Herbicides Linuron Research Articles

Inverse modeling of pesticide degradation and pesticide-degrading population size dynamics in a bioremediation system: Parameterizing the Monod model

Pesticide degradation models are compared which simulate the response of biofilters for treatment of pesticide-contaminated waste water to time-irregular pesticide supply in which the pesticide is used for growth and mineralized. Biofilter microcosms containing a mixture of straw, peat and soil and harboring micropopulations which uses the herbicide linuron for growth, were irrigated with linuron for 28 weeks with a stop in its supply between week 12 and 17. Matrix samples were regularly taken to assay linuron mineralization. A first-order approximation of the Monod model was used to simulate the observed mineralization data, while an inverse modeling framework combining a sensitivity analysis (Morris Sensitivity Analysis) with an inverse modeling approach (Shuffled Complex Evolution Metropolis) adopted to parameterize the model. Lag times in linuron mineralization decreased during the initial weeks of linuron irrigation but increased after supply of linuron ceased. The model well-simulated the lag time dynamics which were related to the dynamics of the predicted linuron-degrading population size in the microcosms. It was predicted that the population size decreased at a rate of 0.031 d −1 after pesticide supply ceased to reach its initial population size after 25 weeks. We conclude that modeling pesticide degradation in biofilters should incorporate biomass dynamics in case the pesticide is used as C-source. First-order approaches without incorporating biomass dynamics could lead to underestimation of the risk of pesticide leaching.

Constitutive mineralization of low concentrations of the herbicide linuron by aVariovoraxsp. strain

The mineralization of the herbicide linuron at concentrations of microg and mg L(-1) was studied in liquid batch experiments with Variovorax sp. strain SRS16. The strain was highly efficient at mineralizing a range of linuron concentrations (0.002-10 mg L(-1)) with 20-60% of the added (14)C-ring-labeled linuron metabolized to (14)CO(2) within hours to days depending on the initial linuron concentration and incubation period. At mg L(-1) linuron concentrations the mineralization activity by SRS16 was inducible and a shift to constitutive mineralization activity was apparent with a reduction in the linuron concentration to microg L(-1) levels. This study revealed that strain SRS16 is a promising candidate for bioaugmentation of water or soil resources contaminated with low linuron concentrations.

The herbicide linuron reduces testosterone production from the fetal rat testis during both in utero and in vitro exposures☆

In utero exposure to linuron, an urea-based herbicide, results in a pattern of malformations of androgen-dependent tissues in adult male rat offspring resembling that produced by some phthalate esters which are known to decrease fetal testosterone production. This study investigated the impact of in utero linuron treatment on fetal testis gene expression and testosterone production. Timed-pregnant Sprague Dawley rats were administered corn oil vehicle, 12.5, 25, 50 or 75mg linuron/day/kg orally from GD13 to 18. Ex vivo testosterone (T) production was significantly decreased at 50 and 75mg/kg when analyzed on a per litter basis. Unlike the phthalate esters, linuron treatment did not affect insl3, cyp17a, cyp11a or StAR mRNA expression. Control GD18 fetal testes were then incubated with increasing concentrations of linuron (1-300microM) to evaluate if linuron inhibited T production in vitro. T production was significantly reduced at 30microM and above. Progesterone production was not affected in any of the studies indicating that linuron directly inhibited testosterone production in the absence of cytotoxicity. These results indicate the malformations induced by linuron and phthalate esters in male offspring are similar because both reduce fetal T levels during the critical period of sex differentiation but suggest that the mechanisms differ.

Comparison of fate and ecological effects of the herbicide linuron in freshwater model ecosystems between tropical and temperate regions

This paper compares the fate and effects of linuron in an outdoor plankton-dominated microcosm study carried out in Thailand with those reported in temperate model ecosystem studies evaluating linuron and other photosynthesis-inhibiting herbicides. Lower linuron concentrations disappeared slightly faster from the water compartment compared to temperate conditions, which appears to be related with the experimental design rather than differences in climatic conditions. Sensitivity of primary producers and zooplankton were similar for the climatic regions, whereas effects on ecosystem functioning were less pronounced in tropical microcosms. Recovery potential of affected endpoints appears higher for tropical ecosystems compared to their temperate counterparts. These findings support the use of toxicity data generated in temperate countries in the tropics. Recommendations for the methodology of tropical model ecosystem experiments are discussed.

Ecological effects of the herbicide linuron in tropical freshwater microcosms

Effects of a single application of the photosynthesis-inhibiting herbicide linuron (0, 15, 50, 150, and 500 μg/L) on the ecology of outdoor plankton-dominated microcosms were studied in Thailand. As a result of the decreased photosynthesis, DO and pH decreased while EC, alkalinity and nutrient concentrations increased. Chlorophytes belonging to the genera Scenedesmus, Coelastrum and Pediastrum were the most sensitive taxa, whereas several other chlorophytes, diatoms, and cryptophytes increased in abundance. Tolerant taxa appeared to be less digestable for several zooplankton taxa, which subsequently decreased in abundances. Chamaesiphon sp. (Cyanobacteria) was the most susceptible periphyton species. As a consequence of functional redundancy, effects of the herbicide on the chlorophyll- a content of periphyton and especially phytoplankton did not always reflect the effects noted on community level.

Effects of linuron and dimethenamid on antioxidant systems in weeds associated with soybean

Abstract Changes in antioxidant systems in soybean and associated weeds (Ambrosia artemisiifolia L., Chenopodium album L., Convolvulus arvensis L and Sinapis arvensis L.) were studied in relation to treatment with herbicides linuron and dimethenamid in the field experiment. Differences in the total superoxide dismutase (SOD) and catalase (Cat) activities were observed in plants after application of herbicide formulation. Quantities of superoxide (O2.-) and hydroxyl (·OH) radicals and malonyldialdehyde (MDA), reduced glutathione (GSH) and total polyphenols content were also determined. In addition to this, potential antioxidant activity of the plant ethanolic extracts were assessed based on the scavenging activity of stable DPPH free radicals. Results obtained suggest that plants investigated 1) expressed different antioxidant systems in response to herbicide treatment; 2) enzymatic and non-enzymatic protective mechanisms were complementary; 3) some weed species showed distinctive and combined activity of several biochemical parameters, such as Ambrosia artemisiifolia.

ENDOCRINE EFFECTS OF THE HERBICIDE LINURON ON THE AMERICAN GOLDFINCH (CARDUELIS TRISTIS)

Abstract Certain contaminants alter normal physiological function, morphology, and behavior of exposed organisms through an endocrine mechanism. We evaluated how the herbicide linuron, an endocrine-active compound, affects physiological parameters and secondary sex characteristics of the American Goldfinch (Carduelis tristis). When administered at relatively low doses (control, 1.0, 4.0, and 16.0 μg linuron per gram of body mass per day), linuron delayed prealternate molt progression in a dose-dependent manner. At the high dose level, linuron exposure lowered hematocrit and female plasma thyroxine concentrations and increased body mass. Neither plasma testosterone concentrations nor the color of plumage or integument of birds in the treatment groups were different from those of the control group. Overall, the physiological effects that were measured suggested disruption of thyroid function. These results highlight the importance of continual monitoring of avian populations for potential effects of exposur...

Architecture and spatial organization in a triple-species bacterial biofilm synergistically degrading the phenylurea herbicide linuron

Members of a triple-species 3-(3,4-dichlorophenyl)-1-methoxy-1-methyl urea (linuron)-mineralizing consortium, i.e. the linuron- and 3,4-dichloroaniline-degrading Variovorax sp. WDL1, the 3,4-dichloroaniline-degrading Comamonas testosteroni WDL7 and the N,O-dimethylhydroxylamine-degrading Hyphomicrobium sulfonivorans WDL6, were cultivated as mono- or multi-species biofilms in flow cells irrigated with selective or nonselective media, and examined with confocal laser scanning microscopy. In contrast to mono-species biofilms of Variovorax sp. WDL1, the triple-species consortium biofilm degraded linuron completely through apparent synergistic interactions. The triple-species linuron-fed consortium biofilm displayed a heterogeneous structure with an irregular surface topography that most resembled the topography of linuron-fed mono-species WDL1 biofilms, indicating that WDL1 had a dominating influence on the triple-species biofilm architecture. This architecture was dependent on the carbon source supplied, as the biofilm architecture of WDL1 growing on alternative carbon sources was different from that observed under linuron-fed conditions. Linuron-fed triple-species consortium biofilms consisted of mounds composed of closely associated WDL1, WDL7 and WDL6 cells, while this association was lost when the consortium was grown on a nonselective carbon source. In addition, under linuron-fed conditions, microcolonies displaying associated growth developed rapidly after inoculation. These observations indicate that the spatial organization in the linuron-fed consortium biofilm reflected the metabolic interactions within the consortium.

Linuron and carbaryl differentially impair baseline amino acid and bile salt olfactory responses in three salmonids

For salmon, amino acid and bile salt detection form the basis for important behaviors including predator evasion and conspecific recognition, respectively. For this reason, decreases in olfactory sensory neuron responses to the amino acid l-serine and the bile salt taurocholic acid (TChA) have been used in studies as indicators of acute olfactory pesticide toxicity to environmental contaminants such as metals and pesticides. In this study, we first compare baseline responses to these two odorant classes across three salmonids, and then explore how two currently used pesticides alter these responses. We found baseline differences in electro-olfactogram (EOG) responses and their sensitivity to pesticide exposure between rainbow trout, coho and sockeye salmon. For example, rainbow trout had lower baseline EOGs than either coho or sockeye (e.g. 10 −5 M TChA EOGs of 1.34 ± 0.17 versus 2.57 ± 0.46 and 2.72 ± 0.43 mV, respectively). At 15 min after exposure to 10 μg/L of the herbicide linuron, rainbow l-serine-evoked EOGs were 49.6% of control versus 78.5 and 69.8% for sockeye and coho, indicating rainbow were more sensitive to linuron. In contrast, at 30 min of exposure to 100 μg/L carbaryl, l-serine-evoked EOGs of sockeye were 49.7% of control versus 60.3 and 62.3% for rainbow and coho, suggesting sockeye were more sensitive to carbaryl. In all species the l-serine-evoked EOGs did not return to baseline by 15 min after 100 μg/L carbaryl exposure, suggesting persisting impairment of amino acid detection. The TChA-evoked EOGs were less affected by carbaryl exposure (i.e. EOGs were 83.3, 84.9 and 66.0% of control 15 min after exposure) and not affected at all by 100 μg/L linuron exposure. Species-specific differences in pesticide sensitivity may limit extrapolation of toxicity across salmonids while the generally greater sensitivity of amino acid olfaction may lead to selective impairment of behaviors such as predator evasion.

Functional and structural impact of linuron on a freshwater community of primary producers: The use of immobilized algae

An approach in determining ecosystem integrity and stress on ecosystem level is to assess processes within ecosystems. The aim of the present study was to evaluate the potential use of an in situ assay with immobilized Chlorella vulgaris as an indicator of effects on ecosystem functioning with regard to primary production. The herbicide linuron, applied in concentrations of 20, 60, and 180 microg linuron/L, was used to induce direct effects on primary producers. Direct and indirect changes in structure and function within outdoor model ecosystems of 3 m3 were monitored. The intermediate and highest concentration of linuron caused a decline in growth of the macrophyte Elodea sp., resulting in a significant increase of concentrations of nutrients. The increase in concentrations of nutrients caused an indirectly stimulated growth of immobilized C. vulgaris at the intermediate concentration, whereas similar concentrations of nutrients, at the highest treatment, did not stimulate Chlorella growth. It appeared that the direct effect of linuron on C. vulgaris growth was masked by nutrient availability at the intermediate but not at the highest linuron concentration. The observed immobilized algal growth was an accumulated effect of toxic and trophic pressures within the ecosystem, resulting in an integrative endpoint to detect actual impairment of ecosystem function.

Time-Dependent Absorption Evidence of Phenylurea-Derived Herbicides on Model Biomembranes: A DSC Study

Environmental Context. The need to improve the quality of agricultural cultivation and to control the weed growth of non-cultivated area has brought herbicides to wide-scale use. Unfortunately, these compounds have been proved to be toxic for many organisms, humans included. With an aim to a better knowledge of the mobility and fate of environmental pollutants, it becomes very important to have an exact knowledge of the role that the medium in which these products are dissolved or dispersed plays on the absorption of these products by biological membranes as a complement to information on the interaction between these compounds and cells. Abstract. Phenylurea derivatives are used as herbicides that inhibit photosynthesis. These materials enter plants via their roots and are employed for selective control of germinating grass and broad-leaved weeds in many crops as well as for total weed control of non-cultivated areas such as roads, railways, and parks. The study of the interaction between the herbicide and lipid membrane is interesting in assessing the relevance of the dispersing medium in the absorption processes. Differential scanning calorimetry (DSC), which detects the effect of foreign molecules on the phase transition from an ordered to a disordered lipid structure when submitted to heating, was employed to study such an interaction. Effects exerted by four phenylurea herbicides (difenoxuron, diuron, metoxuron, and linuron) on the thermotropic behavior of model membranes were here investigated. Aqueous dispersions of dimyristoylphosphatidylcholine (DMPC) were used as model membranes to study herbicide–membrane interactions. Experiments carried out by leaving herbicides, in a powdered form, in contact with DMPC-based multilamellar or unilamellar vesicles show that all the examined herbicides are able, but in different ways, to migrate through the aqueous medium and interact with model membranes. Experiments on herbicide-loaded liposomes in contact with empty ones indicate that the compounds are able to migrate from a loaded membrane to an empty one. The obtained data seem to validate the use of the DSC in demonstrating that bioactive and potentially toxic compounds not only to interact with biological membranes but also adsorb into a cell when dispersed in a lipophilic medium.

Nitrate and pesticide leaching from a processing carrot production system in Nova Scotia

Environmental concerns associated with the continuous application of manure on farmland include potential contamination of surface and subsurface aquatic ecosystems. Our objective was to explore the potential environmental impact of utilizing liquid hog manure (LHM) as a fertilizer in carrot (Daucus carota L.) production. The effects of LHM (169 kg N ha-1; 50% assumed to be available), inorganic fertilizer (IF) (NPK; 70-80-100 kg ha-1) treatments and herbicide (linuron) application on the quality of drainage water from a carrot production system in Nova Scotia were examined. Nitrate-N (NO3−-N) (1 mg NO3−-N L-1 ≈ 4.5 NO3− L-1) concentrations resulting from two applications of 70 t ha-1 of LHM and 70 kg N ha-1 as ammonium nitrate (34-0-0) applied to tile-drained plots were monitored over 2 yr. The average NO3−-N concentrations in the drainage discharge were slightly greater for the LHM treatment (14.4 mg L-1) compared to the IF treatment (12.9 mg L-1), but the difference was not statistically significant (P > 0.05). Most drainage and NO3−-N losses occurred outside the growing season (November-April), but average NO3−-N concentrations in the drainage discharge exceeded 10 mg L-1 both during and outside the growing season. Flow rates of drainage discharge were not significantly affected by the fertility treatments. Less than 0.1% of the linuron herbicide applied to the test plots leached into the drainage water over the study period. Carrot yields were unaffected by the fertility treatments. We conclude that LHM is potentially useful source of nutrients for carrot with minimal harm to the environment, under the rates and management practices used in this study. However, excessive rates of application and/or long-term (>10 yr) repeated applications of manure may negatively impact water quality. Key words: Daucus carota, amendment, leaching, manure, yield

Salt effects on the adsorption of a pesticide on modified bentonites

Adsorption of the herbicide linuron on organo-bentonites was measured in the presence of several salts. The bentonites had been modified by cation exchange with hexadecylpyridinium and hexadecyl tributylphosphonium ions. The organo-bentonites adsorbed distinctly higher amounts of linuron than calcium bentonite and desorption was also reduced. The binding coefficient K (derived from the Freundlich adsorption isotherm) was several times higher than for calcium bentonite. The adsorption isotherms of linuron on the organo-bentonites from salt-free aqueous solutions were of S-type but of J-type from saline water. In the presence of many salts, the amount of linuron adsorbed decreased with increasing salt concentration. These salts reduced the linuron adsorption (at a salt concentration of 20 g/L) in the order NaClO4 ≈ KClO4 < NaCl < NaBr < RbCl < CsCl. Only NaI, CsBr, and CsI increased the adsorption of linuron in comparison to salt-free solutions. Desorption of linuron was also reduced in saline (NaCl) solutions. The salt effect may have environmental importance in developing environmentally friendly formulations of herbicides with reduced mobility in soil and enhanced ground water protection.

Response of paraquat-resistant and -susceptible horseweed (Conyza canadensis) to diquat, linuron, and oxyfluorfen

Horseweed is a winter annual weed that has evolved resistance to multiple herbicide modes of action in 11 countries worldwide. A paraquat-resistant horseweed population in an Ontario orchard that was being managed by a rotation of herbicides began to show increased tolerance to the herbicide linuron. Experiments were conducted in the greenhouse to compare the response of this population and several paraquat-susceptible populations to linuron, diquat, and oxyfluorfen. Plants were sprayed with a range of doses of each herbicide when they were from 5 to 10 wk old, and the ED50, or dose at which shoot dry weight was reduced by 50%, was estimated. There was a sevenfold difference in the ED50values of the paraquat-resistant and -susceptible populations in response to diquat and a threefold difference in response to linuron. The response to oxyfluorfen was age dependent. The ratio of resistance to susceptible ED50values was estimated as 57 for 5-wk-old plants and 11 for 8-wk-old plants in response to oxyfluorfen. Ten-week-old plants from both populations showed no response to oxyfluorfen at rates up to 4.8 kg ai ha−1.

Effects of the herbicide linuron on somatic chromosomes ofHelianthus annuusL. (Sunflower)

Abstract In this study the effects of the herbicide linuron on somatic chromosomes of Helianthus annuus L were investigated. The roots were treated with 30, 120, 240 and 500 ppm concentration of linuron for 3, 6 and 12 hours. The mitotic and phase indexes were determined and chromosomal abnormalities were investigated in both control and test groups. It was found that linuron had a marked mitodepressive action on mitosis. The types of chromosomal abnormalities observed included: fragments, disturbed metaphase, c-mitosis, lagging chromosome, and chromatid bridge. A pronounced toxic effect is observed in concentrations 120 ppm and above its. It is considered that linuron may have genotoxic effects in higher plants.

Verification of the prediction technique for the amount of adsorbed linuron on soils

The Freundlich isotherm was used to estimate the adsorption of the herbicide linuron on 39 Japanese soils to confirm the suitability of the prediction technique used in atrazine adsorption. Linuron was adsorbed on the soils according to the Freundlich isotherm. In conjunction with the log K F prediction equation derived from the soil characteristics, it was possible to predict the linuron adsorption. Comparison of the equations for linuron with those for atrazine, indicated that the difference in the intercept of the 1 / n regression line against log K F reflected the adsorptive characteristics of the herbicides.

A chlorophyll a fluorescence-based Lemna minor bioassay to monitor microbial degradation of nanomolar to micromolar concentrations of linuron.

A plant-microbial bioassay, based on the aquatic macrophyte Lemna minor L. (duckweed), was used to monitor biodegradation of nano- and micromolar concentrations of the phenylurea herbicide linuron. After 7 days of exposure to linuron, log-logistic-based dose-response analysis revealed significant growth inhibition on the total frond area of L. minor when linuron concentrations > or = 80 nM were added to the bioassay. A plant-protective effect was obtained for all concentrations > 80 nM by inoculation with either a bacterial consortium or Variovorax paradoxus WDL1, which is probably the main actor in this consortium. The outcome of the plant-microbe-toxicant interaction was also assessed using pulse amplitude-modulated chlorophyll a fluorescence and chlorophyll a fluorescence imaging. Linuron toxicity to L. minor became apparent as a significant decrease in the effective quantum yield (Delta F/Fm') within 90 min after exposure of the plants to linuron concentrations > or = 160 nM. Inoculation of the bioassay with the linuron-degrading bacteria neutralized the effect on the effective quantum yield at concentrations > or = 160 nM, indicating microbial degradation of these concentrations. The chlorophyll a fluorescence-based Lemna bioassay described here offers a sensitive, fast and cost-effective approach to study the potential of biodegrading microorganisms to break down minute concentrations of photosynthesis-inhibiting xenobiotics.

Biodegradation of linuron in a Phaseolus bioassay detected by chlorophyll fluorescence.

• Measuring chlorophyll fluorescence of sensitive indicator plants is a promising approach to follow microbial degradation of the photosystem II (PSII) inhibiting herbicide linuron in a plant-microbial bioassay. • Both pulse amplitude modulation (PAM) fluorimetry and a stroboscope-based Chla fluorescence imaging system were used to monitor the phytotoxic effect of linuron applied to bean (Phaseolus vulgaris) plants. • Inoculation of a hydroponic model system with a linuron-degrading microbial consortium mostly neutralized the phytotoxic effect of the linuron, applied at 0.1 mg l-1 and 1mgl-1 . This indicated that the inoculum was even able to degrade linuron at substrate concentrations (0.1mgl-1 ) that were not detectable by HPLC analysis. The bioprotective effect of the inoculum was also demonstrated when 5mgl-1 of linuron was spiked into a soil substrate. • This is the first report on the use of chlorophyll fluorescence to demonstrate biodegradation. This method is particularly suited for the detection of low linuron concentrations and could probably also be used for other xenobiotics interfering with photosynthesis.

USE OF SOLID PHASE EXTRACTION AND HPLC FOR DETERMINATION OF HERBICIDE MULTIRESIDUE RECOVERIES IN WATER

A method for simultaneous determination of some herbicide residues in water has been developed. The method involves concentration with C18 solid phase extraction (SPE) cartridges followed by high performance liquid chromatographic (HPLC) analysis using a C18 column with diode array detection, a mobile phase of 50 : 50 (v/v) methanol:water at pH=3.75 (phosphoric acid), and a flow rate of 0.8 mL/min. Method recovery was studied for four different levels of fortification: 0.2, 0.4, 2, and 4 μg/L. A plot of recovery mass x added mass verified the influence of fortification levels in recovery. The recoveries obtained were 58 to 118%, with RSD=1–15% (3–7 replicates) for the herbicides bentazon, cyanazine, 2,4-D, atrazine, simazine, diuron, and linuron in water.

Test of Some Aspects of Modelling the Sorption of Hydrophobic Compounds in Soils

A study was carried out on the sorption of the herbicide linuron in podzolic soil (one of the typical soils of Poland), the sorption isotherms being obtained using batch equilibrium studies. Modelling sorption phenomena involving the interactions of chemicals and particularly herbicides is very difficult because of the strong heterogeneity of the soil matrix. The present work presents the results of applying the most common models, i.e. Freundlich and Linear, as well as the newer concept of the Dual Reactive Domain model. The data obtained were validated using various statistical and chemometric methods. The results suggest that applying the non-linear least-squares method to obtain isotherm parameters gave a much better description of the sorption phenomena than often obtained using linear transformations of the adsorption equations. The study also showed that appropriate weighting schemes should be included in any model calculations. To test the goodness-of-fit of the model to the experimental data both the correlation coefficient and the Residual Root Mean Square Error were obtained. The models were also compared using the Extra Sum of Squares Principle statistical test.