Effects of Organic Herbicides on Phototrophic Microbial Communities in Freshwater Ecosystems - Reviews of Environmental Contamination and Toxicology - page 97

concentrations that ranged between 12 and 125 mg/L. At higher concentrations,
such exposure produced severe community damage characterized by reduced algal
species number and abundance. By contrast, Gustavson and Wängberg ( 1995 )
reported no tolerance induction in phytoplankton and periphyton communities
exposed to 20 mg/L atrazine for 20 days, and Detenbeck et al. ( 1996 ) observed
that periphyton developed atrazine resistance only at a level equal to or exceeding
50 mg/L. According to Guasch et al. ( 2007 ), phosphate concentration is not a param-
eter that affects atrazine tolerance induction in phototrophic communities.
Interestingly, Schmitt-Jansen and Altenburger ( 2005a ) observed similar ranges
of sensitivity by comparing test results from a PICT approach with atrazine and
single-species toxicity data (species sensitivity distribution approach; SSD), despite
the fact that both approaches utilized test systems of different complexity. The
authors emphasized that their SSD approach was facilitated by the existence of a
large and comprehensive atrazine toxicity dataset on various algal species.
Irgarol
Combining short-term bioassay and nanocosm experiments, Nyström et al. ( 2002 )
and Bérard et al. ( 2003 ) showed that the triazine herbicide Irgarol 1051 was more
toxic to Lake Geneva phytoplankton and periphyton than was atrazine. Effects were
observed on phytoplankton photosynthetic activity (short-term effects) and diversity
(long-term effects after 5-24 days of exposure) from exposure to this herbicide at a
level of less than 1 mg/L. Mohr et al. ( 2008a ) also observed effects on planktonic and
periphytic algal communities at exposure concentrations between 0.04 and 5 mg/L.
Nyström et al. ( 2002 ) and Bérard et al. ( 2003 ) concluded that chlorophytes, espe-
cially Chlorella vulgaris , were the most Irgarol-sensitive in natural assemblages. By
contrast, studying highly contaminated ponds (1 and 5 mg/L), Mohr et al. ( 2008a )
observed a decrease in diatoms and an increase in chlorophytes and cyanobacteria.
Given these differences among studies, the authors went on to suggest that Irgarol does
not trigger a group-speciic response, but rather induced a species-level response.
Mohr et al. ( 2008a ) also revealed that recovery processes vary greatly among free
and ixed communities. Indeed, in the same study, the phytoplankton rapidly recov-
ered from a pronounced breakdown immediately after Irgarol exposure, whereas per-
iphytic communities showed no recovery within 150 days after treatment in ponds
contaminated by 1 and 5 mg/L Irgarol. This suggests that the sorption of Irgarol on
periphyton may have prolonged the exposure duration in the tested communities.
Other Triazines
Short-Term Effects
Brown and Lean ( 1995 ) performed bioassays on mesotrophic lake phytoplankton
communities using several triazine herbicides (atrazine, simazine, propazine, and prom-
etryn). Atrazine and propazine exerted the highest toxic effects on phosphate and ammo-