Effects of herbicides on Lemna gibba and recovery from damage after prolonged exposure

Ecotoxicity of Diazinon and Atrazine Mixtures after Ozonation Catalyzed by Na+ and Fe2+ Exchanged Montmorillonites on Lemna minor

The toxicity of two pesticides, diazinon (DAZ) and atrazine (ATR), before and after montmorillonite-catalyzed ozonation was comparatively investigated on the duckweed Lemna minor. The results allowed demonstrating the role of clay-containing media in the evolution in time of pesticide negative impact on L. minor plants. Pesticides conversion exceeded 94% after 30 min of ozonation in the presence of both Na+ and Fe2+ exchanged montmorillonites. Toxicity testing using L. minor permitted us to evaluate the change in pesticide ecotoxicity. The plant growth inhibition involved excessive oxidative stress depending on the pesticide concentration, molecular structure, and degradation degree. Pesticide adsorption and/or conversion by ozonation on clay surfaces significantly reduced the toxicity towards L. minor plants, more particularly in the presence of Fe(II)-exchanged montmorillonite. The results showed a strong correlation between the pesticide toxicity towards L. minor and the level of reactive oxygen species, which was found to depend on the catalytic activity of the clay minerals, pesticide exposure time to ozone, and formation of harmful derivatives. These findings open promising prospects for developing a method to monitor pesticide ecotoxicity according to clay-containing host-media and exposure time to ambient factors.

Potential of Salvinia biloba Raddi for removing atrazine and carbendazim from aquatic environments

In this exploratory study, naturally occurring Salvinia biloba Raddi specimens were assessed for atrazine and carbendazim polluted water remediation. Experiments were carried out over 21 days in glass vessels containing deionized water artificially contaminated with 0, 5, 10, and 20 mg L^-1 of atrazine or carbendazim. Atrazine had a pronounced detrimental impact on S. biloba, as no biomass development was observed in all macrophytes exposed to this herbicide in the entire concentration range. However, carbendazim-treated plants were able to grow and survive in the polluted medium even when subjected to the highest concentration of this fungicide (i.e., 20 mg L^-1). In addition, increased chlorosis and necrosis were also detected in plants subjected to carbendazim as a result of the high phytotoxicity caused by atrazine. A maximal removal efficiency of ~ 30% was observed for both pesticides at 5 mg L^-1 and decreased with increasing concentrations of the pollutants. The spectrum of the FTIR-ATR analysis revealed the existence of various functional groups (e.g., amide, carboxyl, hydroxyl, phosphate, sulfate) on the plants, which could be related to pesticide biosorption. In addition, at the end of the 21-day assay, seven carbendazim-resistant bacteria could be isolated from the roots of fungicide-treated plants. Therefore, the use of autochthonous free-floating S. biloba macrophytes for phytoremediation of aquatic environments contaminated with carbendazim shows great promise. Still, additional research is required to further elucidate the plant-mediated carbendazim elimination process and the role of the herbicide-resistant bacteria, and seek alternative species capable of mitigating atrazine contamination.

Improving pollutants environmental risk assessment using a multi model toxicity determination with in vitro, bacterial, animal and plant model systems: The case of the herbicide alachlor

Several environmental pollutants, including pesticides, herbicides and persistent organic pollutants play an important role in the development of chronic diseases. However, most studies have examined environmental pollutants toxicity in target organisms or using a specific toxicological test, losing the real effect throughout the ecosystem. In this sense an integrative environmental risk of pollutants assessment, using different model organisms is necessary to predict the real impact in the ecosystem and implications for target and non-target organisms. The objective of this study was to use alachlor, a chloroacetanilide herbicide responsible for chronic toxicity, to understand its impact in target and non-target organisms and at different levels of biological organization by using several model organisms, including membranes of dipalmitoylphosphatidylcholine (DPPC), rat liver mitochondria, bacterial (Bacillus stearothermophilus), plant (Lemna gibba) and mammalian cell lines (HeLa and neuro2a). Our results demonstrated that alachlor strongly interacted with membranes of DPPC and interfered with mitochondrial bioenergetics by reducing the respiratory control ratio and the transmembrane potential. Moreover, alachlor also decreased the growth of B. stearothermophilus and its respiratory activity, as well as decreased the viability of both mammalian cell lines. The values of TC₅₀ increased in the following order: Lemna gibba < neuro2a < HeLa cells < Bacillus stearothermophilus. Together, the results suggest that biological membranes constitute a putative target for the toxic action of this lipophilic herbicide and point out the risks of its dissemination on environment, compromising ecosystem equilibrium and human health.

Growth inhibition and recovery patterns of common duckweed Lemna minor L. after repeated exposure to isoproturon

Aquatic non-targeted organisms are more likely to be exposed to herbicides in multiple pulse events then long continuous exposure. The potential of an organism to recover between exposures has an important role in the overall effects of the toxicant. Common duckweeds show high potential for recovery after a single exposure to isoproturon. To evaluate the growth patterns and recovery potential between multiple exposures, L. minor plants were exposed to isoproturon in three repetitive 7-day treatment cycles in three time-variable exposure scenarios with equivalent time-weighted average concentrations. The growth was significantly inhibited during each exposure phase with significant cumulative effects in every subsequent treatment cycle resulting in a cumulative decrease in biomass production. However, inhibitory effects were reversible upon transferring plants to a herbicide-free nutrient solution. These results indicate that L. minor plants have a high recovery potential even after multiple exposures to isoproturon. Observed cumulative decrease in biomass production, as well as the potential for fast and efficient recovery from repeated herbicide exposure, might affect the competitiveness of L. minor in surface water communities. The observations made during each exposure period, recovery patterns, and the resulting cumulative effects over time may contribute to further development, calibration and validation of mechanistic toxicokinetic/toxicodynamic models for simulating the effects of pesticides on aquatic plants populations in the laboratory and environmental conditions.

Phytotoxicity assessment of isoproturon on growth and physiology of non-targeted aquatic plant Lemna minor L. - A comparison of continuous and pulsed exposure with equivalent time-averaged concentrations

Phenylurea herbicides are often present in the aquatic ecosystems and may be accumulated by the non-targeted organisms and impose a negative effect on the organism and the community. This study aims to investigate and compare the effects of two different isoproturon (IPU) pulse exposure scenarios on the non-targeted aquatic plant Lemna minor with effects observed in the standard test with continuous exposure. The obtained results showed that continuous IPU treatment causes significant reduction of photosynthetic pigment concentration and proteins as well as inhibition of L. minor growth. The activities of CAT, G-POX, and APX were significantly induced to diminish the accumulation of ROS under IPU treatment, but the induction of antioxidant enzymes was not sufficient to protect the plants from herbicide-induced oxidative stress. The growth of L. minor under pulse exposure to IPU recovers fast, but pulse treatment results in significant physiological changes in treated plants. The accumulation of H₂O₂ and lipid peroxidation products, alongside the reduced concentration of proteins and photosynthetic pigments in pulse treatment after a recovery period, indicates that IPU causes prolonged oxidative stress in L. minor plants. The recovery potential of L. minor plants after treatment with herbicides may have an important role in maintaining the population of essential primary producers in aquatic ecosystems, but IPU-induced physiological changes could potentially have a significant role in modulating the response of the plants to the next exposure event.

Modelling the effects of PSII inhibitor pulse exposure on two algae in co-culture

A weakness of standard testing procedures is that they do not consider interactions between organisms, and they focus only on single species. Furthermore, these procedures do not take into account pulse exposure. However, pulse exposure is of particular importance because in streams, after crop application and during and after precipitation, herbicide concentrations fluctuate widely and can exceed the Annual Average Environmental Quality Standards (AA-EQS), which aim to protect the aquatic environment. The sensitivity of the algae Scenedesmus vacuolatus and Pseudokirchneriella subcapitata in a co-culture exposed to pulses is thus analysed in this study. As a first step, the growths of the algae in co-culture are investigated. For initial cell densities fixed, respectively, to 100,000 and 50,000 cells/mL, the growth of each alga is exponential over at least 48 h. S. vacuolatus seems to influence the growth of P. subcapitata negatively. Allelopathy is a possible explanation for this growth inhibition. The toxicity of the herbicide isoproturon is later tested on the algae S. vacuolatus and P. subcapitata cultured alone and in the co-culture. Despite the supplementary stress on the algae in the co-culture competing for nutrients, the toxicity of the herbicide is lower for the two algae when they are in the co-culture than when they are in separated culture. A model is adapted and used to predict the cell-density inhibition on the alga S. vacuolatus in the co-culture with the alga P. subcapitata exposed to a pulse concentration of isoproturon. Four laboratory experiments are performed to validate the model. The comparison between the laboratory and the modelled effects shows good agreement. The differences can be considered minor most of time. For future studies, it is important to ensure that the cell count is precise, as it is used to determine the parameters of the model. The differences can be also induced by the fact that the cell number of the alga P. subcapitata re-suspended in a new OECD medium after the centrifugation process cannot be fixed.

Recovery of Lemna minor after exposure to sulfadimethoxine irradiated and non-irradiated in a solar simulator

Sulfonamides are the second most widely used group of veterinary antibiotics which are often detected in the environment. They are eliminated from freshwaters mainly through photochemical degradation. The toxicity of sulfadimethoxine (SDM) was evaluated with the use of Lemna minor before and after 1- and 4-h irradiation in a SunTest CPS+ solar simulator. Eight endpoints consisting of: number and total area of fronds, fresh weight, chlorophylls a and b, carotenoids, activity of catalase and guaiacol peroxidase, and protein content were determined. The total frond area and chlorophyll b content were the most sensitive endpoints with EC50 of 478 and 554 μg  L^-1, respectively. The activity of guaiacol peroxidase and catalase increased at SDM concentrations higher than 125 and 500 μg  L^-1, respectively. The SDM photodegradation rate for first order kinetics and the half-life were 0.259 h^-1 and 2.67  h, respectively. The results show that the toxicity of irradiated solutions was caused by SDM only, and the photoproducts appeared to be either non-toxic or much less toxic to L. minor than the parent compound. To study the recovery potential of L. minor, after 7 days exposure in SDM solutions, the plants were transferred to fresh medium and incubated for the next 7 days. L. minor has the ability to regenerate, but a 7-day recovery phase is not sufficient for it to return to an optimal physiological state.

Comparing the acute sensitivity of growth and photosynthetic endpoints in three Lemna species exposed to four herbicides

An ecological impact assessment of four herbicides (atrazine, diuron, paraquat and simazine) was assessed using the aquatic floating vascular plants, Lemna gibba, Lemna minor and Lemna paucicostata as test organisms. The sensitivity of several ecologically relevant parameters (increase in frond area, root length after regrowth, maximum and effective quantum yield of PSII and maximum electron transport rate (ETR_max), were compared after a 72 h exposure to herbicides. The present test methods require relatively small sample volume (3 mL), shorter exposure times (72 h), simple and quick analytical procedures as compared with standard Lemna assays. Sensitivity ranking of endpoints, based on EC₅₀ values, differed depending on the herbicide. The most toxic herbicides were diuron and paraquat and the most sensitive endpoints were root length (6.0-12.3 μg L^-1) and ETR_max (4.7-10.3 μg L^-1) for paraquat and effective quantum yield (6.8-10.4 μg L^-1) for diuron. Growth and chlorophyll a fluorescence parameters in all three Lemna species were sensitive enough to detect toxic levels of diuron and paraquat in water samples in excess of allowable concentrations set by international standards. CV values of all EC₅₀s obtained from the Lemna tests were in the range of 2.8-24.33%, indicating a high level of repeatability comparable to the desirable level of <30% for adoption of toxicity test methods as international standards. Our new Lemna methods may provide useful information for the assessment of toxicity risk of residual herbicides in aquatic ecosystems.

Getting More Ecologically Relevant Information from Laboratory Tests: Recovery of Lemna minor After Exposure to Herbicides and Their Mixtures

Recovery after exposure to herbicides-atrazine, isoproturon, and trifluralin-their binary and ternary mixtures, was studied under laboratory conditions using a slightly adapted standard protocol for Lemna minor. The objectives of the present study were (1) to compare empirical to predicted toxicity of selected herbicide mixtures; (2) to assess L. minor recovery potential after exposure to selected individual herbicides and their mixtures; and (3) to suggest an appropriate recovery potential assessment approach and endpoint in a modified laboratory growth inhibition test. The deviation of empirical from predicted toxicity was highest in binary mixtures of dissimilarly acting herbicides. The concentration addition model slightly underestimated mixture effects, indicating potential synergistic interactions between photosynthetic inhibitors (atrazine and isoproturon) and a cell mitosis inhibitor (trifluralin). Recovery after exposure to the binary mixture of atrazine and isoproturon was fast and concentration-independent: no significant differences between relative growth rates (RGRs) in any of the mixtures (IC10_Mix, 25_Mix, and 50_Mix) versus control level were recorded in the last interval of the recovery phase. The recovery of the plants exposed to binary and ternary mixtures of dissimilarly acting herbicides was strictly concentration-dependent. Only plants exposed to IC10_Mix, regardless of the herbicides, recovered RGRs close to control level in the last interval of the recovery phase. The inhibition of the RGRs in the last interval of the recovery phase compared with the control level is a proposed endpoint that could inform on reversibility of the effects and indicate possible mixture effects on plant population recovery potential.

Recovery of terrestrial plants in vegetative vigor and seedling emergence tests from exposure to atrazine

Ten species of terrestrial plants, including 6 dicotyledonous and 4 monocotyledonous species, were exposed to a direct overspray of atrazine according to US Environmental Protection Agency seedling emergence and vegetative vigor study guidelines and subsequently evaluated for potential recovery. For each species, no-observed-effect rate (NOER), 10% effect rate, 25% effect rate, and 50% effect rate values were calculated (where possible) for a variety of guideline-required endpoints (but focusing on growth rate) for both the standard experimental phase and a recovery phase; and the rates subsequently were compared. For the seedling emergence study, the standard experimental (designated test 1) and recovery (designated test 2) phases encompassed days 0 to 14 and days 14 to 28, respectively. Similarly, for the vegetative vigor study, test 1 and test 2 encompassed days 0 to 21 and days 21 to 42, respectively. Plants were exposed to atrazine at nominal application rates ranging from 1.1 g active ingredient (a.i.)/ha (0.0010 lb a.i./A) to 28,000 g a.i./ha (25 lb a.i./A), depending on the species; the 28,000 g a.i./ha rate is greater than 12 times the maximum application rate of 2250 g a.i./ha (2 lb a.i./A) registered on corn. For seedling emergence, only 2 of 10 species tested, cabbage and tomato, provided clear rate responses in the initial 14 d of exposure (test 1). Based on a comparison of x% effect rate (ERx) and NOER values for growth rates of shoot length and shoot dry weight for days 0 to 14 relative to days 14 to 28, recovery was apparent for cabbage shoot length growth rate and tomato shoot length and shoot dry weight growth rates. Test application rates selected for the remaining 8 species showed either a weak response that did not allow a clear assessment of recovery or no response at all. For the vegetative vigor study, 9 of the 10 species tested provided clear rate responses in test 1 (days 0-21); corn did not demonstrate any herbicidal response up to the highest rate tested, 28,000 g a.i./ha. Based on comparison of day 0 to 21 (test 1) relative to day 21 to 42 (test 2) ERx and NOER values for shoot length, average growth rates indicated that 8 of 9 species clearly demonstrated an increase in 2 or more metrics (cabbage did not demonstrate a response based on shoot length). Clear recovery was also indicated by an increase in ERx and/or NOER values from test 1 to test 2 for shoot dry weight average growth rates for 7 of the 9 species (corn did not show a response, and oat and soybean showed variable responses). Thus, in most species, where initial herbicidal effects were observed, the effects are largely ameliorated over time.

Effects of pulsed atrazine exposures on autotrophic community structure, biomass, and production in field-based stream mesocosms

The authors performed a multiple-pulsed atrazine experiment to measure responses of autotrophic endpoints in outdoor stream mesocosms. The experiment was designed to synthetically simulate worst-case atrazine chemographs from streams in agricultural catchments to achieve 60-d mean concentrations of 0 μg/L (control), 10 μg/L, 20 μg/L, and 30 μg/L. The authors dosed triplicate streams with pulses of 0 μg/L, 50 μg/L, 100 μg/L, and 150 μg/L atrazine for 4 d, followed by 7 d without dosing. This 11-d cycle occurred 3 times, followed by a recovery (untreated) period from day 34 to day 60. Mean ± standard error 60-d atrazine concentrations were 0.07 ± 0.03 μg/L, 10.7 ± 0.05 μg/L, 20.9 ± 0.24 μg/L, and 31.0 ± 0.17 μg/L for the control, 10-μg/L, 20-μg/L, and 30-μg/L treatments, respectively. Multivariate analyses revealed that periphyton and phytoplankton community structure did not differ among treatments on any day of the experiment, including during the atrazine pulses. Control periphyton biomass in riffles was higher immediately following the peak of the first atrazine pulse and remained slightly higher than some of the atrazine treatments on most days through the peak of the last pulse. However, periphyton biomass was not different among treatments at the end of the present study. Phytoplankton biomass was not affected by atrazine. Metaphyton biomass in pools was higher in the controls near the midpoint of the present study and remained higher on most days for the remainder of the study. Ceratophyllum demersum, a submersed macrophyte, biomass was higher in controls than in 20-μg/L and 30-μg/L treatments before pulse 3 but was not different subsequent to pulse 3 through the end of the present study. Maximum daily dissolved oxygen (DO, percentage of saturation) declined during each pulse in approximate proportion to magnitude of dose but rapidly converged among treatments after the third pulse. However, DO increased in controls relative to all atrazine treatments during the last 17 d of the experiment, likely a result of metaphyton cover in the pools. Finally, atrazine significantly limited uptake of PO4(3-) and uptake and/or denitrification of NO3(-) but only during pulses; percentage of dose removed from the water column was >85% for P and >95% for N after pulse 3 through the end of the present study. Collectively, only DO and metaphyton biomass differed at the end of the present study and only slightly. Some other endpoints were affected but only during pulses, if at all. The high levels of primary production and accumulation of algal biomass in all streams suggest that effects of pulses of atrazine at the concentrations used in the present study appear transient and likely do not represent ecologically significant adverse outcomes to periphyton, phytoplankton, and aquatic macrophytes, particularly in agricultural streams subjected to high nutrient loads.

Modelling the effects of pulse exposure of several PSII inhibitors on two algae

Subsequent to crop application and during precipitation events, herbicides can reach surface waters in pulses of high concentrations. These pulses can exceed the Annual Average Environmental Quality Standards (AA-EQS), defined in the EU Water Framework Directive, which aims to protect the aquatic environment. A model was developed in a previous study to evaluate the effects of pulse exposure for the herbicide isoproturon on the alga Scenedesmus vacuolatus. In this study, the model was extended to other substances acting as photosystem II inhibitors and to other algae. The measured and predicted effects were equivalent when pulse exposure of atrazine and diuron were tested on S. vacuolatus. The results were consistent for isoproturon on the alga Pseudokirchneriella subcapitata. The model is thus suitable for the effect prediction of phenylureas and triazines and for the algae used: S. vacuolatus and P. subcapitata. The toxicity classification obtained from the dose-response curves (diuron>atrazine>isoproturon) was conserved for the pulse exposure scenarios modelled for S. vacuolatus. Toxicity was identical for isoproturon on the two algae when the dose-response curves were compared and also for the pulse exposure scenarios. Modelling the effects of any pulse scenario of photosystem II inhibitors on algae is therefore feasible and only requires the determination of the dose-response curves of the substance and growth rate of unexposed algae. It is crucial to detect the longest pulses when measurements of herbicide concentrations are performed in streams because the model showed that they principally affect the cell density inhibition of algae.

Spatial and temporal variation of algal assemblages in six Midwest agricultural streams having varying levels of atrazine and other physicochemical attributes

Potential effects of pesticides on stream algae occur alongside complex environmental influences; in situ studies examining these effects together are few, and have not typically controlled for collinearity of variables. We monitored the dynamics of periphyton, phytoplankton, and environmental factors including atrazine, and other water chemistry variables at 6 agricultural streams in the Midwest US from spring to summer of 2011 and 2012, and used variation partitioning of community models to determine the community inertia that is explained uniquely and/or jointly by atrazine and other environmental factors or groups of factors. Periphyton and phytoplankton assemblages were significantly structured by year, day of year, and site, and exhibited dynamic synchrony both between site-years and between periphyton and phytoplankton in the same site-year. The majority of inertia in the models (55.4% for periphyton, 68.4% for phytoplankton) was unexplained. The explained inertia in the models was predominantly shared (confounded) between variables and variable groups (13.3, 30.9%); the magnitude of inertia that was explained uniquely by variable groups (15.1, 18.3%) was of the order hydroclimate>chemistry>geography>atrazine for periphyton, and chemistry>hydroclimate>geography>atrazine for phytoplankton. The variables most influential to the assemblage structure included flow and velocity variables, and time since pulses above certain thresholds of nitrate+nitrite, total phosphorus, total suspended solids, and atrazine. Time since a ≥30 μg/L atrazine pulse uniquely explained more inertia than time since pulses ≥ 10 μg/L or daily or historic atrazine concentrations; this result is consistent with studies concluding that the effects of atrazine on algae typically only occur at ≥30 μg/L and are recovered from.

Recovery of photosynthesis and growth rate in green, blue-green, and diatom algae after exposure to atrazine

We evaluated the recovery of photosynthesis and growth rate in green (Pseudokirchneriella subcapitata), blue-green (Anabaena flos-aquae), and diatom (Navicula pelliculosa) algae after pulsed exposure to atrazine. Subsequent to a grow-up period of 24 to 72 h to establish requisite cell density for adequate signal strength to measure photosystem II (PSII) quantum yield, algae were exposed to a pulse of atrazine for 48 h followed by a 48-h recovery period in control media. Photosynthesis was measured at 0, 3, 6, 12, 24, and 48 h of the exposure and recovery phases using pulse amplitude modulation fluorometry; growth rate and cell density were also concomitantly measured at these time points. Exposure to atrazine resulted in immediate, but temporary, inhibition of photosynthesis and growth; however, these effects were transient and fully reversible in the tested species of algae. For all three algal species, no statistically significant reductions (p ≤ 0.05) in growth rate or PSII quantum yield were detected at any of the treatment concentrations 48 h after atrazine was removed from the test system. Effects at test levels up to the highest tested exposure levels were consequently determined to be algistatic (reversible). Both biochemically and physiologically, recovery of photosynthesis and growth rate occur immediately, reaching control levels within hours following exposure. Therefore, pulsed exposure profiles of atrazine typically measured in Midwestern U.S. streams are unlikely to result in biologically meaningful changes in primary production given that the effects of atrazine are temporary and fully reversible in species representative of native populations.

Recovery of duckweed from time-varying exposure to atrazine

The purpose of the present study was to evaluate the recovery of duckweed (Lemna gibba L. G3) after being removed from multiple duration exposures to the herbicide atrazine. Consequently, L. gibba were exposed under various scenarios to atrazine at nominal concentrations ranging from 5 to 160 µg/L and durations of 1, 3, 5, 7, 9, and 14 d under static-renewal test conditions. Exposures were followed by a recovery phase in untreated media for either 7 or 14 d. The 3-, 5-, 7-, 9-, and 14-d median effective concentration (EC50) values were >137, >137, 124, >77, and >75 µg/L, respectively, based on mean growth rate. No clear effect trends were apparent between exposure duration and the magnitude of effective concentrations (EC50s or EC10s). No phytocidal effects of chlorosis or necrosis were identified for any treatment scenario. Nearly all L. gibba plants transferred from treatment groups of different exposure scenarios to media without atrazine during the recovery phase had growth rates that demonstrated immediate recovery, indicating effects were phytostatic in nature and reversible. Only the 1- and 5-d exposure scenarios had growth rates indicating marginally prolonged recovery at the higher concentrations (160 µg/L; additionally, at 40 µg/L for the 5-d exposure). Time to recovery, therefore, was found to be largely independent of exposure duration except at the highest concentrations assessed. Based on growth rate by interval, all treatments demonstrated recovery by the final assessment interval (days 5-7), indicating complete recovery in all exposure scenarios by 7 d, consistent with the mode of action of atrazine.

Myriophyllum aquaticum versus Lemna minor: sensitivity and recovery potential after exposure to atrazine

The relative sensitivity and recovery potential of two aquatic macrophyte species, Lemna minor and Myriophyllum aquaticum, exposed to atrazine (concentration ranges 80-1,280 µg/L and 40-640 µg/L, respectively) were evaluated using slightly adapted standard protocol for Lemna spp.: relative growth rates (RGR) and yield of both plants were measured in 3-d-long intervals during the exposure and recovery phase. Myriophyllum aquaticum was also exposed to atrazine-spiked sediment (0.1-3.7 µg/g) in a water-free system. The results of M. aquaticum sediment contact tests showed that root- and shoot-based growth parameters are equally sensitive endpoints. In the water (sediment-free) test system, L. minor recovered after short (3 d) and longer exposure (7 d) to all atrazine concentrations after only a 5- to 6-d-long recovery phase. The recovery of M. aquaticum after short exposure was slower and less efficient: after 12 d of recovery phase the final biomass of plants exposed to 380 and 640 µg/L was below the initial values. The last interval RGR provides a good indication of plant recovery potential regardless of species growth strategy. If compared to L. minor, the difference in growth rate, sensitivity, lag phase, recovery potential from water-column substances, and also suitability for studies investigating the effect of sediment-bound pollutants advocates the use of M. aquaticum as an additional macrophyte species in risk assessment.

Quizalofop-p-ethyl-induced phytotoxicity and genotoxicity in Lemna minor and Lemna gibba

In this study, the effects of the herbicide, quizalofop-p-ethyl, on pigment contents (total chlorophyll, chlorophyll a/b, carotenoid), antioxidant enzyme [superoxide dismutase (SOD) and guaiacol peroxidase (POD)] activities, lipid peroxidation product (malondialdehyde: MDA) and DNA profiles were investigated in Lemna gibba and Lemna minor. Laboratory-acclimatized plants were treated with quizalofop-p-ethyl at 31.375, 62.75, 125 and 250 mg L(-1) for 24 and 96 h. It was determined that quizalofop-p-ethyl affected both the physiological status and the DNA profiles of L. gibba and L. minor. The photosynthetic pigments of L. gibba were more sensitive to the herbicide than were those of L. minor at both treatment times. SOD and POD activities were elevated in both plants at 24 h. However at 96 h, SOD activity decreased in L. minor and had irregular changes in L. gibba.. Significant increases in the amounts of MDA were observed in L. gibba, whereas the levels of this compound decreased in L. minor at 24 and 96 h. Polymorphism in DNA profiles was determined using the Random Amplified Polymorphic DNA (RAPD) technique. Four primers were used for scoring (appearance and disappearance of DNA polymorphic bands), and equally weighted maximum parsimony analyses were performed. Fewer differences were observed at 24 h, and more new bands were observed at 96 h in L. gibba. The RAPD profiles of L. minor produced by all of the primers were slightly less affected by the herbicide treatment than were those of L. gibba.