment of pesticides

“…Several tropical cladoceran surrogates for the temperate cladoceran Daphnia have been used, e.g., Ceriodaphnia cornuta (Vietnam; Do Hong et al 2004), Moina micrura (Thailand; Daam et al 2008, Burkina Faso;Leboulanger et al 2008), Moinodaphnia macleayi (Northern Australia; Van Dam et al 2004) and Diaphanosoma brachyurum (Brazil; Lopes et al 2007). Freshwater organisms reported as good candidates for the Central American region are the freshwater fish Cichlasoma dovii, the freshwater shrimp Macrobrachium rosenbergii, as well as macro-invertebrate species belonging to trichopterans and ephemeropterans (Castillo et al 1997).…”

“…Hence, aquatic risk assessments in tropical countries often rely on temperate toxicity data (Castillo et al 1997;Karlsson 2004;Kwok et al 2007), even though the fate and effects of pesticides may be different between climatic regions. The need for studies into risk assessments of pesticides under tropical conditions has therefore long been recognized (Bourdeau et al 1989;Widianarko et al 1994;Castillo et al 1997;Racke 2003;Waichman et al 2002;Leboulanger et al 2008). …”