Environmental Engineering Reference
In-Depth Information
concentrations ranging from 5 to 14 mg/L, while Gustavson and Wängberg ( 1995 )
observed that 1-20 mg/L atrazine increased phytoplankton biomass in lake enclo-
sures after 2 weeks of exposure. Similarly, Seguin et al. ( 2001 ) showed that phyto-
plankton chl a concentrations were sometimes higher or lower in outdoor microcosms
that were contaminated by 10 mg/L of atrazine. Atrazine effects on primary produc-
tion also varied considerably across studies (Table 5.2 ), and sometimes varied by
season (Bérard and Benninghoff 2001 ) or were affected by trophic interactions (e.g.,
presence of grazers; Muñoz et al. 2001 ). These results agreed with those of Detenbeck
et al. ( 1996 ), who showed in wetland mesocosms that atrazine effects on periphyton
differed from a priori predictions that were based on laboratory bioassay data. The
reason given was that abiotic parameters, such as temperature or nutrients, grazing
intensity and biotic relationship between organisms, had inluenced outcomes.
Chronic Effects on Community Composition
A series of experimental studies were conducted with atrazine on natural communi-
ties from Lake Geneva. Results of these studies revealed that atrazine (10 mg/L)
consistently acted to restructure the autotrophic community, by modifying species
composition (Bérard et al. 1999a, b ; Bérard and Benninghoff 2001 ; Leboulanger
et al. 2001 ; Seguin et al. 2001 ). Chlorophytes (especially Chlorella vulgaris ) were
usually more sensitive, and diatoms and cryptophytes were more tolerant to atra-
zine, whereas some species, such as the cyanobacterium Oscillatoria limnetica ,
exhibited a variable response to atrazine that depended on seasons and species inter-
actions (Bérard et al. 1999a, b ).
The high sensitivity that chlorophytes had to atrazine was also observed to occur
in phytoplankton (Pannard et al. 2009 ) and periphyton (Downing et al. 2004 ) assem-
blages. By contrast, diatoms were often described as being the most tolerant taxa to
atrazine effects (Jüttner et al. 1995 ; DeLorenzo et al. 1999 ; Downing et al. 2004 ;
Schmitt-Jansen and Altenburger 2005a ). However, atrazine effects on community
composition were not always detectable in either phytoplankton (van den Brink et al.
1995 ; Pinckney et al. 2002 ) or periphyton (Carder and Hoagland 1998 ). Moreover, in
the absence of grazing pressure by snails, Muñoz et al. ( 2001 ) found no difference in
taxonomic composition between unexposed periphyton, or those exposed to 14 mg/L
atrazine for 18 days. However, they did note that atrazine toxicity increased with
grazing, and the main effects detected were on algal community structure. The
authors divided algal taxa into four classes, based on physiognomy, and concluded
that the interaction of atrazine and grazing caused a signiicant decrease in prostrate
growth and ilamentous forms that were the most sensitive to atrazine.
Pollution-Induced Community Tolerance (PICT) Assessment
Atrazine-induced tolerance in phytoplankton communities occurs, but the results
have been variable among experiments. Bérard and Benninghoff ( 2001 ) and Seguin
et al. ( 2002 ) detected a rapid increase in atrazine tolerance in phytoplankton
communities that were exposed to 10 and 30 mg/L atrazine, respectively. Nyström
et al. ( 2000 ) also observed atrazine-induced tolerance in periphyton exposed to
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