2,4-D Mineralization in soil profiles of a cultivated hummocky landscape in Manitoba,Canada

The objective of this study was to quantify 2,4-D (2,4-dichlorophenoxyacetic acid) mineralization in soil profiles characteristic of hummocky, calcareous-soil landscapes in western Canada. Twenty-five soil cores (8 cm inner diameter, 50 to 125 cm length) were collected along a 360 m transect running west to east in an agricultural field and then segmented by soil-landscape position (upper slopes, mid slopes, lower slopes and depressions) and soil horizon (A, B, and C horizons). In the A horizon, 2,4-D mineralization commenced instantaneously and the mineralization rate followed first-order kinetics. In both the B and C horizons, 2,4-D mineralization only commenced after a lag period of typically 5 to 7 days and the mineralization rate was biphasic. In the A horizon, 2,4-D mineralization parameters including the first-order mineralization rate constant (k ₁), the growth-linked mineralization rate constant (k ₂) and total 2,4-D mineralization at the end of the experiment at 56 days, were most strongly correlated to parameters describing 2,4-D sorption by soil, but were also adequately correlated to soil organic carbon content, soil pH, and carbonate content. In both B and C horizons, there was no significant correlation between 2,4-D mineralization and 2,4-D sorption parameters, and the correlation between soil properties and 2,4-D mineralization parameters was very poor. The k ₁ significantly decreased in sequence of A horizon (0.113% day^?1) > B horizon (0.024% day^?1) = C horizon (0.026% day^?1) and in each soil horizon was greater than k ₂. Total 2,4-D mineralization at 56 days also significantly decreased in sequence of A horizon (42%) > B horizon (31%) = C horizon (27%). In the A horizon, slope position had little influence on k ₁ or k ₂, except that k ₁ was significantly greater in upper slopes (0.170% day^?1) than in lower slopes (0.080% day^?1). Neither k ₁ nor k ₂ was significantly influenced by slope position in the B or C horizons. Total 2,4-D mineralization at 56 days was not influenced by slope positions in any horizon. Our results suggest that, when predicting 2,4-D transport at the field scale, pesticide fate models should consider the strong differences in 2,4-D mineralization between surface and subsurface horizons. This suggests that 2,4-D mineralization is best predicted using a model that has the ability to describe a range of non-linear mineralization curves. We also conclude that the horizontal variations in 2,4-D mineralization at the field scale will be difficult to consider in predictions of 2,4-D transport at the field scale because, within each horizon, 2,4-D mineralization was highly variable across the twenty-five soil cores, and this variability was poorly correlated to soil properties or soil-landscape position.     

Fate in soil of 14C-sulfadiazine residues contained in the manure of young pigs treated with a veterinary antibiotic

The fate of ¹⁴C-labeled sulfadiazine (¹⁴C-SDZ) residues was studied in time-course experiments for 218 days of incubation using two soils (A_p horizon of loamy sand, orthic luvisol; A_p horizon of silt loam, cambisol) amended with fresh and aged (6 months) ¹⁴C-manure [40 g kg^?1 of soil; 6.36 mg of sulfadiazine (SDZ) equivalents per kg of soil], which was derived from two shoats treated with ¹⁴C-SDZ. Mineralization of ¹⁴C-SDZ residues was below 2% after 218 days depending little on soil type. Portions of extractable ¹⁴C (ethanol-water, 9:1, v/v) decreased with time to 4–13% after 218 days of incubation with fresh and aged ¹⁴C-manure and both soils. Non-extractable residues were the main route of the fate of the ¹⁴C-SDZ residues (above 90% of total recovered ¹⁴C after 218 days). These residues were high immediately after amendment depending on soil type and aging of the ¹⁴C-manure, and were stable and not remobilized throughout 218 days of incubation. Bioavailable portions (extraction using CaCl₂ solution) also decreased with increasing incubation period (5–7% after 218 days). Due to thin-layer chromatography (TLC), 500 μg of ¹⁴C-SDZ per kg soil were found in the ethanol-water extracts immediately after amendment with fresh ¹⁴C-manure, and about 50 μg kg^?1 after 218 days. Bioavailable ¹⁴C-SDZ portions present in the CaCl₂ extracts were about 350 μg kg^?1 with amendment. Higher concentrations were initially detected with aged ¹⁴C-manure (ethanol-water extracts: 1,920 μg kg^?1; CaCl₂ extracts: 1,020 μg kg^?1), probably due to release of ¹⁴C-SDZ from bound forms during storage. Consistent results were obtained by extraction of the ¹⁴C-manure-soil samples with ethyl acetate; portions of N-acetylated SDZ were additionally determined. All soluble ¹⁴C-SDZ residues contained in ¹⁴C-manure contributed to the formation of non-extractable residues; a tendency for persistence or accumulation was not observed. SDZ's non-extractable soil residues were associated with the soluble HCl, fulvic acids and humic acids fractions, and the insoluble humin fraction. The majority of the non-extractable residues appeared to be due to stable covalent binding to soil organic matter.     

Treating solid dairy manure using microwave-enhanced advanced oxidation process

The microwave enhanced advanced oxidation process (MW/H₂O₂-AOP) was used to treat separated solid dairy manure for nutrient release and solids reduction. The MW/H₂O₂-AOP was conducted at a microwave temperature of 120°C for 10 minutes, and at three pH conditions of 3.5, 7.3 and 12. The hydrogen peroxide dosage at approximately 2 mL per 1% TS for a 30 mL sample was used in this study, reflecting a range of 0.53–0.75 g H₂O₂/g dry sludge. The results indicated that substantial quantities of nutrients could be released into the solution at pH of 3.5. However, at neutral and basic conditions only volatile fatty acids and soluble chemical oxygen demand could be released. The analyses on orthophosphate, soluble chemical oxygen demands and volatile fatty acids were re-examined for dairy manure. It was found that the orthophosphate concentration for untreated samples at a higher % total solids (TS) was suppressed and lesser than actual. To overcome this difficulty, the initial orthophosphate concentration had to be measured at 0.5% TS.     

Heavy metal bioaccumulation in selected medicinal plants collected from Khetri copper mines and comparison with those collected from fertile soil in Haridwar,India

Heavy metal distribution in medicinal plants is gaining importance not only as an alternative medicine, but also for possible concern due to effects of metal toxicity. The present study has been focused on emphasizing the heavy metal status and bioaccumulation factors of V, Mn, Fe, Co, Cu, Zn, Se (essential metals) and Cr, Ni, Cd, As and Pb (potentially toxic metals) in medicinal plants grown under two different environmental conditions e.g., near to Khetri copper mine and those in fertile soils of Haridwar, both in India, using Instrumental Neutron Activation Analysis (relative method) and Atomic Absorption Spectrometry. The copper levels in the medicinal plants from Khetri were found to be 3-4 folds higher (31.6–76.5 mg kg^?1) than those from Haridwar samples (7.40–15.3 mg kg^?1), which is correlated with very high copper levels (763 mg kg^?1) in Khetri soil. Among various heavy metals, Cr (2.60–5.92 mg kg^?1), Cd (1.47–2.97 mg kg^?1) and Pb (3.97–6.63 mg kg^?1) are also higher in concentration in the medicinal plants from Khetri. The essential metals like Mn (36.4–69.3 mg kg^?1), Fe (192–601 mg kg^?1), Zn (24.9–49.9 mg kg^?1) and Se (0.13–0.91 mg kg^?1) and potentially toxic metals like Ni (3.09–9.01 mg kg^?1) and As (0.41–2.09 mg kg^?1) did not show much variations in concentration in the medicinal plants from both Khetri and Haridwar. The medicinal plants from Khetri, e.g., Ocimum sanctum, Cassia fistula, Withania somnifera and Azadirachta Indica were found rich in Ca and Mg contents while Aloe barbadensis showed moderately high Ca and Mg. Higher levels of Ca-Mg were found to correlate with Zn (except Azadirachta Indica). The bioaccumulation factors (BAFS) of the heavy metals were estimated to understand the soil-to-plant transfer pattern of the heavy metals. Significantly lower BAF values of Cu and Cr were found in the medicinal plants from Khetri, indicating majority fraction of these metals are precipitated and were immobilized species unsuitable for plant uptake. Overall, Withania somnifera (Ashwagandha) showed very high metal bioaccumulation.     

Effects of methamidophos on the community structure,antagonism towards Rhizoctonia solani,and phlD diversity of soil Pseudomonas

A microcosm incubation study using an aquic brown soil from northeast China (a Cambisol in the UN Food and Agriculture Organization FAO Soil Taxonomy) was conducted to examine the effects of different concentrations (0, 50, 150, and 250 mg kg^?1) of methamidophos (O,S-dimethyl phosphoramidothioato) on Pseudomonas, one of the most important gram-negative bacteria in soil. Amplified ribosomal DNA restriction analysis (ARDRA) was performed to study the Pseudomonas community structure, an in vitro assay was made to test the antagonistic activity of isolated Pseudomonas strains against soil-borne Rhizoctonia solani, a major member of the pathogens highly related to soil-borne plant diseases, and special primer amplification and sequencing were performed to investigate the diversity of phlD, an essential gene in the biosynthesis of 2, 4-diacetylphloroglucinol (2, 4-DAPG), which has biocontrol activity in phlD ⁺isolates. With exposure to increasing methamidophos concentrations, the total number of soil Pseudomonas ARDRA patterns decreased significantly, but with less change in the same treatments over 1, 3, and 5 weeks of incubation. The number of isolated Pseudomonas strains with antagonistic activity against R. solani as well as the diversity and appearance frequency of the strains' phlD gene also decreased with increasing concentrations of methamidophos, especially at high methamidophos concentrations. Applying methamidophos could increase the risk of soil-borne plant diseases by decreasing the diversity of the soil Pseudomonas community and the amount of R. solani antagonists, particularly those with the phlD gene.     

Application of a permethrin immunosorbent assay method to residential soil and dust samples

A low-cost, high throughput bioanalytical screening method was developed for monitoring cis/trans-permethrin in dust and soil samples. The method consisted of a simple sample preparation procedure [sonication with dichloromethane followed by a solvent exchange into methanol:water (1:1)] with bioanalytical detection using a magnetic particle enzyme-linked immunosorbent assay (ELISA). Quantitative recoveries (83–126 %) of cis/trans-permethrin were obtained for spiked soil and dust samples. The percent difference of duplicate ELISA analyses was within ± 20 % for standards and ± 35 % for samples. Similar sample preparation procedures were used for the conventional gas chromatography/mass spectrometry (GC/MS) analysis except that additional cleanup steps were required. Recoveries of cis/trans-permethrin ranged from 81 to 108 % for spiked soil and dust samples by GC/MS. The ELISA-derived permethrin concentrations were highly correlated with the GC/MS-derived sum of cis/trans-permethrin concentrations with a correlation coefficient (r) of 0.986. The ELISA method provided a rapid qualitative screen for cis/trans-permethrin in soil and dust while providing a higher sample throughput with a lower cost as compared to the GC/MS method. The ELISA can be applied as a complementary, low-cost screening tool to prioritize and rank samples prior to instrumental analysis for exposure studies.     

Bacterial diversity in paclobutrazol applied agricultural soils

The aim of this study was to investigate the bacterial communities on paclobutrazol [(2RS, 3RS)-1-(4-Chlorophenyl)-4, 4-dimethyl-2-(1H-1,2,4-triazol-1-yl) pentan-3-ol]–applied agricultural soils by denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR) amplified 16S rDNA gene fragments. Three different agricultural soil samples were collected from paclobutrazol applied mango and waxapple orchards, peanut fields and untreated rice fields as a control for DGGE analysis. The DGGE pattern of PCR- generated 16S rDNA gene fragments indicated that the bacterial populations from four paclobutrazol–applied soils of peanut fields were closely related to each other and two paclobutrazol–applied soils of mango and waxapple orchards harbored closely related bacterial communities. But, paclobutrazol–free agricultural soils comprised relatively a different bacterial group. However, the bacterial populations of mango and waxapple orchard are completely different from the bacterial communities of peanut field. Further purification and sequence analysis of 40 DGGE bands followed by phylogenetic tree assay showed similar results that soil bacteria from paclobutrazol applied mango and waxapple orchard are phylogenetically related. Based on the phylogenetic analysis, the clone M-4 was clad 100 % (bootstrap value) with Mycobacterium sp. The Mycobacterium sp. has been proved to degrade the phenolic compounds such as phenol, 4-chlorphenol, 2,4-dichlorophenol and paclobutrazol molecule containing chlorobenzene ring.     

Sorption of 3,4-dichloroaniline on four contrasting Greek agricultural soils and the effect of liming

Sorption of 3,4-dichloroaniline (3,4-DCA) on four typical Greek agricultural soils, with distinct texture, organic matter content and cation exchange capacities, was compared by using sorption isotherms and the parameters calculated from the fitted Freundlich equations. The sorption process of 3,4-DCA to the soil was completed within 48–72 h. The 3,4-DCA sorption on all soils was well described by the Freundlich equation and all sorption isotherms were of the L-type. The sandy clay loam soil with the highest organic matter content and a slightly acidic pH was the most sorptive, whereas the two other soil types, a high organic matter and neutral pH clay and a low organic matter and acidic loam, had an intermediate sorption capacity. A typical calcareous soil with low organic matter had the lowest sorption capacity which was only slightly higher than that of river sand. The 3,4-DCA sorption correlated best to soil organic matter content and not to clay content or cation exchange capacity, indicating the primary role of organic matter. The distribution coefficient (K _d) decreased with increasing initial 3,4-DCA concentration and the reduction was most pronounced with the highly sorptive sandy clay loam soil, suggesting that the available sorption sites of the soils are not unlimited. Liming of the two acidic soils (the sandy clay loam and the loam) raised their pH (from 6.2 and 5.3, respectively) to 7.8 and reduced their sorption capacity by about 50 %, indicating that soil pH may be the second in importance factor (after organic matter) determining 3,4-DCA sorption.     

Effects of sewage sludge amendments on pesticide sorption and leaching through undisturbed Mediterranean soils

The Gharb region in Morocco is an important agricultural zone where soils receive pesticide treatments and organic amendments to increase yields. The groundwater aquifer in the Gharb region is relatively shallow and thus vulnerable. The objective of this work was to study the influence of organic amendments on diuron, cyhalofop-butyl and procymidone leaching through undisturbed soil columns. Two soils were sampled from the Gharb region, a Dehs (sandy soil) and a R’mel (loamy clay soil). Following elution (124.5 mm), the amount of pesticide residues in the leachates of the sandy soil (0.06–0.21 %) was lower than in those of the loamy clay soil (0.20–0.36 %), which was probably due to preferential flow through the loamy clay soil. The amount of procymidone leached through the amended soil columns was greater than the control for the sandy soil only. The organic amendments did not significantly influence diuron and cyhalofop-butyl leaching in either of the soils. The application of organic amendments affected the amounts of dissolved organic matter (DOM) eluted and thus pesticide leaching as a function of soil-type. Nevertheless, in some case, the formation of pesticide-DOM complexes appeared to promote pesticide leaching, thus increasing groundwater contamination risks.     

Terpenes and phenolics in response to nitrogen fertilization: A test of the carbon/nutrient balance hypothesis

Nitrogen fertilization resulted in a linear increase in the growth ofAbies grandis seedlings, but linear decrease in foliage concentrations of phenolic compounds. These data are consistent with the inverse relationship between growth and production of carbonbased secondary chemicals predicted by the carbon/nutrient balance (CNB) hypothesis. However, in contrast to predictions of the CNB hypothesis, nitrogen fertilization had no effect on foliage terpene concentrations. The results suggest that not all carbon-based chemicals respond in the same manner to environmental variation, and that the carbon/nutrient balance hypothesis does not adequately explain all patterns of environmentally-induced variation in secondary metabolism.