Sensitivity of submersed freshwater macrophytes and endpoints in laboratory toxicity tests

Feasibility Study on Phytoremediation of Potentially Toxic Elements (Cd, Ni and Pb) in Aquatic Environments Using Suaeda maritima Plant Species, a Case Study: Khorkhoran International Wetland, Persian Gulf

The current study was designed to assess the phytoremediation potential of Suaeda maritima has been assessed for cleanup of contaminated sediments with Cd, Ni and Pb. In so doing, totally, 20 sampling sites were selected in the Khorkhoran International Wetland. The contents of elements in sediments, plant organs and water samples were determined using ICP-OES. The mean contents of Cd, Ni and Pb (mg/kg) in the sediment samples were found to be 0.096, 38.1 and 1.78, respectively. Moreover, the mean levels of Cd, Ni and Pb (mg/kg) in root samples of S. maritime were 0.160, 2.72 and 1.22 respectively; whereas, in leaf samples they were found to be 0.157, 3.34 and 2.23 mg/kg, respectively. Furthermore, the mean contents of Cd, Ni and Pb (µg/L) in water samples were 243, 1440 and 3010, respectively. The values of BCF for Cd, BAF for Cd and Pb, and TF for Ni and Pb were higher than 1, which would indicate that S. maritima could possibly be a suitable candidate for the phytostabilization of Cd and the phytoextraction of Ni and Pb.

The use of the aquatic plant Elodea canadensis to assess the effects of low-dose gamma irradiation

Responses of cytogenetic and growth endpoints of the aquatic plant Elodea canadensis were studied using the plants collected from non-contaminated control areas of the Yenisei River and exposed to external γ-radiation for 11-13 days in the laboratory. Elodea canadensis was exposed to 0.5-25 mGy/day γ-radiation dose rates from a ¹³⁷Cs source. The total number of aberrant cells and total root length were more sensitive elodea endpoints to γ-radiation than total shoot length and mitotic index of elodea. Radiation sensitivity of elodea can be compared with the sensitivity of such a Reference Plant as Wild Grass (1-10 mGy/day) recommended by the ICRP. Thus, the aquatic plant Elodea canadensis can be used as a radiation bioindicator.

Review of Typha spp. (cattails) as toxicity test species for the risk assessment of environmental contaminants on emergent macrophytes

Macrophytes play an important role in aquatic ecosystems, and thus are often used in ecological risk assessments of potentially deleterious anthropogenic substances. Risk assessments for macrophyte populations or communities are commonly based on inferences drawn from standardized toxicity tests conducted on floating non-rooted Lemna species, or submerged-rooted Myriophyllum species. These tests follow strict guidelines to produce reliable and robust results with legal credibility for environmental regulations. However, results and inferences from these tests may not be transferrable to emergent macrophytes due to their different morphology and physiology. Emergent macrophytes of the genus Typha L. are increasingly used for assessing phytotoxic effects of environmental stressors, although standardized testing protocols have not yet been developed for this genus. In this review we present a synthesis of previous toxicity studies with Typha, based on which we evaluate the potential to develop standard toxicity tests for Typha spp. with seven selection criteria: ecological relevance to the ecosystem; suitability for different exposure pathways; availability of plant material; ease of cultivation; uniform growth; appropriate and easily measurable toxicity endpoints; and sensitivity toward contaminants. Typha meets criteria 1-3 fully, criteria 4 and 5 partly based on current limited data, and we identify knowledge gaps that limit evaluation of the remaining two criteria. We provide suggestions for addressing these gaps, and we summarize the experimental design of ecotoxicology studies that have used Typha. We conclude that Typha spp. can serve as future standard test species for ecological risk assessments of contaminants to emergent macrophytes.

Glyphosate Toxicity to Native Nontarget Macrophytes Following Three Different Routes of Incidental Exposure

A major goal of invasive plant management is the restoration of native biodiversity, but effective methods for invasive plant control can be harmful to native plants. Informed application of control methods is required to reach restoration goals. The herbicide glyphosate, commonly applied in invasive plant management, can be toxic to native macrophytes. Our study assessed the response of 2 macrophytes that are endangered in our study area (Ammannia robusta and Sida hermaphrodita) to glyphosate concentrations that mimic incidental exposure from nearby invasive plant control: spray drift of 4 × 10-7 % to 5% glyphosate; pulse and continuous immersion in water containing 2 to 41 µg/L glyphosate; and rhizosphere contact with 5%-glyphosate-wicked invasive plants. We assessed macrophyte sensitivity at 14-d postexposure, and quantified abundance of arbuscular mycorrhizal fungi. Glyphosate spray concentrations as low as 0.1% reduced macrophyte growth. Ammannia was more sensitive overall to glyphosate spray than Sida, although sensitivity varied among measured endpoints. Conversely, macrophytes were not affected by immersion in low concentrations of glyphosate or rhizosphere contact with a glyphosate-wicked plant. Likewise, arbuscular mycorrhizal fungi abundance in roots was similar among glyphosate-sprayed and control plants. Based on our results, we recommend that invasive plant managers reduce risks to native nontarget plants through implementing measures that limit off-target spray drift, and consider the feasibility of more targeted applications, such as with wick equipment. Integr Environ Assess Manag 2021;17:597-613. © 2020 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Aquatic plants and ecotoxicological assessment in freshwater ecosystems: a review

This paper reviews the current state-of-the-art, limitations, critical issues, and new directions in freshwater plant ecotoxicology. We selected peer-reviewed studies using relevant databases and for each (1) publication year, (2) test plant species, (3) reference plant group (microalgae, macroalgae, bryophytes, pteridophytes, flowering plants), (4) toxicant tested (heavy metal, pharmaceutical product, hydrocarbon, pesticide, surfactant, plastic), (5) experiment site (laboratory, field), and (6) toxicant exposure duration. Although aquatic plant organisms play a key role in the functioning of freshwater ecosystems, mainly linked to their primary productivity, their use as biological models in ecotoxicological tests was limited if compared to animals. Also, toxicant effects on freshwater plants were scarcely investigated and limited to studies on microalgae (80%), or only to a certain number of recurrent species (Pseudokirchneriella subcapitata, Chlorella vulgaris, Lemna minor, Myriophyllum spicatum). The most widely tested toxicants on plants were heavy metals (74%), followed by pharmaceutical products and hydrocarbons (7%), while the most commonly utilized endpoints in tests were plant growth inhibition, variations in dry or fresh weight, morpho-structural alterations, chlorosis, and/or necrosis. The main critical issues emerged from plant-based ecotoxicological tests were the narrow range of species and endpoints considered, the lack of environmental relevance, the excessively short exposure times, and the culture media potentially reacting with toxicants. Proposals to overcome these issues are discussed.

Effect of interspecific competition on species sensitivity distribution models: Analysis of plant responses to chemical stress

Species Sensitivity Distributions (SSD) are widely used in environmental risk assessment to predict the concentration of a contaminant that is hazardous for 5% of species (HC₅). They are based on monospecific bioassays conducted in the laboratory and thus do not directly take into account ecological interactions. This point, among others, is accounted for in environmental risk assessment through an assessment factor (AF) that is applied to compensate for the lack of environmental representativity. In this study, we aimed to assess the effects of interspecific competition on the responses towards isoproturon of plant species representative of a vegetated filter strip community, and to assess its impact on the derived SSD and HC₅ values. To do so, we realized bioassays confronting six herbaceous species to a gradient of isoproturon exposure in presence and absence of a competitor. Several modelling approaches were applied to see how they affected the results, using different critical effect concentrations and investigating different ways to handle multiple endpoints in SSD. At the species level, there was a strong trend toward organisms being more sensitive to isoproturon in presence of a competitor than in its absence. At the community level, this trend was also observed in the SSDs and HC₅ values were always lower in presence of a competitor (1.12-11.13 times lower, depending on the modelling approach). Our discussion questions the relevance of SSD and AF as currently applied in environmental risk assessment.

Ecological types and bioindicator macrophyte species of pollution of riparian vegetation of Oued Lârbaa in Taza City of Morocco

The object of our study is devoted to the Spermatophyta of the wetlands of Oued Lârbaa, the main river of the city of Taza, Morocco, and which is under strong anthropic pressure. Our work involved a floristic inventory, to define ecological types and groups of dominant plants in relation to seasonal factors and types of pollution, explaining the meaning of their presence. For this purpose, floristic sampling was carried out along the Oued during the dry periods (2017 and 2018) and the wet period (2018). A total of 66 plant species belonging to 54 genera and 30 families were identified, including 44 species during the wet period (2018) and 27 species during the dry periods (2017 and 2018). This difference is due to the favorable conditions for vegetation development during the period of precipitation and to the increase in pollution rates during the dry season. The inventoried flora shows the dominance of 10 ecological types characterized by the following plants: Cynodon dactylon, Arundo donax, Olea europaea, and Tamarix gallica (common between the two periods); Dittrichia viscosa, Visnaga daucoides, Typha angustifolia, and Ricinus communis (during the dry periods of 2017 and 2018); and Juncus maritimus and Populus nigra (during the wet period of 2018). The ecological types identified in this work decrease from the dry season to the rainy season, while specific richness increases. These dominant plants are all considered as bioindicators of the presence of heavy metals.

Herbicide Exposure and Toxicity to Aquatic Primary Producers

The aim of the present review was to give an overview of the current state of science concerning herbicide exposure and toxicity to aquatic primary producers. To this end we assessed the open literature, revealing the widespread presence of (mixtures of) herbicides, inevitably leading to the exposure of non-target primary producers. Yet, herbicide concentrations show strong temporal and spatial variations. Concerning herbicide toxicity, it was concluded that the most sensitive as well as the least sensitive species differed per herbicide and that the observed effect concentrations for some herbicides were rather independent from the exposure time. More extensive ecotoxicity testing is required, especially considering macrophytes and marine herbicide toxicity. Hence, it was concluded that the largest knowledge gap concerns the effects of sediment-associated herbicides on primary producers in the marine/estuarine environment. Generally, there is no actual risk of waterborne herbicides to aquatic primary producers. Still, median concentrations of atrazine and especially of diuron measured in China, the USA and Europe represented moderate risks for primary producers. Maximum concentrations due to misuse and accidents may even cause the exceedance of almost 60% of the effect concentrations plotted in SSDs. Using bioassays to determine the effect of contaminated water and sediment and to identify the herbicides of concern is a promising addition to chemical analysis, especially for the photosynthesis-inhibiting herbicides using photosynthesis as endpoint in the bioassays. This review concluded that to come to a reliable herbicide hazard and risk assessment, an extensive catch-up must be made concerning macrophytes, the marine environment and especially sediment as overlooked and understudied environmental compartments.

Effects of diclofenac and salicylic acid exposure on Lemna minor: Is time a factor?

The global occurrence of pharmaceuticals in the aquatic environment has been considered a particularly concerning problem with unknown consequences. Non-steroidal anti-inflammatory drugs (NSAIDs) including diclofenac (DCF) and salicylic acid (SA), are among the most frequently prescribed drugs in the world, being consequently commonly found in the aquatic environment. Prolonged experiments (with duration of exposure that surpass those recommended by already established testing guidelines) are important to obtain ecologically relevant data to address the issue of NSAIDs ecotoxicity, because by being more realistically (namely in terms of levels and durations of exposure), such tests may indicate realistic challenges posed to aquatic organisms. Among the most common test species that are used for assessing environmental quality, plants play a leading role. Lemna species are among the most important plants used for ecotoxicity testing. Therefore, the aim of this study was to evaluate the temporal effect of a prolonged exposure of DCF and SA on Lemna minor. To attain this purpose, L. minor plants were chronically exposed to 0, 4, 20, and 100 μg/L of both pharmaceuticals, and samplings were performed at 6, 10 and 14 days of exposure. The analyzed endpoints were: levels of chlorophyll a, b and total, carotenoids; and enzymatic biomarkers, such as catalase, ascorbate peroxidase and glutathione-S-transferases. Diclofenac was responsible for alterations in all analyzed parameters in different intervals of exposure. Salicylic acid exposure was not capable of causing alterations on pigment contents of L. minor, however, enzymatic biomarkers were altered at all sampling intervals. Thus, it is possible to conclude that both pharmaceuticals can cause damage on the tested macrophyte species, biochemical parameters being more sensitive than physiological ones. Additional prolonged experiments are required to understand the chronic effects of different pharmaceuticals in the aquatic environment, especially in plants.

Bioaccumulation and growth characteristics of Vallisneria natans (Lour.) Hara after chronic exposure to metal-contaminated sediments

Metal-contaminated sediments in lakes is a global concern that poses toxicological risk to aquatic organisms. This study performed bioassays using the submerged macrophyte, Vallisneria natans (Lour.) Hara, exposed to contaminated sediments collected from five locations in Dianchi Lake, Yunnan, China. Among the sediments collected, I_geo showed enrichment of As and Cd in Dianchi Lake sediments. In spite of enriched toxic metals at some locations, laboratory bioassays found no significant difference in leaf biomass or leaf photosynthesis rate between the sites. Root biomass and root activity showed significant differences between locations and were negatively correlated with the concentration of As, Cd, Hg, and Pb in sediment but not related to Cr. The above correlations were strongest for Hg and As, respectively. Accumulation of Cd and Pb to leaves of bioassay plants was observed, but this was not evident for As and Cr. Overall, the results indicate that V. natans can be used as a bioassay organism and measures of root toxicity are sensitive to metal concentrations present in Dianchi Lake sediments. Furthermore, the study species holds promise for use as a biomonitor of Cd and Pb sediment metal content.

Effects of nanoplastics and microplastics on the growth of sediment-rooted macrophytes

Plastic debris of all sizes has been detected in marine, terrestrial and freshwater habitats. Effects of plastic debris on macrophytes have hardly been studied, despite their importance in aquatic ecosystems. We provide the first experimental study exploring nano- and microplastic effects on the growth of sediment-rooted macrophytes. Myriophyllum spicatum and Elodea sp. were exposed to sediments amended with six doses of polystyrene (PS) nanoplastic (50-190 nm, up to 3% sediment dry weight) and PS microplastic (20-500 μm, up to 10% dry weight) under laboratory conditions. Both macrophyte species were tested for changes in root and shoot dry weight (DW), relative growth rate (RGR), shoot to root ratio (S:R), main shoot length and side shoot length. Microplastics did not produce consistent dose-effect relationships on the endpoints tested, except that main shoot length was reduced for M. spicatum with increasing microplastic concentration. Nanoplastic significantly reduced S:R for both macrophytes as a result of increased root biomass compared to shoot biomass. Nanoplastic also caused a decrease in M. spicatum main shoot length; however, shoot biomass was not affected. Elodea sp. side shoot length, root and shoot biomass and RGR were positively correlated to the nanoplastic concentration. All effects occurred at higher than environmentally realistic concentrations, suggesting no immediate implications for ecological risks. Our study did not aim for the elucidation of the exact mechanistic processes that cause the effects, however, particle size seems to play an important factor. CAPSULE: Nano- and microplastics affect growth of sediment-rooted macrophytes.

Macrophytes are highly sensitive to the herbicide diquat dibromide in test systems of varying complexity

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.

Aquatic plants: Test species sensitivity and minimum data requirement evaluations for chemical risk assessments and aquatic life criteria development for the USA

Phytotoxicity results from the publicly-available ECOTOX database were summarized for 20 chemicals and 188 aquatic plants to determine species sensitivities and the ability of a species-limited toxicity data set to serve as a surrogate for a larger data set. The lowest effect concentrations reducing the sublethal response parameter of interest by 50% relative to the controls (EC50) usually varied several orders of magnitude for the 119 freshwater and 69 saltwater plants exposed to the same test chemicals. Generally, algae were more sensitive than floating and benthic species but inter-specific differences for EC50 values were sometimes considerable within and between phyla and no consistently sensitive species was identified for the morphologically-diverse taxa. Consistent equivalencies of the phytotoxicity databases for freshwater-saltwater plants and floating-benthic macrophyte species were not demonstrated. Two species-sensitivity distribution plots (SSDs) were constructed for each of the 20 chemicals, one based on all available phytotoxicity information (range = 10-76 test species) and another based on information for only five species recommended for pesticide hazard evaluations. HC5 values (hazardous concentration to 5% of test species) estimated from the two SSDs usually differed four-fold or less for the same chemical. HC5 values for the five species were often conservative estimates of HC5 values for the more species-populated data sets. Consequently, the collective response of the five test species shows promise as an interim aquatic plant minimum data requirement for aquatic life criteria development. In contrast, the lowest EC50 values for the five species usually were greater than HC5 values for the same test chemicals, a finding important to criteria-supporting Final Plant Values. The conclusions may differ for comparisons based on other test chemicals, test species, response parameters and calculations.

Effect of fluoride on photosynthetic pigment content and antioxidant system of Hydrilla verticillata

Fluoride can either inhibit or enhance the growth of aquatic macrophytes, depending upon fluoride concentration and exposure time. To investigate fluoride toxicity, the submerged plant Hydrilla verticillata was treated with various concentrations of fluoride (F) (0, 10, 20, and 40 mg/L) for different lengths of time (7, 14, 21, and 28 days). At exposure to 10 mg/L F, the content of chlorophyll, protein, and carbohydrates content increased in leaves of H. verticillata, and the activity of guaiacol peroxidase (POD) and superoxide dismutase (SOD) slightly increased in plants compared with the control. When fluoride concentration increased to 20 mg/L, the toxic effect generated by fluoride led to a reduction of chlorophyll, protein, and carbohydrates in H. verticillata, but the activity of guaiacol peroxidase and SOD and the amount of ascorbic acid (AsA) and glutathione (GSH) were enhanced significantly. After exposure to fluoride at 40 mg/L for a long period, these physiological parameters showed a sharp decrease, and inactivation was observed in H. verticillata. These results suggested that a certain concentration of fluoride induced antioxidant response, and excess fluoride induced metabolism imbalance and oxidative damage in H. verticillata.

Effect of Potamogeton crispus L. on bioavailability and biodegradation activity of pyrene in aged and unaged sediments

In order to clarify the effect of Potamogeton crispus L. (P. crispus) on bioavailability and biodegradation activity of pyrene in aged and unaged sediments, model calculation based on experimental results was carried out. During a 36-day experiment, the dissipation ratio of pyrene was increased by planting but decreased by aging. P. crispus improved the dissipation more significantly in aged sediments (45.9%) than in unaged sediments (17.6%). Results derived from a two-compartment desorption model showed that the decrease of rapidly desorbing fraction of pyrene was in the order of aged sediments without plant (A)>unaged sediments without plant (U)>unaged sediments with plant (UP)>aged sediments with plant (AP). Moreover, the results of biodegradation kinetic model showed that the first-order biodegradation coefficient was in the order of AP>UP>U and A, which was consistent with that of sediment redox potential. These modeling results indicated that planting could enhance the bioavailability (73.9%) and biodegradation activity (277%) of pyrene more significantly in aged sediments as compared to unaged sediments (13.1% and 150%, respectively), which should be the key reasons leading to more significant dissipation increment of pyrene in aged sediments by P. crispus.

Effects of Funnelliformis mosseae inoculation on alleviating atrazine damage in Canna indica L. var. flava Roxb

Atrazine residue in the environment continually damages plants and therefore requires immediate attention and effective development of methods for its decontamination. The effects of Funnelliformis mosseae inoculation on growth and physiology in atrazine-treated Canna indica L. var. flava Roxb. were investigated. At atrazine concentrations up to 15 mg L^-1, the growth of C. indica plants were negatively affected. Inoculation with F. mosseae alleviated the atrazine inhibition of plant growth and biomass. Furthermore, the chlorophyll content and root function increased under F. mosseae inoculation, and the oxidative stress of malondialdehyde, peroxidase, and superoxide dismutase activities induced by atrazine were also alleviated by F. mosseae inoculation. The removal rate of atrazine by untreated C. indica was significant, with removal rates of 20.5-55.3% by the end of a 14-day experiment; however, F. mosseae inoculation increased the removal rate to 35.6-75.1%. In conclusion, F. mosseae inoculation can alleviate the damage induced by atrazine in C. indica. Accordingly, C. indica inoculated with F. mosseae has excellent potential to be used in phytoremediation in habitats polluted by high atrazine concentrations.

Use of the aquatic plant Elodea canadensis to assess toxicity and genotoxicity of Yenisei River sediments

The toxicity, cytotoxicity, and genotoxicity of bulk sediments from the Yenisei River (Siberia, Russia) were estimated in laboratory bioassays based on several endpoints in the aquatic plant Elodea canadensis. The bottom sediment samples were collected in the Yenisei River upstream and downstream of the sources of chemical and radioactive contamination. The testing revealed different sensitivities of Elodea endpoints to the quality of the bottom sediment: weight of shoots < length of shoots < mitotic index < length of roots < percentage of abnormal cells. The response of the genotoxicity endpoint (percentage of cells with chromosome abnormalities in roots of Elodea) was the highest in sediments with chemical pollution, whereas the highest inhibition of toxicity endpoints (shoot and root length) occurred in sediments with the highest level of radioactive pollution. The extreme response of Elodea endpoints to the quality of certain sediment samples may be regarded as related to the possible presence of unknown toxicants. The results show that E. canadensis can be used as an indicator species in laboratory contact testing of bottom sediment. The responses of shoot and root length growth endpoints of Elodea can be recommended as basic sensitivity indicators of bottom sediment toxicity. Analysis of cells carrying abnormal chromosomes in the apical root meristem of Elodea can be performed optionally in the same test to assess the genotoxicity of sediments.

Some arguments in favor of a Myriophyllum aquaticum growth inhibition test in a water-sediment system as an additional test in risk assessment of herbicides

The present study compares the practicability, reproducibility, power, and sensitivity of a Myriophyllum aquaticum growth inhibition test in a water-sediment system with the recently accepted Myriophyllum spicatum test in an equivalent testing system and the standard Lemna sp. test. Special consideration was given to endpoints based on M. aquaticum control plant growth and variability of relative growth rate and yield: shoot length, fresh weight, dry weight, and root weight. Sensitivity analysis was based on tests performed with 3,5-dichlorophenol, atrazine, isoproturon, trifluralin, 2,4-dichlorophenoloxyacetic acid, and dicamba. Growth rates for average M. aquaticum control plants were 0.119 d(-1) and 0.112 d(-1), with average estimated doubling time 6.33 d and 6.74 d for relative growth rate fresh weight and shoot length, respectively. Intrinsic variability of M. aquaticum endpoints was low: 12.9%, 12.5%, and 17.8% for relative growth rate shoot length, relative growth rate fresh weight and yield fresh weight, respectively. The power of the test was fairly high. When the most sensitive endpoints were used for comparison, the 2 Myriophyllum species were similarly sensitive, more sensitive (in the case of auxin simulators), or at least equally sensitive as Lemna minor to other tested herbicides. The M. aquaticum 10-d test with a 7-d exposure period in a water-sediment system has acceptable sensitivity and can provide repeatable, reliable, and reproducible results; therefore, it should not be disregarded as a good and representative additional test in environmental risk assessment.

Development of a sediment-contact test with rice for the assessment of sediment-bound pollutants

Despite the key role of higher plants in aquatic ecosystems as functional and structural elements, sediment-contact tests with macrophytes are still scarce. Moreover, due to large differences in exposure routes for pollutants as well as in life cycles between the diverse taxa of macrophytes, sensitivities to pollutants vary between taxa. Therefore, the development of new test systems with aquatic macrophytes, in general, is favorable. This study proposes a protocol for a sediment-contact test with Oryza sativa and addresses the main question whether the rice plant is a suitable test organism for sediment toxicity testing with higher plants. As a first evaluation step, the variability and sensitivity of the test was investigated using spiked artificial sediments. Thus, according to the protocol, rice was exposed to arsenic-, cadmium-, chromium-, and nickel-spiked sediments. Additionally, it was investigated which classical endpoints for plant bioassays, such as root and shoot elongation, are suitable for this bioassay. As a second evaluation step, the test system was used for assessment of natural sediments. Thereupon, a sensitivity profile of the presented test protocol was analyzed in comparison to other plant-based test systems. Inhibition of root and shoot elongation turned out to be the most sensitive endpoints for single-substance testing in spiked artificial sediments. However, regarding testing of natural sediments, rice shoots responded more sensitive than rice roots. In conclusion, the rice plant clearly showed pollutant-induced effects on growth in sediments, and thus, it is likely a promising test organism to complement sediment-contact tests with higher plants.

β-Radiation Stress Responses on Growth and Antioxidative Defense System in Plants: A Study with Strontium-90 in Lemna minor

In the following study, dose dependent effects on growth and oxidative stress induced by β-radiation were examined to gain better insights in the mode of action of β-radiation induced stress in plant species. Radiostrontium (⁹⁰Sr) was used to test for β-radiation induced responses in the freshwater macrophyte Lemna minor. The accumulation pattern of 90Sr was examined for L. minor root and fronds separately over a seven-day time period and was subsequently used in a dynamic dosimetric model to calculate β-radiation dose rates. Exposing L. minor plants for seven days to a ⁹⁰Sr activity concentration of 25 up to 25,000 kBq·L⁻¹ resulted in a dose rate between 0.084 ± 0.004 and 97 ± 8 mGy·h⁻¹. After seven days of exposure, root fresh weight showed a dose dependent decrease starting from a dose rate of 9.4 ± 0.5 mGy·h⁻¹. Based on these data, an EDR10 value of 1.5 ± 0.4 mGy·h⁻¹ was estimated for root fresh weight and 52 ± 17 mGy·h⁻¹ for frond fresh weight. Different antioxidative enzymes and metabolites were further examined to analyze if β-radiation induces oxidative stress in L. minor.

Phytotoxicity assessment of atrazine on growth and physiology of three emergent plants

The emergent plants Acorus calamus, Lythrum salicaria, and Scirpus tabernaemontani were exposed to atrazine for 15, 30, 45, and 60 days in a hydroponic system. Effects were evaluated investigating plant growth, chlorophyll (Chl) content, peroxidase (POD) activity, and malondialdehyde (MDA) content. Results showed that selected plants survived in culture solution with atrazine ≤8 mg L(-1), but relative growth rates decreased significantly in the first 15-day exposure. Chla content decreased, but MDA increased with increasing atrazine concentration. S. tabernaemontani was the most insensitive species, followed by A. calamus and L.salicaria. The growth indicators exhibited significant changes in the early stage of atrazine exposure; subsequently, the negative impacts weakened and disappeared. Plant growth may be more representative of emergent plant fitness than physiological endpoints in toxicity assessment of herbicides to emergent plants.

Glyceria maxima as new test species for the EU risk assessment for herbicides: a microcosm study

In its recent guidance document on tiered risk assessment for plant protection products for aquatic organisms, the European Food Safety Authority (EFSA) proposed to use Glyceria maxima as monocotyledonous grass species for the testing of special herbicide groups. However, published toxicity data for this species is very limited and there is no test guideline for Glyceria sp. For this reason a microcosm study was conducted in order to gain experience on the degree of sensitivity of G. maxima to the herbicidal substances clodinafop-propargyl (grass herbicide) and fluroxypyr (auxin) in comparison to the already established test organism water milfoil Myriophyllum spicatum and the duckweed species Landoltia punctata. Five concentrations without replicates were tested for each test substance using 10 microcosms and three microcosms served as controls. The experiment was run for 8 weeks. Morphological endpoints were used to determine growth and EC50 values. The results show that M. spicatum was most sensitive to fluroxypyr (37 days EC50 for roots: 62 µg/L) and G. maxima most sensitive to clodinafop-propargyl (22 days EC50 for total shoot length: 48 µg/L) whereas the duckweed species was considerable less sensitive. Hence, G. maxima turns out to be a good candidate for testing grass specific herbicides, supporting its inclusion as an additional macrophyte test for the risk assessment of herbicides as proposed by the EFSA.

Uptake, translocation, and elimination in sediment-rooted macrophytes: a model-supported analysis of whole sediment test data

Understanding bioaccumulation in sediment-rooted macrophytes is crucial for the development of sediment toxicity tests using macrophytes. Here, we explore bioaccumulation in sediment-rooted macrophytes by tracking and modeling chemical flows of chlorpyrifos, linuron, and six PCBs in water-sediment-macrophyte systems. Chemical fluxes across the interfaces between pore water, overlying water, shoots, and roots were modeled using a novel multicompartment model. The modeling yielded the first mass-transfer parameter set reported for bioaccumulation by sediment-rooted macrophytes, with satisfactory narrow confidence limits for more than half of the estimated parameters. Exposure via the water column led to rapid uptake by Elodea canadensis and Myriophyllum spicatum shoots, followed by transport to the roots within 1-3 days, after which tissue concentrations gradually declined. Translocation played an important role in the exchange between shoots and roots. Exposure via spiked sediment led to gradual uptake by the roots, but subsequent transport to the shoots and overlying water remained limited for the chemicals studied. These contrasting patterns show that exposure is sensitive to test set up, chemical properties, and species traits. Although field-concentrations in water and sediment will differ from those in the tests, the model parameters can be assumed applicable for modeling exposure to macrophytes in the field.

Root length of aquatic plant, Lemna minor L., as an optimal toxicity endpoint for biomonitoring of mining effluents

Lemna minor, a free-floating macrophyte, is used for biomonitoring of mine effluent quality under the Metal Mining Effluent Regulations (MMER) of the Environmental Effects Monitoring (EEM) program in Canada and is known to be sensitive to trace metals commonly discharged in mine effluents such as Ni. Environment Canada's standard toxicity testing protocol recommends frond count (FC) and dry weight (DW) as the 2 required toxicity endpoints-this is similar to other major protocols such as those by the US Environmental Protection Agency (USEPA) and the Organisation for Economic Co-operation and Development (OECD)-that both require frond growth or biomass endpoints. However, we suggest that similar to terrestrial plants, average root length (RL) of aquatic plants will be an optimal and relevant endpoint. As expected, results demonstrate that RL is the ideal endpoint based on the 3 criteria: accuracy (i.e., toxicological sensitivity to contaminant), precision (i.e., lowest variance), and ecological relevance (metal mining effluents). Roots are known to play a major role in nutrient uptake in conditions of low nutrient conditions-thus having ecological relevance to freshwater from mining regions. Root length was the most sensitive and precise endpoint in this study where water chemistry varied greatly (pH and varying concentrations of Ca, Mg, Na, K, dissolved organic carbon, and an anthropogenic organic contaminant, sodium isopropyl xanthates) to match mining effluent ranges. Although frond count was a close second, dry weight proved to be an unreliable endpoint. We conclude that toxicity testing for the floating macrophyte should require average RL measurement as a primary endpoint.

Effects of light and temperature fluctuations on the growth of Myriophyllum spicatum in toxicity tests--a model-based analysis

Laboratory toxicity tests are a key component of the aquatic risk assessments of chemicals. Toxicity tests with Myriophyllum spicatum are conducted based on working procedures that provide detailed instructions on how to set up the experiment, e.g., which experimental design is necessary to get reproducible and thus comparable results. Approved working procedures are established by analyzing numerous toxicity tests to find a compromise between practical reasons (e.g., acceptable ranges of ambient conditions as they cannot be kept completely constant) and the ability for detecting growth alterations. However, the benefit of each step of a working procedure, e.g., the random repositioning of test beakers, cannot be exactly quantified, although this information might be useful to evaluate working procedures. In this paper, a growth model of M. spicatum was developed and used to assess the impact of temperature and light fluctuations within the standardized setup. It was analyzed how important it is to randomly reassign the location of each plant during laboratory tests to keep differences between the relative growth rates of individual plants low. Moreover, two examples are presented on how modeling can give insight into toxicity testing. Results showed that randomly repositioning of individual plants during an experiment can compensate for fluctuations of light and temperature. A method is presented on how models can be used to improve experimental designs and to quantify their benefits by predicting growth responses.

Effects of toxicants with different modes of action on Myriophyllum spicatum in test systems with varying complexity

At the international workshop Aquatic Macrophyte Risk Assessment for Pesticides (AMRAP), it was noted that the EU risk assessment under the directive 91/414/EEC for herbicides, based only on algae and the monocotyledonous duckweed species Lemna sp., offers no certain protection against some growth regulating auxins. Therefore, AMRAP members proposed the introduction of the dicotyledonous water milfoil Myriophyllum as additional test species. This study was aimed to compare toxicity results from three test systems (TS) with varying complexity, namely Water TS, Sediment TS and Microcosm TS using Myriophyllum spicatum as test organism. As test substances, the photosynthesis inhibiting herbicide isoproturon, the growth regulating auxins fluroxypyr and 2,4-dichlorophenoxyacetic acid (2,4-D), and the non-specific acting toxicant 3,5-dichlorophenol (3,5-DCP) were chosen. It was assessed if and why the sensitivity of M. spicatum towards the four toxicants varied in the different test systems and if the addition of sucrose to the medium used in the Water TS had an effect on the sensitivity of Myriophyllum. All TS were suitable for detecting negative effects of toxicants with different modes of action on M. spicatum. The lowest variability of endpoints was found in the Water TS with lowest experimental complexity. For auxins, the endpoint weight did not result in robust EC50 values in all TS, whereas root related endpoints, which are also ecologically relevant, turned out to be very sensitive with low variance. Sucrose in the medium of the Water TS did not seem to influence the sensitivity of M. spicatum towards isoproturon and 3,5-DCP but may have increased the sensitivity of M. spicatum roots when exposed to 2,4-D. However, the findings of all TS resulted in similar risk estimations if root endpoints were not considered.

The relative sensitivity of macrophyte and algal species to herbicides and fungicides: an analysis using species sensitivity distributions

Lemna spp. are the standard test species representing aquatic macrophytes in the current risk assessment schemes for herbicides and plant growth regulators in the European Union and North America. At a Society of Environmental Toxicology and Chemistry (SETAC) 2008 workshop on Aquatic Macrophyte Risk Assessment for Pesticides (AMRAP), a Species Sensitivity Distribution (SSD) working group was formed to address uncertainties about the sensitivity of Lemna spp. relative to other aquatic macrophyte species. For 11 herbicides and 3 fungicides for which relevant and reliable data were found for at least 6 macrophyte species, SSDs were fitted using lognormal regression. The positions of L. gibba (the most commonly tested Lemna species) and Myriophyllum spicatum (for which standardized test methods are under development) in each SSD were determined where data were available. The sensitivity of standard algal test species required for pesticide registration in the United States under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) relative to the macrophytes in each SSD was also examined (algae were not included in the SSD). L. gibba was among the most sensitive macrophyte species for approximately 50% of the chemicals examined. M. spicatum was among the most sensitive macrophytes for approximately 25% of the chemicals. In most cases, the lowest FIFRA algal species endpoint was lower than the most sensitive macrophyte endpoint. Although no single species consistently represented the most sensitive aquatic plant species, for 12 of 14 chemicals L. gibba and the FIFRA algae included an endpoint near or below the 5th percentile of the macrophyte SSD. For the other compounds, M. spicatum was the most sensitive species of all aquatic plants considered.

Effects of linuron on a rooted aquatic macrophyte in sediment-dosed test systems

Effects of linuron on the sediment-rooted aquatic macrophyte Myriophyllum spicatum L. were studied in sediment-dosed test systems following a proposed guideline with extended test duration. Sediment, pore water, overlying water and macrophyte shoots were sampled weekly for chemical analyses. Linuron was stable in the sediments. Sediment and pore water concentrations were in equilibrium after 48 h. Overlying water concentrations increased over time, but did not reach equilibrium with pore water concentrations and were 100 times lower. Mass balances showed a rapid uptake of linuron by macrophyte roots. Known pathways and the compound's properties support the conclusion that Myriophyllum takes up linuron from pore water directly through the roots. Hence, effects on macrophytes in this type of sediment toxicity test should be expressed in terms of pore water concentrations. Pore water concentration is the most relevant parameter for describing effects on macrophytes.

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.

Can time-weighted average concentrations be used to assess the risks of metsulfuron-methyl to Myriophyllum spicatum under different time-variable exposure regimes?

We tested the effects of the herbicide metsulfuron-methyl on growth of the submerged macrophyte Myriophyllum spicatum under laboratory conditions using different exposure scenarios. The exposures of each scenario were comparable in the concentration × time factor, viz., the same 21-d time-weighted average (TWA) concentrations but variable in peak exposure concentrations (ranging from 0.1 to 21000 ng ai L⁻¹) and exposure periods (1, 3, 7, 14 or 21 d). To study recovery potential of the exposed M. spicatum plants we continued the observation on shoot and root growth for another 21 d in herbicide-free medium so that the total observation period was 42 d. Non-destructive endpoints, length and number of new shoots and roots, were determined weekly from day 14 onwards. Destructive endpoints, dry-weight (DW) of main shoots, new shoots and new roots, were measured at the end of the experiment (t=42 d). Metsulfuron-methyl exposure in particular inhibited new tissue formation but was not lethal to main shoots. On days 21 and 42 after start exposure, EC₁₀/EC₅₀ values for new tissues expressed in terms of peak concentration (=measured concentration during exposure periods of different length) showed large differences between exposure scenarios in contrast to EC₁₀/EC₅₀ values for days 21 and 42 expressed in terms of 21-d and 42-d TWA concentrations, respectively. At the end of the experiment (day 42), 42-d TWA EC(x) values were remarkably similar between exposure scenarios, while a similar trend could already be observed on day 21 for 21-d TWA EC(x) values. For the macrophyte M. spicatum and exposure to the herbicide metsulfuron-methyl the TWA approach seems to be appropriate to use in the risk assessment. However, the data from the toxicity experiment suggest that on day 21 also the absolute height of the pulse exposure played a (minor) role in the exposure - response relationships observed.

Toxic effects of Hydrilla verticillata exposed to toluene, ethylbenzene and xylene and safety assessment for protecting aquatic macrophytes

Little information is available about the toxicity of toluene, ethylbenzene and xylene acting on macrophytes, and their toxicity data are rarely used in regulation and criteria decisions. The results extended the knowledge on toxic effects of toluene, ethylbenzene and xylene on aquatic plants. The responses of Hydrilla verticillata to these pollutants were investigated. Chlorophyll levels, lipid peroxidation, and antioxidant enzymes (superoxide dismutase and guaiacol peroxidase) showed diverse responses at different concentrations of toluene, ethylbenzene and xylene. The linear regression analyses were performed respectively, suggesting the concentrations of toluene, ethylbenzene and xylene expected to protect aquatic macrophytes were 7.30 mg L⁻¹, 1.15 mg L⁻¹ and 2.36 mg L⁻¹, respectively. This study emphasized that aquatic plants are also sensitive to organic pollutants as fishes and zooplanktons, indicating that macrophytes could be helpful in predicting the toxicity of these pollutants and should be considered in regulation and criteria decisions for aquatic environment protection.

Toxicity of phenanthrene in freshwater sediments to the rooted submersed macrophyte, Vallisneria spiralis

A study was conducted to determine the response of the rooted submersed macrophyte, Vallisneria spiralis to phenanthrene in freshwater sediments with initial phenanthrene concentrations from 0 to 80 mg kg(-1) dry sediment. The sensitivity of various morphological endpoints was evaluated after 90 days of exposure. The most sensitive toxicity test endpoints were those that reflected root growth. Toxicological sensitivity of the endpoints changed with the effect level selected. The toxicity threshold from a plot of the EC(10) values was 1-2 orders of magnitude lower than those calculated for the threshold from plots of the EC(25) or EC(50) values. In addition, stimulatory responses (hormesis) on root growth were observed at subtoxic concentrations of phenanthrene, and a hormetic model should thus be incorporated for ecological risk assessment.

Copper uptake and translocation in a submerged aquatic plant Hydrilla verticillata (L.f.) Royle

A comprehensive understanding of the uptake, tolerance and transport of heavy metals in the wetland system through aquatic plants will be essential for the development of phytoremediation technologies. Copper accumulation and translocation of a submersed macrophyte Hydrilla verticillata (L.f.) Royle were investigated. Plant shoots showed a significant accumulation of Cu with a maximum of 30830 mg Cu kg⁻¹ dry weight after exposed to 4000 μg L⁻¹ Cu for 4d. Both roots and shoots can directly take up Cu from solution and Cu mainly accumulated in cell wall fractions. Moreover, H. verticillata predominantly accumulated Cu through shoots from the aqueous solutions because of the higher weights and bioaccumulation factors of shoots than those of roots. Acropetal translocation of Cu in the plant is higher than the basipetal translocation, which implies that upward translocation of Cu is mainly via the xylem and downward translocation is mainly through the phloem. These findings contribute to the application of submerged aquatic plants to copper removal from moderately contaminated waters.

Accumulation of metals in Elodea canadensis and Elodea nuttallii: implications for plant-macroinvertebrate interactions

Elodea nuttallii and Elodea canadensis are considered good candidates for metal studies. Metal pollution can disturb the interactions between trophic levels. Our goals were 1) to analyse the metal content in plants, sediment and water from three polluted sites, and 2) to analyse the impact of metal contamination on plant consumption by macroinvertebrates. The concentrations of Cd, Cr, Cu, Mn, Ni, Pb, Zn and Fe and S were measured in water, sediment and in the two Elodea species during two years. Our results showed that metal accumulation varied according to site, metal and season. The ability to uptake metal was similar in E. canadensis and in E. nuttallii. No significant seasonal metal accumulation was established for plants or sediment. Metal accumulation in Elodea species in polluted sites had no impact on their palatability. The plant palatability depends on the season and varies according to the part of the plant. In autumn, apex was less consumed than defoliated and foliated stems.

The species sensitivity distribution approach compared to a microcosm study: a case study with the fungicide fluazinam

We assessed the sensitivity of freshwater organisms (invertebrates and algae) to the fungicide Shirlan (active ingredient fluazinam) in single-species laboratory tests and in microcosms. Species sensitivity distribution (SSD) curves were constructed by means of acute toxicity data for 14 invertebrate species, since algae were much less sensitive. The EC(10)-based SSD gave a median HC(5) value of 0.6microgL(-1) and a 90% confidence interval of 0.1-1.9 microgL(-1). The EC(50)-based SSD gave a median HC(5) value of 3.9 microgL(-1) (90% confidence interval: 0.9-9.9 microgL(-1)). The microcosms were treated four times with Shirlan (concentration range: 0.4-250 microgL(-1)). Responses of the microcosm communities were followed. The 2 microgL(-1) treatment was the no-observed-effect concentration (NOEC(microcosm)). The 10 microgL(-1) treatment resulted in short-term effects on a few zooplankton taxa. Clear effects were observed at 50 and 250 microgL(-1). The responses in the microcosms were in line with the toxicity data for the tested lab species. The median EC(10)-based HC(5) and the lower limit EC(50)-based HC(5) were lower, and the median EC(50)-based HC(5) was slightly higher than the NOEC(microcosm). This is consistent with other studies that compared SSDs with responses in model ecosystems that received repeated applications of pesticides.

A microcosm system to evaluate the toxicity of the triazine herbicide simazine on aquatic macrophytes

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.

Phytotoxicity of atrazine, isoproturon, and diuron to submersed macrophytes in outdoor mesocosms

The submersed macrophytes Elodea canadensis, Myriophyllum spicatum and Potamogeton lucens were constantly exposed over a five-week period to environmentally relevant concentrations of atrazine, isoproturon, diuron, and their mixture in outdoor mesocosms. Effects were evaluated investigating photosynthetic efficiency (PE) of the three macrophytes and growth of M. spicatum and E. canadensis. Adverse effects on PE were observed on days 2 and 5 after application. M. spicatum was found to be the more sensitive macrophyte. E. canadensis and P. lucens were less sensitive to atrazine, diuron and the mixture and insensitive to isoproturon. PE of M. spicatum was similarly affected by the single herbicides and the mixture demonstrating concentration addition. Growth of E. canadensis and M. spicatum was not reduced indicating that herbicide exposure did not impair plant development. Although PE measurements turned out to be a sensitive method to monitor PSII herbicides, plant growth remains the more relevant ecological endpoint in risk assessment.

Toxic and accumulative potential of the antifouling biocide and TBT successor irgarol on freshwater macrophytes: a pond mesocosm study

After the ban of tributyltin (TBT) for vessels not longer than 25 m in 1986, Irgarol has become a commonly used antifouling biocide. Irgarol is highly toxic to autotrophic organisms and has the potential to accumulate in organic material. In the literature, environmental concentrations of Irgarol up to 2.4 microg L(-1) were reported forfreshwater. Within a comprehensive freshwater mesocosm study, experiments were conducted to gain more information on the effects of Irgarol on macrophytes. Six indoor pond mesocosms were contaminated once with concentrations between 0.04 and 5 microgl(-1) Irgarol and monitored for 150 days; two mesocosms served as controls. The mesocosm study revealed that all macrophytes were directly affected by this single application. Myriophyllum verticillatum was the most sensitive macrophyte with an EC50 (Day 150) of 0.21 microg L(-1) Irgarol. The duckweed Spirodela polyrhiza was the least sensitive species tested in the mesocosms and number of fronds even increased with increasing Irgarol concentrations. Time-weighted average calculations yielded high BCF values of up to 10,580 L kg(-1) dry weight for M. verticillatum indicating a high potential for accumulation. The results give cause for concern that natural macrophyte communities are impaired at actual environmental concentrations.

Acute exposure of the aquatic macrophyte Callitriche obtusangula to the herbicide oxadiazon: the protective role of N-acetylcysteine

In this study we investigated the acute exposure of the aquatic macrophyte Callitriche obtusangula to the herbicide oxadiazon (Ronstar). The toxic effects on C. obtusangula were evaluated, 24h after exposure, by assessing visible necrotic leaf lesions and, 12 h after exposure, via analyses of dead cells and hydrogen peroxide (H2O2) deposits localized by histocytochemical analysis with Trypan blue and 3,3'-diaminobenzidine (DAB), respectively. As a result, we found that 0.1275 microg L(-1) a.i. (active ingredient) oxadiazon was the maximum concentration that produced no observable adverse effects (NOAEC) both at leaf and tissue levels, at any considered exposure time. Additionally, we assayed the protective effect of pre-treatment with 0.25 mM N-acetylcysteine (NAC), a cysteine donor, on the damage caused by the toxic herbicidal dose of 6.37 microg L(-1) a.i to C. obtusangula, correlating the NAC observed protection to the direct H2O2-scavenging and to the enhancement of glutathione parameters. NAC-treated plants showed a fourfold increase in the GSH (reduced glutathione)+GSSG (oxidised glutathione) content (149.2 nmol g(-1) FW) compared to controls (36.1 nmol g(-1) FW); in the NAC+oxadiazon treatments, the GSH+GSSG content was more than fivefold higher (202.1 nmol g(-1) FW). GSH showed a similar trend in NAC and NAC+oxadiazon treatments, being six- (130.0 nmol g(-1) FW) and eightfold (185.0 nmol g(-1) FW) higher, respectively, compared to controls (20.7 nmol g(-1) FW). Accordingly, the GSH/GSSG ratio in NAC- and NAC+oxadiazon-treated plants was significantly increased compared to controls, indicating alleviation of oxidative stress.

Effects of four fungicides on nine non-target submersed macrophytes

We tested the sensitivity of nine submersed macrophyte species to the fungicides chlorothalonil, pentachlorophenol, fluazinam, and carbendazim. Endpoints determined 3 weeks after the start of the treatment were based on shoot and root growth in water. Carbendazim proved not or only moderately toxic to these macrophytes. Pentachlorophenol and chlorothalonil were more toxic than fluazinam. Taking all endpoints into consideration, toxicity levels differed very substantially. Although root endpoints reflecting root growth were in some cases more sensitive than shoot endpoints, shoot growth endpoints like relative growth turned out to be more reliable than the root growth endpoints. Due to the large differences in the type of mode of action between fungicides, it is very difficult to predict their potential effect in the environment or even to predict whether non-target organisms like macrophytes are likely to be sensitive. Ideally, therefore, the registration of fungicides requires an extensive risk-assessment procedure, which also covers non-target groups like macrophytes.

Comparing growth development of Myriophyllum spp. in laboratory and field experiments for ecotoxicological testing

BACKGROUND, GOALS AND SCOPE: Risk assessment of herbicides and the evaluation of contaminated sediments based on algae and the macrophyte Lemna sp. alone may underestimate the potential hazard of certain compounds. Therefore, various test systems with Myriophyllum spp. have been developed recently to assess the phytotoxicity in surface waters and natural sediments. In the present study, experiments investigating the growth development of Myriophyllum spp. were performed in the laboratory under defined conditions and in mesocosms under environmentally realistic exposure conditions to evaluate the suitability of these species as potential standard test organisms in ecotoxicological testing. This study provides data on the endpoints biomass, plant length and root development.

MATERIALS AND METHODS

Six independent experiments were performed to investigate the plant development of Myriophyllum spp. under control conditions. The main difference in the experiments was the complexity of the test systems ranging from simple laboratory experiments to complex outdoor mesocosm studies. At the start of each experiment, uniform cuttings of Myriophyllum spp. were placed in vessels with or without sediments to reduce variability between replicates. The endpoints considered in this investigation were biomass (fresh weight of the whole plant), length of the main shoot, length of the side shoots, total length of the plant (calculated from the length of the main and side shoots) and root formation. Root to shoot ratios were calculated as a further measure for plant development. Relative growth rates (RGR) based on plant length (RG(L)R) and on biomass (RG(B)R) were calculated.

RESULTS

Despite the various experimental conditions, comparable growth was obtained in all test systems and the variability of endpoints, such as total length and biomass of plants, was low. It was observed that the RGR of M. spicatum in the simple laboratory test system with sediment were comparable to growth data obtained for M. verticillatum and M. spicatum grown in indoor and outdoor mesocosms, thus indicating that Myriophyllum growth tends to increase by the addition of sediment. High variability was determined for the endpoints length of the side shoots, total root length and biomass of roots.

DISCUSSION

One challenge for a test design to investigate phytotoxicity on aquatic plants is to obtain good growth of the plants. From the results, it can be concluded that the experimental conditions in the various test systems were suitable to study the plant development of Myriophyllum spp. because obtained growth rates were comparable between laboratory and field investigations. Another challenge for developing a plant biotest system is the definition of sensitive endpoints. Low variability is preferred to detect minor effects of chemicals or polluted sediments on plant development. In our studies, the variability of the endpoints biomass and total length of plant was low and, therefore, they have much potential as endpoints for assessing toxicity.

CONCLUSIONS

The methodologies presented in this study have applications within the risk assessment for aquatic plants and have the advantage of assessing effects taking into account the relevant exposure pathways via water and/or sediment for compounds under investigation.

RECOMMENDATIONS AND PERSPECTIVES

Setting safe quality criteria for surface water and sediments is one of the challenges authorities are facing today. Myriophyllum spp. is recommended as suitable test species to investigate phytotoxicity in surface water and sediments. These results, thus, might serve as a basis for the compilation of a new harmonised guideline for ecotoxicological testing with aquatic macrophytes.