Does the effect of herbicide pulse exposure on aquatic plants depend on Kow or mode of action?

Department of Agricultural Sciences, The Royal Veterinary and Agricultural University (KVL), Højbakkegård Allé 9, DK-2630 Taastrup, Denmark.
Aquatic Toxicology (Impact Factor: 3.51). 03/2005; 71(3):261-71. DOI: 10.1016/j.aquatox.2004.11.010
Source: PubMed

ABSTRACT The highest concentrations of herbicides measured in flowing surface waters are often only present for short periods of time. These herbicide pulses can reach concentrations that would affect aquatic plants if present over a long time. The aim of this study was to assess the effect of a 3-h herbicide pulse relative to the effects of long-term (4 and 7 days) exposure of six herbicides with different sites of action and different K(ow) on the growth of the floating macrophyte Lemna minor. The herbicides were the two photosynthetic inhibitors: diquat and terbuthylazine, the inhibitors of acetolactate syntase (ALS), imazamox and metsulfuron-methyl and the microtubule assembly inhibitors propyzamide and pendimethalin. The log K(ow) ranged from -4.6 to 5.2. For imazamox, metsulfuron-methyl, propyzamide and pendimethalin a 3-h pulse induced the effect on area-specific growth as did a 4-day exposure at an approximate 10-fold higher concentration. For diquat and terbuthylazine a concentration closer to a factor of 100 or more was needed for a 3-h pulse to induce an effect similar to that of a 4-day exposure. For diquat, the low pulse-effect was most likely due to a slow uptake of the hydrophilic ion (log K(ow) = -4.6), as no effect was observed on chlorophyll fluorescence within 8 h after exposure. The chlorophyll fluorescence parameters are expected to respond quickly to a PSI inhibitor as diquat. For terbuthylazine, fluorescence measurements showed an effect on photosynthesis within 1h of exposure, and reached a minimum after 3 h. Recovery was fast, and initial fluorescence was restored within 24 h. Hence, the small pulse effect on area-specific growth was due to rapid recovery of photosynthesis. In contrast to terbuthylazine, the stop in area-specific growth observed for the ALS-and microtubule assembly inhibitors, took up to 4 days to recover from. Such a long recovery time after a pulse of only 3 h indicate that at realistic pulse exposures of up to a day or two, pulse-effects will approach the effects obtained in long-term studies. When investigating the effects of pulse exposures on aquatic plants, we should therefore focus more on non-photosynthetic inhibitors, which might not appear in pulses in as large concentrations as the PSII inhibitors investigated up till now, but whose effect, even in a shorter pulse, can be more damaging.

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Available from: Nina Cedergreen, Mar 10, 2014
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    • "Among these, hydrophobicity is one of the most important properties explaining the removal potential of plants. Organic chemicals with an octanol–water partition coefficient (logK ow ) between 0.5 and 3 are considered hydrophobic compounds able to move through the lipid bilayer of membranes, but still water-soluble enough to travel into the cell fluids (Cedergreen et al. 2005). Dimethomorph, with a log K ow of 2.63, can enter plants rapidly, explaining why removal was almost maximum after 96 h. "
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    ABSTRACT: Effects of two fungicides, copper and dimethomorph ((E,Z)4-[3-(4-chlorophenyl)-3-(3-4dimethoxyphenyl) acryloyl] morpholine) on Lemna minor growth and phytoremediation were evaluated. The toxicity of copper and dimethomorph alone and in combination, was assessed by growth inhibition of L. minor cultures after 96 and 168 h. Copper had a severe impact on growth (max. inhibition: 90 % at 1,000 μg L(-1)) while dimethomorph (as pure ingredient or formulated as Forum) did not (inhibition <45 % at 1,000 μg L(-1)) after 168 h of treatment. When both chemicals were combined, synergism was observed after 96 h of exposure to copper and Forum. However, this interaction was a simple additivity after 168 h. Additivity was also observed when the pure active ingredient (dimethomorph) replaced Forum in the mixture of copper and dimethomorph at 96 and 168 h. L. minor showed an excellent performance in removing copper from the medium since after 96 h, 36, 60, and 76 % removal were reached for 10, 20, and 30 μg L(-1) of Cu respectively. Copper accumulated in the plants. The removal of copper increased with Forum concentration. After 96 h copper (10 μg L(-1) initial concentration) elimination increased from 36.39 ± 5.86-60.70 ± 6.06 % when Forum concentration increased from 0 to 500 μg L(-1). Accumulation of copper in plants was also increased by Forum but not by the active ingredient alone. Depuration of Forum by L. minor varied between 10 and 40 % after 96 h and it was generally more efficient than that of the pure ingredient. This depuration decreased in the presence of copper possibly due to the metal toxicity.
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    • "Until now, pulse exposure studies of effects of pesticides have primarily been made with freshwater invertebrates and insecticides (Andersen et al., 2006; Ashauer et al., 2007; Cold and Forbes, 2004; Forbes and Cold, 2005; Heckmann and Friberg, 2005; Mugni et al., 2011; Naddy et al., 2000; Naddy and Klaine, 2001; Parsons and Surgeoner, 1991; Reinert et al., 2002). It is, however, also important to study the effects of pesticide application to non-target primary producers since these are important in terms of provision of food and habitats for animals and for conservation of ecosystems, but only a few studies have investigated effects of pesticide pulse exposure on macrophytes (Belgers et al., 2011; Cedergreen et al., 2005) and algae (Vallotton et al., 2008; Vallotton et al., 2009). Pulse exposure may also be a result of fast transformations or phase distributions after application, causing a fast decrease in exposure concentrations (Reinert et al., 2002, Hommen et al., 2010). "
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    • "Most laboratory toxicity tests performed with herbicides and macrophytes are characterized by either a constant or regular pulsed (static or semi-static) exposure regime (Cedergreen et al., 2004a,b; Belgers et al., 2007; Turgut, 2007; Arts et al., 2008; Huiyun et al., 2009). These tests usually do not provide insight in the effects of time–variable exposures, which are more often the rule rather than the exception in edge-of-field surface waters (Handy, 1994; Cedergreen et al., 2005; Brock et al., 2010). In the current (EC, 2002) and recently proposed (Maltby et al., 2010) European pre-registration risk assessment procedures for herbicides and aquatic vascular plants the predicted peak concentration (PEC max ) for edge-of-field surface waters is compared with the laboratory EC 50 of test species like Lemna sp. and Myriophyllum sp (Brock et al., 2010). "
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