Compliance analysis of phenylurea and related compounds in drinking water by liquid chromatography/electrospray ionization/mass spectrometry coupled with solid-phase extraction

Direct Spectrofluorimetric Method for the Analysis of Carbofuran and Fluometuron in Senegalese Natural Waters

In this work, analytical study of carbofuran (CAF) and fluometuron (FLM) pesticides was carried out using direct spectrofluorimetric method in various solvents. Results showed that CAF and FLM are naturally fluorescent in all solvents under study including organic (MeOH, MeCN, DMF) and aqueous micellar one (CTAC, SDS, Brij-700). For the analysis of FLM, CTAC give the best fluorescence signal enhancement. Analytical performances, such as limit of detection (LOD) and quantification (LOQ) was evaluated after solvent optimization and were found to vary, respectively, between 0.1 and 11 ng mL- 1 and between 0.3 and 36.6 ng mL- 1. Analytical application in various environmental aqueous samples matrices (sea, tap, runoff and well waters) give satisfactory recovery rates in the limits of 73.7-113.7% for both pesticides. This method is described for its simplicity for routine analysis.

Monoclonal Antibody-Based Immunosensor for the Electrochemical Detection of Chlortoluron Herbicide in Groundwaters

Chlortoluron (3-(3-chloro-p-tolyl)-1,1-dimethyl urea) is an herbicide widely used in substitution to isoproturon to control grass weed in wheat and barley crops. Chlortoluron has been detected in groundwaters for more than 20 years; and dramatic increases in concentrations are observed after intense rain outbreaks. In this context; we developed an immunosensor for the determination of chlortoluron based on competitive binding of specific monoclonal antibodies on chlortoluron and immobilized biotinylated chlortoluron; followed by electrochemical detection on screen-printed carbon electrodes. The optimized immunosensor exhibited a logarithmic response in the range 0.01-10 µg·L-1; with a calculated detection limit (LOD) of 22.4 ng·L-1; which is below the maximum levels allowed by the legislation (0.1 µg·L-1). The immunosensor was used for the determination of chlortoluron in natural groundwaters, showing the absence of matrix effects.

A core-shell structured magnetic covalent organic framework as a magnetic solid-phase extraction adsorbent for phenylurea herbicides

In this work, a core-shell structured magnetic covalent organic framework named as M-TpDAB was constructed with 3,3'-diaminobenzidine (DAB) and 1,3,5-triformylphloroglucinol (Tp) as building units. M-TpDAB was characterized by infrared spectroscopy, nitrogen adsorption-desorption isotherms, powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Using the M-TpDAB as adsorbent, a simple and highly effective method was proposed for preconcentrating phenylurea herbicides before high performance liquid-phase chromatography analysis. In the optimized conditions, a good linearity was achieved within the range of 0.15-100 ng mL^-1 for water sample, 1.0-100.0 ng mL^-1 for tea drink samples. The limits of detection for the analytes were 0.05-0.15 ng mL^-1 for water sample and 0.30-0.50 ng mL^-1 for drink samples. Satisfactory recoveries of spiked target compounds were in the range of 84.6%-105% for water sample and 80.3%-102% for tea drink samples. Finally, the M-TpDAB based method was successfully used to determine phenylurea herbicides in tea drinks and water samples, demonstrating a good alternative for analyzing trace level of phenylurea herbicides in water samples.

Growth-Stimulatory Effect of Quorum Sensing Signal Molecule N-Acyl-Homoserine Lactone-Producing Multi-Trait Aeromonas spp. on Wheat Genotypes Under Salt Stress

Salinity is one of the major threats to agricultural productivity worldwide. Soil and plant management practices, along with inoculation with plant-beneficial bacteria, play a key role in the plant’s tolerance toward salinity stress. The present study demonstrates the potential of acyl homoserine lactone (AHL)-producing plant growth promoting rhizobacteria (PGPR) strains of Aeromonas sp., namely, SAL-17 (accession no. HG763857) and SAL-21 (accession no. HG763858), for growth promotion of two wheat genotypes inherently different for salt tolerance potential. AHLs are the bacterial signal molecules that regulate the expression of various genes in bacteria and plants. Both Aeromonas spp., along with innate plant-growth-promoting (PGP) and salt tolerance traits, showed AHL production which was identified on tandem mass spectrometry as C6-HSL, 3-OH-C5-HSL, 3-OH-C6-HSL, 3-oxo-C7-HSL C10-HSL, 3-oxo-C10-HSL, 3-OH-C10-HSL, 3-oxo-C12-HSL and C6-HSL, and 3-oxo-C10-HSL. The exogenous application of purified AHLs (mix) significantly improved various root parameters at 200 mM NaCl in both salt-sensitive (SSG) and salt-tolerant (STG) genotypes, where the highest increase (≈80%) was observed where a mixture of both strains of AHLs was used. Confocal microscopic observations and root overlay assay revealed a strong root colonization potential of the two strains under salt stress. The inoculation response of both STG and SSG genotypes was evaluated with two AHL-producing strains (SAL-17 and SAL-21) and compared to non-AHL-producing Aeromonas sp. SAL-12 (accession no. HG763856) in saline (EC = 7.63 ms/cm²) and non-saline soil. The data reveal that plants inoculated with the bacterial consortium (SAL-21 + SAL-17) showed a maximum increase in leaf proline content, nitrate reductase activity, chlorophyll a/b, stomatal conductance, transpiration rate, root length, shoot length, and grain weight over non-inoculated plants grown in saline soil. Both STG and SSG showed relative effectiveness toward inoculation (percent increase for STG: 165–16%; SSG: 283–14%) and showed a positive correlation of grain yield with proline and nitrate reductase activity. Furthermore, principal component analysis (PCA) and categorical PCA analysis clearly showed an inoculation response in both genotypes, revealing the effectiveness of AHL-producing Aeromonas spp. than the non-AHL-producing strain. The present study documents that the consortium of salt-tolerant AHL-producing Aeromonas spp. is equally effective for sustaining the growth of STG as well as SSG wheat genotypes in saline soil, but biosafety should be fully ensured before field release.

Characteristics of N-Acylhomoserine Lactones Produced by Hafnia alvei H4 Isolated from Spoiled Instant Sea Cucumber

This study aimed to identify N-acylhomoserine lactone (AHL) produced by Hafnia alvei H4, which was isolated from spoiled instant sea cucumber, and to investigate the effect of AHLs on biofilm formation. Two biosensor strains, Chromobacterium violaceum CV026 and Agrobacterium tumefaciens KYC55, were used to detect the quorum sensing (QS) activity of H. alvei H4 and to confirm the existence of AHL-mediated QS system. Thin layer chromatography (TLC) and high resolution triple quadrupole liquid chromatography/mass spectrometry (LC/MS) analysis of the AHLs extracted from the culture supernatant of H. alvei H4 revealed the existence of at least three AHLs: N-hexanoyl-l-homoserine lactone (C6-HSL), N-(3-oxo-octanoyl)-l-homoserine lactone (3-oxo-C8-HSL), and N-butyryl-l-homoserine lactone (C4-HSL). This is the first report of the production of C4-HSL by H. alvei. In order to determine the relationship between the production of AHL by H. alvei H4 and bacterial growth, the β-galactosidase assay was employed to monitor AHL activity during a 48-h growth phase. AHLs production reached a maximum level of 134.6 Miller unites at late log phase (after 18 h) and then decreased to a stable level of about 100 Miller unites. AHL production and bacterial growth displayed a similar trend, suggesting that growth of H. alvei H4 might be regulated by QS. The effect of AHLs on biofilm formation of H. alvei H4 was investigated by adding exogenous AHLs (C4-HSL, C6-HSL and 3-oxo-C8-HSL) to H. alvei H4 culture. Biofilm formation was significantly promoted (p < 0.05) by 5 and 10 µM C6-HSL, inhibited (p < 0.05) by C4-HSL (5 and 10 µM) and 5 µM 3-oxo-C8-HSL, suggesting that QS may have a regulatory role in the biofilm formation of H. alvei H4.

Functional characterization of a soybean growth stimulator Bradyrhizobium sp. strain SR-6 showing acylhomoserine lactone production

A soybean nodule endophytic bacterium Bradyrhizobium sp. strain SR-6 was characterized for production of acyl homoserine lactones (AHLs) as quorum sensing molecules. Mass spectrometry analysis of AHLs revealed the presence of C6-HSL, 3OH-C6-HSL, C8-HSL, C10-HSL, 3oxoC10-HSL, 3oxo-C12-HSL and 3OH-C12-HSL which are significantly different from those reported earlier in soybean symbionts. Purified AHL extracts significantly improved wheat and soybean seedling growth and root hair development along with increased soybean nodulation under axenic conditions. A positive correlation was observed among in vivo nitrogenase and catalase enzyme activities of the strain SR-6. Transmission electron microscopic analysis showed the cytochemical localization of catalase activity within the bacteroids, specifically attached to the peribacteroidal membrane. Root and nodule colonization proved rhizosphere competence of SR-6. The inoculation of SR-6 resulted in increased shoot length (13%), plant dry matter (50%), grain weight (16%), seed yield (20%) and N-uptake (14%) as compared to non-inoculated soybean plants. The symbiotic bacterium SR-6 has potential to improve soybean growth and yield in sub-humid climate of Azad Jammu and Kashmir region of Pakistan. The production and mass spectrometric profiling of AHLs as well as in vivo cytochemical localization of catalase enzyme activity in soybean Bradyrhizobium sp. have never been reported earlier elsewhere before our these investigations.

Investigation of photodegradation and hydrolysis of selected substituted urea and organophosphate pesticides in water

INTRODUCTION

Photodegradation and hydrolysis of two substituted urea herbicides, monolinuron [3-(4-chlorophenyl)-1-methoxy-1-methylurea] and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], and one organophosphorous insecticide, phoxim [2-(diethoxyphosphinothioyloxyimino)-2-phenylacetonitrile], were studied using buffered sterilized distilled water (pH 4, 7 and 9).

METHODS

Experiments were performed in the absence and presence of light (320-740 nm), while the effect of nitrates and humic acids on photodegradation was investigated for all pH values. An analytical method was developed and validated for the determination of target compounds in water samples using liquid chromatography positive ion electrospray-mass spectrometry.

RESULTS

According to the results, substituted ureas neither hydrolyzed, at all tested pH values, nor photodegraded at pH 7 and 9. Slow photodegradation of the compounds was observed at pH 4. During 70 days of light exposure, initial concentrations of linuron and monolinuron were decreased by 54% and 31%, respectively, while the presence of nitrates slightly enhanced photodegradation of these compounds. On the other hand, phoxim was found to be very unstable for all the tested conditions and an increase of pH resulted to higher degradation. During hydrolysis experiments, the degradation of the compound ranged from 41% (pH 4) to 85% (pH 9) and the half-lives varied from 10 h (pH 9) to 204 h (pH 4). The presence of light enhanced phoxim degradation and as a result half-lives of 37, 22 and 9h were calculated for pH 4, 7 and 9, respectively. The addition of nitrates and humic acids did not significantly affect the photodegradation of phoxim.

CONCLUSIONS

The results indicated that among the three tested pesticides, phoxim found to be the most sensitive in both photodegradation and hydrolysis.

Fate of organohalogens in US wastewater treatment plants and estimated chemical releases to soils nationwide from biosolids recycling

This study examined the occurrence in wastewater of 11 aromatic biocides, pesticides and degradates, and their fate during passage through US treatment plants, as well as the chemical mass contained in sewage sludge (biosolids) destined for land application. Analyte concentrations in wastewater influent, effluent and sludge from 25 facilities in 18 US states were determined by liquid chromatography electrospray (tandem) mass spectrometry. Dichlorocarbanilide, fipronil, triclocarban, and triclosan were found consistently in all sample types. Dichlorophene, hexachlorophene, and tetrachlorocarbanilide were detected infrequently only, and concentrations of the phenyl urea pesticides diflubenzuron, hexaflumuron, and linuron were below the limit of detection in all matrixes. Median concentrations (+/-95% confidence interval) of quantifiable compounds in influent ranged from 4.2 +/- 0.8 microg L(-1) for triclocarban to 0.03 +/- 0.01 microg L(-1) for fipronil. Median concentrations in effluent were highest for triclocarban and triclosan (0.23 +/- 0.08 and 0.07 +/- 0.04 microg L(-1), respectively). Median aqueous-phase removal efficiencies (+/-95% CI) of activated sludge treatment plants decreased in the order of: triclosan (96 +/- 2%) > triclocarban (87 +/- 7%) > dichlorocarbanilide (55 +/- 20%) > fipronil (18 +/- 22%). Median concentrations of organohalogens were typically higher in anaerobically than in aerobically digested sludges, and peaked at 27 600 +/- 9600 and 15 800 +/- 8200 microg kg(-1) for triclocarban and triclosan, respectively. Mass balances obtained for three primary pesticides in six activated sludge treatment plants employing anaerobic digestion suggested a decreasing overall persistence from fipronil (97 +/- 70%) to triclocarban (87 +/- 29%) to triclosan (28 +/- 30%). Nationwide release of the investigated organohalogens to agricultural land via municipal sludge recycling and into surface waters is estimated to total 258 000 +/- 110 00 kg year(-1) (mean +/- 95% confidence interval), with most of this mass derived from antimicrobial consumer products of daily use. This study addresses some of the data gaps identified by the National Research Council in its 2002 study on standards and practices of biosolids application on land.