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The co-occurrence of aquatic contaminants, such as antibiotics and herbicides, has motivated investigations into their interactive effects on aquatic organisms. We examined the combined effects of environmental concentrations of the antibiotic Enrofloxacin (Enro; 0-2.25 μg l -1 ) and Roundup Original DI (Roundup ® ; 0-0.75 μg active ingredient l -1 ), a glyphosate based-herbicide, on Elodea canadensis. Enro alone was not toxic, but the plants were highly sensitive to Roundup ® whose toxicity is related to the induction of oxidative stress. The metabolism of Enro by plants into Ciprofloxacin (Cipro) was observed, and although former is not phytotoxic, oxidative events associated with Cipro generation were observed. The activity of cytochrome P450 was shown to be involved in Enro degradation in E. canadensis. As a cytochrome P450 inhibitor, Roundup ® decreases Enro metabolism in plants. Enro, in turn, increases glyphosate uptake and toxicity, so that Enro and Roundup ® have synergistic effects, disrupting the physiological processes of E. canadensis. Our results suggest E. canadensis as a potential candidate for the reclamation of Enro in contaminated waters, but not for Roundup ® due to its high sensitivity to that herbicide., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The herbicide diquat dibromide is used in North America to manage nuisance macrophytes. However, its effect on native macrophytes is less clear and it could cause indirect effects on other aquatic biota. This study determined the sensitivity of both native and non-native macrophytes grown in test systems with varying complexity to diquat dibromide applied directly to water following label directions. In an outdoor mesocosm experiment and single species greenhouse concentration-response tests, Elodea canadensis Michx., Myriophyllum spicatum L., Ceratophyllum demersum L. and Hydrocharis morsus-ranae L. were exposed to a range of diquat dibromide concentrations (4.7 - 1153 µg/L), corresponding to 0.4 - 100% of the recommended label rate of the formulated product. The mesocosm experiment contained all four plant taxa in the same system along with caged amphipods (Hyalella azteca Saus.), tadpoles (Lithobates pipiens Schreber), phytoplankton and periphyton; however, this study focuses on the macrophytes only. In both test systems, severe direct effects of diquat dibromide on macrophytes were detected, with almost 100% mortality of all macrophytes in both test systems at 74 µg/L. The most sensitive species in the single species tests, E. canadensis, showed almost 100% mortality at concentrations below the HPLC-based method detection limit of 5 µg/L. Effects occurred very rapidly and showed no difference in severity between native and non-native macrophytes or complexity of test systems. These results suggest that diquat dibromide could be applied at a considerably lower label rate, depending on the characteristics of the waterbody, while still achieving effective control of nuisance macrophytes., (Crown Copyright © 2018. Published by Elsevier Inc. All rights reserved.)

Aquatic plants in agricultural landscapes play a vital role in maintaining the ecological integrity within the aquatic systems while facing an array of disturbances. Among them, information on herbicide exposure on non-target aquatic plants is scarce. The present study was designed to fill this information gap by detecting the impacts of 2-methyl-4-chlorophenoxyacetic acid (MCPA) on Hydrilla verticillata using morpho-anatomical and physiological biomarkers and assessing the environmental risk of MCPA to the non-target environment. H. verticillata was exposed to different MCPA concentrations (10, 100, 500, 1000 μg/L) and control (0 μg/L) for 7 days. At the end of the experiment, plant growth, pigments, H 2 O 2 content, peroxidase activity (POD) and plant anatomy were compared. The environmental risk was assessed using predicted environmental concentration/predicted no effect concentration (PEC:PNEC) ratio, hazard quotient (HQ) and hazard index (HI). Control plants exhibited the highest growth, and a growth decline was noted in parallel to MCPA exposure, where a similar trend was detected for the plant pigment contents. MCPA induced chlorosis and oxidative stress in H. verticillata. Risk analysis detected high values for PEC:PNEC ratios (3-9), HQ (1.92-5.79) and HI (28.15). MCPA-exposed H. verticillata could recover once those plants received natural conditions. Overall, present findings showed the negative impacts of MCPA on non-target aquatic plant H. verticillata. These findings will be useful to clarify the interaction between agrochemicals and non-target aquatic plants. Such information would benefit to decide the criteria in aquatic ecosystem management.

Interest in stream mesocosms has recently revived for higher tier aquatic macrophyte risk assessment of plant protection products mainly because 1) the highest predicted environmental concentrations for the assessment of effects are frequently derived from stream scenarios, and 2) they allow an effect assessment using stream-typical pulse exposures. Therefore, the present stream mesocosm study used an herbicide pulse exposure and evaluated the responses of Elodea canadensis and Myriophyllum spicatum. Macrophytes were exposed for 24 h to 1 μg/L, 3 μg/L, 10 μg/L, and 30 μg/L of the herbicide iofensulfuron-sodium with a subsequent recovery period of 42 d. Biological endpoints were growth rates of the main, side, and total shoot length, the shoot number, the maximum root length, and the dry weight. The total shoot length was identified as the most sensitive endpoint; the growth rate of the total shoot length was inhibited by up to 66% and 45% in M. spicatum and E. canadensis, respectively. The lowest no observed effect concentrations (NOECs) were observed at day 7 and/or day 14 after herbicide treatment and were 1 μg/L for M. spicatum and 3 μg/L for E. canadensis. The no-observed-ecologically-adverse-effect concentrations (NOEAECs) were 10 μg/L and 30 μg/L for M. spicatum and E. canadensis, respectively. Such or similar mesocosm designs are useful to simulate typical stream exposures and estimate herbicide effects on aquatic macrophytes in stream systems. Environ Toxicol Chem 2017;36:1090-1100. © 2016 SETAC., (© 2016 SETAC.)

Light intensity can have a profound influence on the degree of phytotoxicity experienced by plants exposed to photosystem II (PSII) inhibiting herbicides. This relationship was evaluated in the submerged aquatic macrophyte Elodea canadensis exposed to three different concentrations of atrazine (510, 1000 and 2000 μg a.i./L) plus an untreated control at three different light intensities (0, 500 and 6000 lx) under static-renewal conditions for 14 days. Under 500 lx light intensity, control plants demonstrated a rapid increase in shoot length but minimal increase in dry shoot weight, suggesting limited photosynthesis. Based on shoot-length and biomass, growth was not affected by any atrazine exposure relative to controls under dark conditions (0 lx). Under low-light conditions at 500 lx, exposures to 510, 1000 and 2000 μg a.i./L atrazine significantly decreased net shoot lengths by 34%, 38% and 35%, respectively, relative to corresponding (500 lx) controls. However, atrazine exposure under this light condition did not significantly decrease biomass (dry shoot weight). Compared to 6000 lx, only approximately 8% of photosynthetically active radiation (PAR) was measured under 500 lx intensity, indicating that minimal PAR was available for photosynthesis. Under optimal light conditions (6000 lx), net shoot lengths significantly decreased in the treated atrazine groups by 48%, 51% and 68%, and net dry shoot weights (biomass) were significantly decreased by 79%, 81% and 91%, respectively, relative to corresponding (6000 lx) controls. These data show that under low light conditions, atrazine-induced effects on dry shoot weight (biomass) are dependent on available PAR and active photosynthesis., (Copyright © 2011 Elsevier Inc. All rights reserved.)

A mesocosm study with three photosystem-II inhibitors and an equipotent mixture was performed to address the value of functional and structural endpoints in evaluating the impact of herbicides on aquatic systems. The herbicides atrazine, diuron, and isoproturon were dosed in the ratio of their relative potencies as HC30 for the single substance treatments and as 1/3 HC30 for the mixture treatment to obtain comparable effect concentrations. To investigate the effects of the three herbicides and their mixture on photosynthesis of the whole system, the physical-chemical parameters pH, dissolved oxygen, and conductivity were monitored. To address effects on photosynthesis more specifically, the photosynthetic efficiency of phytoplankton and three submersed macrophytes (Elodea canadensis, Myriophyllum spicatum, and Potamogeton lucens) were investigated applying in vivo chlorophyll fluorescence as an indicator for their activity. As a structural endpoint, the species abundance and community structure of the phytoplankton community was determined. Effects were continuously monitored over a five week period of constant exposure, and during a 3 month post-exposure period. The sensitivity, expressed as maximum effect during constant exposure, was higher for the structural parameters (total and single species abundances and PRC) than for the functional parameters. The mean coefficient of variation (CV) for the physical-chemical parameters was below 10%, for the photosynthesis measurement of the phytoplankton and macrophytes below 10 and 30%, respectively. Structural parameters, however, yielded higher variability with mean CVs for phytoplankton abundance data and single sensitive species reaching up to 96%. Effects on the phytoplankton photosynthesis measured via in vivo chlorophyll fluorescence were constant during the exposure period; whereas macrophytes recovered quickly from photosynthesis inhibition despite constant exposure. Effects on total system photosynthesis, determined via physical-chemical parameters, lasted for a shorter period than for the phytoplankton photosynthesis demonstrating the importance of the macrophytes for total primary production. Thus, the evaluation of effects on communities in model ecosystems such as micro- and mesocosms should not be based on structural endpoints only due to their comparably high inherent variability. Instead, we recommend complementing the risk assessment with data obtained from sensitive functional endpoints addressing the specific mode of action of the respective compound for the most sensitive group of organisms to avoid over-estimation of the recovery potential of the aquatic system., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Accelerated eutrophication is common to many freshwater and marine environments and often co-occurs with the presence of anthropogenic chemicals. However, the toxic effects of common chemical stressors such as herbicides in the presence of elevated nutrients are not well understood for most aquatic flora, particularly vascular species. To provide insight, field-collected Vallisneria americana Michx. (wild celery) were sequentially exposed to three nutrient concentrations for 3 months and then to nominal 11 and 110 microg L(-1) atrazine for 96 h. Nutrient concentrations (combined NH(4)(+), NO(2)(-), NO(3)(-), PO(4)(-)) were based on ambient concentrations in the St. Johns River (FL) and ranged from 0.013 to 0.668 mg L(-1). Nutrient pretreatment potentiated the toxicity of atrazine as determined by chlorophyll fluorescence activity. Electron transport rates (ETR) were significantly less (48-59%) for plants pretreated with low and ambient nutrient levels in the presence of an average of 107.5-128.1 microg L(-1) atrazine. Significant ETR reductions were also observed for plants exposed to an average of 11.4 microg L(-1) atrazine after exposure to nutrients three times the ambient concentration in the St. Johns River. The results indicate the importance of considering the presence of nutrients in chemical hazard assessments, particularly for phytotoxicants and nontarget vascular plants.

This study evaluates the effects of the triazine herbicide simazine in an outdoor pond microcosm test system that contained two submerged rooted species (Myriophyllum spicatum and Elodea canadensis) and two emergent rooted species (Persicaria amphibia and Glyceria maxima) over a period of 84 days. Simazine was applied to the microcosms at nominal concentrations of 0.05, 0.5 and 5 mg/L. General biological endpoints and physiological endpoints were used to evaluate herbicide toxicity on macrophytes and the algae developing naturally in the system. Concentration-related responses of macrophytes and algae were obtained for the endpoints selected, resulting in a no observed ecologically adverse effect concentration (NOEAEC) at simazine concentrations of 0.05 mg active ingredient/L after 84 days. E. canadensis was the most negatively affected species based on length increase, which was consistently a very sensitive parameter for all macrophytes. The experimental design presented might constitute a suitable alternative to conventional laboratory single-species testing., (Copyright (c) 2009 Elsevier Ltd. All rights reserved.)

Vallisneria americana Michx. (tapegrass) is an ecologically important submersed, vascular aquatic plant that provides food and shelter for many aquatic and waterfowl species. This plant often occurs close to land areas where herbicides are used. Nontarget exposure of these plants to herbicides may compromise ecological structure and function. The objective of the present study was to evaluate the suitability of several endpoint measurements for determining no-observable-adverse effect concentrations (NOAECs), lowest-observable-adverse effect concentrations (LOAECs), and median effective concentration values (EC50s) for tapegrass exposed to the herbicides bromacil (0-0.092 mg/L) and simazine (0-0.592 mg/L) following a 13-d single-pulse exposure and 15-d (bromacil) or 14-d (simazine) postexposure periods. The NOAEC/LOAEC/EC50 for fresh weight gains, new leaf production, and total leaf growth after 13-d exposure to bromacil were 0.020/0.036/0.032, 0.036/0.054/0.036, and 0.036/0.054/0.043 mg/L, respectively. The same respective NOAEC/LOAEC/EC50s for simazine were <0.058/0.058/0.067, 0.229/0.344/0.154, and 0.058/0.116/0.081 mg/L. Reductions in quantity and fresh weight of daughter plants produced and stolon fresh weights occurred at bromacil concentrations > or = 77, 0.020, and 0.036 mg/L, respectively; and simazine concentrations > or = 0.344, >0.592, and > or = 0.116 mg/L, respectively. Neither herbicide affected leaf greenness, total chlorophyll concentrations, or carbohydrate allocation. Although toxicity was shown for many endpoints, most EC50 values were greater than aquatic life benchmark values for algae used by the U.S. Environmental Protection Agency (U.S. EPA), but less than for aquatic plants, indicating that V. americana would likely be protected by use of the algal benchmark criteria.

The physiological effects of 4 herbicides (butachlor, quinclorac, bensulfuron-methyl and atrazine) on 3 submerged macrophytes (Ceratophyllum demersum, Vallisneria natans and Elodea nuttallii) were tested in laboratory. The variables of the relative growth rate and the photosynthetic pigment content showed that all of the tested herbicides affected the growth of the plants obviously, even at the lowest concentration (0.0001 mg/L). Except for the C. demersum treated with quinclorac at 0.005 and 0.01 mg/L, the relative growth rates of the plants were inhibited significantly (p < 0.01). Statistical analysis of chlorophyll a (Chl-a) contents was carried out with both the t-test and one-way ANOVA to determine the difference between the treatment and control. The results showed that Chl-a contents of the plants in all treatment groups were affected by herbicides significantly, except for the C. demersum treated with bensulfuron-methyl at 0.0005 mg/L. The decrease in Chl-a content was positively correlated to the dosage of the herbicides in most treatment groups. It was suggested that herbicides in water bodies might potentially affect the growth of aquatic macrophytes. Since the Chl-a content of submerged macrophytes responded to the stress of herbicides sensitively and directly, it could be used as a biomaker in environmental monitoring or in the ecological risk assessment of herbicide contamination.

The study evaluated the effects of benzalkonium chloride (BAC) and atrazine on the macrophyte Elodea canadensis (Michaux) using a miniaturised monitoring test system consisting of a microbioreactor of reduced volume and integrated sensors for the online measurement of physiologic parameters, like oxygen production and different parameters of fluorescence. Different concentrations of both chemicals were applied to leaves of E. canadensis and the physiologic endpoints evaluated after 1h. A concentration-dependent reduction of the oxygen production and of the effective quantum yield of energy conversion was recorded. The mini-PAM technique implemented in the presented system allowed for a clear monitoring of the kinetic of BAC and atrazine, showing their distinct mode of action. No observable adverse effects were recorded up to concentrations of 2.5 mg/L and 10 microg/L, for BAC and atrazine, respectively. These values are in accordance with available results in the literature, hence indicating that the microbioreactor test system might be suitable, on the one hand, for the laboratory screening of potential short-term toxicity of contaminants on aquatic plants, and on the other hand, serve as an in situ field biomonitoring system for the rapid detection of pollutants in water.

Vallisneria americana (Michx.) (common name tapegrass) is a submersed, vascular aquatic plant that reproduces vegetatively and by seed. The objective of this study was to determine the no-observable-effects concentrations (NOECs) and lowest-observable-effects concentrations (LOECs) for tapegrass exposed to the herbicide norflurazon (0-0.1 mg/L) following a 14-d exposure and a postexposure period. The primary symptom of norflurazon toxicity was bleaching of newly emerged leaf blades at concentrations of 0.04 mg/L and higher after 14 d of exposure. Leaf greenness effect levels were 0.04 mg/L (NOEC) and 0.06 mg/L (LOEC). All other endpoints measured resulted in a NOEC greater than 0.1 mg/L following the exposure period. Latent effects were observed 14 d postexposure for new leaf production and fresh weight gains, with a NOEC and LOEC of 0.08 and 0.1 mg/L, respectively. Total leaf growth was the least sensitive endpoint measured. Following the exposure/postexposure periods, significant effects on vegetative reproduction were apparent, with no effects occurring at concentrations up to 0.08 mg/L, but with significant reduction at the 0.1 mg/L treatment level. Root and stolon dry weights were significantly reduced at the 0.1 and 0.08 mg/L treatments, respectively. Total soluble sugars (TSS) and hexose content in shoots was reduced at concentrations of 0.04 mg/L and higher. TSS, hexose, and sucrose contents were higher in roots of plants exposed to 0.1 mg/L. Some recovery was apparent for all treatment concentrations following the postexposure period, indicating that the effects were at least partially reversible.

Three natural somatic mutations at codon 304 of the phytoene desaturase gene (pds) of Hydrilla verticillata (L. f. Royle) have been reported to provide resistance to the herbicide fluridone. We substituted the arginine 304 present in the wild-type H. verticillata phytoene desaturase (PDS) with all 19 other natural amino acids and tested PDS against fluridone. In in vitro assays, the threonine (Thr), cysteine (Cys), alanine (Ala) and glutamine (Gln) mutations imparted the highest resistance to fluridone. Thr, the three natural mutations [Cys, serine (Ser), histidine (His)] and the wild-type PDS protein were tested in vitro against seven inhibitors of PDS representing several classes of herbicides. These mutations conferred cross-resistance to norflurazon and overall negative cross-resistance to beflubutamid, picolinafen and diflufenican. The T3 generation of transgenic Arabidopsis thaliana plants harbouring the four selected mutations and wild-type pds had similar patterns of cross-resistance to the herbicides as observed in the in vitro assays. The Thr304 Hydrilla pds mutant proved to be an excellent marker for the selection of transgenic plants. Seedlings harbouring Thr304 pds had a maximum resistance to sensitivity (R/S) ratio of 57 and 14 times higher than that of the wild-type for treatments with norflurazon and fluridone, respectively. These plants exhibited normal growth and development, even after long-term exposure to herbicide. As Thr304 pds is of plant origin, it could become more acceptable than other selectable markers for use in genetically modified food.

Hydrilla [Hydrilla verticillata (Lf) Royle] is one of the most serious invasive aquatic weed problems in the USA. This plant possesses numerous mechanisms of vegetative reproduction that enable it to spread very rapidly. Management of this weed has been achieved by the systemic treatment of water bodies with the herbicide fluridone. At least three dioecious fluridone-resistant biotypes of hydrilla with two- to fivefold higher resistance to the herbicide than the wild-type have been identified. Resistance is the result of one of three independent somatic mutations at the arginine 304 codon of the gene encoding phytoene desaturase, the molecular target site of fluridone. The specific activities of the three purified phytoene desaturase variants are similar to the wild-type enzyme. The appearance of these herbicide-resistant biotypes may jeopardize the ability to control the spread of this non-indigenous species to other water bodies in the southern USA. The objective of this paper is to provide general information about the biology and physiology of this aquatic weed in relation to its recent development of resistance to the herbicide fluridone, and to discuss how this discovery might lead to a new generation of herbicide-resistant crops., (Copyright 2005 Society of Chemical Industry)

Herbicides entering the aquatic environment by spray drift, run-off and leaching to field drains may cause adverse effects on non-target aquatic vegetation. The potential for such effects has typically been evaluated from tests with floating, monocotyledonous Lemna sp. However, concern has been expressed as to whether this species could be used to indicate potential effects on other vegetation types, particularly rooted, submerged, emergent or dicotyledonous species. In 1997, the Centre for Aquatic Plant Management undertook development of new tests based on the additional species, Glyceria maxima (Hartm) Holmb, Lagarosiphon major (Ridl) Moss and Myriophyllum spicatum L. The resulting methodology was used to assess the effects of the sulfonylurea herbicide, sulfosulfuron on these species. Data presented here demonstrate that exposure to initial sulfosulfuron concentrations of 3.33 microg litre(-1) for up to 21 days was tolerated by these species and that adverse effects were observed only when plants were exposed to initial concentrations of 3.33 and 10 microg litre(-1) for 70 days. As the occurrence of such high initial concentrations for long periods is unlikely in the aquatic environment, sulfosulfuron is not expected to have adverse effects on the growth of these species. This study has also demonstrated that G maxima, L major and M spicatum grown in small outdoor tanks can be used successfully to assess the effects of crop-protection products on non-target aquatic flora.