Long-term fate of the herbicide cinosulfuron in lysimeters planted with rice over four consecutive years

In order to elucidate the long-term fate of the sulfonylurea herbicide cinosulfuron, the 14C-labelled chemical was applied to a clay loam soil, encased in two lysimeters, 22 days after rice (Oryza sativa L.) transplanting, and rice plants were grown for four consecutive years. Throughout the experimental period, leaching through soil profiles, absorption and translocation by rice plants, and distribution of 14C by downward movement in the soil layers were clarified. The total volume of leachates collected through the lysimeter soil over the four years amounted to 168 and 146 L in lysimeters I and II, respectively. The leachates contained 2.43% and 2.99% of the originally applied 14C-radioactivity, corresponding to an average concentration of 0.29 and 0.41 microg/L as the cinosulfuron equivalent in lysimeters I and II, respectively. The total 14C-radioactivity translocated to rice plants in the third and fourth year was 0.69% and 0.60% (lysimeter I), and 1.02% and 0.84% (lysimeter II) of the 14C applied, respectively. Larger amounts of cinosulfuron equivalents (0.54-0.75%) remained in the straw in the fourth year than in any other parts. The 14C-radioactivities distributed down to a depth of 70 cm after four years were 56.71-57.52% of the 14C applied, indicating the continuous downward movement and degradation of cinosulfuron in soil. The non-extractable residues were more than 88% of the soil radioactivity and some 45-48% of them was incorporated into the humin fraction. The 14C-radioactivity partitioned into the aqueous phase was nearly 30% of the extractable 14C, suggesting strongly that cinosulfuron was degraded into some polar products during the experimental period. It was found out in a supplemental investigation that flooding and constant higher temperature enhanced mineralization of [14C]cinosulfuron to 14CO2 in soil, indicating the possibility of chemical hydrolysis and microbial degradation of the compound in the flooded lysimeter soil.     

Leaching of pesticides through normal-tillage and low-tillage soil--a lysimeter study. II. Glyphosate

Glyphosate is a widely used non-selective herbicide. Leaching of glyphosate (N-(phosphonomethyl)glycine) and/or its metabolite AMPA (aminomethylphosphonic acid) was studied in four lysimeters, two of them being replicates from a low-tillage field (lysimeter 3 and 4), the other two being replicates from a normal tillage field (lysimeter 5 and 6). In both cases the soil was a sandy loam soil with 13-14% clay. The lysimeters had a surface area of 0.5 m2 and a depth of 110 cm. Lysimeter 3 and 4 were sprayed with a mixture of 14C-labelled glyphosate and unlabelled glyphosate, while lysimeter 5 and 6 were sprayed with unlabelled glyphosate. The spraying took place September 18, 1997. The total amount of glyphosate sprayed onto each lysimeter was 40 mg, corresponding to 0.8 kg active ingredient per ha. The lysimeters were installed in an outdoor system in Research Centre Flakkebjerg and were thus exposed to normal climatic conditions of the area. A mean of 260 l drainage water were collected from lysimeter 3 and 4 and a mean of 375 litres from lysimeter 5 and 6. The mean yearly concentration of leached glyphosate and/or AMPA was significantly below 0.1 microg/l from both sets of lysimeters, and thus no significant difference between the two lysimeter sets was shown. However, in both sets of lysimeters several single findings at concentrations above 0.1 microg/l was seen, which might be due to the leaching of particle-bound compounds. A significant difference between the soil residual concencentrations of AMPA was seen, the higher concentration was found in the set of lysimeter where low-tillage had been practiced and where Round Up had been used several times in the years before sampling of the lysimeter soil.     

Leaching and degradation of corn and soybean pesticides in an Oxisol of the Brazilian Cerrados

Pesticide pollution of ground and surface water is of growing concern in tropical countries. The objective of this pilot study was to evaluate the leaching potential of eight pesticides in a Brazilian Oxisol. In a field experiment near Cuiabá, Mato Grosso, atrazine, chlorpyrifos, lambda-cyhalothrin, endosulfane alpha, metolachlor, monocrotofos, simazine, and trifluraline were applied onto a Typic Haplustox. Dissipation in the topsoil, mobility within the soil profile and leaching of pesticides were studied for a period of 28 days after application. The dissipation half-life of pesticides in the topsoil ranged from 0.9 to 14 d for trifluraline and metolachlor, respectively. Dissipation curves were described by exponential functions for polar pesticides (atrazine, metolachlor, monocrotofos, simazine) and bi-exponential ones for apolar substances (chlorpyrifos, lambda-cyhalothrin, endosulfane alpha, trifluraline). Atrazine, simazine and metolachlor were moderately leached beyond 15 cm soil depth, whereas all other compounds remained within the top 15 cm of the soil. In lysimeter percolates (at 35 cm soil depth), 0.8-2.0% of the applied amounts of atrazine, simazine, and metolachlor were measured within 28 days after application. Of the other compounds less than 0.03% of the applied amounts was detected in the soil water percolates. The relative contamination potentials of pesticides, according to the lysimeter study, were ranked as follows: metolachlor > atrazine = simazine > monocrotofos > endsulfane alpha > chlorpyrifos > trifluraline > lambda-cyhalothrin. This order of the pesticides was also achieved by ranking them according to their effective sorption coefficient Ke, which is the ratio of Koc to field-dissipation half-life.     

Leaching of pesticides through normal-tillage and low-tillage soil--a lysimeter study. I. Isoproturon

Isoproturon is a herbicide, which was used in Denmark against grass weeds and broad-leaved weeds until 1998. Isoproturon has frequently been detected in ground water monitoring studies. Leaching of isoproturon (N,N-dimethyl-N'-(4-(1-methylethyl)-phenyl)urea) and its metabolites, N'-(4-isopropylphenyl)-N-methylurea and N'-(4-isopropylphenyl)urea was studied in four lysimetres, two of them being replicates from a low-tillage field (lysimeter 3 and 4), the other two being replicates from a normal tillage field (lysimeter 5 and 6). In both cases the soil was a sandy loam soil with 13-14% clay. The lysimetres had a surface area of 0.5 m2 and a depth of 110 cm. Lysimeter 3 and 4 were sprayed with unlabelled isoproturon while lysimeter 5 and 6 was sprayed with a mixture of 14C-labelled and unlabelled isoproturon. The total amount of isoproturon sprayed onto each lysimeter was 63 mg, corresponding to 1.25 kg active ingredient per ha. The lysimeters were sprayed with isoproturon on October 26, 1997. The lysimetres were installed in an outdoor system in Research Centre Flakkebjerg and were thus exposed to normal climatic conditions of the area. A mean of 360 l drainage water were collected from lysimeter 3 and 4 and a mean of 375 litres from lysimeter 5 and 6. Only negligible amounts of isoproturon and its primary metabolites were found in the drainage water samples, and thus no significant difference between the two lysimeter sets was shown. In a total of 82 drainage water samples, evenly distributed between the four lysimetres isoproturon was found in detectable amounts in two samples and N'-(4-isopropylphenyl)urea was found in detectable amounts in two other samples. The detection limit for all the compounds was 0.02 microg/l. 48% and 54% of the added radioactivity were recovered from the upper 10 cm soil layer in lysimeter 5 and 6, respectively, and 17 and 14% from 10-20 cm's depth. By extraction first with an aquatic CaCl2 solution 0.49% of the added radioactivity was extracted from the upper 10 cm layer in lysimeter 5. In the subsequent extraction with acetonitril, 1.19% of the added radioactivity was extracted. In lysimeter 6, upper 10 cm, 0.2% were extracted with water and 0.56% were extracted with acetonitril. Below 10 cm's depth no measurable amounts could be extracted.     

Aged and bound herbicide residues in soil and their bioavailability. Part 2: Uptake of aged and non-extractable (bound) [carbonyl-14C]methabenzthiazuron residues by maize

[Carbonyl-14C]methabenzthiazuron (MBT) was applied to growing winter wheat in an outdoor lysimeter. The amount applied corresponded to 4 kg Tribunil/ha. 140 days after application the 0-2.5 cm soil layer was removed from the lysimeter. This soil contained about 40% of the applied radioactivity. Using 0,01 M CaCl2 solution or organic solvents, the extractable residues were removed from the soil. The bioavailability of the non-extractable as well as aged residues remaining in the soil was investigated in standardized microecosystems containing 1.5 kg of dry soil. During a 4 weeks period the total uptake (4 maize plants/pot) amounted up to 3.6; 2.2; and 0.9% of the radioactivity from soils containing aged MBT residues, MBT residues non-extractable with 0.01 M CaCl2 or MBT residues non-extractable with organic solvents, respectively. About 20% of the radioactivity found in maize leaves represented chromatographically characterized parent compound. At the end of the plant experiment the soil was extracted again with 0.01 M CaCl2 and with organic solvents. The soil extracts and also the organic phases obtained from the aqueous fulvic acid solution contained unchanged parent compound.     

Equilibrium partitioning of (14)C-benzo(a)pyrene and (14)C-benazolin between fractionated phases from an arable topsoil

Equilibrium partitioning of hydrophobic (14)C-benzo(a)pyrene and hydrophilic (14)C-benazolin between fractionated phases from an arable topsoil of Merzenhausen (Germany) was investigated. Topsoil samples were collected from lysimeters which were incubated with different residual crops. A physical soil fractionation based on sedimentation and centrifugation steps was performed after water extraction. Four soil phases were obtained designated sediment (SED) phase (>20 microm), microaggregate (MA) phase (2 microm-20 microm), colloid (COL) phase (<2 microm) and electrolyte (EL) phase. The distribution of (14)C-benzo(a)pyrene, (14)C-benazolin and organic carbon between the soil phases was established. Enrichment factors for the two chemicals and organic carbon are higher in the COL and MA phases than in the SED phase. The distribution constant K(d) of chemicals for Merzenhausen topsoil was calculated according to two-phase or three-phase partitioning models. The three-phase partitioning model presumes the contribution of the organic carbon for the binding of chemicals. A log K(oc) of 5.55 can be calculated in the case of (14)C-benzo(a)pyrene, which is typical of the hydrophobic association with the soil organic carbon. In the case of (14)C-benazolin, much higher K(d) and K(oc) values were calculated than found with parent molecules after short-time experiments. Long-term aging processes must be considered. Specific effects on the chemical distribution due to the different crop residues were not detected.     

Impact of soil water regime on degradation and plant uptake behaviour of the herbicide isoproturon in different soil types

The environmental fate of the worldwide used herbicide isoproturon was studied in four different, undisturbed lysimeters in the temperate zone of Middle Europe. To exclude climatic effects due to location, soils were collected at different regions in southern Germany and analyzed at a lysimeter station under identical environmental conditions. ¹⁴C-isoproturon mineralization varied between 2.59% and 57.95% in the different soils. Barley plants grown on these lysimeters accumulated ¹⁴C-pesticide residues from soil in partially high amounts and emitted ¹⁴CO₂ in an extent between 2.01% and 13.65% of the applied ¹⁴C-pesticide. Plant uptake and ¹⁴CO₂ emissions from plants were inversely linked to the mineralization of the pesticide in the various soils: High isoproturon mineralization in soil resulted in low plant uptake whereas low isoproturon mineralization in soil resulted in high uptake of isoproturon residues in crop plants and high ¹⁴CO₂ emission from plant surfaces. The soil water regime was identified as an essential factor that regulates degradation and plant uptake of isoproturon whereby the intensity of the impact of this factor is strongly dependent on the soil type.     

Fate of metolachlor under subirrigation in a sandy soil: a lysimeter study

A three-year field lysimeter study was conducted to investigate the role of subirrigation systems in reducing the risk of water pollution from metolachlor (2-chloro-N-(2-ethyl-6-methlphenyl)-N-(2-methoxy-1-methylethyl)ace tamide). Nine large PVC lysimeters, 1 m long x 0.45 m diameter, were packed with a sandy soil. Three water table management treatments, i.e. two subirrigation treatments with constant water table depths of 0.4 and 0.8 m, respectively, and a free drainage treatment in a completely randomized design with three replicates were used. Corn (Zea mays L.) was grown in each lysimeter, and at the beginning of summer of each year metolachlor was applied, at the locally recommended rate of 2.75 kg a.i./ha. Soil and water samples were collected at different time intervals after each natural or simulated rainfall event. Metolachlor was extracted from these samples and analyzed using Gas Chromatography. Results obtained in this three year study, (1993-1995), lead to the conclusion that metolachlor is quite mobile since it leached to a depth of 0.85 m below the soil surface quite early in the growing season. Metolachlor concentrations decreased with depth as well as with time. The shallower water table in the 0.4 m subirrigation treatment showed less residues in the soil solution than that of other treatments. However, a mass balance study, supported by an independent laboratory investigation, shows that water table management, statistically, has no significant effect on the reduction of metolachlor residues in sandy soils.     

The influence of maize residues on the mobility and binding of benazolin: investigating physically extracted soil fractions

The amount of non-extractable residues and the distribution of benazolin and its metabolites were evaluated three months after herbicide application (14C-labelled) in physically extracted soil fractions of topsoil layers of undisturbed soil columns with and without incorporated maize straw (14C-labelled). In addition, a variety of wet-chemical and spectroscopic methods were used to characterise the structure of organic carbon within the different soil fractions. The addition of crop residues increased the amount of dissolved organic carbon, enhanced the aromaticity of the organic carbon structure and enforced the aggregation of organomineral complexes. After incorporation of crop residues, an increase in the formation of metabolic compounds of benazolin and of non-extractable residues was detected. These results indicate that the addition of crop residues leads to a decrease in mobility and bioaccessibility of benazolin and its metabolites.     

Persistence of C-labeled atrazine and its residues in a field lysimeter soil after 22 years

Twenty-two years after the last application of ring-¹⁴C-labeled atrazine at customary rate (1.7 kg ha⁻¹) on an agriculturally used outdoor lysimeter, atrazine is still detectable by means of accelerated solvent extraction and LC-MS/MS analysis. Extractions of the 0-10 cm soil layer yielded 60% of the residual ¹⁴C-activity. The extracts contained atrazine (1.0 μg kg⁻¹) and 2-hydroxy-atrazine (42.5 μg kg⁻¹). Extractions of the material of the lowest layer 55-60 cm consisting of fine gravel yielded 93% of residual ¹⁴C-activity, of which 3.4 μg kg⁻¹ was detected as atrazine and 17.7 μg kg⁻¹ was 2-hydroxy-atrazine. The detection of atrazine in the lowest layer was of almost four times higher mass than in the upper soil layer. These findings highlight the fact that atrazine is unexpectedly persistent in soil. The overall persistence of atrazine in the environment might represent a potential risk for successive groundwater contamination by leaching even after 22 years of environmental exposure.     

Influence of humic fractions on retention of isoproturon residues in two Moroccan soils

The influence of different fractions of soil organic matter on the retention of the herbicide isoproturon (IPU) has been evaluated. Water and methanol extractable residues of (14)C labeled isoproturon have been determined in two Moroccan soils by beta -counting-liquid chromatography. The quantification of bound residues in soil and in different fractions of soil humic substances has been performed using pyrolysis/scintillation-detected gas-chromatography. Microbial mineralization of the herbicide and soil organic matter has been also monitored. Retention of isoproturon residues after 30-days incubation ranged from 22% to 32% (non-extractable fraction). The radioactivity extracted in an aqueous environment was from 20% to 33% of the amount used for the treatment; meanwhile, methanol was able to extract another 48%. Both soils showed quantities of bound residues into the humin fraction higher than humic and fulvic acids. The total amount of residues retained into the organic matter of the soils was about 65 % of non-extractable fraction, and this percentage did not change with incubation time; on the contrary, the sorption rate of the retention reaction is mostly influenced by the clay fraction and organic content of the soil. Only a little part of the herbicide was mineralized during the experimental time.     

Dissipation of chlorpyrifos in two soil environments of semi-arid India

The dissipation of chlorpyrifos (20 EC) at environment-friendly doses in the sandy loam and loamy sand soils of two semi-arid fields and the presence of pesticide residues in the harvested groundnut seeds, were monitored. The movement of chlorpyrifos through soil and its binding in the loamy sand soil was studied using 14C chlorpyrifos. Chlorpyrifos was moderately stable in both loamy sand and sandy loam soils, with half-life of 12.3 and 16.4 days, respectively. With 20 EC treatments the dissipation was slower for standing crop than seed treatment, indicative of the high degradation rates in the bioactive rhizosphere. In soil, 3,5,6-trichloro-2-pyridinol (TCP) was the principal breakdown product. Presence of 3,5,6-trichloro-2-methoxypyridine (TMP), the secondary metabolite, detected in the rhizospheric samples during this study, has not been reported earlier in field soils. The rapid dissipation of the insecticide from the soil post-application might have resulted from low sorption due to the alkalinity of the soil and its low organic matter content, fast topsoil dissipation possibly by volatilization and photochemical degradation, aided by the low water solubility, limited vertical mobility due to confinement of residues to the upper 15 cm soil layers and microbial mineralization and nucleophilic hydrolysis. Contrary to the reports of relatively greater mobility of its metabolites in temperate soils, TMP and TCP remained confined to the top 15 cm soil. The formation of bound residues (half-life 13.4 days) in the loamy sand soil was little and not "irreversible." A decline in bound residues could be correlated to decreasing TCP concentration. Higher pod yields were obtained from pesticide treated soils in comparison to controls. Post-harvest no pesticide residues were detected in the soils and groundnut seeds.     

Fate of metolachlor under subirrigation in a sandy soil: A lysimeter study

Abstract

A three‐year field lysimeter study was conducted to investigate the role of subirrigation systems in reducing the risk of water pollution from metolachlor (2‐chloro‐N‐(2‐ethyl‐6‐methlphenyl)‐N‐(2‐methoxy‐l‐methylethyl)acetamide). Nine large PVC lysimeters, 1 m long x 0.45 m diameter, were packed with a sandy soil. Three water table management treatments, i.e. two subirrigation treatments with constant water table depths of 0.4 and 0.8 m, respectively, and a free drainage treatment in a completely randomized design with three replicates were used. Corn (Zea mays L.) was grown in each lysimeter, and at the beginning of summer of each year metolachlor was applied, at the locally recommended rate of 2.75 kg a.i./ha. Soil and water samples were collected at different time intervals after each natural or simulated rainfall event. Metolachlor was extracted from these samples and analyzed using Gas Chromatography.

Results obtained in this three year study, (1993–1995), lead to the conclusion that metolachlor is quite mobile since it leached to a depth of 0.85 m below the soil surface quite early in the growing season. Metolachlor concentrations decreased with depth as well as with time. The shallower water table in the 0.4 m subirrigation treatment showed less residues in the soil solution than that of other treatments. However, a mass balance study, supported by an independent laboratory investigation, shows that water table management, statistically, has no significant effect on the reduction of metolachlor residues in sandy soils.     

Effect of organic amendment on degradation and formation of bound residues of methabenzthiazuron in soil under constant climatic conditions

Abstract

The degradation of [phenyl‐U‐¹⁴C]methabenzthiazuron (MBT) and formation of bound residues in the surface soil of an orthic luvisol were studied under constant climatic conditions (20°C, 40 % of maximum water holding capacity). In two treatments (with and without preincubation in the soil) maize straw was amended at a rate of 1.5 g/100 g dry soil in addition to the application of MBT. The mineralization of uniformly labeled maize straw was studied simultaneously. In additional flasks, MBT was incubated at 0, 10 and 30°C with and without addition of maize straw.

The turnover of the amended maize straw led to an enhanced dissipation of MBT which was mainly due to the formation of bound residues. This corresponded to a higher microbial activity in the soil after straw amendment and the intensive mineralization of the radiolabeled maize straw. About 2–3 % of the applied radioactivity from the radiolabeled maize straw was measured in the soil microbial biomass 10 and 40 days after application whereas ¹⁴C from MBT was only incorporated into soil microbial biomass in the treatments with straw amendment.

Within the bound residue fractions relatively more radioactivity was measured in fulvic and humic acids after straw amendment. Increasing temperatures promoted the dissipation of MBT and the formation of bound residues in both treatments, but without amendment of maize straw these effects were far less pronounced. The laboratory scale degradation experiment led to similar results as were found in a corresponding lysimeter study. Differences that were observed could be explained by different temperature regimes of the experiments and time of aging in soil.     

Characterization of non-extractable residues of the fungicide dithianon in soil using 13C/14C-labelling techniques

The fate of the (14)C-labelled fungicide dithianon in soil is characterized by the formation of non-extractable, "bound" residues of approximately 63% of applied amount in 64 d. Humic acids containing these "bound" residues were isolated after conducting degradation studies of the active ingredient in an orthic luvisol under standardized conditions. In the same way, (13)C-labelled dithianon was incubated in an artificial soil which was produced by humification of (13)C-depleted straw in an incinerated soil. The "bound" residues of the (13)C-labelled dithianon in the humic acid fraction of the artificial soil were analyzed using (13)C-NMR techniques. There was no evidence of a covalent bonding of the residues to the humic substances. Results of polarity gradient high performance thin layer chromatography (AMD-HPTLC) of "bound" residues of the (14)C-labelled dithianon in the humic acid fraction indicate a sequestration process of metabolites into the humic substance as a possible binding mechanism.     

Organochlorine compounds in bovine milk from the state of Mato Grosso do Sul – Brazil

Organochlorines are highly hydrophobic, synthetic organic pollutants that accumulate in the environment and in food webs. The primary route of human exposure to organochlorines is through food-mainly fat-rich food of animal origin such as meat, fish, and dairy products. Here we determined the presence and concentration of organochlorine residues in pasteurized milk from Mato Grosso do Sul, Brazil, to monitor consumer exposure to these contaminants. Organochlorine pesticides in milk samples were analyzed using solid phase extraction in octadecyl silica-prepacked columns and identified by gas chromatography using an electron capture detector. Of the 100 composite samples analyzed, more than 90% contained residues of organochlorine pesticides: aldrin was present in 44% of the samples, followed by ∑DDT (36%), mirex (34%), endosulfan (32%), chlordane (17%), dicofol (14%), heptachlor (11%) and dieldrin (11%). Compared to the values established by law, the concentration of the compounds in some samples was above the reference values. Given the importance that milk and its products have in the human diet, it is essential to know whether the levels of pesticide residues are kept well below the recommended levels to minimize the risk to human health.     

Influence of humic fractions on retention of isoproturon residues in two Moroccan soils

The influence of different fractions of soil organic matter on the retention of the herbicide isoproturon (IPU) has been evaluated. Water and methanol extractable residues of ¹⁴C labeled isoproturon have been determined in two Moroccan soils by β -counting–liquid chromatography. The quantification of bound residues in soil and in different fractions of soil humic substances has been performed using pyrolysis/scintillation-detected gas-chromatography. Microbial mineralization of the herbicide and soil organic matter has been also monitored. Retention of isoproturon residues after 30-days incubation ranged from 22% to 32% (non-extractable fraction). The radioactivity extracted in an aqueous environment was from 20% to 33% of the amount used for the treatment; meanwhile, methanol was able to extract another 48%. Both soils showed quantities of bound residues into the humin fraction higher than humic and fulvic acids. The total amount of residues retained into the organic matter of the soils was about 65 % of non-extractable fraction, and this percentage did not change with incubation time; on the contrary, the sorption rate of the retention reaction is mostly influenced by the clay fraction and organic content of the soil. Only a little part of the herbicide was mineralized during the experimental time.     

Poplar for the phytomanagement of boron contaminated sites

Boron (B) is a widespread environmental contaminant that is mobile relative to other trace elements. We investigated the potential of hybrid poplar (Populus sp.) for B phytomanagement using a lysimeter experiment and a field trial on B-contaminated wood-waste. In both studies, poplars enhanced evapotranspiration from the wood-waste, reduced B leaching, and accumulated B in the aerial portions of the tree. When grown in a substrate containing 30 mg/kg B, poplar leaves had an average B concentration of 845 mg/kg, while the stems contained 21 mg/kg B. Leaf B concentrations increased linearly with leaf age. A decomposition experiment revealed that abscised leaves released 14% of their B during the winter months. Fertiliser application enhanced tree growth without decreasing the leaf B concentrations. Harvesting alternate rows of trees on a contaminated site would reduce leaching from the site while removing B. Harvested plant material may provide bioenergy, stock fodder, or an amendment for B-deficient soils.     

Persistence of the mixture of chlorfenvinphos and cypermethrin (Survan) in citrus fruits

The Survan (a mixture of the insecticides chlorfenvinphos and cypermethrin) persistence in lemon citrus fruits, verna variety, is studied. In all the cases, residues of both compounds have been detected in the juices of the fruits treated. When the mixture of the insecticides is used at a concentration of 0.20%, the levels of chlorfenvinphos after 14 days is not higher than 0.14 ppm; however, when it is used at a 0.15% concentration, this value is overpassed in all the samples. The residues of the cypermethrin component are not higher than 0.35 ppm throughout the whole experiment.