Environmental Engineering Reference
In-Depth Information
possible nutrient leakage from the macrophyte leaves following herbicide exposure.
Changes were also detected on the species composition of periphytic algal commu-
nities in enclosures exposed to 20 mg/L, while metsulfuron-methyl did not alter
phytoplankton community biomass or composition. This suggests that the toxicity
of sulfonylurea herbicides on phytoplankton is limited, as asserted by Seguin et al.
( 2001 ) and Leboulanger et al. ( 2001 ), who showed that nicosulfuron was far less
toxic to phytoplankton than was atrazine. Nevertheless, they emphasized that nico-
sulfuron (10 mg/L) can affect phytoplankton species composition by inhibiting more
diatoms than chlorophytes. Abdel-Hamid et al. ( 1996 ) also observed community
composition effects on lake phytoplankton from exposure (1, 10, and 100 mg/L) to
another sulfonylurea herbicide, chlorosulfuron.
2.1.5
Glyphosate
Effects of High Glyphosate Concentrations
Vera et al. ( 2010 ) showed that a high concentration of the commercial formulation
of Roundup ® (8 mg/L of the active molecule glyphosate) produced a clear delay in
periphytic colonization and reduced periphytic dry weight, as well as chl a , in com-
parison with control mesocosms. This occurred despite a signiicant increase in
total phosphorus concentrations in the treated mesocosms. Pérez et al. ( 2007 ) also
observed a signiicant phosphorus release in mesocosms after the addition of
Roundup ® (6 and 12 mg/L of the active ingredient glyphosate), which was associ-
ated with structural changes in the planktonic and periphytic microbial assem-
blages, within a few days. In treated mesocosms, total phytoplankton abundance
decreased, whereas primary production and picocyanobacteria abundance increased.
Similar patterns have been observed in periphyton, which showed increasing abun-
dance of cyanobacteria following glyphosate exposure (Vera et al. 2010 ). Schaffer
and Sebetich ( 2004 ) also found that Rodeo ® treatments (0.125 and 12.5 mg/L of the
active ingredient glyphosate) led to signiicant stimulation of primary productivity
of a lake phytoplankton community during a 7-h incubation period. They hypothe-
sized that this effect could have resulted from the use of the nitrogen and phospho-
rus released through the glyphosate degradation process. Similarly, Relyea ( 2005 )
observed an increase in periphytic algal biomass after a 2-week Roundup ® exposure
(3.8 mg glyphosate/L), which, he suggested, could result from a decrease in grazing
pressure caused by Roundup ® effects on herbivorous organisms.
Chronic Effects of Environmentally Relevant Glyphosate Concentrations
Using a more environmentally relevant glyphosate concentration (i.e., 6.9 mg/L),
Relyea ( 2009 ) showed that Roundup ® caused insigniicant effects on an aquatic
food web comprising periphyton, phytoplankton, and other higher trophic level
organisms. This was consistent with results from Pesce et al. ( 2009 ), who demon-
strated that any effects of glyphosate (10 mg/L; 14 days) on riverine algal communi-
ties was limited to ones of community composition (assessed by microscopic
Search WWH ::




Custom Search