Degradation of diphenyl ether herbicides in soils

The gas chromatographic determination of CNP (2,4,6-trichlorophenyl 4-nitrophenyl ether), nitrofen (2,4-dichlorophenyl 4′-nitrophenyI ether), chlomethoxynil (2,4-dieblorophenyl 3′-methoxy-4′-nitrophenyl ether), CFNP (2,4-dichloro-6-fluorophenyl 4-nitrophenyl ether) and their amino derivatives in soils were carried out. Good recoveries from soils were obtained for the diphenyl ethers. On the other hand, satisfactory recoveries from soils were also obtained for the amino derivatives at high concentrations, but the recoveries at lower concentrations averaged about 66% for the least recovered compound.

The degradation of several diphenyl ether herbicides in two paddy soils were compared under flooded and upland conditions. The degradation was much slower under upland than under flooded conditions. Considerable amounts of their amino derivatives were produced in soils under flooded conditions, but not under upland conditions. It was suggested that the diphenyl ethers to the amino derivatives involved both chemical and microbial processes. CNP and chlomethoxynil degraded faster at lower concentrations than at higher ones.     

除草剂莠去津和灭草松单用和混用在土壤中的降解

The application of a mixture of bentazone （3-isopropyl-1H-2,1,3-benzothiadiazin-4（3H）-one-2,2-dioxide） and atrazine （6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine） is a practical approach to enhance the herbicidal effect. Laboratory incubation experiments were performed to study the degradation of bentazone and atrazine applied in combination and individually in maize rhizosphere and non-rhizosphere soils. After a lag phase, the degradation of each individual herbicide in the non-autoclaved soil could be adequately described using a first-order kinetic equation. During a 30-d incubation, in the autoclaved rhizosphere soil, bentazone and atrazine did not noticeably degrade, but in the non-autoclaved soil, they rapidly degraded in both non-rhizosphere and rhizosphere soils with half-lives of 19.9 and 20.2 d for bentazone and 29.1 and 25.7 d for atrazine, respectively. The rhizosphere effect significantly enhanced the degradation of atrazine, but had no significant effect on bentazone. These results indicated that biological degradation accounted for the degradation of both herbicides in the soil. When compared with the degradation of the herbicide applied alone, the degradation rates of the herbicides applied in combination in the soils were lower and the lag phase increased. With the addition of a surfactant, Tween-20, a reduced lag phase of degradation was observed for both herbicides applied in combination. The degradation rate of bentazone accelerated, whereas that of atrazine remained nearly unchanged. Thus, when these two herbicides were used simultaneously, their persistence in the soil was generally prolonged, and the environmental contamination potential increased.     

Degradation of chloroacetanilide herbicides by anodic fenton treatment

Anodic Fenton treatment (AFT) is an electrochemical treatment employing the Fenton reaction for the generation of hydroxyl radicals, strong oxidants that can degrade organic compounds via hydrogen abstraction. AFT has potential use for the remediation of aqueous pesticide waste. The degradation rates of chloroacetanilides by AFT were investigated in this work, which demonstrates that AFT can be used to rapidly and completely remove chloroacetanilide herbicides from aqueous solutions. Acetochlor, alachlor, butachlor, metolachlor, and propachlor were treated by AFT, and parent compound concentrations were analyzed over the course of the treatment time. Degradation curves were plotted and fitted by the AFT kinetic model for each herbicide, and AFT model kinetic parameters were used to calculate degradation rate constants. The reactivity order of these five active ingredients toward hydroxyl radical was acetochlor approximately metolachlor > butachlor approximately alachlor > propachlor. Treatment of the chloroacetanilides by AFT removed the parent compounds but did not completely mineralize them. However, AFT did result in an increase in the biodegradability of chloroacetanilide aqueous solutions, as evidenced by an increase in the 5-day biochemical oxygen demand to chemical oxygen demand ratio (BOD5/COD) to >0.3, indicating completely biodegradable solutions. Several degradation products were formed and subsequently degraded, although not always completely. Some of these were identified by mass spectral analyses. Among the products, isomers of phenolic and carbonyl derivatives of parent compounds were common to each of the herbicides analyzed. More extensively oxidized products were not detected. Degradation pathways are proposed for each of the parent compounds and identified products.     

Degradation of PCP in soils

In laboratory experiments, the degradation of PCP in soil with regard to the relationship to soil properties was studied under upland and flooded conditions using gas-chromatographic techniques. The degradation products and their behavior were elucidated by using 10 diCferent soils collected from rice fields and adjacent upland fields and one sample of a subsoil from the forest. The results are as follows:

1) The degradation of PCP in soils was faster under flooded conditions than upland conditions.

2) The degradation under flooded conditiont was more rapid in soils collected from rice fields than in those from adjacent upland fields, Tbe reverse was true under upland conditions.

3) The degradation rate was highly correlated with the organic matter content of the soil. Almost 100% of the PCP remained in the subsoil sample even after 50 days of incubation. The rate was slightly correlated with the clay mineral composition, free iron content, phosphate absorption coefficient and C.E.C., but hardly at all with texture, clay content, degree of base saturation, soil pH and available phosphorus content.

4) As the degradation products of PCP, 3 tetrachlorophenols, 4 or 5 trichlorophenols and PCP methyl ether were detected, PCP methyl elher and 2, 3, 4, 5-tetrachlorophenol were the major products, but the amount of the latter varied greatly during the course of incubation.     

Soil microbial community response to surfactants and herbicides in two soils

The environmental impacts of herbicides on desirable plants and the soil biota are of public concern. The surfactants that are often used with herbicides are also under scrutiny as potentially harmful to soil biological systems. To address these concerns, we used two soils, a silt loam and a silty, clay loam from south central Missouri, to investigate the impacts of herbicides and surfactants on soil microbial communities using phospholipid fatty acid (PLFA) analysis. The surfactants used in this study were alkylphenol ethoxylate plus alcohol ethoxylate (Activator 90), polyethoxylate (Agri-Dex), and a blend of ammonium sulfate, drift reduction/deposition polymers and anti-foam agent (Thrust). The herbicides were glyphosate, atrazine and bentazon. Surfactants and herbicides were applied to soils at label rate, either alone or combined, to 4000 g soil per pot. The two soils differed in history, texture, some chemical characteristics and several microbial community characteristics. A few of the chemicals altered some of the components of the microbial community after only one application of the chemical at field-rate. The Cole County, MO silt loam showed larger changes in the microbial community with application of treatments. For the Boone County, MO silty clay loam, Activator 90, Agri-Dex and bentazon treatments increased microbial biomass determined by PLFA; Thrust decreased PLFA markers, bacteria to fungi ratio; and Agri-Dex at both rates decreased monounsaturated fatty acids. Changes in the microbial community due to herbicides or surfactants were minimal in this study of a single application of these chemicals, but could be indicators of potential long-term effects. Long-term studies are needed to determine the changes in the microbial community after several years of annual applications of herbicides and surfactants on a wide array of soil types and management practices.     

Hydrolysis of sulfonylurea herbicides in soils and aqueous solutions: a review

Sulfonylureas are a unique group of herbicides used for controlling a range of weeds and some grasses in a variety of crops and vegetables. They have been extremely popular worldwide because of their low mammalian toxicity, low use rate, and unprecedented herbicidal activity. Knowledge about the fate and behavior of sulfonylurea herbicides in the soil-water environment appears to be of utmost importance for agronomic systems and environmental protection. Because these herbicides are applied at a very low rate, and their mobility is greatly affected by the chemicals' anionic nature in alkaline soils, a thorough understanding of their degradation/hydrolysis processes and mechanisms under aqueous and soil systems is important. This review brings together published information on the hydrolysis of several sulfonylureas in aqueous and soil solutions that includes the effects of pH, temperature, functional relationship between pH vs hydrolysis rate constants, and hydrolysis behavior of sulfonylureas in the presence of minerals. In addition, the transformations of sulfonylureas in soil, under laboratory and field experiments, have been discussed in connection with the compounds' varied structural features, i.e., sulfonylueas that are with or without the pyridinic, pyrimidine, and triazinic ring.     

Degradation of trichloroacetic acid in Saskatchewan soils

The persistence of ¹⁴C-trichloroacetic acid in three Saskatchewan soils was investigated at different moisture regimes under laboratory conditions at 25 ± 1°C. Following soil extraction with 0.1 m calcium chloride soln, radiochemical analytical procedures were used to monitor the breakdown. At rates equivalent to 4.4 kg/ha, degradation was most rapid in a high organic soil, with complete breakdown occurring within 3 weeks at moisture levels in excess of the wilting point. On a sandy loam and on a heavy clay breakdown was somewhat slower.     

Degradation processes and nutrient constraints in sodic soils

Accumulation of excess sodium (Na⁺) in a soil causes numerous adverse phenomena, such as changes in exchangeable and soil solution ions and soil pH, destabilization of soil structure, deterioration of soil hydraulic properties, and increased susceptibility to crusting, runoff, erosion and aeration, and osmotic and specific ion effects on plants. In addition, serious imbalances in plant nutrition usually occur in sodic soils, which may range from deficiencies of several nutrients to high levels of Na⁺. The structural changes and nutrient constraints in such soils ultimately affect crop growth and yield. The principal factor that determines the extent of adverse effects of Na⁺ on soil properties is the accompanying electrolyte concentration in the soil solution, with low concentration promoting the deleterious effects of exchangeable Na⁺ even at exchangeable sodium percentage (ESP) levels less than 5. Consequent to an increase in the use of poor quality waters and soils for crop production, the problems of sodic soils can be expected to increase in future. The mechanisms that explain sodic behaviour can provide a framework in which slaking, swelling and dispersion of clay together with nutrient constraints in sodic soils may be assessed so that the practices to manage such soils can be refined for long‐term sustainable agriculture. Copyright © 2002 John Wiley & Sons, Ltd.     

Degradation of phenyl carbamate herbicides by Pseudomonas alcaligenes isolated from soil

A bacterial strain isolated from soil and identified as Pseudomonas alcaligenes, was able to hydrolyze four phenylcarbamate herbicides (CIPC, BIPC, IPC and swep) to corresponding anilines and alcohols by co-metabolism. The pH of the growth medium had little influence on bacterial growth and rate of herbicide transformation. Increase in CIPC and BIPC concentrations resulted in a significant inhibition of bacterial growth and herbicide degradation. Using a range of antibiotics it was shown that the enzyme involved in degradation was inducible.     

土壤中磺酰脲除草剂降解机制研究进展

磺酰脲除草剂是一种高效、低毒、低用量(10～40g/hm~2)的新型除草剂,广泛应用于水稻、小麦和玉米等田间杂草的控制,在土壤中降解途径主要为水溶性光分解、醇解、化学水解和微生物分解,且4种降解途径下各自产生不同的降解产物。对土壤中磺酰脲除草剂降解产物的测定多采用气相色谱、液相色谱、酶连免疫吸附和生物检测,各测定方法均有利弊,色谱法需繁琐的纯化程序提纯样品以达到检测极限0.1μg/kg,生物检测和免疫吸附法测定快速、灵敏度高但缺乏专一性。结合生物降解模型研究,阐述了磺酰脲除草剂的降解机制。     

Degradation and sorption of pirimiphos-methyl in two Nigerian soils

This research is a continuation of a study on the behavior of hydrophobic organic compounds in the environment and describes the simultaneous abiotic degradation and sorption of pirimiphos-methyl (O-2-diethylamino-6-methylpyrimidin-4-yl O,O-dimethylphosphorothioate) under controlled conditions in soil/water slurries. A microfiltration-HPLC technique was employed to follow these processes in two well-characterized soils from the Middle Belt region of Nigeria. Rapid sorption of the pesticide occurs during the first 10 min of equilibration and accounted for 37% of the original pirimiphos-methyl in the Rhodic Kandiustalf soil and for 41% of the original concentration in Aquic Ustropept soil. Subsequent slow processes were followed during the remaining 30 days of the experiment. During this time, first-order rate constants for disappearance from solution of pirimiphos-methyl were found to have values of 6.1 x 10(-)(7) and 9.8 x 10(-)(7) s(-)(1) for the Rhodic and Aquic soils, respectively. Similarly, rate constants for production of the product, pyrimidinol, were calculated to be 6.0 x 10(-)(7) and 9.4 x 10(-)(7) s(-)(1) for the Rhodic and Aquic soils, respectively, giving pesticide degradation half-lives of 13 and 8.5 days. Disappearance of the pesticide is discussed in terms of a scheme involving both sorptive uptake by the soil and degradation by hydrolysis in the presence of the soil matrix. The labile sorption capacities for pirimiphos-methyl in the Rhodic and Aquic soils were found to be 0.75 and 0.90 micromol g(-)(1), respectively.     

Degradation and remediation of soils polluted with oil-field wastewater

The changes in the properties of gray forest soils and leached chernozems under the impact of contamination with highly saline oil-field wastewater were studied in a model experiment. It was shown that the soil contamination results in the development of technogenic salinization and alkalization leading to worsening of the major soil properties. The salinization of the soils with oil-field wastewater transformed the soil exchange complex: the cation exchange capacity decreased, and the exchangeable sodium percentage increased to up to 25% of the CEC upon the wastewater infiltration and up to 60% of the CEC upon the continuous soil saturation with the wastewater independently of the soil type. The content of exchangeable magnesium also increased due to the phenomenon of super-equivalent exchange. Despite the saturation of the soil adsorption complex with sodium, no development of the soil alkalization took place in the presence of the high concentration of soluble salts. However, the soil alkalization was observed upon the soil washing from soluble salts. The gypsum application to the washed soils lowered the exchangeable sodium concentration to acceptable values and normalized the soil reaction. The gypsum application without the preliminary washing of the soils from soluble salts was of low efficiency; even after six months, the content of exchangeable sodium remained very high. The subsequent soil washing resulted in the removal of the soluble salts but did not affect the degree of the soil alkalization.