Widely-used Herbicide Research Articles

The people behind the papers - Julia Grzymkowski and Nanette Nascone-Yoder.

As the digestive system develops, the gut tube lengthens and convolutes to correctly package the intestine. Intestinal malrotation is a prevalent birth anomaly, but its underlying causes are not well understood. In this new study, Nanette Nascone-Yoder and colleagues show that exposure of Xenopus embryos to atrazine, a widely-used herbicide, can disrupt cellular metabolism in the developing gut tube and lead to intestinal malrotation. We caught up with first author Julia Grzymkowski and corresponding author Nanette Nascone-Yoder, Professor at North Carolina State University, to hear more about the story.

Glyphosate decreases survival, increases fecundity, and alters the microbiome of the natural predator Harmonia axyridis (ladybird beetle)

Glyphosate is a widely-used herbicide that shows toxicity to non-target organisms. The predatory natural enemy Harmonia axyridis may ingest glyphosate present in pollen and aphid prey. The present study characterized the responses of adult H. axyridis to environmentally relevant concentrations of glyphosate (5, 10, and 20 mg/L) for one or five days. There were no obvious effects on adult H. axyridis survival rates or fecundity in response to 5 or 10 mg/L glyphosate. However, exposure to 20 mg/L glyphosate significantly reduced the survival rate and increased fecundity. Analysis of the adult H. axyridis microbiota with 16S rRNA sequencing demonstrated changes in the relative and/or total abundance of specific taxa, including Serratia, Enterobacter, Staphylococcus, and Hafnia-Obesumbacterium. These changes in symbiotic bacterial abundance may have led to changes in survival rates or fecundity of this beetle. This is the first report of herbicide-induced stimulation of fecundity in a non-target predatory natural enemy, reflecting potentially unexpected risks of glyphosate exposure in adult H. axyridis. Although glyphosate resistant crops have been widely planted, the results of this study indicate a need to strengthen glyphosate management to prevent over-use, which could cause glyphosate toxicity and threaten environmental and human health.

Prolonged exposure to the herbicide atrazine promotes kidney fibrosis by activating Wnt/β-catenin signaling in rats.

Exposure to atrazine(ATR),awidely-usedherbicide,is a potential harmful to human health due to its long-term environmental persistence and bioaccumulation. The effects of chronic exposure to ATR on renal function in rats were evaluated in this research. Female Sprague-Dawley rats at 4 weeks of age were treated with different concentrations of ATR for 6months. No significant differences intermsofrenalfunctions were observed afterATRtreatment. In histopathological examination of the kidney, Hematoxylin-Eosin staining indicated the development of degenerative changes in a dose-dependent manner. The results revealed that ATR exposure leads to renal fibrosis and that activation of the Wnt/β-catenin pathway plays a potential role in ATR-related renal fibrosis. Levelsof transforming growth factor (TGF)-β and TGF-β1 levels andthereactiveoxygenspecieswere significantly upregulated after ATR treatment. In conclusion, long-term exposure to ATR could cause kidney fibrosis, which is the result of epithelial-mesenchymal transition caused by inflammation and oxidative stress.

Comparative study of bacterial community dynamics in different soils following application of the herbicide atrazine

Microbial communities in cultivated soils control the fate of pollutants associated with agricultural practice. The present study was designed to explore the response of bacterial communities to the application of the widely-used herbicide atrazine in three different crop fields that differ significantly in their physicochemical structure and nutritional content: the nutrient-rich (with relatively high carbon and nitrogen content) Newe Yaar (NY) and Ha-Ogen (HO) soils and the nutrient-poor, sandy Sde-Eliyahu (SE) soil. The 16 S rRNA gene amplicon sequencing revealed the nutrient poor HO soil differs in its response to atrazine in comparison to the two nutrient-rich soils both in the shortest persistence of atrazine and its effect on community structure and composition. Potential reported bacterial degraders of atrazine such as Pseudomonas, Clostridium and Bacillus were more abundant in contaminated sandy/poor soils (HO) whereas bacteria known for nitrogen cycling such as Azospirillum, Sinorhizobium, Nitrospira and Azohydromonas were significantly more abundant in the nutrient rich contaminated SE soils. No significant increase of potential indigenous degrader Arthrobacter was detected in SE and NY soils whereas a significant increase was recorded with HO soils. An overall shift in bacterial community composition following atrazine application was observed only in the nutrient poor soil. Understanding atrazine persistence and microbiome response to its application of in dependence with soil types serve the design of precision application strategies.

Hydroxyl radical-initiated decomposition of metazachlor herbicide in the gaseous and aqueous phases: Mechanism, kinetics, and toxicity evaluation

The oxidation of widely-used herbicide metazachlor (MTZ) by hydroxyl radical (HO•) in the gas and the aqueous phases was investigated in terms of mechanistic and kinetic behaviors using the M06–2X/6–311++G (3df, 3pd)//M06–2X/6-31 + G (d,p) level of theory over the temperature range 250–400 K. The formal hydrogen transfer, HO•-addition, and single electron transfer mechanisms were considered. The overall rate constants in the gas phase range from 8.40 × 1010 to 8.31 × 109 M−1 s−1 at the temperature from 250 to 400 K, respectively, while the ones in the aqueous phase are close to diffusion-controlled rates, with diffusion-corrected rate constants being 1.31 × 109 to 1.27 × 109 M−1 s−1. The formal hydrogen transfer mechanism is the most dominant in the gas phase, whereas the HO•-addition is the most favorable in the aqueous phase. The H-abstraction at two methyl groups and the HO•-addition to C11 and C12 atoms (pyrazole ring), C16 and C18 atoms (benzyl ring) are significant. The short lifetime in the environment, equal to only 4.16 h, requires more attention to this herbicide compound, whereas its lifetime in the aqueous condition varies sharply from half second to several thousand days depending on the HO• concentration. The ecotoxicity estimation of MTZ and its principal transformation products to aquatic organisms suggests that they are harmful or toxic substances. Moreover, the MTZ is a developmental toxicant and mutagenicity-positive, while its decomposed products are developmental toxicants with no mutagenic toxicity. Their bioaccumulation in aquatic organisms is negligible.

Time-resolved proteome and transcriptome of paraquat-induced pulmonary fibrosis

BackgroundsPulmonary fibrosis (PF) is a pathological state presenting at the progressive stage of heterogeneous interstitial lung disease (ILD). The current understanding of the molecular mechanisms involved is incomplete. This clinical toxicology study focused on the pulmonary fibrosis induced by paraquat (PQ), a widely-used herbicide. Using proteo-transcriptome analysis, we identified differentially expressed proteins (DEPs) derived from the initial development of fibrosis to the dissolved stage and provided further functional analysis. MethodsWe established a mouse model of progressive lung fibrosis via intratracheal instillation of paraquat. To acquire a comprehensive and unbiased understanding of the onset of pulmonary fibrosis, we performed time-series proteomics profiling (iTRAQ) and RNA sequencing (RNA-Seq) on lung samples from paraquat-treated mice and saline control. The biological functions and pathways involved were evaluated through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) Pathway analysis. Correlation tests were conducted on comparable groups 7 days and 28 days post-exposure. Differentially expressed proteins and genes following the same trend on the protein and mRNA levels were selected for validation. The functions of the selected molecules were identified in vitro. The protein level was overexpressed by transfecting gene-containing plasmid or suppressed by transfecting specific siRNA in A549 cells. The levels of endothlial-mesenchymal transition (EMT) markers, including E-cadherin, vimentin, FN1, and α-SMA, were determined via western blot to evaluate the fibrotic process. ResultsWe quantified 1358 DEPs on day 7 and 426 DEPs on day 28 post exposure (Fold change >1.2; Q value < 0.05). The top 5 pathways – drug metabolism-cytochrome P450, metabolism of xenobiotics by cytochrome P450, complement and coagulation cascades, chemical carcinogenesis, protein digestion and absorption — were involved on both day 7 and day 28. Several pathways, including tight junction, focal adhesion, platelet activation, and ECM-receptor interaction, were more enriched on day 28 than on day 7. Integrative analysis of the proteome and transcriptome revealed a moderate correlation of quantitative protein abundance ratios with RNA abundance ratios (Spearman R = 0.3950 and 0.2477 on days 7 and 28, respectively), indicating that post-transcriptional regulation plays an important role in lung injury and repair. Western blot identified that the protein expressions of FN1, S100A4, and RBM3 were significantly upregulated while that of CYP1A1, FMO3, and PGDH were significantly downregulated on day 7. All proteins generally recovered to baseline on day 28. qPCR showed the mRNA levels of Fn1, S100a4, Rbm3, Cyp1a1, Fmo3, and Hpgd changed following the same trend as the levels of their respective proteins. Further, in vitro experiments showed that RBM3 was upregulated while PGDH was downregulated in an EMT model established in human lung epithelial A549 cells. RBM3 overexpression and PGDH knockout could both induce EMT in A549 cells. RBM3 knockout or PGDH overexpression had no reverse effect on EMT in A549 cells. ConclusionsOur proteo-transcriptomic study determined the proteins responsible for fibrogenesis and uncovers their dynamic regulation from lung injury to repair, providing new insights for the development of biomarkers for diagnosis and treatment of fibrotic diseases.

Glyphosate and Non-Hodgkin Lymphoma

The herbicide “glyphosate” known with the trade name of “Round-Up” has been using for 50 years and it is the world’s most widely used herbicide. It has helped to increase the agricultural yields of crops around the world, thus assisting to feed billions of peoples. After Round-Up was declared “probable carcinogen” in 2015 by the International Agency for Research on Cancer (IARC), there has been a growing number of claims that glyphosate is the cause of the types of cancer of the most poorly understood origin, such as non-Hodgkin lymphoma. From an analysis of the available literature, the link between non-Hodgkin lymphoma and “Round-Up” is shown to be extremely weak.

Electrochemical Detection of Small Volumes of Glyphosate with Mass-Produced Non-Modified Gold Chips

Abstract Mass-produced printed circuit board (PCB) electrodes were used as electrochemical cells to detect the widely-used herbicide glyphosate. Square wave voltammetry (SWV) was used to determine the presence of glyphosate in aqueous Cu(NO3)2 solution. Optimal measurement conditions for the detection of glyphosate with PCB electrodes were found. It was determined that glyphosate was able to soak into the growing plants from the substrate. Glyphosate-contaminated plant juice was distinguished from control samples using the PCB electrode. Glyphosate-contaminated plants were found to have DNA mutations.

Development of spectral indices for identifying glyphosate-resistant weeds

Glyphosate as the most common and widely-used herbicide in agricultural crops has resulted in the explosion of resistant weeds around the world. An early detection of resistant weeds before observing the visible symptoms of glyphosate application in weeds can contribute to the crop protection in precision agriculture. This paper aims at developing and evaluating spectral weed indices (SWIs) to identify glyphosate-resistant weeds 72 h after herbicide application. A greenhouse experiment was conducted on three common weed species, namely, kochia (Kochia scoparia), ragweed (Ambrosia artemisiifolia L.) and waterhemp (Amaranthus rudis), including resistant and susceptible types to collect canopy spectral reflectance after glyphosate spraying. To generate SWI, the best weighted combination of single wavelength and a normalized wavelength difference in the range of 450–920 nm was established. Relief-F algorithm selected the most discriminative feature wavelengths, and two band normalized differences to differentiate weeds with higher degree of resistance, and changes in the hyperspectral signature caused by glyphosate application. The performance of optimized SWIs on resistant weeds identification was assessed by employing machine learning Random Forest (RF) method. The RF classification model achieved a classification accuracy of 96%, 100% and 97% in detecting resistant kochia, ragweed and waterhemp, respectively. A comparison between introduced SWIs in this study and previously published hyperspectral vegetation indices (VIs) indicated that the SWIs provided better agreement with real data in glyphosate-resistant weeds identification.

Enhanced 2,4-D Metabolism in Two Resistant Papaver rhoeas Populations from Spain.

Corn poppy (Papaver rhoeas), the most problematic broadleaf weed in winter cereals in Southern Europe, has developed resistance to the widely-used herbicide, 2,4-D. The first reported resistance mechanism in this species to 2,4-D was reduced translocation from treated leaves to the rest of the plant. However, the presence of other non-target site resistance (NTSR) mechanisms has not been investigated up to date. Therefore, the main objective of this research was to reveal if enhanced 2,4-D metabolism is also present in two Spanish resistant (R) populations to synthetic auxins. With this aim, HPLC experiments at two 2,4-D rates (600 and 2,400 g ai ha−1) were conducted to identify and quantify the metabolites produced and evaluate possible differences in 2,4-D degradation between resistant (R) and susceptible (S) plants. Secondarily, to determine the role of cytochrome P450 in the resistance response, dose-response experiments were performed using malathion as its inhibitor. Three populations were used: S, only 2,4-D R (R-703) and multiple R to 2,4-D and ALS inhibitors (R-213). HPLC studies indicated the presence of two hydroxy metabolites in these R populations in shoots and roots, which were not detected in S plants, at both rates. Therefore, enhanced metabolism becomes a new NTSR mechanism in these two P. rhoeas populations from Spain. Results from the dose-response experiments also showed that pre-treatment of R plants with the cytochrome P450 (P450) inhibitor malathion reversed the phenotype to 2,4-D from resistant to susceptible in both R populations. Therefore, it could be hypothesized that a malathion inhibited P450 is responsible of the formation of the hydroxy metabolites detected in the metabolism studies. This and previous research indicate that two resistant mechanisms to 2,4-D could be present in populations R-703 and R-213: reduced translocation and enhanced metabolism. Future experiments are required to confirm these hypotheses, understand the role of P450, and the relationship between both NTSR mechanisms. On this basis, selection pressure with synthetic auxins bears the risk of promoting the evolution enhanced metabolism in Papaver rhoeas.

Degradation of atrazine by ZnxCu1−xFe2O4 nanomaterial-catalyzed sulfite under UV–vis light irradiation: Green strategy to generate SO4[rad

Degradation of atrazine, a widely-used herbicide, by a novel advanced oxidation process was investigated through photo-catalyzing sulfite, the precursor of sulfate radical (SO4−) in this study, by zinc-copper ferrites (ZnxCu1−xFe2O4) under UV–vis light irradiation. The ZnxCu1−xFe2O4 with different ratios of Zn to Cu was synthesized through a facile sol-gel combustion method, and characterized by X-ray powder diffractometry, scanning electron microscopy, transmission electron microscopy, porosimetry, and UV–vis diffuse reflectance spectroscopy, and by a vibrating sample magnetometer and Mössbauer spectrometer. The Zn0.8Cu0.2Fe2O4 demonstrated the highest photocatalytic ability to activate sulfite for the degradation of atrazine under current experimental conditions. The sulfate radical generated in the UV–vis light/Zn0.8Cu0.2Fe2O4/sulfite system was identified as the main reactive species through radical quenching experiments and measuring two important byproducts (atrazine-desethyl and atrazine-desisopropyl). The XPS spectra of fresh and used catalysts were analyzed to further elucidate the reaction mechanisms. There are two possible approaches to produce SO4−: the oxidation of sulfite by photo-generated holes and the accelerated decomposition of metal-sulfito complexes (Fe(III)-sulfito and Cu(II)-sulfito) on the surface of Zn0.8Cu0.2Fe2O4. Based on the detected byproducts, the transformation pathways of atrazine by UV–vis light/Zn0.8Cu0.2Fe2O4/sulfite were proposed as well. After the complete decomposition of atrazine, the used catalysts could be magnetically recovered using a magnet and no sulfite remained in the system. The results suggest that the UV–vis light/Zn0.8Cu0.2Fe2O4/sulfite system is a “green” advanced oxidation technology for future application in wastewater treatment.

Fitness Outcomes Related to Glyphosate Resistance in Kochia (Kochia scoparia): What Life History Stage to Examine?

A fast-spreading weed, kochia (Kochia scoparia), has developed resistance to the widely-used herbicide, glyphosate. Understanding the relationship between the occurrence of glyphosate resistance caused by multiple EPSPS gene copies and kochia fitness may suggest a more effective way of controlling kochia. A study was conducted to assess fitness cost of glyphosate resistance compared to susceptibility in kochia populations at different life history stages, that is rate of seed germination, increase in plant height, days to flowering, biomass accumulation at maturity, and fecundity. Six kochia populations from Scott, Finney, Thomas, Phillips, Wallace, and Wichita counties in western Kansas were characterized for resistance to field-use rate of glyphosate and with an in vivo shikimate accumulation assay. Seed germination was determined in growth chambers at three constant temperatures (5, 10, and 15 C) while vegetative growth and fecundity responses were evaluated in a field study using a target-neighborhood competition design in 2014 and 2015. One target plant from each of the six kochia populations was surrounded by neighboring kochia densities equivalent to 10 (low), 35 (moderate), or 70 (high) kochia plants m−2. In 2015, neighboring corn densities equivalent to 10 and 35 plants m−2 were also evaluated. Treatments were arranged in a randomized complete block design with at least 7 replications. Three kochia populations were classified as glyphosate-resistant (GR) [Scott (SC-R), Finney (FN-R), and Thomas (TH-R)] and three populations were classified as glyphosate-susceptible (GS) [Phillips (PH-S), Wallace (WA-S) and Wichita (WI-S)]. Of the life history stages measured, fitness differences between the GR and GS kochia populations were consistently found in their germination characteristics. The GR kochia showed reduced seed longevity, slower germination rate, and less total germination than the GS kochia. In the field, increases in plant height, biomass accumulation, and fecundity were not clearly different between GR and GS kochia populations (irrespective of neighbor density). Hence, weed management plans should integrate practices that take advantage of the relatively poor germination characteristics of GR kochia. This study suggests that evaluating plant fitness at different life history stages can increase the potential of detecting fitness costs.

Embryonic exposure to the widely-used herbicide atrazine disrupts meiosis and normal follicle formation in female mice

The widely-used herbicide atrazine (ATZ) is detected in ground and surface water in many countries. Several studies in animals have demonstrated that ATZ has endocrine-disrupting effects on male and female reproduction in many vertebrate species. In this study, we investigated the effects of ATZ exposure on meiosis, a key step in gametogenesis in mammals. The treatment was initiated before oocyte entry into meiosis, which occurs during the embryonic period in females. We found that embryonic exposure to ATZ increases the level of 8-oxo-guanine in the nucleus of meiotic cells, reflecting oxidative stress and affecting meiotic double-strand break repair, chromosome synapsis and crossover numbers. Finally, embryonic exposure to ATZ reduces the number of primordial follicles and increases the incidence of multi-oocyte follicles in adult mice. Our data demonstrate that embryonic exposure to ATZ disrupts prophase I of meiosis and affects normal follicle formation in female mice.

A study of the age-related effects of lactational atrazine exposure

A growing number of reports have demonstrated that the widely-used herbicide Atrazine (ATR) can cause injury to dopamine (DA) neurons, but the exact mechanism remains unclear. In this study, we examined the effects of lactational ATR exposure in Sprague-Dawley rats on dopaminergic neuron health later in life.Compared with control rats, rats exposed to ATR during a critical period of neural development showed decreased striatal DA content and increased rates of DA turnover. The expression of Monoamine oxidase (MAO), which is associated with DA degradation, was up-regulated, and the expression of Vesicular Monoamine Transporter 2 (VMAT2), which is associated with DA transport, was down-regulated. The expression of transcription factor Nuclear Receptor Related Factor 1 (Nurr1), which is associated with DA neuron development, was down-regulated. Increased age (6–12 months old) increased the statistical significance of the differences of the above indicators in the ATR-treated rats compared to the control rats (P<0.05).Taken together, our results indicate that ATR exposure during the critical neural development period causes a down-regulation of Nurr1, which in turn affects Nurr1 target genes, including MAO, VMAT2 and DAT, which are involved in DA degradation and transport. Reduced expression of these genes impairs the capacity for vesicular storage or reuptake of DA, causing decreased levels of striatal DA, which can ultimately lead to DA neuron injury. DA neuron injuries become more severe over time, which suggests that aging can synergistically promote the ATR-associated DA neuron injuries.

Root-level exposure reveals multiple physiological toxicity of triazine xenobiotics in Arabidopsis thaliana

Herbicides are pollutants of great concern due to environmental ubiquity resulting from extensive use in modern agriculture and persistence in soil and water. Studies at various spatial scales have also highlighted frequent occurrences of major herbicide breakdown products in the environment. Analysis of plant behavior toward such molecules and their metabolites under conditions of transient or persistent soil pollution is important for toxicity evaluation in the context of environmental risk assessment. In order to understand the mechanisms underlying the action of such environmental contaminants, the model plant Arabidopsis thaliana, which has been shown to be highly responsive to pesticides and other xenobiotics, was confronted with varying levels of the widely-used herbicide atrazine and of two of its metabolites, desethylatrazine and hydroxyatrazine, which are both frequently detected in water streams of agriculturally-intensive areas. After 24h of exposure to varying concentrations covering the range of triazine concentrations detected in the environment, root-level contaminations of atrazine, desethylatrazine and hydroxyatrazine were found to affect early growth and development in various dose-dependent and differential manners. Moreover, these differential effects of atrazine, desethylatrazine and hydroxyatrazine pointed to the involvement of distinct mechanisms directly affecting respiration and root development. The consequences of the identification of additional targets, in addition to the canonical photosystem II target, are discussed in relation with the ecotoxicological assessment of environmental xenobiotic contamination.

Seasonal detection of atrazine and atzA in man-made waterways receiving agricultural runoff in a subtropical, semi-arid environment (Hidalgo County, Texas, USA).

Atrazine is a widely-used herbicide that can impact non-target organisms in the environment but can be biologically degraded by several types of microorganisms. In this study, the gene atzA, which encodes for the initial step in bacterially-mediated atrazine degradation, was used as an indicator of atrazine pollution in agricultural canals located in Hidalgo County, Texas, USA. The concentration of atrazine and atzA were monitored once per month for 12 months during 2010-2011. Atrazine was measured using an enzyme-linked immunosorbent assay; atzA abundance was monitored using Quantitative Polymerase Chain Reaction (Q-PCR) analyses. Abundance of atrazine and atzA were compared with rainy versus dry months and during planting versus non-planting months. Results showed that atrazine levels varied from below detection to 0.43ppb and were not influenced by precipitation or planting season. Concentrations of the gene atzA were significantly different in rainy versus dry months; during planting versus non-planting times of the year; and in the interaction of precipitation and planting season. The highest concentration of atzA, approx. 4.57 × 108 gene copies ml-1, was detected in July 2010-a rainy, planting month in Hidalgo County, South Texas. However, atrazine was below detection during that month. We conclude that Q-PCR using atzA as an indicator gene is a potential method for monitoring low levels of atrazine pollution in environmental samples.

Quantification and characterization of glyphosate use and loss in a residential area

Urban runoff can be a significant source of pesticides in urban streams. However, quantification of this source has been difficult because pesticide use by urban residents (e.g., on pavements or in gardens) is often unknown, particularly at the scale of a residential catchment. Proper quantification and characterization of pesticide loss via urban runoff require sound information on the use and occurrence of pesticides at hydrologically-relevant spatial scales, involving various hydrological conditions. We conducted a monitoring study in a residential area (9.5ha, Flanders, Belgium) to investigate the use and loss of a widely-used herbicide (glyphosate) and its major degradation product (aminomethylphosphonic acid, AMPA). The study covered 13 rainfall events over 67days. Overall, less than 0.5% of glyphosate applied was recovered from the storm drain outflow in the catchment. Maximum detected concentrations were 6.1μg/L and 5.8μg/L for glyphosate and AMPA, respectively, both of which are below the predicted no-effect concentration for surface water proposed by the Flemish environmental agency (10μg/L), but are above the EU drinking water standard (0.1μg/L). The measured concentrations and percentage loss rates can be attributed partially to the strong sorption capacity of glyphosate and low runoff potential in the study area. However, glyphosate loss varied considerably among rainfall events and event load of glyphosate mass was mainly controlled by rainfall amount, according to further statistical analyses. To obtain urban pesticide management insights, robust tools are required to investigate the loss and occurrence of pesticides influenced by various factors, particularly the hydrological and spatial factors.

Environmentally-relevant concentrations of atrazine induce non-monotonic acceleration of developmental rate and increased size at metamorphosis in Rhinella arenarum tadpoles

Despite of the various studies reporting on the subject, anticipating the impacts of the widely-used herbicide atrazine on anuran tadpoles metamorphosis remains complex as increases or decreases of larval period duration are almost as frequently reported as an absence of effect. The aim of the present study was to examine the effects of environmentally-relevant concentrations of atrazine (0.1, 1, 10, 100, and 1000μg/L) on the timings of metamorphosis and body size at metamorphosis in the common South American toad, Rhinella arenarum (Anura: bufonidae). None of the atrazine concentrations tested significantly altered survival. Low atrazine concentrations in the range of 1–100μg/L were found to accelerate developmental rate in a non-monotonic U-shaped concentration–response relationship. This observed acceleration of the metamorphic process occurred entirely between stages 25 and 39; treated tadpoles proceeding through metamorphosis as control animals beyond this point. Together with proceeding through metamorphosis at a faster rate, tadpoles exposed to atrazine concentrations in the range of 1–100μg/L furthermore transformed into significantly larger metamorphs than controls, the concentration–response curve taking the form of an inverted U in this case. The no observed effect concentration (NOEC) was 0.1μg atrazine/L for both size at metamorphosis and timings of metamorphosis. Tadpoles exposed to 100μg/L 17β-estradiol presented the exact same alterations of developmental rate and body size as those treated with 1, 10 and 100μg/L of atrazine. Elements of the experimental design that facilitated the detection of alterations of metamorphosis at low concentrations of atrazine are discussed, together with the ecological significance of those findings.

Exposure of the snail Potamopyrgus antipodarum to herbicide boosts output and survival of parasite infective stages.

Anthropogenic stressors such as pollutants can modulate levels of parasitic infections in aquatic animals by suppressing host immunity or through some other mechanisms. One such mechanism could involve increases in either the quantity or quality of infective stages produced by parasites. We investigated the effect of exposure of infected snails, Potamopyrgus antipodarum, to different concentrations of the widely-used herbicide glyphosate, on (i) the production of infective cercariae by three trematode species, Coitocaecum parvum, Apatemon sp. and an undescribed renicolid, and (ii) the survival of cercariae of the latter species. For all three trematode species, infected snails exposed over a month to low (0.36mga.i.L(-1)) or medium (3.6mga.i.L(-1)) formulated glyphosate concentrations released between 1.5 and 3 times more cercariae per day than snails under control conditions. The similar pattern seen in all trematodes suggests a general weakening of the host benefiting any of its parasites rather than some parasite species-specific mechanism. In addition, the survival of renicolid cercariae improved with increasing glyphosate concentrations, with cercariae living about 50% longer in the medium concentration (3.6mga.i.L(-1)) than in control conditions. Our results demonstrate a clear interaction between glyphosate pollution and parasitism by trematodes in freshwater systems, occurring at glyphosate concentrations recorded in aquatic habitats, and within the environmental exposure limit allowed in New Zealand freshwaters. Future risk assessments and toxicity tests need to consider indirect impacts resulting from infections to invertebrate and vertebrate species penetrated by cercariae and serving as second intermediate hosts of trematodes.

Fluorescence characterization of the interaction Suwannee river fulvic acid with the herbicide dichlorprop (2-(2,4-dichlorophenoxy)propionic acid) in the absence and presence of aluminum or erbium

This study uses fluorescence spectroscopy to better understand the role of environmental metal ions in the interaction of charged herbicides with biochemical degradation product Suwannee River fulvic acid (SRFA). The interactions between the widely-used herbicide dichlorprop (2-(2,4-dichlorophenoxy)propionic acid) (DCPPA) with Al 3+ and the comparative metal Er 3+ were probed at pH 4.0. Fluorescence experiments on binary solutions at pH 4.0 clearly indicated that Al 3+ and Er 3+ strongly interact with both SRFA and DCPPA alone in solution as demonstrated by fluorescence quenching with DCPPA and enhancement with SRFA by Al 3+ and fluorescence quenching of both SRFA and DCPPA fluorescence by Er 3+. Titrating Al 3+ or Er 3+ to SRFA-DCPPA quenched SRFA fluorescence as compared to the SRFA-metal ion binary complexes. Formation constants were determined using the Ryan-Weber model for the titration data. The DCPPA fluorescence results strongly support the formation of DCPPA-Al 3+ and DCPPA-Er 3+ complexes at pH values above the pK a (3.0) of DCPPA. Excitation and emission data obtained on ternary solutions of SRFA-Al 3+-DCPPA and SRFA-Er 3+-DCPPA complexes at pH 4.0 suggest that at this pH where the predominant DCPPA species is negatively-charged, Al 3+ and Er 3+ metal ions may function to “bridge” negatively-charged fulvic acids to negatively-charged pesticides. Fluorescence data collected on UV-irradiated ternary complexes indicate that both metals can also bridge DCPPA interactions with SRFA under those conditions. The results of our studies suggest that creation of a herbicide-free boundary corridor is recommended near mines and runoff areas with metal ions in surface waters to control possible complexation among fulvic acids, DCPPA and metal ions that maintains these molecules in a bioavailable state to plants and animals.