Degradation products of chlomethoxynil (X-52) in soil

The degradation of unlabelled and ^l4C-labelled chlomethoxynil (2,4-dichlorophenyl 3′-methoxy-4′-nitrophenyl ether) in a flooded soil was studied in the laboratory, using thin-layer chromatography (TLC) and combined gas chromatography-mass spectrometry (GC-MS).

Chlomethoxynil was rapidly degraded, and labelled chlomethoxynil was largely transformed into substances which were unextractable with organic solvents. Moreover, most of the radioactive substances extracted with organic solvents were not “free” compounds but complexes. The degradation products identified were the amino derivative (2,4-dichlorophenyl 4′-amino-3-methoxyphenyl ether), the demethyl derivative (2,4-dichlorophenyl 3′-hydroxy-4′-nitrophenyl ether), the formylamino derivative (2,4-dichlorophenyl 4-formylamino-3′-methoxyphenyl ether), the acetylamino derivative (2,4-dichlorophenyl 3-methoxy-4′-acetylaminophenyl ether), thepropionylamino derivative (2,4-dichlorophenyl 4-propionylaminophenyl ether), 2,4-dichlorophenol, and several other minor compounds.     

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.     

Degradation of 2, 4-D, 2, 4, 5-T,and picloram in two Philippine soils

The degradation of 2, 4-D, 2, 4, 5-T, and picloram in two Philippine soils was investigated under upland and flooded (submerged) conditions. These herbicides degraded in both upland and flooded Maahas clay and Luisiana clay soils. The rate of degradation of the herbicides was more rapid in the Maahas clay soil than in the Luisiana clay soil. Among the three herbicides, 2, 4-D was the least persistent and picloram was the most persistent in both soils under both submerged and upland conditions. 2, 4, 5-T degraded more actively in the two Philippine soils in this study than studies previously reported in the available literature. The fact that both the 2, 4-D and 2, 4, 5-T did not degrade in sterilized soils during the incubation period suggests that the degradation is due to the microbial activity in the soils.     

Molybdenum status and critical limit in the soil for green gram (Vigna radiata) growing in Madurai and Sivagangai districts of Tamil Nadu,India

Abstract

The decay of rice residue was investigated after incubation periods of from 1 to 24 months at 30°C under both flooded and upland soil conditions. Tops and roots of rice plants were cut into about 10-mm length, and separately incorporated in soil which had been passed through a 0.5-mm sieve. Plant debris were fractionated physically according to their sizes and divided into five groups (>4 mm, 4-2 mm, 2-1 mm, 1-0.5 mm, and 0.5-0.25 mm).

Carbon loss from the soils amended with rice residues and decrease in the weight of total plant debris proceeded at a rapid speed in the early periods (around 4 months) and then at a slow speed in the subsequent periods under both flooded and uplana soil conditions. The distribution of the plant debris in the decomposition processes differed under flooded and upland conditions. Under flooded conditions, 2–4 mm-sized plant debris were retained for a long period with slow transformation into the smaller fractions. In contrast, under upland conditions, change of plant debris from large to small size fractions proceeded gradually. This continuous change could be attributed to the high decomposing activities of fungi under upland conditions.     

Microbial degradation of fomesafen by a newly isolated strain Pseudomonas zeshuii BY-1 and the biochemical degradation pathway

Fomesafen is a diphenyl ether herbicide used to control the growth of broadleaf weeds in bean fields. Although the degradation of fomesafen in soils was thought to occur primarily by microbial activity, little was known about the kinetic and metabolic behaviors of this herbicide. This paper reported the capability of the newly isolated strain Pseudomonas zeshuii BY-1 to use fomesafen as the sole source of carbon in pure culture for its growth. Up to 88.7% of 50 mg of L(-1) fomesafen was degraded by this bacterium in mineral medium within 3 days. Strain BY-1 could also degrade other diphenyl ethers, including lactofen, acifluorfen, and fluoroglycofen. During the fomesafen degradation, five metabolites were detected and identified by liquid chromatography-mass spectrometry and tandem mass spectrometry. The primary degradation pathway of fomesafen might be the reduction of the nitro group to an amino group, followed by the acetylation of the amino derivative, dechlorination, and cleavage of the S-N bond. The addition of the BY-1 stain into soils treated with fomesafen resulted in a higher degradation rate than that observed in uninoculated soils, and the bacteria community in contaminated soil recovered after inoculation of the BY-1 stain. On the basis of these results, strain P. zeshuii BY-1 has the potential to be used in the bioremediation of fomesafen-contaminated soils.     

Relationships between microbial biomass and dissipation of 2,4-D and dicamba in soil

A study was conducted to evaluate relationships between microbial biomass and the dissipation of 2,4-D (2,4-dichlorophenoxy acetic acid) and dicamba (2-methoxy-3,6-dichlorobenzoic acid) in soil. We hypothesized that the size of the microbial biomass should be a strong predictor of the pesticide degradation capacity of a particular soil. Soils with a high microbial biomass should have relatively high levels of general microbial activity and should support a diversity of degradation pathways. In this study, we quantified the degradation of 2,4-D and dicamba in a range of soils with different concentrations of microbial biomass. The herbicides 2,4-D and dicamba were added to similar soils collected from five different land use types (home lawn, cornfield, upland hardwood forest, wetland forest, and aquifer material) and incubated for 80 days under laboratory conditions. Herbicide residue and microbial biomass (C and N) analyses were performed 5, 10, 20, 40, and 80 days following herbicide application. Microbial biomass-C and -N and soil organic matter content were positively correlated with dissipation of 2,4-D and dicamba. The results suggest that there are relationships between the size of the soil microbial biomass and the herbicide degradation capacity of an ecosystem. These relationships may be useful for developing approaches for evaluating and predicting the fate of pesticides in different ecosystems.     

Relationships between microbial biomass and dissipation of 2,4-D and dicamba in soil

A study was conducted to evaluate relationships between microbial biomass and the dissipation of 2,4-D (2,4-dichlorophenoxy acetic acid) and dicamba (2-methoxy-3,6-dichlorobenzoic acid) in soil. We hypothesized that the size of the microbial biomass should be a strong predictor of the pesticide degradation capacity of a particular soil. Soils with a high microbial biomass should have relatively high levels of general microbial activity and should support a diversity of degradation pathways. In this study, we quantified the degradation of 2,4-D and dicamba in a range of soils with different concentrations of microbial biomass. The herbicides 2,4-D and dicamba were added to similar soils collected from five different land use types (home lawn, cornfield, upland hardwood forest, wetland forest, and aquifer material) and incubated for 80 days under laboratory conditions. Herbicide residue and microbial biomass (C and N) analyses were performed 5, 10, 20, 40, and 80 days following herbicide application. Microbial biomass-C and -N and soil organic matter content were positively correlated with dissipation of 2,4-D and dicamba. The results suggest that there are relationships between the size of the soil microbial biomass and the herbicide degradation capacity of an ecosystem. These relationships may be useful for developing approaches for evaluating and predicting the fate of pesticides in different ecosystems.     

Fate of 14C-carbofuran in soils

The degradation of¹⁴ C-Carbofuran was studied in sterilized, unsterilized and green manure amended clay soil under moist and flooded conditions overa period of 30 days. The¹⁴ C mass balance showed that carbofuran did not undergo any degradation in sterilized moist soil. In sterilized flooded soil bound residues were formed to the extent of about 47% of the applied radioactivity at the end of 30 days. Carbofuran underwent considerable degradation in unsterilized moist and flooded soils. In moist soil about 48% of the applied¹⁴ C activity was recovered as bound activity while in flooded soil, about 23% of the activity was bound. Green manure amendment resulted in formation of more bound residues under moist conditions while it enhanced the degradation of carbofuran under flooded conditions. In flooded amended soil about 44% of the applied^l4 C-activity was recovered as against about 54% in the unamended flooded soil. The notable degradation products formed under flooded soil conditions were 3-keto carbofuran and 3-hydroxy carbofuran.     

可溶性有机质对凹凸棒土负载铁/镍降解黄棕壤中BDE47的影响

多溴联苯醚(PBDEs)是一类广泛使用的溴代阻燃剂,在大气、水体、土壤、生物体等环境介质中普遍检出,严重威胁环境安全和人体健康。本文以凹凸棒土负载铁/镍材料(A-Fe/Ni)为修复剂,以普遍检出的2,2′,4,4′-四溴联苯醚(BDE47)为模式化合物,开展了可溶性有机质(DOM)存在条件下,A-Fe/Ni对黄棕壤中BDE47的降解动力学过程研究,探讨了DOM对材料降解BDE47的影响机制。结果表明:A-Fe/Ni可高效地降解黄棕壤–甲醇/水体系中的BDE47,降解过程符合假二级动力学方程,BDE47可被降解成一溴~三溴联苯醚和联苯醚。体系中加入3种DOM(胡敏酸、柠檬酸和草酸)后,DOM在Fe/Ni颗粒表面形成钝化层,抑制了降解过程中的传质和电子传递作用,不同程度降低了A-Fe/Ni对黄棕壤–甲醇/水体系中BDE47的降解效率,并影响其降解产物物质的量的组成。实验结果为使用零价纳米铁及零价纳米铁基双金属材料修复污染土壤中PBDEs提供了理论依据和参考。     

Microbial community responsible for the decomposition of rice straw in a paddy field: estimation by phospholipid fatty acid analysis

To estimate the microbial communities responsible for rice straw decomposition in paddy field, phospholipid fatty acid (PLFA) composition of leaf sheaths and blades was analyzed during the decomposition of both residues under upland conditions after harvest and under flooded conditions at the time of transplanting of rice plants. In addition, rice straw that had been placed in the field under upland conditions (November to April) was taken out in spring, and placed again in the same field under flooded conditions at the time of transplanting. High proportions of the branched-chain PLFAs were observed under flooded conditions (June to September); the proportions of straight mono-unsaturated and straight poly-unsaturated PLFAs were high under upland conditions in the winter season for 4 months. The dominant PLFAs in straight mono-unsaturated, straight poly-unsaturated and branched-chain PLFA groups were 18:19, 18:17 and 16:17c, 18:26c and i15:0, i17:0 and ai15:0, respectively, under both upland and flooded conditions. These findings indicated the important roles of Gram-negative bacteria and fungi under upland conditions and of Gram-positive bacteria and anaerobic Gram-negative bacteria under flooded conditions. Cluster analysis of PLFA composition showed the difference of community structure of microbiota in rice straw between upland and flooded conditions. In addition principal component analysis revealed the difference between leaf sheaths and blades under upland conditions and indicated that the content of straight unsaturated PLFAs (sheaths > blades) characterized their community structures.     

Characteristics of Humic Substances in Paddy Soils

In the present paper,the composition of humus and the charateristics of humic acid from seven paddy soils were compared with those of upland (and/or natural) soils.Results show that:(1) in each group of the soil samples for comparison the HA/FA ratio of the humus of a paddy soil,in most cases,was appreciable higher than that of adjacent upland(and/or natural) soil derived from the same parent material;(2) the humic acid extracted from the paddy soils was characterized by a higher C/O ratio,a higher content of methoxyl groups,and a lower content of carboxyl groups than those from the corresponding upland (and/or natural) flooded soils,implying that the humic acid formed under rice cultivation is in a lower degree of humification than that formed under upland(and/or natural) conditions;and (3) the humic acid of paddy soils,however,was not always characterized by a lower aromaticity than that of the corresponding upland(and/or natural) soils.     

Fate of Microelements Applied to a Tropical Peat Soil: Column Experiment

Lack of microelements is a major problem in crop production in tropical peatland. For their efficient application, the fate of copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) in a Histosol was investigated in a 3-month column experiment. Leaching of Cu, Fe, Mn, and Zn accounted for 2, –2 to 7, 28 to 32, and 21 to 23% of the amounts applied, respectively, in both the flooded and upland soils. The microelement application enhanced the leaching of calcium (Ca), potassium (K), magnesium (Mg), sodium (Na), and phosphorus (P). Replacement of exchangeable cations by the microelements was suggested in the successive extraction of elements from the soils after incubation. Under the upland conditions, 31–33% of the Cu and Fe increased in soil was extracted with diethylenetriaminepentaacetic acid?/?triethanolamine (bound to humus), whereas 26–31% of the Mn and Zn increased was exchangeable. Extractability was smaller under the flooded conditions for all the microelements, suggesting that fertilization in the dry season is more effective.     

Factors affecting triadimefon degradation in soils

The degradation of triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl)butan-2-one] was studied in two soils, mollisol and inseptisol, under varying conditions of moisture and temperature, and the role of cow manure amendment and soil sterilization on fungicide degradation was ascertained. The soil moisture content affected the pathway followed for triadimefon degradation. In nonflooded soils (60% water-holding capacity), triadimefon was reduced to triadimenol, and in flooded soils, it was metabolized to the diol derivative [1-(1H-1,2,4-triazol-1-yl)-3,3-dimethylbutan-2-one-1,4-diol]. In nonflooded soils, triadimefon was more persistent in soil having more organic carbon content (mollisol), and the amendment of cow manure (5%) further enhanced its persistence. On the contrary, in flooded soil systems, the higher the soil organic carbon content was, the less persistent was the fungicide, and amendment of cow manure further enhanced its degradation. Triadimefon degradation was faster at 35 degrees C than at 27 degrees C. Triadimefon degradation in soils was mediated by the microorganisms, and no triadimefon degradation was observed in sterile soils. Triadimefon (1 mg/kg) did not affect soil phosphatase activity in either of the soils; however, soil dehydrogenase activity was significantly reduced, especially in mollisol soil.     

Hydrolysis of organic and inorganic phosphorus compounds added to soils

The rates of hydrolysis of seven organic and two inorganic phosphorus compounds applied to soils at a rate of 500 ppm P and incubated at 20°C for various times under aerobic and waterlogged conditions were studied. Monomethyl phosphate, β-glycerophosphate, and α-D-glucose-1-phosphate were hydrolyzed at similar rates in the three soils used, but the rates were somewhat faster under aerobic than under waterlogged conditions. Organic P compounds in which two hydrogens of the orthophosphoric acid are replaced (e.g., diphenyl phosphate) were hydrolyzed at slower rates than those in which one hydrogen is replaced (e.g., phenyl phosphate). The rate of hydrolysis of diphenyl phosphate was lower than that of bis-p-nitrophenyl phosphate. Of the two inorganic P compounds studied, ammonium tetrametaphosphimate did not hydrolyze in soil, and the rate of hydrolysis of phosphonitrilic hexaamide was very small (6–13% hydrolyzed in 7 days) compared with those of the organic phosphates (30–98%).     

Conversion factor (k factor) for estimation of soil microbial biomass potassium by the chloroform-fumigation extraction method

The conversion factor, k_K, for estimation of microbial biomass potassium (K) by the chloroform-fumigation extraction method was determined for some arable soils: upland field soils under different fertilization conditions, an upland field soil under a greenhouse condition, and a paddy field soil under a flooded condition. The k_K value varied with land utilization (paddy or upland) or fertilization (chemical or organic fertilizer). Value of k_K was different between paddy field soil (0.28–0.38) and upland field soil (0.41–0.73). This study indicates that the value could be useful for the estimation of microbial biomass K in soil by the chloroform-fumigation extraction method and further investigation of the amounts of biomass K in different types of soils under conditions with varied field managements will be necessary.     

Effect of Lime and Flooding on Phosphorus Availability and Rice Growth on Two Acidic Lowland Soils

Abstract

Loss of soil‐water saturation may impair growth of rainfed lowland rice by restricting nutrient uptake, including the uptake of added phosphorus (P). For acidic soils, reappearance of soluble aluminum (Al) following loss of soil‐water saturation may also restrict P uptake. The aim of this study was to determine whether liming, flooding, and P additions could ameliorate the effects of loss of soil‐water saturation on P uptake and growth of rice. In the first pot experiment, two acid lowland soils from Cambodia [Kandic Plinthaqult (black clay soil) and Plinthustalf (sandy soil)] were treated with P (45 mg P kg^?1 soil) either before or after flooding for 4 weeks to investigate the effect of flooding on effectiveness of P fertilizer for rice growth. After 4 weeks, soils were air dried and crushed and then wet to field capacity and upland rice was grown in them for an additional 6 weeks. Addition of P fertilizer before rather than after flooding depressed the growth of the subsequently planted upland rice. During flooding, there was an increase in both acetate‐extractable Fe and the phosphate sorption capacity of soils, and a close relationship between them (r²=0.96–0.98). When P was added before flooding, Olsen and Bray 1‐extractable P, shoot dry matter, and shoot P concentrations were depressed, indicating that flooding decreased availability of fertilizer P. A second pot experiment was conducted with three levels of lime as CaCO₃ [to establish pH (CaCl₂) in the oxidized soils at 4, 5, and 6] and four levels of P (0, 13, 26, and 52 mg P kg^?1 soil) added to the same two acid lowland rice soils under flooded and nonflooded conditions. Under continuously flooded conditions, pH increased to over 5.6 regardless of lime treatment, and there was no response of rice dry matter to liming after 6 weeks' growth, but the addition of P increased rice dry matter substantially in both soils. In nonflooded soils, when P was not applied, shoot dry matter was depressed by up to one‐half of that in plants grown under continuously flooded conditions. Under the nonflooded conditions, rice dry matter and leaf P increased with the addition of P, but less so than in flooded soils. Leaf P concentrations and shoot dry matter responded strongly to the addition of lime. The increase in shoot dry matter of rice with lime and P application in nonflooded soil was associated with a significant decline in soluble Al in the soil and an increase in plant P uptake. The current experiments show that the loss of soil‐water saturation may be associated with the inhibition of P absorption by excess soluble Al. By contrast, flooding decreased exchangeable Al to levels below the threshold for toxicity in rice. In addition, the decreased P availability with loss of soil‐water saturation may have been associated with a greater phosphate sorption capacity of the soils during flooding and after reoxidation due to occlusion of P within ferric oxyhydroxides formed.     

Persistence and biodegradation of selected organophosphorus insecticides in flooded versus non-flooded soils

Summary The persistence of parathion, methyl parathion and fenitrothion in five tropical soils of varying physicochemical characteristics was compared under flooded and non-flooded conditions. The degradation of all the three insecticides was more rapid under flooded conditions than under non-flooded conditions in four out of five soils. Degradation of these insecticides proceeded by hydrolysis under non-flooded conditions and essentially by nitro group reduction and to a minor extent by hydrolysis under flooded conditions. Kinetic analysis indicated that degradation of the three insecticides followed a first-order reaction irrespective of the soil and water regime. The degradation of these organophosphorus insecticides was accelerated after repeated applications to flooded alluvial soil. Nitro group reduction was the major pathway of degradation for all the three insecticides after the first addition while the rate of hydrolysis increased after each successive addition.     

Vegetated ridge and sandbag may not reduce soil erosion and loss of carbon and nutrients from upland fields

ABSTRACT

Though construction of vegetated ridge (VR) and placement of sandbag (SB) across the slope of upland fields are believed to be effective in reducing soil erosion and nutrient loss, relevant data are lacking to confirm such expectations. In this study, the effects of VR and SB on loss of soils, carbon (C), nitrogen (N), and phosphorus (P) (CNP) were investigated through both artificial (in dry season) and natural (in rainy season) runoff experiments on upland fields cultivated with maize (Zea mays L. var. ceratina). Contrary to expectations, both VR and SB were not effective in reducing the loss of soils and CNP. For VR, accelerated convergent flow caused by ridge failure, which occurred when part of the ridges collapsed because the amount of water collected in the furrows exceeded the water storage capacity of the ridges, led to excessive loss of soils and CNP. For SB, the loss of soils and CNP could be ascribed to the malfunction of SB; i.e., soil and CNP were lost by seepage through the gaps between SBs and between SB and soil surface. Maize growth and yield were not affected by VR and SB, coinciding with the lack of beneficial effects of VR and SB on soil and nutrient loss. As VR and SB are easy to be implemented and cost-effective, however, further study is necessary to correct the flaws of VR and SB found in this study.     

Aerobic versus Anaerobic Microbial Degradation of Etofenprox in a California rice field soil

The microbial degradation of etofenprox, an ether pyrethroid, was characterized under anaerobic (flooded) and aerobic (nonflooded) California rice field soil conditions by determination of its half-life (t1/2) and dissipation rate constant (k) and identification and quantification of degradation products at both 22 and 40 °C using LC-MS/MS. The overall anaerobic t1/2 at 22 °C ranged from 49.1 to 100 days (k=-0.0141 to -0.0069 days(-1)) compared to 27.0 days (k=-0.0257 days(-1)) at 40 °C, whereas under aerobic conditions the overall t1/2 was 27.5 days (k=-0.0252 days(-1)) at 22 °C compared to 10.1-26.5 days (k=-0.0686 to -0.0262 days(-1)) at 40 °C. The biphasic dissipation profiles were also fit to a first-order model to determine the t1/2 and k for both the fast and slow kinetic regions of the dissipation curves. Hydroxylation at the 4'-position of the phenoxy phenyl ring was the major metabolic process under anaerobic conditions for both 22 °C (maximum% yield of applied etofenprox mass=1.3±0.7%) and 40 °C (max % yield=1.2±0.8%). Oxidation of the ether moiety to the ester was the major metabolite under aerobic conditions at 22 °C (max% yield=0.5±0.1%), but at 40 °C increased amounts of the hydroxylated form were produced (max% yield=0.7±0.2%, compared to 0.3±0.1% for the ester). The hydrolytic product of the ester, 3-phenoxybenzoic acid (3-PBA), was not detected in any samples. Sterilized control soils showed little etofenprox degradation over the 56-day incubation period. Thus, the microbial population in a flooded soil was able to transform and contribute to the overall dissipation of etofenprox. The simulated summer temperature extreme (40 °C) increased the overall degradation.     

Biodegradation of chlorinated phenols in subsurface soils

Microcosm studies were employed to determine the subsurface biodegradation rates of phenol, 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and pentachlorophenol (PCP). Soil samples were taken from sites in Pennsylvania and Virginia from depths up to 31 m, and all samples contained significant microbial populations. Soil from both sites readily biodegraded all five compounds. Biodegradation rates increased as initial concentrations increased, and all biodegradation rates appeared to follow first-order kinetics with regard to the initial compound concentrations. Biodegradation rates for the five compounds followed the order: phenol = 2-CP > 2,4,6-TCP > 2,4-DCP. PCP was degraded more slowly than phenol or 2-CP, but similarly to 2,4,6-TCP and 2,4-DCP. Different soils exhibited different degradation rates, and the soil characteristics that may influence the rates are discussed. The data suggest that biological degradation is a significant attenuation mechanism for phenol and its chlorinated derivatives in subsurfaces saturated and unsaturated zones.