The degradation of methazole in soil. II. Studies with methazole,methazole degradation products and diuron

[¹⁴C]-Labelled methazole, 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU), 1-(3,4-dichlorophenyl)urea (DCPU), and diuron were incubated in soil at 20°C and field capacity soil moisture content. Decomposition followed first-order kinetics; half-lives for degradation of these four compounds were 2.4, 144, 30 and 108 days respectively. The amount of DCPMU and DCPU that could be extracted decreased with time and the decrease was accompanied by the generation of an equivalent amount of ¹⁴CO₂. This was not so in the studies with diuron and methazole, however, and the decrease in the concentrations of radioactivity extracted from soil treated with these compounds could not be entirely accounted for as carbon dioxide. It is concluded that the unextractable radiochemical that was present was DCPMU. Methazole appeared to be degraded through DCPMU to 3,4-dichloroaniline (DCA) with the production of only traces of DCPU.     

Metabolic fate of bioxone in cotton

The metabolic fate of the ¹⁴C-labeled herbicide, 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (bioxone), in cotton (Gossypium hirsutum L. “Acala 4-42-77”) was studied using thin-layer chromatography, autoradiography, and counting. Bioxone-¹⁴C was readily metabolized by cotton tissue to 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU) and 1-(3,4-dichlorophenyl)urea (DCPU). Leaf discs metabolized bioxone-¹⁴C rapidly; 12 hr posttreatment, 65% of the ¹⁴C in methanol extracts was in forms other than intact herbicide. Excised leaves treated through the petiole with either heterocyclic ring-labeled or phenyl ring-labeled herbicide contained little bioxone-¹⁴C after 1 day; DCPMU was formed early then decreased with time. DCPU accounted for 55–70% of the ¹⁴C in excised leaves 3 days posttreatment. In intact plants treated via the roots, the herbicide was rapidly metabolized in the roots to DCPMU and DCPU; little or no intact herbicide was translocated to the leaves. Little radioactivity accumulated in the roots with time; the radioactivity in the leaves accounted for 80–90% of the methanol-soluble ¹⁴C 47 days posttreatment. Most of the ¹⁴C in the leaves was recovered as DCPU (50–60%) and unidentified polar metabolite(s) which remained at the origin of the thin-layer plates (30–40%). The percentage of radioactivity which remained in cotton residue after methanol extraction increased with time. Digestion of the plant residues with the proteolytic enzyme pronase indicated that some of the nonextractable ¹⁴C may be DCPMU and DCPU complexed with proteins. Similar metabolic patterns were noted after treatment with either heterocyclic ring-labeled or phenyl ring-labeled bioxone-¹⁴C. Generally, bioxone was metabolized to DCPMU which in turn was demethylated to DCPU. The herbicide and DCPMU were 20 times as toxic as DCPU to oat (Avena sativa L.), a susceptible species.     

Aspects of the selective phytotoxicity of methazole. II. Behaviour in plants following root exposure

The absorption, translocation and degradation of methazole were examined in onion, Stellaria media, Matricaria matricarioides and Veronica persica grown in culture solution. After a short period of initial rapid uptake, all four species absorbed herbicide and water in the same proportions. Translocation of herbicide to the shoots was directly proportional to transpiration, but the apparent solute concentration in the xylem was less than that in the external solution and varied between the species. A smaller percentage of the total absorbed herbicide was translocated to the shoot in V. persica, the most tolerant species. Methazole was relatively stable in M. matricariodes and was degraded slowly to 3-(3,4-dicnlorophenyl)-1-methylurea (DCPMU). It was degraded rapidly to DCPMU in the other three species and this accumulated in onion and S. media. In V. persica DCPMU was degraded further to 3-(3,4-dichlorophenyl) urea (DCPU). Methazole was not an active inhibitor of photosynthesis by isolated spinach chloroplasts. Both DCPMU and DCPU inhibited photosynthesis but DCPMU was 200-times more active than DCPU. Variations in the concentrations of DCPMU in the shoots of the different species largely accounted for the variations in their response to methazole applied pre-emergence.     

Metabolic fate of methazole in purple and yellow nutsedge

The mechanisms for the tolerance of purple nutsedge (Cyperus rotundus L.) and susceptibility of yellow nutsedge (Cyperus esculentus L.) to methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] were studied. Both species absorbed and translocated[¹⁴C]methazole and metabolites from nutrient solution; however, greater amounts of ¹⁴C per unit weight were detected in yellow than in purple nutsedge. Although intact plants and excised leaves of both species rapidly metabolized methazole to DCPMU [1-(3,4-dichlorophenyl)-3-methylurea], detoxification of DCPMU to DCPU [1-(3,4-dichlorophenyl) urea] occurred more slowly in yellow than in purple nutsedge. Compared to yellow nutsedge, a greater percentage of the radioactivity in purple nutsedge was recovered as polar products. Polar products were converted to the free forms of the parent herbicide and to phytotoxic DCPMU by proteolytic enzyme digestion. Based on the findings of this study, at least three mechanisms (differential absorption, metabolism, and formation of polar products) account for the differential tolerance of these two species to methazole.     

Aspects of the selective phytotoxicity of methazole. HI. Behaviour in plants following foliar treatment

Absorption of methazole by leaves of onion (Allium cepa), Stellaria media, Matricaria matricarioides and Veronica persica was rapid for the first 24 h after treatment and continued at a slower rate for up to 6 days to reach a maximum of between 35 and 60% of the amount applied. Differences in absorption between species were generally small. Absorption by the cotyledon of onion was greater than absorption into true leaves. Methazole on the leaf surface degraded to 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU) and small amounts of this degraded to 3-(3,4-dichlorophenyl) urea (DCPU). Methazole absorbed into leaves was relatively stable in M. matricarioides and DCPMU accumulated slowly. The rate of degradation was more rapid in the cotyledons than in the true leaves. Both in leaves and in cotyledons of onion and S. media, methazole degraded rapidly to DCPMU and this accumulated; in those of V. persica, DCPMU was degraded quickly to DCPU and unidentified products. The amount of DCPMU accumulated in the shoots was broadly correlated with the relative phytotoxicity of methazole to the different species, except for young seedlings of V. persica which contained no DCPMU but were susceptible to methazole.     

Comparative uptake and metabolism of methazole in prickly sida and cotton

The comparative uptake and metabolism of ¹⁴C-labeled 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (methazole), a herbicide, in prickly sida (Sida spinosa L.) and cotton (Gossypium hirsutum L.) were investigated as physiological bases for herbicidal selectivity, using thin layer chromatography, autoradiography, and liquid scintillation counting. Prickly sida and cotton readily absorbed and translocated ¹⁴C from nutrient solution containing [¹⁴C]methazole. Only acropetal translocation of ¹⁴C was observed. Methazole was rapidly metabolized to 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU) and other metabolites by both species. Although metabolism appeared to be qualitatively the same, quantitative differences between species were evident. Methazole was converted to DCPMU (also phytotoxic) more readily by prickly sida than cotton; however, DCPMU was more readily detoxified to 1-(3,4-dichlorophenyl) urea (DCPU) by cotton than prickly sida. More ¹⁴C per unit weight was present in the prickly sida shoots than in cotton shoots. Also, a larger portion of the methanol-extractable ¹⁴C was herbicidal in the shoots of prickly sida than of cotton. Thus, the differential tolerances of prickly sida and cotton to methazole may be explained, in part, by differential uptake and metabolism of methazole and DCPMU.     

The effect of the herbicide diuron on soil microbial activity

The inhibitory effect of the herbicide diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] on microbial activity in red Latosol soil was followed using microcalorimetry. The activity of the micro-organisms in 1.50 g of soil sample was stimulated by addition of 6.0 mg of glucose and 6.0 mg of ammonium sulfate under 35% controlled humidity at 298.15 (+/- 0.02) K. This activity was determined by power-time curves that were recorded for increasing amounts of diuron, varying from zero to 333.33 micrograms g-1 soil. An increase in the amount of diuron in soil caused a decrease of the original thermal effect, to reach a null value above 333.33 micrograms g-1 of herbicide. The power-time curve showed that the lag-phase period and peak time increased with added herbicide. The decrease of the thermal effect evolved by micro-organisms and the increase of the lag-phase period are associated with the death of microbial populations caused by diuron, which strongly affects soil microbial communities.     

The degradation of methazole in soil. I. Effects of soil type,soil temperature and soil moisture content

[¹⁴C]-Labelled methazole was incubated in six soils at 25°C and with soil moisture at field capacity. Under these conditions, methazole was unstable, the concentration declined following first-order kinetics with half-life values in the soils ranging from 2.3 to 5.0 days. The main degradation product was 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU) which was more stable than the parent compound. After about 160 days, DCPMU accounted for 30 to 45% of the initial methazole concentration. Degradation of methazole and DCPMU was affected by soil temperature and moisture content. With methazole, half-lives in one soil at field capacity moisture content and temperatures of 25, 15 and 5°C were 3.5, 8.7 and 31.1 days respectively. The half-life at 25°C was increased to 5.0 days at 50% of field capacity and 9.6 days at 25% of field capacity. A proportion of the initial radioactivity added to the soil could not be extracted and this proportion increased with time. After 160 days this unextractable radioactivity accounted for up to 70% of the amount applied.     

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.     

Residues of diuron and phytotoxic degradation products in aquatic situations. I. Analytical methods for soil and water

Thin-layer and gas-liquid chromatography, ultraviolet analysis and bioassay with Chlorella spp. have been used to investigate the pathway of degradation of diuron to phytotoxic derivatives when diuron was used as a soil-residual herbicide in irrigation canals. Observations suggest that 1-(3,4-dichlorophenyl)-3-methylurea and 1-(3,4-dichlorophenyl)urea make a contribution to total residues equivalent to a maximum of about 40 and 55%, respectively, of diuron concentrations. Application of a phyto-toxicity rating suggests that in this environment, measurement of diuron specifically would underestimate the total phytotoxicity of residues by a maximum of about 7%.     

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     

Pirimiphos-methyl and benalaxyl losses in surface runoff from plots cultivated with potatoes

Abstract: Losses of pirimiphos-methyl and benalaxyl in runoff water from clay soil plots cultivated with potatoes and of differing soil surface slopes were determined over approximately 120 days (1 October 1999-28 January 2000). The plot slopes were 0, 1, 2.5 and 5%, and soil erosion increased with the slope from 610 to 1760kgha(-1). The runoff of surface water was between 3.1 and 16.6% of the rainfall. Surface runoff was highest for the fifth and seventh runoff events due to rainfall, 51 days and 72 days after the first pesticide application. The maximum concentrations of the two pesticides in runoff occurred in the plots with the greatest slope (5%) during the fifth runoff event, November 21, 1999 reaching 8.4 and 12.3 microg litre(-1) for pirimiphos-methyl and 17.8 and 20.2 microg litre(-1) for benalaxyl in tilled and untilled plots respectively. The cumulative losses of pirimiphos-methyl in surface runoff from tilled and untilled plots with a slope 5% were estimated at only 0.37 and 0.59% of the initial applied active ingredient, respectively, while for plots with a slope 0% the percentages were 0.013 and 0.018%. For benalaxyl the corresponding values from tilled and untilled plots were 1.69 and 1.76% (slope 5%), and 0.062 and 0.085 (slope 0%). Degradation of the pesticides in the topsoil was monitored from October 1999 and May 2000. Cultivation of potatoes decreased the half-life of the two pesticides compared to the untilled fields, for pirimiphos-methyl from 16.7 to 9.2 days and for benalaxyl from 26.7 to 12.6 days. The slope of soil surface and the different sorption capacities for the compounds are the main parameters which influenced the transportation of studied pesticides, pirimiphos-methyl and benalaxyl residues via surface water in soil-water systems.     

Desorption of diuron and isoproturon from undispersed clay loam soil

Studies were conducted to investigate the desorption of diuron and isoproturon adsorbed on undispersed clay loam soil, and the influence of residence time in soil on desorption. The soil was treated at 0·6 or 3 mg kg^-1, at 70% moisture content and in the presence of sodium azide to prevent degradation. Measurement of herbicide concentrations in soil solution sampled by means of glass microfibre filters showed that adsorption mainly occurred for one day but long-term sorption proceeded for >two weeks. After a one-day or three-week residence time, soil solution was partly replaced (28%). Measurement of concentrations in solution showed rapid desorption, with equilibria being achieved within 1 h (diuron) or a few hours (isoproturon). After 16 successive desorptions done at 30-min or 12-h intervals, equilibration times tended to be longer. For the short residence time, desorption and long-term sorption could occur simultaneously and equilibration might be faster. Residence time had no significant effect on desorption kinetics nor on the small hysteresis observed for diuron. The aging effect, involving long-term sorption only, decreased the proportion of diuron removed from the soil by successive desorptions but, for isoproturon, desorption frequency and desorption kinetics were more important. © 1997 SCI     

Herbicide loss following application to a railway

Railways have been identified as a potential source of herbicides detected in surface and groundwaters, but there are few data to support this theory. Two studies were undertaken to investigate the fate of herbicides applied to railway trackbeds: a pilot study in a section of a disused, but intact, cutting where runoff and throughflow were sampled from trenches adjacent to the treated area, and a larger scale study on 0.75 km of embankment where surface water from the drainage ditch at the base of the embankment and groundwater were sampled. In the pilot study, peak concentrations of atrazine, diuron and glyphosate (1280, 210 and 15 microg litre(-1) respectively) were detected 6days after treatment (DAT). Oxadiazon, oryzalin and isoxaben were not detected above their limits of quantification. Lower concentrations were detected 81 DAT (10 and 0.8 microg litre(-1) of atrazine and glyphosate respectively). In the larger scale study, herbicides were not detected, in either the surface water or groundwater, at concentrations above the limit of detection that could be attributed to application to the railway. Rainfall volume and depth to sampling point may partly explain the different results obtained from the two studies. The findings are compared with herbicide losses from other 'hard surfaces'.     

Anaerobic microbial degradation of diuron by pond sediment

Anaerobic degradation of the herbicide diuron, 3-(3,4-dichlorophenyl-1,1)dimethylurea, was studied. Enrichment cultures were established with seven different media in the presence of diuron (40 mg/liter). Media included combinations of sediment extract, mineral salts, and various organic amendments. Cultures were inoculated with aliquots of sediment collected from a pond previously treated with diuron and were maintained under an atmosphere of 95% N₂ and 5% CO₂. All enrichment cultures completely degraded diuron in 17–25 days. In all cultures showing diuron degradation, the product identified as 3-(3-chlorophenyl)-1,1-dimethylurea appeared in approximately stoichiometric amounts. Reinjection of diuron into each culture after 26 days resulted in rapid degradation of the parent herbicide with the appearance of proportionately more 3-(3-chlorophenyl)-1,1-dimethylurea. No other product was detected after 80 days in culture and the metachloro derivative was not degraded further during this time.     

Atrazine soil metabolism in maize fields treated with organic fertilizers

The metabolism of atrazine in soil was studied in two maize fields located in regions with different soil types. Treatments were cow manure or pig slurry (50 tonnes each ha^-1) applied once either in March or in November before sowing, or green manure incorporated in March. Control plots were not treated with organic fertilizers. Atrazine at 0.75 or 1.0 kg a.i. ha^-1 was applied after sowing. In the 0-12 cm soil layer, the main atrazine metabolites found were deethylatrazine and hydroxyatrazine. Low concentrations of deisopropylatrazine and 6-chloro-1, 3, 5-triazine-2, 4-diamine were also observed. During the 4 months after sowing, the organic fertilizers decreased the rate of atrazine degradation, but subsequently there were no differences between treated and control plots. At harvest, the concentrations of atrazine and its metabolites were very low and similar in all plots. The organic fertilizers thus did not cause atrazine metabolites to accumulate in soil. In addition, atrazine and its metabolites were never detected below 12 cm in any of the plots.     

山西太岳山不同林分土壤有机碳储量研究

基于山西太岳山系灵空山景区侧柏林、油松林、辽东栎林、辽东栎和油松混交林4种林分调查,通过密集采样和样品分析研究不同林分土壤不同层次(0-10cm、10-20cm、20-30cm、30-50cm、50-100cm)有机碳含量、有机碳密度和有机碳储量及分布特征。结果如下:山西太岳山森林平均1m土层土壤的有机碳储量一般不超过30g·kg-1,调查的四种林分在16.2g·kg-1到29.6g·kg-1;所调查的四种林分的土壤有机碳储量、碳密度随着土层深度递减,其中油松林、侧柏林、辽东栎林30cm以上土壤中有机碳储量占到100cm土层中有机碳储量的85%以上,表层土壤碳储量贡献大;阔叶林碳储量高于针叶林,混交林碳储量高于纯林,辽东栎油松针阔混交林土壤有机碳含量是油松林土壤碳含量的2.4倍,辽东栎林土壤碳储量大约分别是侧柏林、油松林的1.4和1.9倍。因此为增加森林土壤固碳,建议使用混交林并减少人类活动对森林表土层的干扰和破坏。     

The fate of imazapyr in a Swedish railway embankment

The long-term fate of the herbicide imazapyr [2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid] applied to a Swedish railway embankment was studied. Imazapyr was applied at 750 and 1500 g ha(-1) by a spraying train used for full-scale herbicide treatment operations. Soil and groundwater were sampled twice a year for 8 years after application of the herbicide, and the dissipation of imazapyr was studied by HPLC analysis of the residues in soil and groundwater. A clean-up procedure including solid-phase extraction was performed prior to detection by HPLC. Recoveries of imazapyr from soil and water samples were 76-98% and 61-90%, respectively, and detection levels were 0.003 mg kg(-1) and 0.05 microg litre(-1), respectively. Sorption, desorption and microbial amount and activity were also measured at the two locations. The organic matter content correlated positively and the pH negatively to the adsorption of imazapyr on soil, and increasing organic matter contents decreased desorption. Apart from the 0-10-cm top layers of both sites, the microbial amount and activity were small. The main proportion of imazapyr was found in the upper 30 cm of the soil, and degraded with a half-life in the range 67-144 days. Small amounts were transported to lower soil layers and to the groundwater in proportion to the amounts applied. Traces of imazapyr were detected in the groundwater even 8years after application. It was concluded that environmental risks from the use of herbicides on railway embankments could be reduced by including adsorption layers in the embankment during their construction and by reducing the dose of the herbicide used.     

A monitoring programme for 1,3-dichloropropene and metabolites in groundwater in five EU countries

BACKGROUND: 1,3 Dichloropropene (1,3-D) is a preplanting soil fumigant for the control of cyst and free-living nematodes and is currently undergoing a resubmission under Annex 1 listing of Directive 91/414/EEC. The characteristics of 1,3-D are such that the risk of it or its soil metabolites leaching through the soil profile cannot be excluded. As such, groundwater monitoring programmes were established in five EU countries representing a wide range of agricultural, climatic and hydrogeological situations, covering a range of groundwater vulnerability scenarios. All monitoring was conducted in areas where there has been historical use of 1,3-D. RESULTS: Over 5000 groundwater samples were analysed for the presence of 1,3-D and its metabolites over a 2 year period. Almost all analyses (for parent and metabolites) yielded concentrations of <0.1 microg L(-1). There were just two detections of >0.1 microg L(-1) (0.12 microg L(-1) and 0.4 microg L(-1)) for the 3-chloroacrylic acid metabolite in shallow groundwater samples of the alluvial gravels of the River Tiétar in the Caceres region of Spain. CONCLUSION: Groundwater monitoring programmes have been conducted in the EU in five countries. These have demonstrated that there is negligible contamination of groundwater with 1,3-D or its metabolites across a range of agroclimatic regions where 1,3-D is known to have been used for a number of years. Local scientific knowledge of geological features, hydrology, agricultural practice and specific local issues was essential to the conduct of the study.     

Residues of atrazine, simazine, linuron and diuron after repeated annual applications in a peach orchard

Annual applications of the herbicides atrazine, simazine, linuron and diuron at 45 kg/ha were made to the same plots for 9 consecutive years from 1963 to 1971 in a peach (Prunus persica (L.) Batsch.) orchard located on sandy loam soil near Harrow, Ontario. Soil samples from these plots were collected in late October for the last 3 years (1969–1971) and trees were cut down in December, 1969. Herbicide residues were determined by bioassays based on the fresh and dry weight of oats (Avena sativa L.) and in one year results were confirmed by chemical analysis. Significant accumulation of herbicides was not observed. The maximum residue levels measured in October over the 3 years of sampling were 7′3 kg/ha for diuron, 3–8 kg/ha for linuron, 1–6 kg/ha for simazine and 04 kg/ha for atrazine in the top 15 cm of the soil profile. Simazine and atrazine showed a rapid decrease in amount after treatment but diuron and linuron were degraded more slowly. Measurable residues of all herbicides were confined to the upper 15 cm of the soil profile and the majority of herbicide remained in the 0–5-cm soil layer. Oats were planted in the orchard plots from 1972 to 1974 to follow the disappearance of the herbicides. All herbicides caused highly significant yield decreases in 1972, atrazine causing the least (38%) and diuron the greatest (86%) reductions. Diuron reduced the yield of oats in 1973 and caused a highly significant decrease in the weight of young oat plants in 1974.