Effects of fomesafen, alone and in combination with an adjuvant, on plankton communities in freshwater outdoor pond mesocosms

Abstract

Ecotoxicological effects of the diphenyl ether herbicide fomesafen, applied alone or in combination with the adjuvant Agral 90 (mixture of polyethoxylated derivatives of nonylphenol), were assessed on planktonic communities in 18-m3 outdoor mesocosms during a nine-month study. Four mesocosms were treated with fomesafen only (nominal concentration: 40 microg/L), four were treated with the mixture fomesafen-Agral 90 (nominal concentration: 40 microg/L and 90 microg/L, respectively), and four were kept as the controls. Five treatments were performed every three weeks from April 18, 2000. Mean (+/- standard error [SE]) values of fomesafen concentration in water of 62.5 (+/-5.3) and 19.4 (+/-7.6) microg/L were measured at the end of the treatment period in fomesafen- and mixture-treated mesocosms, respectively. Fomesafen, either alone or in mixture with Agral 90, had a significant positive effect on the abundance and biovolume of Cyanobacteria, Cryptophyceae, Dinophyceae, and Bacillariophyceae. Chlorophyceae were inhibited by the herbicide and laboratory toxicity tests confirmed that green algae were more sensitive toward fomesafen than other algal classes. A positive effect of treatments on phytoplankton taxonomic diversity also was observed, indicating that, like natural disturbances of intermediate strength, xenobiotics sometimes may enhance the diversity of algal communities. Fomesafen alone did not have any clear effect on zooplankton. Abundance of calanoid copepods was reduced significantly in the mixture-treated ponds, suggesting either a direct effect of the adjuvant and/or an enhancement of herbicide toxicity by Agral 90. The abundance of other zooplanktonic herbivorous groups increased due to a reduced competition for food for herbivorous species and a higher availability of preys for predators. No algal bloom was observed in the treated ponds, presumably because of grazing pressure and the low availability of nutrients.

Do macrophytes support harmful cyanobacteria? Interactions with a green alga reverse the inhibiting effects of macrophyte allelochemicals on Microcystis aeruginosa

“…Error bars show standard errors (n = 4), differences between control and M. verticillatum treatment are indicated by asterisks (*p < 0.05, **p < 0.01, ***p < 0.001), statistical differences between initial compositions are provided in Tables 2 and 3. A complete reversal of the competitive outcome between a cyanobacterium and a green alga has also been reported for the photosynthesis-inhibiting herbicide metribuzin tested on singleand mixed cultures of M. aeruginosa and the green alga S. obliquus (Lü rling and Roessink, 2006). Furthermore, an increase in the abundance of cyanobacteria was recorded for natural phytoplankton communities in dialysis bags or outdoor pond mesocosms under the influence of allelopathically-active macrophytes (Jasser, 1995), after addition of the diphenyl-ether herbicide fomesafen (Caquet et al, 2005) and in natural periphyton communities after adding of the PS II inhibitor isoproturon (Schmitt-Jansen and Altenburger, 2007).…”

Allelopathic effects of submerged macrophytes on phytoplankton

“…Furthermore, an increase in the abundance of cyanobacteria was recorded for natural phytoplankton communities in dialysis bags or outdoor pond mesocosms under the influence of allelopathically active macrophytes , after addition of the diphenylether herbicide fomesafen (Caquet et al, 2005) and in natural periphyton communities after adding of the PS II inhibitor isoproturon (Schmitt-Jansen and Altenburger, 2007).…”

Effect of a toxicant on phagocytosis pathways in the freshwater snail Lymnaea stagnalis

“…In addition, the duration of exposure was compatible with the half-life for fomesafen, the concentration of which remained stable for 21 days (Caquet et al 2005).…”