The environmental fate of diuron under a conventional production regime in a sugarcane farm during the plant cane phase

BACKGROUND: Field studies of diuron and its metabolites 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU), 3,4-dichlorophenylurea (DCPU) and 3,4-dichloroaniline (DCA) were conducted in a farm soil and in stream sediments in coastal Queensland, Australia. RESULTS: During a 38 week period after a 1.6 kg ha(-1) diuron application, 70-100% of detected compounds were within 0-15 cm of the farm soil, and 3-10% reached the 30-45 cm depth. First-order t(1/2) degradation averaged 49+/-0.9 days for the 0-15, 0-30 and 0-45 cm soil depths. Farm runoff was collected in the first 13-50 min of episodes lasting 55-90 min. Average concentrations of diuron, DCPU and DCPMU in runoff were 93, 30 and 83-825 microg L(-1) respectively. Their total loading in all runoff was >0.6% of applied diuron. Diuron and DCPMU concentrations in stream sediments were between 3-22 and 4-31 microg kg(-1) soil respectively. The DCPMU/diuron sediment ratio was >1. CONCLUSION: Retention of diuron and its metabolites in farm topsoil indicated their negligible potential for groundwater contamination. Minimal amounts of diuron and DCMPU escaped in farm runoff. This may entail a significant loading into the wider environment at annual amounts of application. The concentrations and ratio of diuron and DCPMU in stream sediments indicated that they had prolonged residence times and potential for accumulation in sediments. The higher ecotoxicity of DCPMU compared with diuron and the combined presence of both compounds in stream sediments suggest that together they would have a greater impact on sensitive aquatic species than as currently apportioned by assessments that are based upon diuron alone.     

Diuron mineralisation in a Mediterranean vineyard soil: impact of moisture content and temperature

BACKGROUND: The diuron‐mineralising ability of the microbiota of a Mediterranean vineyard soil exposed each year to this herbicide was measured. The impact of soil moisture and temperature on this microbial activity was assessed. RESULTS: The soil microbiota was shown to mineralise diuron. This mineralising activity was positively correlated with soil moisture content, being negligible at 5% and more than 30% at 20% soil moisture content. According to a double Gaussian model applied to fit the dataset, the optimum temperature/soil moisture conditions were 27.9 °C/19.3% for maximum mineralisation rate and 21.9 °C/18.3% for maximum percentage mineralisation. The impact of temperature and soil moisture content variations on diuron mineralisation was estimated. A simulated drought period had a suppressive effect on subsequent diuron mineralisation. This drought effect was more marked when higher temperatures were used to dry (40 °C versus 28 °C) or incubate (28 °C versus 20 °C) the soil. The diuron kinetic parameters measured after drought conditions were no longer in accordance with those estimated by the Gaussian model. CONCLUSION: Although soil microbiota can adapt to diuron mineralisation, its activity is strongly dependent on climatic conditions. It suggests that diuron is not rapidly degraded under Mediterranean climate, and that arable Mediterranean soils are likely to accumulate diuron residues. Copyright © 2010 Society of Chemical Industry     

The in vitro sensitivity of some species of Chlorophyceae to a selected range of herbicides

A survey was undertaken to establish the sensitivity of seventeen algal strains belonging to the Chlorophyceae to a selected range of herbicides up to a concentration maximum of 10 ppm under in vitro conditions. The herbicides were found to vary considerably in their toxicity to algae and a sequence was established based upon the magnitude of this toxicity: diuron > bromacil > paraquat> monuron> diquat> linuron> 2, 4-DB >barban> dicamba, dichlobenil, dalapon, picloram> bromoxynil, 2,3,6-TBA > 2.4-DP. 2,4,5-T and EPTAM. Of the algae, the most sensitive genera were Hormidium and Haematococcus, and the strain most sensitive to a wide range of herbicides was Hormidium barlowi (strain 335/la).     

10种除草剂对斜生栅藻的生长抑制活性研究

本文采用吸光度法测定了10个除草剂对斜生栅藻的生长抑制活性,其中包括3个原药和7个制剂产品,涉及12种有效成分。结果表明有5个药剂对斜生栅藻表现高毒,2个药剂为中等毒性,仅3个药剂为低毒。总体上磺酰脲类除草剂以及敌草隆、酰苯胺类吡唑草胺和吡氟酰草胺对斜生栅藻的毒性均较高。     

Influence of adsorption–desorption phenomena on pesticide run-off from soil using simulated rainfall

The surface run-off of a number of pesticides (diuron, isoproturon, atrazine, alachlor, aclonifen, trifluralin, lindane and simazine), chosen for their range of adsorption behaviours, was studied using simulated rainfall applied to small plots over a short time (one hour). Pesticides were applied together onto bare soil using two different sandy loam soils from Jaillière and Coet Dan sites. The surface run-off samples were collected throughout the running of the event and concentrations of pesticides were measured in both liquid and solid phases. Sorption isotherms for isoproturon and diuron on Jaillière soil as well as eroded particles were measured under equilibrium conditions and compared to their partitioning during surface run-off. At the rainfall intensity used, both soils generated a large load of eroded particles. The average run-off flow rate increased with time for the Jalliére soil, while it remained relatively constant at a higher level for the Coet Dan soil. The concentrations of each pesticide in the run-off samples decreased as the experiments proceeded. The pesticides were classified into two types by their partitioning between the solid and liquid phases. Atrazine, simazine, diuron, isoproturon and alachlor were mainly transported in surface run-off water. By contrast, 90% of trifluralin and aclonifen was adsorbed onto eroded particles. Lindane was intermediate, with a 37% adsorption level. When the contribution of eroded particles was minor, the agrochemical concentrations were inversely proportional to the water flow rate. We have proposed a model that describes the mass of chemicals extracted from soil into surface water during a surface run-off event of a given average duration and flow rate. This model takes into account the dilution of the soil solution and the desorption of chemicals through two parameters called, respectively, the dilution factor and the extraction retardation factor. The desorption kinetic was the limiting step in the surface run-off of weakly sorbed chemicals, such as isoproturon. © 1999 Society of Chemical Industry     

Residues of diuron and phytotoxic degradation products in aquatic situations. II. Diuron in irrigation water

When diuron is used as a soil-residual herbicide in irrigation canals, water quality is protected in standard practice by ‘flushing’–the diversion of the first discharge of water to the drainage system before irrigation is resumed. In three canals treated with diuron at about 40–45 kg ha^?1, flushing for 4 h was relatively inefficient, removing 15% or less of the residual diuron in the sediment. In one other canal approximately 40% was removed during flushing. Cumulative loss of diuron was proportional to the square root of the time of water discharge. The effect of the time interval between treatment and flushing was investigated in trials on soils of typically heavy texture. When flushing closely followed treatment about 6 kg diuron ha^?1 was removed but in three trials, for a range of times from treatment of 5–15 weeks, losses were similar and about 2.5 kg ha^?1, suggesting that a restriction of longer than 5 weeks is unlikely to reduce contamination. In a contrasting soil of sandier texture greater movement of diuron away from the sediment surface probably contributed to a five-fold reduction of diuron extracted in flushing. These data were used to calculate the effects of flushing time on both the concentrations of diuron in water discharged to drains for subsequent re-use and the concentrations in the irrigation water, to aid assessment of hazard to crops. Flushing times required for residues in water to reach 0.1 μg ml^?1, calculated by extrapolation, were in the order of days so that it may be necessary to restrict the use of diuron to farms which can retain the discharge water within their own boundaries, or to areas where dilution in receiving waters can be shown to be adequate.     

Potential for microbial diuron mineralisation in a small wine‐growing watershed: from treated plots to lotic receiver hydrosystem

BACKGROUND: Since biological degradation processes are known to be a major driver of the natural attenuation of pesticide residues in the environment, microbial communities adapted to pesticide biodegradation are likely to play a key environmental role in reducing pesticide exposure in contaminated ecosystems. The aim of this study was to assess the diuron‐mineralising potential of microbial communities at a small‐scale watershed level, including a diuron‐treated vineyard (pollution source), its associated grass buffer strip (as a river protection area against pesticide runoff) and the lotic receiver hydrosystem (sediments and epilithon), by using radiorespirometry. RESULTS: Comparison of results obtained at different sampling sites (in both soil and aquatic systems) revealed the importance of diuron exposure in the adaptation of microbial communities to rapid diuron mineralisation in the vineyard but also in the contaminated grass strip and in downstream epilithic biofilms and sediments. CONCLUSION: This study provides strong suggestive evidence for high diuron biodegradation potential throughout its course, from the pollution source to the final receiving hydrosystem, and suggests that, after microbial adaptation, grass strips may represent an effective environmental tool for mineralisation and attenuation of intercepted pesticides. Copyright © 2009 Society of Chemical Industry     

Chemical weed control in rainfed cowpea (Vigna unguiculata (L.) Walp) in the Guinea savanna zone of Nigeria

In a field trial in 1978 at Mokwa, southern Guinea savanna zone of Nigeria, metolachlor at 1.5 and 3.0, prometryne at 2.0 and norflurazon and diuron at 1.6 kg/ha combined good weed control with high grain yield of cowpeas. The grain yields with these herbicides were comparable to those of the hoe-weeded and significantly higher than the weedy controls. In 1979, under wetter conditions, crop injury was observed with prometryne and linuron at 2.0 kg/ha. However, the grain yields obtained with alachlor, metolachlor, chloramben, pendimethalin and norflurazon and their mixtures with prometryne, linuron, diuron or metobromuron were comparable to that of the hoe-weeded treatment. In 1979 at Samaru, northern Guinea savanna, pendimethalin at 1.5, metolachlor at 3.0 and chlorbromuron and linuron at 1.0 kg/ha gave selective weed control. Prometryne at 2.0 kg/ha was the only herbicide that gave a significantly lower broad-leaved weed weight than the weedy check but it reduced the crop stand. At 1.0 kg/ha it was tolerated by the crop but failed to control grasses. Metolachlor at 1.5 kg/ha had a significantly higher broad-leaved weed weight than the weedy check. All theherbicides, except pendimethalin at 3.0 kg/ha, controlled the annual sedges at Samaru.     

THE CONTROL OF WEEDS IN TEA BY HERBICIDES IN MAURITIUS

Summary. Weed control experiments carried out in tea plantations showed that diuron at doses 2·4, 3·2 and 4·8 lb/ac a.i. resulted in better and more persistent weed control than siamazine.
Shoot absorption experiments carried out on three tea jats, dark, medium and light, showed that the tea jats differed in their tolerance to both diuron and simazine, the light one being the most susceptible.
A difference IN the expression of phytotoxic effects between leaf and root absorption was observed for diuron only. At equivalent doses, 2-year-old plants were in general more susceptible to diuron than to simazine.
Diuron and simazine used alone at 2·4, 3·2 and 4·8 lb/ac a.i. or with addition of sodium chlorate at 6 lb/ac to improve the kill of emerged weeds, did not affect yield of either pruned unpruned 6-year-oId tea. Dalapon, on the other hand, at 6 lb/ac significantly reduced the yield of unpruned tea but not of pruned lea.
Le désherbage chimique du théè l'lle Maurice     

Rainfastness and adsorption of herbicides on hard surfaces

Herbicides are still used to control weeds on hard surfaces, including municipal, private and industrial sites. Used under unfavourable conditions, especially when rain occurs shortly after application, herbicides may run off to surface waters. Such losses of herbicides from hard surfaces are estimated to be much higher than for herbicides used in arable fields. In this study, three kinds of hard surface were evaluated: asphalt, concrete surface and gravel (fine and coarse). Three herbicides were applied: glyphosate, diuron and diflufenican. Adsorption isotherms of diuron and diflufenican to the three surfaces were determined. At different times after treatment with the herbicides, rainfall was simulated by use of a rain-droplet spray nozzle, and the run-off was collected for analysis. After this run-off event, the materials were immersed in water to measure desorption which, together with the compound in the run-off, gave a measure of the dislodgable residues. The apolar herbicides diuron and especially diflufenican adsorbed strongly to asphalt. The polar herbicide glyphosate lost 75% in run-off from asphalt but was adsorbed strongly to soil and concrete pavement.     

OBSERVATIONS ON THE RELATIONSHIP BETWEEN THE ADSORPTION OF DIURON AND THE NATURE OF THE ADSORBENT

Summary. A series of adsorption experiments was carried out in order to determine if there was significant competition for adsorption sites between diuron and water. Adsorption of diuron was much lower on hydrophilic materials such as cellulose, chitin, aluminium oxide and a soil mineral fraction than on the less hydrophilic ion exchange resins, lignin, carbon and a soil organic fraction. Methylation with methanolic HCL or diazomethane increased adsorption by the soil organic material, but methylation with dimethyl sulphate did not.
The soil mineral fraction adsorbed considerably more diuron from petroleum spirit solution than from aqueous solution, but the organic matter preparation adsorbed more from aqueous than from petroleum solution.
It was concluded that there is competition between water and diuron for adsorption sites and that diuron is a more effective competitor at soil organic matter surfaces than at soil mineral matter surfaces.
Observations sur la relation entre l'adsorption du diuron el la nature de l'adsorbant     

Study of diuron in soil solution by means of a novel simple technique using glass microfibre filters

Retention by a glass fibre filter of the liquid phase of a clay loam soil treated with ¹⁴C-diuron provides a novel method for analysis of the herbicide in soil solution. At 26.3% (w/w) soil moisture content, less than 10% of the applied diuron was found in solution, and this percentage decreased slightly with diuron dose. The herbicide was rapidly adsorbed on soil during the first day, but adsorption continued and the concentration of diuron in solution could be further reduced by 36–50% during the following 6 days. Drying the soil after treatment, with possible crystallization of herbicide applied at high doses, tended to fix the solution concentrations. Ethanol (3% v/v) in soil water favoured herbicide dissolution. Increasing soil moisture to 36.3% (w/w) slightly decreased the concentration of the herbicide in solution, but increased the percentage held in solution. Frost and a drying-rewetting cycle had little or no subsequent effect on diuron concentration in soil solution.     

ROOTING CHARACTERISTICS AND VARIETAL TOLERANCE OF SUGARCANE TO DIURON

Summary. The relative susceptibility of six commercial sugarcane varieties to diuron previously described was confirmed in a second similar experiment. A significant correlation was found between the susceptibility of these varieties to 10 kg/ha diuron and their rooting characteristics. The more susceptible varieties were found to produce larger sett-roots and smaller shoot-roots, both of which also tended to be more easily injured by diuron. The root injury appeared as'burnt'root tips resulting from contact with the layer of soil treated by the herbicide. The roots of tolerant varieties seemed to be immune to such injury and continued growing after penetrating the contaminated soil layers. Retarded plant growth appeared to result from the root injury.
Uptake of diuron through shoot-roots of the susceptible variety F 156 resulted in 68·5% growth retardation. This damage was reduced by 15·5% if the plants were allowed to develop sett-roots from two-bud cutting. Death of the plant resulted when both root systems received the same dose of herbicide.     

Relationships between substituted urea herbicides and soil urease activity

Fenuron, monuron, diuron, siduron, linuron and neburon were tested for their inhibition of soil urease activity in order to investigate relationships between fertilizers and herbicides. The inhibition of urea hydrolysis in the selected soils was 10–33% for fenuron, 10–39% for monuron, 10–35% for diuron, 8–38% for siduron, 9–36% for linuron and 12–30% for neburon. In the field greater effects might be expected since the fertilizer/herbicide ratio would be lower than the one considered here. Some agronomic aspects of the relationship between fertilizers and herbicides are discussed.     

A psbA mutation in Kochia scoparia (L) Schrad from railroad rights-of-way with resistance to diuron, tebuthiuron and metribuzin

Kochia [Kochia scoparia (L) Schrad] has become resistant to many herbicides used in cropland and railroad rights-of-way in North Dakota and Minnesota. Kochia scoparia plants that had survived annual treatments with diuron and tebuthiuron were sampled along railroad rights-of-way in North Dakota and Minnesota. The samples were screened in the greenhouse for resistance to diuron, tebuthiuron, metribuzin and bromoxynil from 0.5x to 32x the recommended use rates. A resistant K scoparia accession (MN-3R) was confirmed with resistance up to 16-fold higher than recommended use rates for tebuthiuron and diuron and up to 4-fold higher for metribuzin. However, the resistant K scoparia accession was susceptible to bromoxynil even at 50% of the recommended use rate. The herbicide binding region of the psbA gene fragment of eight resistant (R) and seven susceptible (S) K scoparia accessions was PCR-amplified and sequenced for detection of mutations. The psbA gene of four R K scoparia accessions was mutated at residue 219 with substitution of isoleucine for valine (GenBank accession number AY251265). The seven S K scoparia accession sequences were wild-type at this residue (GenBank accession number AY251266). The other four R accessions sequences showed a previously known triazine R mutation with substitution of glycine for serine at residue 264. All 15 K scoparia accessions were wild-type at all other psbA residues within the region analyzed. Resistance to diuron, tebuthiuron and metribuzin among the railroad rights-of-way K scoparia is probably due to the mutation at residue 219 of the psbA gene in some plants, but due to the previously reported Ser(264)Gly substitution in other plants. Target-site resistance associated with a change of valine to isoleucine at residue 219 of the psbA target-site in weeds has previously been reported for Poa annua L selected in diuron-treated grass seed fields, and for Amaranthus powelli S Wats selected in linuron-treated carrot fields. This is the first report of the mutation in herbicide-resistant K scoparia.     

Effects of repeated applications of ten soil-active herbicides on weed population,residue accumulation and nitrification*

Ten herbicides, bromacil, chlorthal-dimethyl, diphenamid, diuron, fluometuron, neburon, prometryne, pyrazon, simazine and trifluralin at two doses were repeatedly sprayed, in autumn and in spring, for 4 consecutive years on non-cultivated, sprinkler-irrigated field plots. Herbicidal effect was assessed at 1–2 month intervals on the natural weed population and after each observation a paraquat + diquat spray destroyed emerged weeds. The response of various weed species to herbicides varied markedly but a herbicide-induced shift in the composition of weed population did not occur, presumably because of the paraquat treatment. The overall phytotoxicity to weeds present was, in decreasing order: diuron, bromacil, simazine, trifluralin, prometryne, neburon, fluometuron, pyrazon, diphenamid, chlorthal-dimethyl. Persistence of herbicides was in decreasing order: diuron = bromacil, simazine, neburon (at higher rate), fluometuron, trifluralin, prometryne. Control produced by pyrazon improved with the number of applications, but that of diphenamid and chlorthal-dimethyl remained weak and short. After repeated applications, the activity of these herbicides increased or remained at similar level, but in no case decreased. Soil samples were taken 5 months after each application and bioassayed. Phytotoxic residues were detected beneath the disturbed top-soil from bromacil, diuron, fluometuron and simazine after the first application, and from neburon after the second application; residues from trifluralin were found in the top soil only after the fifth application. After the seventh spraying, residues of bromacil were found in the 45–60-cm soil layer. Ammonia content in soil samples taken from treated plots after the fourth, sixth and seventh application was generally similar to the untreated control. In these samples, nitrate content appeared to be correlated negatively with remaining weed number; the control thus contained less nitrate than efficient herbicidal treatments. Soil samples taken after the seventh application of bromacil, diuron, fluometuron, neburon and simazine, which contained appreciable residual concentrations, did not show significant differences from control, in an in vitro nitrification test.     

Effect of cropping cycles and repeated herbicide applications on the degradation of diclofop-methyl, bentazone, diuron, isoproturon and pendimethalin in soil

A greenhouse study was conducted to investigate the ability of four crops (wheat, corn, oilseed rape and soybean) to influence the degradation of bentazone, diclofop-methyl, diuron, isoproturon and pendimethalin in soil. The present study showed that microbial biomass-carbon was significantly higher in planted soils than in bulk soil, especially with wheat and corn, after several cropping cycles. The biomass in corn and soybean planted soils was adversely affected by bentazone but recovered after three cropping cycles. In wheat-planted soils, diclofop-methyl application resulted in persistent increase of the amount of microbial biomass. Bentazone did not show accelerated degradation even after five successive treatments, differing from diclofop-methyl, for which two applications were sufficient to enhance significantly its rate of degradation. Enhanced degradation of diclofop-methyl was even more pronounced in wheat-planted soil. The rates of mineralisation of diuron, isoproturon and pendimethalin were not affected after the first cropping cycle, but were significantly increased in planted soils after five cropping cycles. The results confirm that plants may promote pesticide degradation in soil by stimulating biodegradation processes. In the case of diclofop-methyl, stimulation of accelerated degradation was observed.     

棉花脱叶催熟剂药液理化性质的变化及对植保无人飞机喷施效果的影响

为了科学配制棉花脱叶催熟剂药液,通过室内和田间试验评价了 4 种脱叶催熟剂药液体系在不同放置时间内理化性质的变化及其对植保无人飞机(UAV)喷施作业效果的影响。结果表明:540 g/L噻苯 ? 敌草隆悬浮剂药液体系在配制后 0 h的悬浮率和持留量最优,分别为95.5%和 5.49 mg/cm2;68%噻苯 ? 敌草隆可湿性粉剂药液体系配制后0 h在棉花叶片上接触角最优(0°);81%噻苯 ? 敌草隆水分散粒剂药液体系和12%噻苯 ? 敌草隆可分散油悬浮剂药液体系中噻苯隆的稳定性均较好,配制后24 h分别降低了11.63%和14.47%。总体上,4种脱叶催熟剂药液体系的悬浮率、持留量和噻苯隆含量均随着放置时间的延长而降低,且在 0.5～1 h时内降幅最为显著。药液放置时间对UAV喷施后的雾滴体积中径 (VMD,D_v50)、雾滴覆盖率和均匀性均有不同程度的影响。4 种药液体系的田间脱叶率均随放置时间的延长而降低,在 0～1 h内下降最快,放置超过 1 h会对棉花脱叶率产生显著影响,其中 12 h后影响最大。该研究结果可为棉花脱叶催熟剂药液的科学配制和UAV喷施作业提供参考。     

Influence of Soil Moisture on Long-Term Sorption of Diuron and Isoproturon by Soil

Long-term sorption of diuron and isoproturon by a clay loam soil was investigated for nine weeks at two herbicide doses (0·6 or 3 mg kg⁻¹) and two soil moisture contents (35 or 62% w/w, i.e. 3·16 or 1 kPa) by measuring changes in herbicide concentrations in the soil solution sampled by means of glass microfibre filters in presence of sodium azide (200 mg litre⁻¹) which inhibited biodegradation for more than four weeks. After the first day equilibration period, where adsorption mainly occurred (>70% adsorbed), herbicide concentrations in the soil solution decreased (about 50% for diuron; up to 38% for isoproturon) for two weeks but equilibration required about one month. Small amounts of herbicides were sorbed during this process (<10% of the initial (24-h) adsorption). These were similar for both herbicides, although diuron was initially more adsorbed. Values of the partition coefficients of herbicides between soil and soil solution were increased (75–125% for diuron; 29–67% for isoproturon). High soil moisture enhanced sorption speed for both herbicides and increased final sorption only for diuron. Sodium azide inhibited long-term sorption of the more stable diuron and this effect was reversed by low temperature only at the low soil moisture. Sodium azide action might be complex (competition, effect on soil micro-organisms) and was not elucidated.     

Generation of reactive oxygen species by a novel anthraquinone derivative in the cyanobacterium Planktothrix perornata (Skuja)

A water-soluble anthraquinone derivative (2-[methylamino-N-(1′-methylethyl)]-9,10-anthraquinone monophosphate), previously found to be selectively toxic towards Planktothrix perornata at submicromolar concentrations, was studied to determine its toxic mode of action towards this cyanobacterium. Chlorophyll fluorescence was monitored as an indicator of photosynthetic efficiency, and measurement of reactive oxygen species (ROS) was performed using the ROS-sensitive probe 2′,7′-dichlorodihydrofluorescein diacetate. The effects of the herbicide paraquat (a ROS generator) as well as ascorbate and α-tocopherol (ROS scavengers) on ROS formation by P. perornata were studied. Also, the effects of different concentrations of ascorbate, α-tocopherol, and the herbicide diuron on reducing the toxicity of the water-soluble anthraquinone derivative towards P. perornata were determined. Our results indicate that the water-soluble anthraquinone derivative does not inhibit photosynthetic electron transport directly, but does generate ROS at levels that may cause toxicity towards P. perornata.