Kinetics of the transformation of phenyl-urea herbicides during ozonation of natural waters: rate constants and model predictions

Oxidation of four phenyl-urea herbicides (isoproturon, chlortoluron, diuron, and linuron) was studied by ozone at pH=2, and by a combination of O3/H2O2 at pH=9. These experiments allowed the determination of the rate constants for their reactions with ozone and OH radicals. For reactions with ozone, the following rate constants were obtained: 1.9 +/- 0.2, 16.5 +/- 0.6, 393.5 +/- 8.4, and 2191 +/- 259 M(-1) s(-1) for linuron, diuron, chlortoluron, and isoproturon, respectively. The rate constants for the reaction with OH radicals were (7.9 +/- 0.1) x 10(9) M(-1) s(-1) for isoproturon, (6.9 +/- 0.2) x 10(9) M(-1) s(-1) for chlortoluron, (6.6 +/- 0.1) x 10(5) M(-1) s(-1) for diuron, and (5.9 +/- 0.1) x 10(9) M(-1) s(-1) for linuron. Furthermore, the simultaneous ozonation of these selected herbicides in some natural water systems (a commercial mineral water, a groundwater, and surface water from a reservoir) was studied. The influence of operating conditions (initial ozone dose, nature of herbicides, and type of water systems) on herbicide removal efficiency was established, and the parameter Rct (proposed by Elovitz, M.S., von Gunten, U., 1999. Hydroxyl radical/ozone ratios during ozonation processes. I. The Rct concept. Ozone Sci. Eng. 21, 239-260) was evaluated from simultaneous measurement of ozone and OH radicals. A kinetic model was proposed for the prediction of the elimination rate of herbicides in these natural waters, and application of this model revealed that experimental results and predicted values agreed fairly well. Finally, the partial contributions of direct ozone and radical pathways were evaluated, and the results showed that reaction with OH radicals was the major pathway for the oxidative transformation of diuron and linuron, even when conventional ozonation was applied, while for chlortoluron and isoproturon, direct ozonation was the major pathway.     

The F684/F735 chlorophyll fluorescence ratio: a potential tool for rapid detection and determination of herbicide phytotoxicity in algae

The use of herbicides constitutes the principal method of weed control but the introduction of these compounds into the aquatic environment (primarily through runoff) may have severe consequences for non-target plants. In this study, we describe a sensitive and inexpensive method for detection of photosynthesis-inhibiting herbicides, based on chlorophyll (Chl) fluorescence emission. Algae exhibited a Chl fluorescence signature with two maxima around 684 and 735 nm, correlated with the total Chl content of the algal suspension. The ratio of these two maxima (i.e. F684/F735) can be used as an indicator of stress in the photosynthetic apparatus, and thus represents a very simple method for in vivo evaluation of the health status of algae. Determination of the F684/F735 fluorescence ratio revealed the presence and phytotoxicity of atrazine, metribuzin, terbuthylazine, diuron, DCPMU, DCPU and paraquat. The toxic effect of these pollutants was estimated by monitoring the increase in the F684/F735 value, which reflects photosystem II and photosystem I photochemistry. We observed a drastic increase in the magnitude of this ratio, correlating quantitatively with herbicide concentration and corresponding to a decline in algal photosynthetic activity. For the tested herbicides affecting photosynthetic electron transport, the magnitude of the effect was as follows: diuron= DCPMU > metribuzin > atrazine > terbuthylazine > paraquat > DCPU. The F684/F735 Chl fluorescence ratio thus gives toxicity responses which compare favourably with tests such as the algal growth inhibition test, and could therefore be used to detect the presence and phytotoxicity of herbicides in aquatic environments.     

Pesticide contamination and phytotoxicity of sediment interstitial water to tropical benthic microalgae

Many organic compounds including some herbicides concentrate in sediment, thus it may be expected that interstitial waters contain higher concentrations of these contaminants than the water column. To estimate benthic microalgal exposure to pesticides, sediment and interstitial water sampled in the dry season from four major rivers in north Queensland, Australia, were analysed for these contaminants. Interstitial water extracts from the sediments were tested for acute phytotoxicity to benthic microalgae using PAM fluorometry and the results were compared with chemical analyses of the same water samples. A range of pesticides were detected in both sediment and interstitial waters from all sites, notably the herbicide diuron at concentrations ranging from 0.3 to 11 μg kg⁻¹ dry weight sediment, and up to 68 ng L⁻¹ in interstitial waters. Herbicide concentrations estimated from partition coefficients and the sediment concentrations typically overestimated analytically determined concentrations present in interstitial water by an order of magnitude. The analytically determined herbicide concentrations in the interstitial water explained most of the phytotoxicity measured with the bioassay; however, photoinhibition was slightly higher than expected based on analytical results, indicating the presence of unidentified phytotoxins. These results demonstrate the presence of pesticides in interstitial waters in the Tropical dry season, sometimes at concentrations that may affect sensitive benthic organisms, and supports the use of the I-PAM bioassay as a valuable tool in exposure- and environmental risk- and impact-assessments.     

Occurrence of cotton herbicides and insecticides in playa lakes of the High Plains of West Texas

During the summer of 1997, water samples were collected and analyzed for pesticides from 32 playa lakes of the High Plains that receive drainage from both cotton and corn agriculture in West Texas. The major cotton herbicides detected in the water samples were diuron, fluometuron, metolachlor, norflurazon, and prometryn. Atrazine and propazine, corn and sorghum herbicides, were also routinely detected in samples from the playa lakes. Furthermore, the metabolites of all the herbicides studied were found in the playa lake samples. In some cases, the concentration of metabolites was equal to or exceeded the concentration of the parent compound. The types of metabolites detected suggested that the parent compounds had been transported to and had undergone degradation in the playa lakes. The types of metabolites and the ratio of metabolites to parent compounds may be useful in indicating the time that the herbicides were transported to the playa lakes. The median concentration of total herbicides was 7.2 microg/l, with the largest total concentrations exceeding 30 microg/l. Organophosphate insecticides were detected in only one water sample. Further work will improve the understanding of the fate of these compounds in the playa lake area.     

Interactions of diuron with dissolved organic matter from organic amendments

Diuron is frequently detected in some drinking water reservoirs under the Burgundy vineyards, where organic amendments are applied. The environmental effect of these amendments on pesticide transport is ambiguous: on the one hand it could enhance their retention by increasing soil organic carbon content; on the other hand, dissolved organic matter (DOM) could facilitate their transport. Elutions were performed using columns packed with glass beads in order to investigate DOM-diuron interactions, and the possible co-transport of diuron and DOM. Four organic amendments (A, B, C and D) were tested; C and D were sampled at fresh (F) and mature (M) stages. An increase in diuron leaching was observed only for A and D_F amendments (up to 16% compared to the DOM-free blank samples), suggesting a DOM effect on diuron transport. These results could be explained by the higher DOM leaching for A and D_F compared to B, C_F, C_M and D_M increasing diuron-DOM interactions. These interactions seem to be related to the aromatic and aliphatic content of the DOM, determining formation of hydrogen and non-covalent bonds. The degree of organic matter maturity does not seem to have any effect with amendment C, while a reduction in diuron leaching is observed between D_F and D_M. After equilibrium dialysis measurement of diuron-DOM complexes, it appeared that less than 3% of the diuron applied corresponded to complexes with a molecular weight > 1000 Da. Complexes < 1000 Da could also take part in this facilitated transport.     

Gas chromatography in water analysis—II selective detection methods

Gas chromatographic methods using selective detectors have been applied successfully to the determination of haloforms, herbicides and chlorophosphate esters in water extracts.

Electron capture detection has been used for the determination of the four haloforms, CHCl₃, CHCl₂Br, CHClBr₂ and CHBr₃ in pentane extracts. The very low detection limits render both the extracts and calibration solutions highly susceptible to contamination, and precautions necessary for their handling and storage are described.

Mass spectrometric single ion monitoring of gas chromatographic effluents has been used for the determination of the herbicides MCPA, MCPB and Mecoprop in methylated ether extracts. Possible interference from other components of the water extracts is discussed, and it is concluded that more than one ion should be monitored for each herbicide to minimise the interference.

A flame photometric method involving detection at 528 nm has been developed for the determination of chlorophosphate esters in dichloromethane extracts. The method is extremely specific for phosphorus compounds, but some interference from sulphur compounds may be observed. This can be minimised by the use of high efficiency capillary columns.

Detection limits and linear response ranges for the methods are given, and detector selectivities are discussed. Typical chromatograms are shown, and representative results for raw and treated waters are also given.     

Routine determination of sulfonylurea, imidazolinone, and sulfonamide herbicides at nanogram-per-liter concentrations by solid-phase extraction and liquid chromatography/mass spectrometry

Sulfonylurea (SU), imidazolinone (IMI), and sulfonamide (SA) herbicides are new classes of low-application-rate herbicides increasingly used by farmers. Some of these herbicides affect both weed and crop species at low dosages and must be carefully used. Less is known about the effect of these compounds on non-crop plant species, but a concentration of 100 ng/l in water has been proposed as the threshold for possible plant toxicity for most of these herbicides. Hence, analytical methods must be capable of detecting SUs, IMIs, and SAs at concentrations less than 100 ng/l in ambient water samples. The authors developed a two-cartridge, solid-phase extraction method for isolating 12 SU, 3 IMI, and 1 SA herbicides by using high-performance liquid chromatography/electrospray ionization-mass spectrometry (HPLC/ESI-MS) to identify and quantify these herbicides to 10 ng/l. This method was used to analyze 196 surface- and ground-water samples collected from May to August 1998 throughout the Midwestern United States, and more than 100 quality-assurance and quality-control samples. During the 16 weeks of the study, the HPLC/ESI-MS maintained excellent calibration linearity across the calibration range from 5 to 500 ng/l, with correlation coefficients of 0.9975 or greater. Continuing calibration verification standards at 100-ng/l concentration were analyzed throughout the study, and the average measured concentrations for individual herbicides ranged from 93 to 100 ng/l. Recovery of herbicides from 27 reagent-water samples spiked at 50 and 100 ng/l ranged from 39 to 92%, and averaged 73%. The standard deviation of recoveries ranged from 14 to 26%, and averaged 20%. This variability reflects multiple instruments, operators, and the use of automated and manual sample preparation. Spiked environmental water samples had similar recoveries, although for some herbicides, the sample matrix enhanced recoveries by as much as 200% greater than the spiked concentration. This matrix enhancement was sample- and compound-dependent. Concentrations of herbicides in unspiked duplicate environmental samples were typically within 25% of each other. The results demonstrate the usefulness of HPLC/ESI-MS for determining low-application-rate herbicides at ambient concentrations.     

Emerging pesticide metabolites in groundwater and surface water as determined by the application of a multimethod for 150 pesticide metabolites

A recently developed multimethod for the determination of 150 pesticide metabolites was exemplarily applied to 58 samples of groundwater and surface water. 37 of these metabolites were detected in at least two samples with a concentration ≥0.025 μg/L. The detected metabolites were ranked according to their concentration and frequency of detection. Findings are clearly dominated by metabolites of chloroacetanilide herbicides, but metabolites of sulfonylurea and thiocarbamate herbicides and other herbicides (dichlobenil) together with metabolites of some fungicides (tolylfluanid, chlorothalonil, trifloxystrobin) were also prominent. A number of 17 of the ranked metabolites are denoted as emerging metabolites because no reports on their previous detection in groundwater or surface water were found. Most of them, however, were correctly predicted to occur in the summary reports of the European pesticide approval process. Median total concentrations of the analysed pesticide metabolites summed up to 0.62 μg/L in groundwater and 0.33 μg/L in surface waters. While the concentration of the individual metabolites is usually low (<0.1 μg/L) the diversity of metabolites found in one sample can be large; between two and six metabolites were detected most frequently (maximum of 12 metabolites). Runoff from urban surfaces was investigated in this study and also here previously undetected pesticide (biocide) metabolites were detected. The emerging pesticide metabolites detected in environmental water samples in this study require more extended monitoring.     

Removal of diuron and amitrole from water under static and dynamic conditions using activated carbons in form of fibers, cloth, and grains

This study investigated the removal of the herbicides diuron and amitrole from water under static and dynamic conditions using different activated carbons in the form of fibers, cloth, and grains. In all cases, there was much greater adsorption of diuron than of amitrole due to the lower solubility, greater hydrophobicity, and larger dipolar moment of the former. The activated carbon cloth was the best adsorbent for diuron under dynamic conditions because it had the largest mesopore volume, water-accessible pore volume, and surface area. However, the best adsorbent for amitrole under dynamic conditions was the granular activated carbon due to its higher surface basicity. Comparisons using the best adsorbent for each herbicide showed that diuron was removed by the activated carbon more efficiently compared with amitrole under both dynamic and static conditions.     

In situ relationships between spatio-temporal variations in diuron concentrations and phototrophic biofilm tolerance in a contaminated river

Microbial biofilms are useful indicators for monitoring the ecological state of rivers. When assessing the effects of toxicants on microbial communities in natural ecosystems, special attention must be paid to the distinction between such effects and those resulting from other environmental variables. The pollution-induced community tolerance (PICT) approach offers the means to partially isolate effects of individual toxicants within a complex ecosystem by studying shifts in community sensitivity. To validate PICT for site-specific risk assessment, we investigated how closely diuron tolerance acquisition by photoautrophic biofilm communities could reflect their previous in situ exposure to this herbicide. To this end, a field survey was conducted for 9 months in a French river contaminated by diuron inputs from adjacent vineyards. Spatio-temporal variations in diuron tolerance capacities of photoautotrophic communities were estimated monthly using short-term photosynthetic bioassays. The biological survey was coupled with intensive physico-chemical monitoring to analyze the environmental factors influencing tolerance induction. We revealed a possible influence of three co-varying environmental variables (nitrates, conductivity and temperature), but statistical analysis clearly demonstrated that the main factor explaining variation in diuron sensitivity was the mean in situ diuron exposure level during biofilm colonization periods. A remarkable exponential correlation between EC₅₀ values and in situ diuron concentrations (R² = 0.90, p < 0.0001) was recorded, confirming that PICT can be a powerful tool for the environmental monitoring of rivers.     

混凝土透视仪在古建筑中的运用

喜利得PS1000混凝土透视仪可用于无损结构检测,探测钢筋混凝土结构和内部埋置物体,包括各类金属埋置物,如钢筋,预应力钢绞线,铜管,铝管,钢筋网,钢板,压型钢板等及各类非金属埋置物,如木材,空孔,塑料管道(水管),电缆等,并且定位深度可达30 cm,能高效评估和检查钢筋,钢筋网和检测物体内部的空心楼板,空腔。此次为检测古建筑北面墙体中是否有钢筋网及钢筋网方向、保护层厚度、锈蚀情况,采用喜利得PS1000混凝土透视仪进行无损检测,在达到检测目的同时又不损坏古建筑。     

Assessment of copper bioavailability and toxicity in vineyard runoff waters by DPASV and algal bioassay

The aim of this study was to assess the toxicity of runoff waters in an agricultural multipollution context through an in-depth assessment of copper bioavailability and toxicity. Runoff waters were screened for major ions, metals and diuron. The potential environmental impact of these runoff waters was evaluated using the conventional 72-h growth inhibition test with the green alga Pseudokirchneriella subcapitata. The results suggested that the toxicity detected in the calcareous vineyard field was due to the presence of diuron, whereas the non-calcareous runoff waters were non-toxic. Chemical speciation modelling by MINEQL revealed that most of the copper present in the non-toxic natural runoff waters was complexed by organic matter. These samples were spiked with copper, and then the toxicity and the electrochemically bioavailable copper fraction were measured. Differential pulse anodic stripping voltammetry (DPASV) was used to detect labile complexes and free copper. This combined approach highlighted the presence of some labile copper complexes in samples reaching the EC10-these could have contributed to the copper toxicity.     

Neutral degradates of chloroacetamide herbicides: occurrence in drinking water and removal during conventional water treatment

Treated drinking water samples from 12 water utilities in the Midwestern United States were collected during Fall 2003 and Spring 2004 and were analyzed for selected neutral degradates of chloroacetamide herbicides, along with related compounds. Target analytes included 20 neutral chloroacetamide degradates, six ionic chloroacetamide degradates, four parent chloroacetamide herbicides, three triazine herbicides, and two neutral triazine degradates. In the fall samples, 17 of 20 neutral chloroacetamide degradates were detected in the finished drinking water, while 19 of 20 neutral chloroacetamide degradates were detected in the spring. Median concentrations for the neutral chloroacetamide degradates were ∼2-60 ng/L during both sampling periods. Concentrations measured in the fall samples of treated water were nearly the same as those measured in source waters, despite the variety of treatment trains employed. Significant removals (average of 40% for all compounds) were only found in the spring samples at those utilities that employed activated carbon.     

Removal of phenyl-urea herbicides in ultrapure water by ultrafiltration and nanofiltration processes

Membrane filtration of four phenyl-urea herbicides (linuron, diuron, chlortoluron, and isoproturon) dissolved in ultrapure water was studied in a laboratory cross-flow device in batch concentration mode (with recycling of the retentate stream). Three UF (MWCO of 20 000, 5000 and 2000 Da) and three NF (MWCO of 150-300 Da) membranes were used. The influence of the main operating conditions (transmembrane pressure, tangential velocity, temperature, pH, and MWCO of the membranes) on the steady-state permeate fluxes and the retention factors of the phenyl-ureas was evaluated. The herbicide mass adsorbed onto the membranes was also determined, and the contribution of the fouling resistance to the total resistance to permeate flux was much lower than the inherent resistance of the clean membranes.     

Analysing transformation products of herbicide residues in environmental samples

High-performance liquid chromatography (HPLC) methods were developed for the optimised determination of five herbicide residues (dichlorprop, isoproturon, mecoprop, metsulfuron-methyl and 2,4,5-T) and major metabolites. These compounds represent important groups of herbicides and several residues have been found as contaminants in groundwater. The methods make it possible to study these herbicides and several transformation products through simultaneous detection and quantification. Culture media as well as cleaned up extracts from sediment and groundwater can be analysed. Using HPLC with UV detection the general limit of quantification was 1.8 ng injected corresponding to a detection limit of 1-2 micrograms/l when analysing a cleaned up extract from a 20 ml water sample. The method was verified by analysing herbicide residues in groundwater collected from a wetland area. Cleaning up 20 ml groundwater with a residue level of 25 micrograms/l the general recovery was within 58-82%.     

An algal biosensor for the monitoring of water toxicity in estuarine environments

An algal biosensor for toxicity assessment of estuarine waters is proposed. The sensor was obtained by coupling a suited algal bioreceptor (the cyanobacterium Spirulina subsalsa) to an amperometric gas diffusion electrode. The analytical device allows the monitoring of the evolution of photosynthetic O2 and the detection of alterations due to toxic effects caused by environmental pollutants present in the medium. Four chemical species representative of three main different classes of pollutants (heavy metals, triazinic herbicides, carbamate insecticides) were tested at different concentrations using a standardized natural water as experimental medium. In all the cases a toxic response was detected (i.e. a dose-related inhibition of photosynthetic activity was recorded) with good reproducibility.     

Optimization and validation of a California halibut environmental estrogen bioassay using a heterologous ELISA

Vitellogenin, the estrogen-inducible yolk protein precursor, serves as an indicator of exposure to estrogen mimicking environmental contaminants. An ELISA for the measurement of California halibut plasma vitellogenin was optimized and validated using a commercially-available antibody developed for another flatfish species, turbot. Attempts to enhance assay performance by addition of a biotinylated antibody, polyethylene glycol, and Tween-20, and altering the preincubation step are described. Inclusion of overnight preincubation was critical for low detection limits. Increasing the amount of Tween-20 to 0.05% in buffers was most effective in achieving accurate quantification of spiked plasma samples. At the IC50, the average recovery of spiked plasma samples was 104% and the interplate CV was 12%. The working range of the assay was 33-1000 ng/mL, while the detection limit in a plasma sample is 2.2 μg/mL. The performance of this assay compared very well to a homologous assay demonstrating that commercially-available antibodies can facilitate the development of bioassays for local environmentally-relevant species. The dose response relationship of halibut Vg to the model compounds 17β-estradiol and pnonylphenol show that it is a suitable model for further studies of estrogen mimicking contaminants.     

Monitoring of trifluoroacetic acid concentration in environmental waters in China

It is critically important and extremely meaningful to determine the concentration of TFA in the environmental water in China. This will create background reference for the effects of analyzing the extensive employment of the substitutes to CFCs in China. In this paper a set of analytical methods was described for use in monitoring of trifluoroacetic acid (TFA) concentration of environmental waters including collecting, pre-treatment measures, preserving, concentrating and derivatization of samples from different kinds of environmental waters. The GC with electrical capture detector (ECD) and headspace auto sampler were used in the analysis. The lowest detection limit of the instrument is 0.0004 ng methyl trifluoroacetic acid (MTFA), and the lowest detected concentration with the method is 3.0 ng/ml TFA. TFA collected in various environmental water samples (including rainfall, inland surface water, ground water, and waste water) from nine provinces and autonomous regions in China have been determined by applying the analytical methods created and defined in this work. The results indicate that the concentrations of TFA in nine rainfalls and three snowfalls through the period from 2000 to 2001 ranged from 25 to 220 ng/l, the TFA concentration in the inland surface water samples ranged from 4.7 to 221 ng/l, the concentration of TFA in groundwater samples collected in Beijing was 10 ng/l, and the TFA concentration in coastal water samples ranged from 4.2 to 190.1 ng/l.     

Rapid detection of Escherichia coli in water using a hand-held fluorescence detector

The quantification of pathogenic bacteria in an environmental or clinical sample commonly involves laboratory-based techniques and results are not obtained for 24-72 h after sampling. Enzymatic analysis of microbial activity in water and other environmental samples using fluorescent synthetic substrates are well-established and highly sensitive methods in addition to providing a measure of specificity towards indicative bacteria. The enzyme β-d-glucuronidase (GUD) is a specific marker for Escherichia coli and 4-methylumbelliferone-β-d-glucuronide (MUG) a sensitive substrate for determining the presence of E. coli in a sample. However, currently used procedures are laboratory-based and require bench-top fluorimeters for the measurement of fluorescence resulting from the enzyme-substrate reaction. Recent developments in electronic engineering have led to the miniaturisation of fluorescence detectors. We describe the use of a novel hand-held fluorimeter to directly analyse samples obtained from the River Thames for the presence of E. coli. The results obtained by the hand-held detector were compared with those obtained with an established fluorescent substrate assay and by quantifying microbial growth on a chromogenic medium. Both reference methods utilised filtration of water samples. The miniaturised fluorescence detector was used and incubation times reduced to 30 min making the detection system portable and rapid. The developed hand-held system reliably detected E. coli as low as 7 cfu/mL river water sample. Our study demonstrates that new hand-held fluorescence measurement technology can be applied to the rapid and convenient detection of bacteria in environmental samples. This enables rapid monitoring to be carried out on-site. The technique described is generic and it may, therefore, be used in conjunction with different fluorescent substrates which allows the assessment of various target microorganisms in biological samples.     

Routine analysis of off-flavor compounds in water at sub-part-per-trillion level by large-volume injection GC/MS with programmable temperature vaporizing inlet

"Earthy-musty" off-flavor problem in water samples are due to organic compounds present at the sub-part-per-trillion level. Most of the developments in the analysis of tastes and odorous compounds focus on the extraction pre-concentration technique, with detection at picogram per liter level of the earthy-musty off-flavor compounds difficult to be achieved. The objective of this study is to develop a new method involving the large-volume injection (LVI) GC/MS via programmable temperature vaporizing (PTV) inlet and continuous liquid-liquid extraction, to attain analytical sensitivity equal to or better than olfactory sensitivity. Six "earthy-musty" organic compounds, 2-methylisoborneol (MIB), geosmin, 2,4,6-trichloroanisole, 2,3,6-trichloroanisole, 2,3,4-trichloroanisole and 2,4,6-tribromoanisole, were used as probes for this study. It was found that LVI via PTV could greatly improve system sensitivity towards off-flavor compound detection. Variable instrument conditions and sample preparation conditions were studied in detail. This reliable and efficient method has been optimized and validated. The method detection limit were found to be from 35 to 70 pg/L for haloanisoles, 50 pg/L for geosmin and 0.34 ng/L for MIB, with relative standard deviation of calibration curve ranging from 4.7% to 15.1% and recovery ranging from 58% to 96%. This method has been successfully applied to test off-flavor compounds in different types of water samples with satisfactory results.