Formation Of Non-extractable Residues Research Articles

Modifications to atrazine degradation pathways in a loamy soil after addition of organic amendments

The effects of two organic amendments, a municipal solid waste compost and a composted straw, on [U- ring- 14C]atrazine degradation pathways in a loamy soil (Grignon, Yvelines, France) were studied during laboratory incubations under controlled conditions. Three month conditionings were conducted under sterile or non-sterile conditions, with soil plus atrazine, organic amendment plus atrazine, or soil plus organic amendment. Then either an organic amendment or soil or atrazine was added, respectively, to these three treatments and incubated for an additional 3 months under non-sterile conditions. Both organic amendments modified the behaviour of atrazine in soil but via different processes. The addition of municipal compost increased atrazine sorption and decreased its availability for degradation by soil microorganisms. The effect of the composted straw was mainly related to its high enzymatic activity, which appeared to be responsible for the production of large amounts of hydroxyatrazine. This hydroxylation favoured the opening of the triazine ring and its subsequent mineralization in the soil. At the end of the incubations, less atrazine was mineralized in the presence of the two types of organic amendment, which both increased the formation of non-extractable residues of atrazine. The addition of municipal compost preserved larger amounts of extractable atrazine, while the addition of composted straw enhanced hydroxyatrazine production. In all cases, the greatest effects were found when atrazine was directly in contact with the organic amendment during conditioning.

The use of 13C-labelled polycyclic aromatic hydrocarbons for the analysis of their transformation in soil

The formation of non-extractable residues during biodegradation and humification processes in soils and sediments represents a major sink for organic contaminants. The mode of incorporation of polycyclic aromatic hydrocarbons (PAH) and their metabolites into macromolecular organic matter during microbial degradation was studied applying 13C-labelled compounds. Mineralisation rates were determined by measuring the 13CO 2 production. An incorporation of 13C-PAH-fragments into humic material could be traced by isotopic analysis of the bulk organic matter. Furthermore, selective chemical degradation reactions were performed to analyse the precise chemical structure of covalently bound 13C-labelled PAH fragments in soil humic substances. Structural assignments by GC-MS combined with isotope measurements on the bulk organic carbon and at the molecular level (Isotope Ratio Monitoring-GC-MS) provided useful information on the fate of xenobiotics within the soil.

Triazine dispersion and distribution in the unsaturated zone of drained soils in the Brie (France)

The purpose of this study was to investigate the fate of triazines and their metabolites in the unsaturated zone in the field conditions during a period from the spring sowings to the autumn tillages. The study was performed upon two soils treated for corn culture during the year 1992. The investigations were presented after the wet weather by subsurface drainage and surface runoff. Throughout the 6 months survey, the relative importance of the triazines is by decreasing order: atrazine > simazine > desethylatrazine (DEA). After the application, the herbicides were only found in the first 40 cm of the soil during the dry period of the cultivation. They were dragged towards the depth by percolation water mainly during the first water infiltrations when the drains were set in again in autumn or winter. The losses of herbicides after the cultivation cycle (october) expressed as a ratio of the initial input ranged from 40 to 73% for the atrazine and from 40 to 44% for the simazine and depended on the importance of the application amount. In autumn and winter, the losses originating in percolation were higher than those due to volatilization and/or degradation (abiotic and biodegradation), as the soil conditions were unpropicious to the formation of non-extractable residues.

Sorption and Desorption of Atrazine, Deethylatrazine, and Hydroxyatrazine by Soil and Aquifer Solids

AbstractAdsorption kinetics and adsorption/desorption isotherms of atrazine (AT), and its degradation products, deethylatrazine (DEA) and hydroxyatrazine (HyA) on solids from two depths of a gleyic planosol and the underlying sandy aquifer were studied using laboratory batch systems. Adsorption of the three molecules decreased with the sampling depth of the solid. Atrazine and DEA were not adsorbed on the aquifer solids, whereas HyA was. For all three solids, the adsorption increased in the order DEA < AT << HyA. Adsorption equilibrium was reached after 72 h for the upper soil sample (0‐0.33 m) and after 24 h for the deeper soil sample (0.9–1.05 m) for all three molecules. For HyA, equilibrium was reached after 24 h for the aquifer solid (6–7 m). High pressure liquid chromatography (HPLC) analyses showed no significant degradation of the three molecules after 72 h. The adsorption isotherms of the three molecules were described by Freundlich equations. The Kfads values ranged from 3.1 to 0.4 L kg−1 for AT, 1.5 to 0.3 L kg−1 for DEA and 7.9 to 0.9 L kg−1 for HyA. The Koc values suggested that the affinity for the organic matter bound to the solid increased in the order DEA < AT << HyA. The desorption isotherms were also described by Freundlich equations. The Kfdes value was 7.5 L kg−1 for AT in the upper soil sample and ranged from 0.1 to 31.1 L kg−1 for DEA and from 0.7 to 96.8 L kg−1 for HyA, depending on the sample. In the upper soil sample, desorption was hysteretic and DEA and HyA formed nonextractable residues, HyA more so than DEA. For the deeper soil sample for all three compounds and the aquifer solids for HyA, adsorption was completely reversible and did not lead to the formation of nonextractable residues.

Metabolism of the Pesticide Metabolite 4-[U-14C]Nitrophenol inDatura stramonium(L.) Cell Suspension Culture—A Model for Processing of Xenobiotic Carbohydrate Conjugates and Formation of Nonextractable Residues

The biotransformation of the pesticide metabolite 4[U-14C]nitrophenol was studied in cell suspension cultures ofDatura stramonium(L.), which were routinely subcultured every 9 or 10 days. In a standard metabolism experiment (48 hr of incubation) starting 7 days after subcultivation, the xenobiotic was found conjugated to its β-glucoside (ca.22% of applied14C) and gentiobioside, Glc-β(1→6)-Glc-β-4-nitrophenol (ca.64%); about 7% of the parent remained unchanged. The conjugates were identified using TLC, HPLC, and their UV spectra. In contrast to previous, analogous studies with carrot, soybean, and wheat, a greater portion of nonextractable residues (11.2%) was detected. A time-course study (started 6 days after subcultivation for 96 hr) demonstrated that the disaccharide was formed from Glc-β-4-nitrophenol, and that the major percentage of bound residues (7.1 of 12.2%) emerged in the last 72 hr of incubation. The data suggested this portion was due to a turnover of 4-nitrophenol conjugates. Two time-course experiments started directly after subcultivation and performed for 10 and 16 days confirmed that this turnover was confined to late rapid growth and stationary phases of the culture cycle. The main metabolite Glc-β(1→6)-Glc-β-4-nitrophenol proved to be only a temporary product which was degraded considerably (ca.22%) during this period in favor of the β-glucoside and nonextractable residues. According to these data, xenobiotic conjugates may be regarded as temporary storage products subject to turnover in the plant, as reported frequently for those of secondary compounds. The metabolic processes observed were attributed to differentiation processes possibly occurring especially during the stationary phase of the cell culture. In general, these are characterized by initiation of structural organization and increased cell aggregation and lignification and are known in particular for cell cultures of solanaceous species.

Investigations on the Behaviour of Fenpropimorph and its Metabolite Fenpropimorphic Acid in Soils

The fate of fenpropimorph and its metabolite fenpropimorphic acid was investigated in a silty sand soil and in a clayey silt soil. In laboratory and field experiments fenpropimorph disappeared without a lag phase. A few days after application fenpropimorphic acid was detected. Additional laboratory experiments with [ 14 C]fenpropimorph emphasized the significance of mineralization and the formation of non-extractable residues. The determination of soil/water distribution coefficients of parent compound and metabolite yielded a higher leaching potential for fenpropimorphic acid due to its higher polarity. This was confirmed by performing a laboratory column test under worst-case conditions. Under field conditions, however, fenpropimorphic acid was detected only in the superficial soil layers (0-5 cm) of both investigation sites at very low concentrations.

Persistence and leaching of atrazine in corn culture in the experimental site of La Côte Saint André (Isère, France)

The fate of atrazine in corn culture was studied under field conditions during the years 1991–1992. After a preemergence treatment (1000 g/ha atrazine used under a flowable formulation) occurring at the end of April, samples of soil-water and soil were collected periodically at different depths in the one-meter-thick upper layer of the soil, supporting the corn culture at the Experimental Farm of La Cote Saint Andre (Isere, France). Atrazine and its metabolites deethylatrazine and deisopropylatrazine, measured by GC analysis, were present throughout the year in soil samples and soil-water samples at every sampling date and at each depth. Atrazine concentration varied from 0.2 to 14.7 μg/L in soil-water samples. The total content of atrazine, deethylatrazine, and deisopropylatrazine dissolved in the soil water of the one-meter-thick upper soil layer varied throughout the year from 33 to 94 g/ha. Under our conditions of sampling, the total amount (atrazine and metabolites) leached annually was tentatively estimated as the product of the weekly concentration of the soil water at 80 cm depth by the total volume of water drained for the corresponding week. The total amount of atrazine plus metabolites obtained through this estimation procedure was close to 50 g/ha, representing approximately 5% of the treatment applied (0.6% when atrazine alone was taken into account). Due to the importance of the rapid macropore transport of water after a heavy rainfall in the fluvio-glacial type of soil studied here, there most probably was an important leaching of free atrazine on the occasion of abundant rains during the first month after treatment. The amount dissolved in soil-water seemed to be but remotely associated with the adsorbed content in soil since partition equilibrium conditions, as shown, for example, in experiments establishing Koc values, were probably only rarely obtained between soil and soil-water under field conditions. Atrazine, initially exclusively located on the soil surface, appears progressively at all levels of the one-meter layer studied. One year after the spraying of 1 kg/ha atrazine, only 15% of the initial deposit was still present (in the form of atrazine, deethyatrazine, or deisopropylatrazine) in the one-meter-thick upper layer. The major part of the atrazine deposit (close to 80–85%) was dissipated essentially through metabolization, early leaching, and volatilization, while the role played by plant absorption and formation of non-extractable residues remained low. Just before a new crop season, the average amount of atrazine and metabolites in the one-meter layer was measured to be close to 400 g/ha (150, 125, and 125 for atrazine, deethylatrazine, and deisopropylatrazine, respectively).

Atrazine and Metolachlor Dissipation in Soils Incubated in Undisturbed Cores, Repacked Cores, and Flasks

AbstractThis study compared three different laboratory methods for determining soil pesticide dissipation kinetics and pathways. The dissipation kinetics of the herbicides atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine) and metolachlor (2‐chloro‐6′‐ethyl‐N‐(2‐methoxy‐1‐methylethyl)acet‐o‐toluidine) were examined in three soils (sandy loam, loam, clay loam) incubated for 63 d in flasks or intact cores (20 by 20 cm) under controlled moisture (field capacity) and temperature (25°C) conditions in the laboratory. The dissipation of metolachlor and atrazine were also examined in repacked cores of the loam soil adjusted to the field bulk density. The rates of atrazine or of metolachlor dissipation in soils incubated in flasks or in intact cores were indistinguishable (P<0.05). The rate of net accumulation of extractable transformation products from radiolabeled atrazine and the rate of nonextractable residue formation in soils incubated in flasks and intact cores were likewise the same. However, the rate of dissipation of metolachlor, the rate of accumulation of atrazine transformation products, and the rate of formation of nonextractable atrazine residues were all significantly slower in repacked cores of the loam soil. These results indicate that, under controlled laboratory conditions, atrazine and metolachior dissipation occured at the same rate in undisturbed soil cores and in flask incubations with soil that had been disrupted by previous air‐drying and sieving. We conclude that, at least in some soils, structure need not necessarily be maintained in laboratory soil pesticide dissipation experiments.

Sorption and Desorption of Imazethapyr and 5-Hydroxyimazethapyr in Minnesota Soils

Laboratory batch equilibrium studies were conducted to evaluate the sorption-desorption behavior of imazethapyr and its major plant metabolite, 5-hydroxyimazethapyr, in three Minnesota soils. Sorption of both compounds on all soils was low, and pH did not significantly influence sorption in the range of 4,8 to 7.1. Less 5-hydroxyimazethapyr was sorbed than imazethapyr on the same soil. Once sorbed, both compounds were only partially desorbable from all soils. Significant hysteresis and formation of nonextractable residues indicate that the small amount of chemical sorbed is bound to selective surfaces with strong bonds. Webster clay loam had greater irreversibility than Waukegen silt loam and Estherville sandy loam soil. The hysteresis observed in desorption may be responsible for the difference between mobility estimations made from laboratory sorption studies and the limited mobility observed in field experiments.

Formation and degradation of soil-bound [ 14C] fenitrothion residues in two agricultural soils

The formation of non-extractable residues of [ 14C]fenitrothion and their degradation in a black earth and a red yellow podzolic soil was studied. After a 65-day incubation, non-extractable radioactivity represented 73.7 and 59.35% of the applied radioactivity in the black earth and podzolic soil respectively, while evolved 14CO 2 accounted for only 9.4 and 12.7%. The effects of various amendments and treatments on the degradation of the non-extractable residues to 14CO 2 was studied. All of the amendments produced a priming effect and significantly increased the formation of 14CO 2 in both soils. The addition of unlabelled fenitrothion and 3-methyl-4-nitrophenol to the black earth and 3-methyl-4-nitrophenol to the podzolic soil produced the greatest increases in 14CO 2 evolution. The evidence presented suggests that a part of the unextractable residue is either fenitrothion or 3-methyl-4-nitrophenol.