Phytotoxic activity of crop residues from Burdock and an active substance

Abstract

Problems related to weed management such as outbreaks of herbicide-resistant weeds have recently increased. An interesting approach to such problems is to use plant materials with phytotoxic activity. Burdock (Arctium lappa L.) is a biennial herb belonging to Asteraceae and is cultivated in several countries. The present study investigated the phytotoxic activity of burdock and its active substances. Extracts of both burdock leaves and roots inhibited the shoot and root growth of cress and barnyard grass, where the level of inhibition increased with increasing extract concentration. The leaf extracts had 2.0–2.5 times higher activity than the root extracts. Bioassay-guided separations of the leaf extracts led to isolation of a phytotoxic substance, onopordopicrin. Onopordopicrin significantly inhibited the shoot and root growth of cress and barnyard grass. The concentrations of the substance required for 50% growth inhibition were 0.27 and 0.26?mM for cress shoots and roots, respectively, and 1.86 and 0.35?mM for barnyard grass shoots and roots, respectively. The present results suggest that burdock leaves have high phytotoxic activity and onopordopicrin may play a major role in the activity. Burdock leaves may be a good resource for weed management.     

Nematicidal activity of terpenoids

Thirty four phytoterpenoids were evaluated for their nematicidal effect using the model nematode Caenorhabditis elegans. Nematicidal activities of the tested compounds at concentrations of 50 μg/mL showed wide variation in their effects ranging from no effect, weak, moderate and strong effects. Terpenoids exerting 50% or higher mortality at 50 μg/mL were further tested at five different concentrations to calculate the concentration that will kill 50% of the nematode population (LC₅₀). Among the most effective terpenoids were carvacrol, thymol, nerolidol, α-terpinene, geraniol, citronellol, farnesol, limonene, pseudoionone and eugenol in a descending order. These compounds exhibited a dose-dependent effect. The results suggest that the selected monoterpenoids and essential oils with a high concentration of these compounds mayprovide potential natural nematicides and merit further study as botanical nematicides for the control of both plant and animal parasitic nematodes. In general, oxygenated terpenoids and phenolic terpenoids exhibited higher nematicidal activity than hydrocarbons terpenoids.     

In vitro toxicity of fungicides with different modes of action to alfalfa anthracnose fungus,Colletotrichum destructivum

Abstract

Sensitivity of 24 isolates of Colletotrichum destructivum O’Gara, collected from alfalfa plants in Serbia, to eight selected fungicides, was investigated in this study. Molecular identification and pathogenicity test of isolates tested were also performed. Fungicide sensitivity was evaluated in vitro, using mycelial growth assay method. All isolates exhibited significant pathogenicity, causing necrosis at the alfalfa seedling root tips two days after inoculation. Using the primer pair GSF1-SR1 and by comparing the amplified fragments of the tested isolates with the marker (M), the presence of the amplicon of the expected size of about 900?bp was determined for all isolates. The isolates tested in this study showed different sensitivity towards fungicides in vitro. Mycelial growth was highly inhibited by QoI (quinone outside inhibitors) fungicide pyraclostrobin (mean EC₅₀=0.39?µg mL^?1) and by DMI (demethylation-inhibiting) fungicide tebuconazole (mean EC₅₀=0.61?µg mL^?1), followed by azoxystrobin (mean EC₅₀=2.83?µg mL^?1) and flutriafol (mean EC₅₀=2.11?µg mL^?1). Multi-site fungicide chlorothalonil and MBC (methyl benzimidazole carbamate) fungicide thiophanate-methyl evinced moderate inhibition with mean EC₅₀=35.31 and 62.83?µg mL^?1, respectively. Thirteen isolates were sensitive to SDHI (succinate dehydrogenase inhibitors) fungicide boscalid and fluxapyroxad, (mean EC₅₀=0.49 and 0.19?µg mL^?1, respectively), while the rest of isolates were highly resistant.     

Bioassay for Determining Sensitivity to Sulfosulfuron on Seven Plant Species

This study presents a bioassay procedure, based on the root and shoot growth parameters, for the determination of the herbicide sulfosulfuron (1-(4,6 dimethoxypyrimidin-2-yl)-3-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonil)urea) sensitivity on seven vegetal species. Plant response to sulfosulfuron was calculated with the equations fitted to the root growth data as a function of the logarithm of the herbicide concentration by non-linear regression and was used to calculate the doses for 10, 30 and 50% inhibition of root growth (EC₁₀, EC₃₀ and EC₅₀). The results indicate that the phytotoxic effect of sulfosulfuron in all the species assayed followed the order: flax > maize > onion > vetch > lepidium sativum > tomato > barley. These species showed phytotoxicity at low levels of sulfosulfuron and flax appeared to be the most susceptible species to sulfosulfuron (0.001 mg/L).     

Mixture Toxicity of the Antifouling Compound Irgarol to the Marine Phytoplankton Species Dunaliella tertiolecta

This study examined the toxicity of irgarol, individually and in binary mixtures with three other pesticides (the fungicide chlorothalonil, and the herbicides atrazine and 2,4-D), to the marine phytoplankton species Dunaliella tertiolecta. Standard 96-h static algal bioassays were used to determine pesticide effects on population growth rate. Irgarol significantly inhibited D. tertiolecta growth rate at concentrations ≥ 0.27 μ g/L. Irgarol was significantly more toxic to D. tertiolecta than the other pesticides tested (irgarol 96 h EC₅₀ = 0.7 μ g/L; chlorothalonil 96 h EC₅₀ = 64 μ g/L; atrazine 96 h EC₅₀ = 69 μ g/L; 2,4-D 96 h EC₅₀ = 45,000 μ g/L). Irgarol in mixture with chlorothalonil exhibited synergistic toxicity to D. tertiolecta, with the mixture being approximately 1.5 times more toxic than the individual compounds. Irgarol and atrazine, both triazine herbicides, were additive in mixture. The toxicity threshold of 2,4-D was much greater than typical environmental levels and would not be expected to influence irgarol toxicity. Based on these interactions, overlap of certain pesticide applications in the coastal zone may increase the toxicological risk to resident phytoplankton populations.     

Chemoreception of botanical nematicides by Meloidogyne incognita and Caenorhabditis elegans

Plant-parasitic nematodes, such as Meloidogyne incognita, cause serious damage to various agricultural crops worldwide, and their control necessitates environmentally safe measures. We have studied the effects of plant secondary metabolites on M. incognita locomotion, as it is an important factor affecting host inoculation inside the soil. We compared the effects to the respective behavioral responses of the model saprophytic nematode Caenorhabditis elegans. The tested botanical nematicides, all reported to be active against Meloidogyne sp. in our previous works, are small molecular weight molecules (acids, alcohols, aldehydes, and ketones). Here, we specifically report on the attractant or repellent properties of trans-anethole, (E,E)-2,4-decadienal, (E)-2-decenal, fosthiazate, and 2-undecanone. The treatments for both nematode species were made at sublethal concentration levels, namely, 1 mM (<EC₅₀), and the chemical controls used for the experiments were the commercial nematicides fosthiazate and oxamyl. According to our results, trans-anethole, decenal, and oxamyl attract C. elegans, while 2-undecanone strongly attracts M. incognita. These findings can be of use in the development of nematicidal formulations, contributing to the disruption of nematode chemotaxis to root systems.     

IMPACT OF FOUR PESTICIDES ON THE GROWTH AND METABOLIC ACTIVITIES OF TWO PHOTOSYNTHETIC ALGAE

The acute toxicity was determined for soil algae Chlorella kesslerei and Anabaena inaequalis, exposed to pesticides lindane, pentachlorophenol (PCP), isoproturon (IPU), and methyl parathion (MP). Toxicity markers included growth inhibition, chlorophyll biosynthesis, and total carbohydrate content, as a function of dose and time. Concentration response functions (EC₅₀) were estimated by probit data transformation and weighted linear regression analyses. Lindane's toxicity to Chlorella increased sharply with time (EC₅₀=7490, 10.3, 0.09 mg L^?1; 24, 48, 72 h), but remained nearly constant through 72 h with Anabaena (8.7?6.7 mg L^?1; 24–72 h). PCP at low concentrations stimulated algal growth and chlorophyll a production, an effect reversed at higher doses. Anabaena was less tolerant of PCP and MP than was Chlorella. The 96-h static EC₅₀ values for Chlorella were: 0.003, 34, 0.05, and 291 mg L^?1 for lindane, PCP, isoproturon, and MP, respectively; for Anabaena, these were 4.2, 0.13, 0.21, and 19 mg L^?1. Carbohydrate production responses were similar to those of cell density (growth) and chlorophyll biosynthesis, with MP having the lowest adverse impact. The overall relative toxicity among the four tested pesticides was: for Chlorella, lindane>IPU?PCP?MP; and for Anabaena, PCP>IPU>lindane>MP. The results confirm that toxicants such as these pesticides may affect individual (though related) species to significantly different degrees.     

QSPR for prediction of subcooled vapor pressures (log PL) of polychlorinated trans-azobenzenes

In this study the values of subcooled vapor pressures (log P_L) were estimated for 209 trans chloroazobenzenes (Ct-ABs) that fill some gaps in analytical and experimental data on these compounds. There are 209 chloro derivatives of trans azobenzenes that are relatively stable and more environmentally relevant than 209 chloro cis congeners. The calculations models were based on the Quantitative Structure-Property Relationship (QSPR) scheme using the semi-empirical method (PM6) in molecular package (MOPAC) software and density functional theory (DFT) method using B3LYP functional and 6-311++G** basis set) in Gaussian 03 software method and the artificial neural networks (ANNs) prediction. The values of log P_L predicted by models used varied between ?3.94 to ?2.66 for Mono-; ?4.85 to ?2.97 for Di-; ?5.18 to ?3.17 for Tri-; ?6.02 to ?3.77 for Tetra-; ?6.64 to ?4.64 for Penta-; ?7.36 to ?4.76 for Hexa-; ?7.54 to ?5.79 for Hepta-; ?7.75 to ?6.64 for Octa-; ?7.89 to ?7.44 for Nona-Ct-Abs; and ?8.09 and ?8.13 for Deca-Ct-AB. Based on these values Ct-ABs can be grouped localized among relatively low (log P_L ?4 to ?2) and low (log P_L < ?4) mobile Persistent Organic Pollutants (POPs). Both the calculation methods employed were characterized by similar prediction ability of subcooled vapor pressure values of Ct-ABs, while those of PM6 are much more efficient due to a cheaper hardware used and around 300-fold less time spent on calculations.     

Phytotoxicity and antioxidative enzymes of green microalga (Desmodesmus subspicatus) and duckweed (Lemna minor) exposed to herbicides MCPA,chloridazon and their mixtures

In this study, we evaluate the toxicity of MCPA (auxin-like growth inhibitor), chloridazon (CHD) (PSII-inhibitor) and their mixtures to floating plants and planktonic algae. Toxicity of MCPA (4-chloro-2-methylphenoxyacetic acid) and CHD (5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone) was first assessed in two growth inhibition tests with Lemna minor (ISO/DIS 20079) and Desmodesmus subspicatus (ISO 8692). Next, herbicide mixtures at concentrations corresponding to the EC values were used to assess their interactive effects, and the biomarkers were: for duckweed fresh weight, frond area, chlorophyll content and number of fronds, and for algae cell count and cell volume. The 3d EC₁₀ and EC₅₀ values using cell counts of D. subspicatus were 142.7 and 529.1 mg/L for MCPA and 1.7 and 5.1 mg/L for CHD. The 7d EC₁₀ and EC₅₀ values using frond number of L. minor amounted to 0.8 and 5.4 mg/L for MCPA and 0.7 and 10.4 mg/L for CHD. Higher sensitivity of reproductive (number of cells/fronds) than growth processes (cell volume/frond area) to herbicides applied individually and in mixtures was especially pronounced in the responses of Desmodesmus. Herbicide interactions were assessed by the two-way ANOVA and Abbott's formula. Generally, an antagonistic interaction with Lemna was revealed by MCPA and chloridazon, whereas additive effect of both herbicides was observed for Desmodesmus. A significant stimulation of SOD and APX activity by binary mixtures was noted in algal cells mainly after 24 and 48 hours of exposure. The extremely high stimulation of the activity of both enzymes was induced by the combination EC₁₀CHD + EC₅₀MCPA (48 h). Presumably due to oxidative stress, the treatment with CHD at concentration EC₅₀ after 72h was lethal for algae grown in aerated cultures, in contrast to standardized test conditions. Taking into account the consequences of risk assessment for herbicide mixtures we can state that a relatively low toxicity, as well as the lack of significant synergy between MCPA and CHD to non-target plants appears to be the most important result.     

Comparative effect of thymol or its glucose conjugate,thymol-β-d-glucopyranoside,on Campylobacter in avian gut contents

Campylobacter jejuni is an important human food-borne pathogen that can contaminate meat and poultry during processing. Consequently, strategies are sought to reduce the carriage of C. jejuni in food animals before they arrive at the abattoir. Thymol is a natural product that reduces survivability of Campylobacter in vitro, but its rapid absorption from the proximal alimentary tract limits its bactericidal efficacy in vivo. Thymol-β-d-glucopyranoside is more resistant to absorption than free thymol, but its administration to chickens has not been reported. In the present studies, 1 mM thymol-β-d-glucopyranoside was shown to exhibit near equal anti-Campylobacter activity as 1 mM thymol when incubated anaerobically in avian crop or cecal contents in vitro, resulting in reductions of 1.10–2.32 log₁₀ colony forming units mL^?1 in C. jejuni concentrations after 24 h incubation. In a follow-up live animal study, oral administration of thymol-β-d-glucopyranoside, but not free thymol, significantly lowered (>10-fold) recovery of Campylobacter from the crop of market-aged broilers when compared to placebo-treated controls (n = 6 broilers/treatment). Neither thymol-β-d-glucopyranoside nor thymol affected recovery of Campylobacter from cecal contents of the treated broilers. These results indicate that rapid absorption or passage of free thymol from the crop precluded its anti-Campylobacter activity at this site and throughout the entire gastrointestinal tract. Conversely, lower recovery of Campylobacter from the crop of birds treated with thymol-β-d-glucopyranoside indicates this conjugate was retained and able to be hydrolyzed to biologically active free thymol at this site as intended, yet was not sufficiently protected to allow passage of efficacious amounts of the intact glycoside to the lower gut. Nevertheless, these results warrant further research to see if higher doses or encapsulation of thymol-β-d-glucopyranoside or similar glycosides may yield an efficacious additive to reduce carriage of Campylobacter as well as other pathogens throughout the avian gut.     

Assessing the toxicity of organophosphorous pesticides to indigenous algae with implication for their ecotoxicological impact to aquatic ecosystems

This study aimed to determine the toxicity of three organophosphorous pesticides, chlorpyrifos, terbufos and methamidophos, to three indigenous algal species isolated from local rivers and algal mixtures. The diatom Nitzschia sp. (0.30–1.68 mg L^?1 of EC₅₀ -the estimated concentration related to a 50% growth reduction) and the cyanobacteria Oscillatoria sp. (EC₅₀ of 0.33–7.99 mg L^?1) were sensitive to single pesticide treatment and the chlorophyta Chlorella sp. was the most tolerant (EC₅₀ of 1.29–41.16 mg L^?1). In treatment with the mixture of three pesticides, Chlorella sp. became the most sensitive alga. The antagonistic joint toxic effects on three indigenous algae and algal mixtures were found for most of the two pesticide mixtures. The results suggested that mixture of pesticides might induce the detoxification mechanisms more easily than the single pesticide. The synergistic interactions between terbufos and methamidophos to algal mixtures and between methamidophos and chlorpyrifos to Nitzschia sp. indicated methamidophos might act as a potential synergist. Differential sensitivity of three families of algae to these pesticides might result in changes in the algal community structures after river water has been contaminated with different pesticides, posing great ecological risk on the structure and functioning of the aquatic ecosystem.     

Application of various methods to determine the lipophilicity parameters of the selected urea pesticides as predictors of their bioaccumulation

Different lipophilicity procedures including a newly developed (based on O?cik's equation) was applied in order to compare various urea pesticides with herbicidal and also insecticidal activity, such as monolinuron, chlorotoluron, diuron, isoproturon, linuron, dimefuron, diflubenzuron, teflubenzuron and lufenuron. Lipophilicity parameters (R_MWS and R_MW0) of nine examined pesticides were determined on the chromatographic plates RP-8F₂₅₄ with the use of methanol–water as a mobile phase_. Similarity analysis enabled to group all examined pesticides depending on their lipophilic character and allowed to perform a more objective comparison of different lipophilicity parameters obtained for investigated compounds by means of thin-layer chromatography and by the use of computational methods. It was stated that with the number of fluorine in examined pesticides, the lipophilic character of insecticides and also their tendency to bioaccumulation in the living systems increases noticeably. The results of this work confirmed that a new procedure for determining the lipophilicity parameter (R_MW0) by O?cik's equation could be a suitable tool in the prediction of pesticide bioaccumulation in living system and may be used as an indicator in design of new urea pesticides, which will be safe for humans and the environment.     

Design and development of novel insect growth regulators: Synthesis,characterization and effect of benzoyl thymyl thioureas and ureas on total haemocyte count of Dysdercus koenigii

Insect-growth regulators (IGRs) have been receiving foremost attention as potential means of selective insect control. Benzoyl phenyl urea (BPU) is a well-known IGR having chitin synthesis inhibitor activity. Mimics of BPU have been synthesized by suitable derivatization of a naturally occurring monoterpenoid, thymol (2-isopropyl-5-methyl phenol) to form a = series of substituted benzoyl thymyl thioureas (BTTUs) [IVa-f] and benzoyl thymyl ureas (BTUs) [Va-f]. The synthesized compounds have been characterized by ¹H and ¹³C NMR, LC-MS and elemental analysis. These derivatives have been screened for their effect on total haemocyte count of Dysdercus koenigii. It has been observed that the introduction of substituted benzoyl thiourea and urea linkage into a thymol ring via an amino group results in higher activity than the parent compound thymol and a comparable pattern of results with the standard insect-growth regulators, Penfluron. Urea [Va-f] compounds exhibited greater effect on Total Haemocyte Count (THC) than thiourea [IVa-f]. Fluoro substitution enhanced the effect on THC more than chloro substituted compounds, while ortho-substitution resulted in a better effect than para-substitution. The results described in this paper are promising and provide new array of synthetic chemicals that may be utilized as insect growth regulators.     

Time-dependent degradation and toxicity of diclofop-methyl in algal suspensions

Background, aim, and scope  As emerging contaminants, transformation products of the pollutants via various environmental processes are rather unknown, and some may predominately contribute to the environmental risks of the parent compounds. Hence, studies on transformation products complement the assessment of the environmental safety of the parent compounds. In this study, degradation experiments and toxicity tests using diclofop-methyl (DM), a widely used herbicide, and selected major transformation products were carried out in algal cultures to assess the time course of DM toxicity and its relevance in the formation of new breakdown products. Methods  The alga Chlorella vulgaris was maintained in the algal growth medium HB IV. The inhibition of algal growth was determined by measuring optical density at 680 nm (OD₆₈₀). Initially, DM and two selected breakdown products were added to the algal cultures, and following degradation experiments analyses were carried out by high performance liquid chromatography. In addition, the possible relationship between DM degradation and toxicity was assessed, based on physico-chemical properties of the compounds and their toxicity. Results  DM was rapidly absorbed onto the surface of the algal cells where it was hydrolyzed to diclofop (DC). Further degradation to 4-(2, 4-dichlorophenoxy) phenol (DP) occurred in the cells. However, only a minor amount of DC was degraded to DP under the same conditions when DC was initially added to the algal culture. When C. vulgaris was exposed to these compounds for 96 h, the determined EC₅₀ showed that DC was about ten times less toxic than DM (EC₅₀ = 0.42 mg/L) and that DP (EC₅₀ = 0.20 mg/L) was the most toxic. Discussion  Due to strong hydrophobicity and rare dissociation, DM has tendency toward absorption as compared to DC. The higher average degradation rates of DC initially treated by DM revealed the damage of the cell membranes caused by the DM and, thus, enhanced movement of DC into the cells. Following occurrence of phenolic breakdown products, DP suggested that DC should be intracellularly degraded to DP, which had a more potent mode of action and a higher acute toxicity. Moreover, the results for EC₅₀ at various intervals were in accordance with degradation processes of the initial compounds, in which rapid formation of DP was attributed to an increasing toxicity of DM. Conclusions  The toxicity of DM in algal suspensions increased with time due to its degradation to DP, which contributed significantly to the determined toxicity. These results indicate that the toxicity of the pesticide probably depends significantly on degradation. It is thus important to consider the time-dependent environmental processes when evaluating the toxicological effects of pesticides for proper risk assessment. Recommendations and perspectives  Increasing transformation products of these contaminants are identified in the environment, although they seem to be unknown in terms of the lacking studies on environmental behavior and ecotoxicity concerning them. Certain breakdown products probably greatly contribute to the apparent toxicity of the parent compounds, which is ascribed to the parent compounds in general studies ignoring the dependence of their toxicity on various transformation pathways. These studies that identify new intermediates and assess their toxicity via the environmental processes will be helpful to distinguish the nature of toxicity of the parent contaminants.     

Effects of methanol, ethanol and n-propanol on development of Artemia salina cysts

The current study proposes an ecotoxicological test that makes use of Artemia salina cyst; the results obtained made it possible to calculate the percentage of cyst mortality (no sign of development), and growth inhibition (a delay in normal development), as well as the percentage of larva malformation, and mortality. The dehydrated cysts were directly exposed for forty-eight hours to the action of three alcohols, methanol, ethanol, and n-propanol. No teratogenic or lethal effects on larvae were found at any methanol or ethanol concentrations. Predicted values of effect concentration, EC₁, EC₁₀ and EC₅₀ were calculated from the estimated probit models for larva growth inhibition, GI, and for cyst lethal concentration, LC. At concentrations of 0.21 M methanol and 0.13 M ethanol, there were no signs of alterations in Artemia salina cyst development; these concentrations show a NOEC (No Observed Effect Concentration) value, and properly employed do not interfere with effects due to a given chemical. The n-propanol was only used to verify the extreme resistance of the dried cysts to various environmental factors.     

Analysis of phytochelatin complexes in the lead tolerant vetiver grass [Vetiveria zizanioides (L.)] using liquid chromatography and mass spectrometry

Ethylenediamene tetraacetic acid (EDTA) has been used to mobilize soil lead (Pb) and enhance plant uptake for phytoremediation. Chelant bound Pb is considered less toxic compared to free Pb ions and hence might induce less stress on plants. Characterization of possible Pb complexes with phytochelatins (PC_n, metal-binding peptides) and EDTA in plant tissues will enhance our understanding of Pb tolerance mechanisms. In a previous study, we showed that vetiver grass (Vetiveria zizanioides L.) can accumulate up to 19,800 and 3350 mg Pb kg⁻¹ dry weight in root and shoot tissues, respectively; in a hydroponics set-up. Following the basic incubation study, a greenhouse experiment was conducted to elucidate the efficiency of vetiver grass (with or without EDTA) in remediating Pb-contaminated soils from actual residential sites where Pb-based paints were used. The levels of total thiols, PC_n, and catalase (an antioxidant enzyme) were measured in vetiver root and shoot following chelant-assisted phytostabilization. In the presence of 15 mM kg ⁻¹ EDTA, vetiver accumulated 4460 and 480 mg Pb kg⁻¹ dry root and shoot tissue, respectively; that are 15- and 24-fold higher compared to those in untreated controls. Despite higher Pb concentrations in the plant tissues, the amount of total thiols and catalase activity in EDTA treated vetiver tissues was comparable to chelant unamended controls, indicating lowered Pb toxicity by chelation with EDTA. The identification of glutathione (referred as PC₁) (m/z 308.2), along with chelated complexes like Pb-EDTA (m/z 498.8) and PC₁-Pb-EDTA (m/z 805.3) in vetiver root tissue using electrospray tandem mass spectrometry (ES-MS) highlights the possible role of such species towards Pb tolerance in vetiver grass.     

Aufnahme von Cyanid in Pflanzen

Zusammenfassung  Cyanide entstehen bei der Pyrolyse von Kohle, und bei der Gasreinigung wird Blaus?ure als Berliner Blau gef?llt. Diese Abf?lle sind heute h?ufig Bestandteil von innerst?dtischen Altlasten. Cyanwasserstoff HCN (Blaus?ure) ist ein schnell wirksames und starkes Gift; eisenkomplexierte Cyanide im Boden sind jedoch weit weniger giftig. Die Phytotoxizit?t von freiem Cyanid wurde für Korbweiden (Sálix viminális) mit dem Baum-Transpirationstest bestimmt. Der EC₁₀ liegt für t=72 h bei 0,76 mg KCN (0,3 mg CN) je Liter, der EC₅₀ bei 4,47 mg/l KCN. Langfristig sind 5 mg/l KCN t?dlich. Balsampappeln (Pópulus trichocárpa) k?nnen in bis zu 2500 mg/l Ferroferricyanid (Berliner Blau) überleben, wenn auch mit Wachstumsst?rungen. Weiden überlebten in einem Gaswerksboden mit bis zu 452 mg/kg Gesamt-CN. Aus der N?hrl?sung wurde mehr freies CN aufgenommen als aus dem Boden. M?glicherweise wird auch komplexiertes Cyanid in die Bl?tter verlagert. In Erlenmeyern mit Pflanzen wurde freies Cyanid bei sublethaler Dosis rasch aus der N?hrl?sung eliminiert. Die Bepflanzung mit geeigneter Vegetation k?nnte eine L?sung für viele cyanid-kontaminierte Gaswerks- und Minengel?nde sein. OnlineFirst: 09. 01. 2001     

Acute and chronic toxicity of benzotriazoles to aquatic organisms

Purpose

Resulting from their intensive use as corrosion inhibitors in aircraft deicing and anti-icing fluids (ADAF) and for silver protection in dishwasher detergents benzotriazoles (BTs) are widespread in European surface waters. The current study aimed on an ecotoxicological characterization of 1H-benzotriazole (1H-BT) and 5-methyl-1H-benzotriazole (5MBT).

Methods

Acute and chronic OECD guideline tests were conducted with primary producers (Desmodesmus subspicatus, Lemna minor) and two daphnia species (Daphnia magna, Daphnia galeata) to characterize the hazard of these chemicals. Additionally, the estrogenic activity of both BTs was analyzed in vitro using a recombinant yeast estrogen screen (YES).

Results

Both BTs revealed significant effects in acute and chronic experiments, but exhibited no estrogenic activity in the YES. The algal growth test displayed an inhibited cell number increase with effect concentration (EC) values of EC₁₀ 1.18 and 2.86?mg?l^-1 for 1H-BT and 5MBT, respectively. In the Lemna test, EC₁₀ values were 3.94?mg?l^-1 (1H-BT) and 2.11?mg?l^-1 (5MBT). D. magna was also affected with EC₅₀ (48?h) values of 107?mg?l^-1 for 1H-BT and 51.6?mg?l^-1 for 5MBT. D. galeata was more sensitive with an EC₅₀ (48?h) of 14.7?mg 1H-BT l^-1 and 8.13?mg 5MBT l^-1. In the 21-day reproduction tests with D. magna, the EC₁₀ for 5MBT was 5.93?mg?l^-1 while 1H-BT showed no adverse effects. D. galeata turned out to be more sensitive in the chronic study with EC₁₀ values of 0.97?mg?l^-1 for 1H-BT and 0.40?mg?l^-1 for 5 MBT.

Conclusion

Because BTs are regularly found in the aquatic environment at lower ??g l^-1 concentrations reflecting their persistence and poor elimination during wastewater treatment processes, a preliminary risk assessment was conducted. There is little indication that BTs pose a risk for aquatic ecosystems at current exposure levels during most of the year. However, it cannot be excluded that in winter with a higher usage of ADAFs environmental concentrations may well exceed the level that is considered safe for aquatic organisms.     

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 21 000 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.     

Toxicity of metalaxyl,azoxystrobin, dimethomorph,cymoxanil, zoxamide and mancozeb to Phytophthora infestans isolates from Serbia

A study of the in vitro sensitivity of 12 isolates of Phytophthora infestans to metalaxyl, azoxystrobin, dimethomorph, cymoxanil, zoxamide and mancozeb, was conducted. The isolates derived from infected potato leaves collected at eight different localities in Serbia during 2005–2007. The widest range of EC₅₀ values for mycelial growth of the isolates was recorded for metalaxyl. They varied from 0.3 to 3.9 μg mL^?1 and were higher than those expected in a susceptible population of P. infestans. The EC₅₀ values of the isolates were 0.16–0.30 μg mL^?1 for dimethomorph, 0.27–0.57 μg mL^?1 for cymoxanil, 0.0026–0.0049 μg mL^?1 for zoxamide and 2.9–5.0 μg mL^?1 for mancozeb. The results indicated that according to effective concentration (EC₅₀) the 12 isolates of P. infestans were sensitive to azoxystrobin (0.019–0.074 μg mL^?1), and intermediate resistant to metalaxyl, dimethomorph and cymoxanil. According to resistance factor, all P. infestans isolates were sensitive to dimethomorph, cymoxanil, mancozeb and zoxamide, 58.3% of isolates were sensitive to azoxystrobin and 50% to metalaxyl. Gout's scale indicated that 41.7% isolates were moderately sensitive to azoxystrobin and 50% to metalaxyl.