Effects of four fungicides on nine non-target submersed macrophytes

A cell-free fluorescence biosensor based on allosteric transcription factor NalC for detection of pentachlorophenol

Pentachlorophenol (PCP) was once used as a pesticide, germicide, and preservative due to its stable properties and resistance to degradation. This study aimed to design a biosensor for the quantitative and prompt detection of capable of PCP. A cell-free fluorescence biosensor was developed while employing NalC, an allosteric Transcription Factor responsive to PCP and In Vitro Transcription. By adding a DNA template and PCP and employing Electrophoretic Mobility Shift Assay while monitoring the dynamic fluorescence changes in RNA, this study offers evidence of NalC's potential applicability in sensor systems developed for the specific detection of PCP. The biosensor showed the capability for the quantitative detection of PCP, with a Limit of Detection (LOD) of 0.21 μM. Following the addition of Nucleic Acid Sequence-Based Amplification, the fluorescence intensity of RNA revealed an excellent linear relationship with the concentration of PCP, showing a correlation coefficient (R2) of 0.9595. The final LOD was determined to be 0.002 μM. This study has successfully translated the determination of PCP into a fluorescent RNA output, thereby presenting a novel approach for detecting PCP within environmental settings.

Rpg7: A New Gene for Stem Rust Resistance from Hordeum vulgare ssp. spontaneum

Wheat stem rust (causal organism: Puccinia graminis f. sp. tritici) is an important fungal disease that causes significant yield losses in barley. The deployment of resistant cultivars is the most effective means of controlling this disease. Stem rust evaluations of a diverse collection of wild barley (Hordeum vulgare ssp. spontaneum) identified two Jordanian accessions (WBDC094 and WBDC238) with resistance to a virulent pathotype (P. graminis f. sp. tritici HKHJC) from the United States. To elucidate the genetics of stem rust resistance, both accessions were crossed to the susceptible landrace Hiproly. Segregation ratios of F₂ and F₃ progeny indicated that a single dominant gene confers resistance to P. graminis f. sp. tritici HKHJC. Molecular mapping of the resistance locus was performed in the Hiproly/WBDC238 F₂ population based on 3,329 single-nucleotide polymorphism markers generated by genotyping-by-sequencing. Quantitative trait locus analysis positioned the resistance gene to the long arm of chromosome 3H between the physical/genetic positions of 683.8 Mbp/172.9 cM and 693.7 Mbp/176.0 cM. Because this resistance gene is novel, it was assigned the new gene locus symbol of Rpg7 with a corresponding allele symbol of Rpg7.i. At the seedling stage, Rpg7 confers resistance against a number of other important P. graminis f. sp. tritici pathotypes from the United States (MCCFC, QCCJB, and TTTTF) and Africa (TTKSK) as well as an isolate (92-MN-90) of the rye stem rust pathogen (P. graminis f. sp. secalis) from Minnesota. The resistance conferred by Rpg7 can be readily transferred into breeding programs because of its simple inheritance and clear phenotypic expression.

Fungicides: An Overlooked Pesticide Class?

Fungicides are indispensable to global food security and their use is forecasted to intensify. Fungicides can reach aquatic ecosystems and occur in surface water bodies in agricultural catchments throughout the entire growing season due to their frequent, prophylactic application. However, in comparison to herbicides and insecticides, the exposure to and effects of fungicides have received less attention. We provide an overview of the risk of fungicides to aquatic ecosystems covering fungicide exposure (i.e., environmental fate, exposure modeling, and mitigation measures) as well as direct and indirect effects of fungicides on microorganisms, macrophytes, invertebrates, and vertebrates. We show that fungicides occur widely in aquatic systems, that the accuracy of predicted environmental concentrations is debatable, and that fungicide exposure can be effectively mitigated. We additionally demonstrate that fungicides can be highly toxic to a broad range of organisms and can pose a risk to aquatic biota. Finally, we outline central research gaps that currently challenge our ability to predict fungicide exposure and effects, promising research avenues, and shortcomings of the current environmental risk assessment for fungicides.

The Response of Lemna minor to Mixtures of Pesticides That Are Commonly Used in Thailand

In the field, aquatic organisms are exposed to multiple contaminants rather than to single compounds. It is therefore important to understand the toxic interactions of co-occurring substances in the environment. The aim of the study was to assess the effects of individual herbicides (atrazine, 2,4-D, alachlor and paraquat) that are commonly used in Thailand and their mixtures on Lemna minor. Plants were exposed to individual and binary mixtures for 7 days and the effects on plant growth rate were assesed based on frond area measurements. Experimental observations of mixture toxicity were compared with predictions based on single herbicide exposure data using concentration addition and independent action models. The single compound studies showed that paraquat and alachlor were most toxic to L. minor, followed by atrazine and then 2,4-D. For the mixtures, atrazine with 2,4-D appeared to act antagonistically, whereas alachlor and paraquat showed synergism.

Natural α-methylenelactam analogues: Design, synthesis and evaluation of α-alkenyl-γ and δ-lactams as potential antifungal agents against Colletotrichum orbiculare

In our continued efforts to improve the potential utility of the α-methylene-γ-lactone scaffold, 62 new and 59 known natural α-methylenelactam analogues including α-methylene-γ-lactams, α-arylidene-γ and δ-lactams, and 3-arylideneindolin-2-ones were synthesized as the bioisosteric analogues of the α-methylenelactone scaffold. The results of antifungal and cytotoxic activity indicated that among these derivatives compound (E)-1-(2, 6-dichlorobenzyl)-3-(2-fluorobenzylidene) pyrrolidin-2-one (Py51) possessed good selectivity with the highest antifungal activity against Colletotrichum orbiculare with IC₅₀ = 10.4 μM but less cytotoxic activity with IC₅₀ = 141.2 μM (against HepG2 cell line) and 161.2 μM (against human hepatic L02 cell line). Ultrastructural change studies performed by transmission electron microscope showed that Py51 could cause important cell morphological changes in C. orbiculare, such as plasma membrane detached from cell wall, cell wall thickening, mitochondria disruption, a dramatic increase in vacuolation, and eventually a complete loss in the integrity of organelles. Significantly, mitochondria appeared one of the primary targets, as confirmed by their remarkably aberrant morphological changes. Analysis of structure-activity relationships revealed that incorporation of the aryl group into the α-exo-methylene and the N-benzyl substitution increased the activity. Meanwhile, the α-arylidene-γ-lactams have superiority in selectivity over the 3-arylideneindolin-2-ones. Based on the results, the N-benzyl substituted α-(2-fluorophenyl)-γ-lactam was identified as the most promising natural-based scaffold for further discovering and developing improved crop-protection agents.

Aquatic ecotoxicity of the fungicide pyrimethanil: effect profile under optimal and thermal stress conditions

The aquatic ecotoxic profile of the fungicide pyrimethanil and its acute and chronic thermal dependence in two aquatic invertebrates Chironomus riparius and Daphnia magna were investigated. The ecotoxicity of pyrimethanil at optimal thermal conditions did not depend on the trophic level, but was species-specific. The acute pyrimethanil-toxicity on C. riparius increased with higher temperature. The chronic response of Daphnia magna to the NOEC of the fungicide was examined in a multigenerational experiment under three near-natural temperature regimes. A pyrimethanil-induced increase of total mortality was buffered by the strongly related increase of the general reproductive capacity, while population growth was stronger influenced by temperature than by the fungicide. At a LOEC, however, a second generation could not be established with D. magna at all thermal regimes. This clearly shows that thermal and multigenerational effects should be considered when appraising the ecotoxicity of pesticides and assessing their future risk for the environment.

Toxicity of pentachlorophenol to native aquatic species in the Yangtze River

INTRODUCTION

While the literature is replete with studies of the toxic potency of pentachlorophenol (PCP), site-specific criteria for native aquatic species that can be used in ecological risk assessments has been lacking and application of toxicity information for non-native species is controversial.

MATERIALS AND METHODS

In the present study, acute and chronic toxicities of PCP to six aquatic species native to the Yangtze River were determined. The HC₅ and HC₅₀ (hazardous concentration for 5% and 50% of species) were derived from dose-response curves for these native aquatic species and were then compared with those derived for non-native species.

RESULTS

The acute toxicity values for the native species ranged from 8.8 × 10⁻² mg l⁻¹ (Plagiognathops microlepis) to 1.1 mg l⁻¹ (Soirodela polyrhiza), while chronic toxicity values based on no observed effect concentrations (NOECs) ranged from 0.01 mg l⁻¹ (Macrobrachium superbum) to 0.25 mg l⁻¹ (Soirodela polyrhiza). Native aquatic benthos was more sensitive to acute PCP exposure than non-native species. There was no significant difference in NOECs derived from native fish species and those based on non-native fish species. The median acute HC₅ and HC₅₀ derived from the toxicity data of native taxa were both less than those derived from non-native taxa. There was no significant difference between chronic HC₅s derived from the two sets of taxa. However, the median chronic HC₅₀ derived from native taxa was less than that derived from non-native taxa.

CONCLUSION

The study upon which we report here provides site-specific toxicity information developed for native species which can be used for the protection of local aquatic life from a common contaminant, PCP.

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.

Nontarget deposition and losses of chlorothalonil in irrigation runoff water from a commercial foliage plant nursery

Commercial foliage plant production requires the use of pesticides for controlling pests and pathogens that can reduce aesthetic qualities of crops, rendering them unwanted by consumers. Chlorothalonil is a common, broad-spectrum, foliar fungicide used for protecting plants from a variety of fungal diseases. This fungicide may also be acutely toxic to nontarget aquatic organisms due to its mode of action. This study evaluated the amount of chlorothalonil deposited on nontarget ground surfaces during normal sprayer applications at a commercial nursery using Teflon targets. One day following application, irrigation runoff events were initiated and runoff water samples were collected and analyzed for chlorothalonil. Discharge volumes were also measured to allow estimation of the total mass of chlorothalonil discharged during each event. Results indicated that 9.8 to 53.6% of the active ingredient applied landed on nontarget ground surfaces depending on plant size, spacing, and row lengths (short rows sprayed from one side vs. longer rows sprayed from both ends). On an entire production-area scale, 29.2% of the active ingredient applied was deposited on ground surfaces. Of the total nontarget deposition, 0.25 to 0.53% was detected in runoff water discharged from the production area. Concentrations ranged from 1.2 to 500 microg/L during the first runoff events following application.

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.

Herbicide effects of metazachlor on duckweed (Lemna minor and Spirodela polyrhiza) in test systems with different trophic status and complexity

Growth of common duckweed Lemna minor under optimal standard test conditions was compared to growth of L. minor exposed to nutrient-poor water in both a modified standardised test and in oligo- to mesotrophic indoor pond mesocosms in order to test the impact of trophic conditions and test system complexity on the effect of the herbicide metazachlor (2-chloro-N-(pyrazol-1-ylmethyl)acet-2',6'-xylidide) on aquatic macrophytes. In the mesocosms L. minor was replaced by greater duckweed Spirodela polyrhiza after 3 weeks due to high mortality even in the controls. The pond systems contained other macrophytes and biota as well as sediment and were thus more complex than standard test systems. For L. minor front area, the ErC(50) (50% effective concentration related to growth rate) was 2.8 microg L(-1) metazachlor in the standardised and 4.7 microg L(-1) in the modified laboratory test after 7 days (4.9 microg L(-1) and 52.9 microg L(-1) metazachlor when using front number). In the oligo- to mesotrophic pond mesocosms, similar sensitivities to metazachlor (ErC(50) 4.5-6.4 microg L(-1)) were noted for S. polyrhiza after 21 and 28 days of exposure. In comparison with dicotyledonous macrophytes, duckweed species are more sensitive for irreversible enzyme inhibitors of growth such as metazachlor independent of trophic status and complexity of the test system.

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.