Environmental Engineering Reference
In-Depth Information
The tests that are most widely used to assess the toxicity of herbicides on
autotrophic microorganisms (especially microalgae) are monospeciic toxicity tests;
such tests combine low cost with satisfactory reproducibility and ease of execution
(Seguin et al. 2001 ). The results of single-species toxicity tests with algae have
produced large herbicide-dependent sensitivity differences (Table 5.1 ; DeLorenzo
et al. 2001 ). However, discernment is required when extrapolating results from
monospeciic assays to ecosystem impairment, and many authors have cited the
importance of reinforcing the ecological relevance of toxicological studies to
improve ecotoxicological risk assessment (Chapman 2002 ; Relyea and Hoverman
2006 ; Filser 2008 ; Schmitt-Jansen et al. 2008 ). A irst step in such reinforcement is
to evaluate toxic effects at the community level by applying community ecology
concepts to ecotoxicology testing (Schmitt-Jansen et al. 2008 ; Clements and Rohr
2009 ; Geiszinger et al. 2009 ).
On the basis of the foregoing considerations, the purpose of this paper is as follows:
1. To provide a broad bibliographical review of experimental and in situ studies
performed over the last 15 years that address the effects of herbicides, either alone
or in pesticide mixtures, on free and attached autotrophic microbial communities
2. To identify potential research areas that can beneit from future research
2
Experimental Studies
2.1
Effects of Single Herbicides
2.1.1
Triazines
Atrazine
The effects of atrazine on freshwater phototrophic microorganisms have been widely
studied over the past 15 years (Table 5.2 ; Solomon et al. 1996 ; DeLorenzo et al.
2001 ).
Chronic Effects on Biomass and Primary Production
Concentrations of chlorophyll a (chl a ) are generally used to estimate the biomass of
photosynthetic microorganisms. Many authors have observed a decrease in phyto-
plankton chl a (Seguin et al. 2002 ; Perschbacher et al. 2008 ) or periphyton chl a
(DeLorenzo et al. 1999 ; Nyström et al. 2000 ; Seguin et al. 2002 ; Downing et al.
2004 ; Rohr and Crumrine 2005 ; Schmitt-Jansen and Altenburger 2005a ; Guasch
et al. 2007 ) following atrazine exposure at concentrations ranging from 20 to
1,000 mg/L. At lower concentrations, the effects of atrazine on algal biomass are
more variable (Table 5.2 ). For example, chl a concentrations in phytoplankton (van
den Brink et al. 1995 ; Leboulanger et al. 2001 ; Relyea 2009 ) and periphyton
(Gruessner and Watzin 1996 ; Muñoz et al. 2001 ) were not affected by atrazine
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