Parent Herbicides Research Articles

Herbicides and herbicide degradates in shallow groundwater and the Cedar River near a municipal well field, Cedar Rapids, Iowa

Water samples were collected near a Cedar Rapids, Iowa municipal well field from June 1998 to August 1998 and analyzed for selected triazine and acetanilide herbicides and degradates. The purpose of the study was to evaluate the occurrence of herbicides and herbicide degradates in the well field during a period following springtime application of herbicides to upstream cropland. The well field is in an alluvial aquifer adjacent to the Cedar River. Parent herbicide concentrations generally were greatest in June, and decreased in July and August. Atrazine was most frequently detected and occurred at the greatest concentrations; acetochlor, cyanazine and metolachlor also were detected, but at lesser concentrations than atrazine. Triazine degradate concentrations were relatively small (<0.50 μg/l) and generally decreased from June to August. Although the rate of groundwater movement is relatively fast (approx. 1 m per day) in the alluvial aquifer near the Cedar River, deethylatrazine (DEA) to atrazine ratios in groundwater samples collected near the Cedar River indicate that atrazine and DEA probably are gradually transported into the alluvial aquifer from the Cedar River. Deisopropylatrazine (DIA) to DEA ratios in water samples indicate most DIA in the Cedar River and alluvial aquifer is produced by atrazine degradation, although some could be from cyanazine degradation. Acetanilide degradates were detected more frequently and at greater concentrations than their corresponding parent herbicides. Ethanesulfonic-acid (ESA) degradates comprised at least 80% of the total acetanilide-degradate concentrations in samples collected from the Cedar River and alluvial aquifer in June, July and August; oxanilic acid degradates comprised less than 20% of the total concentrations. ESA-degradate concentrations generally were smallest in June and greater in July and August. Acetanilide degradate concentrations in groundwater adjacent to the Cedar River indicate acetanilide degradates are transported into the alluvial aquifer in a manner similar to that indicated for atrazine and DEA.

Sulfonic and Oxanilic Acid Metabolites of Acetanilide Herbicides: Separation of Diastereomers and Enantiomers by Capillary Zone Electrophoresis and Identification by 1H NMR Spectroscopy

Biological degradation of acetanilide herbicides in soil results in the formation of the ethanesulfonic acid (ESA) and oxanilic acid (OXA) derivatives. These molecules exist in two (alachlor), four (acetochlor), and eight (metolachlor) stereoisomeric forms. Due to the hindered s-cis/s-trans isomerization of the amide bond, most of the diastereomers of the ESA and OXA compounds were separable by capillary zone electrophoresis (CZE). Using γ-cyclodextrin as chiral selector in CZE, complete separation of all four isomers of enantiomerically enriched (5S)-metolachlor OXA was achieved. The enantiomers of acetochlor ESA, acetochlor OXA, and racemic metolachlor OXA were partially separated. The proton nuclear magnetic resonance (1H NMR) spectra showed separated signals for all diastereomers in achiral environment and enantiomers with γ-cyclodextrin as chiral selector. The assignment of these signals to the corresponding absolute configurations was used for the identification of observed CZE peaks. Rate constants for the amide s-cis/s-trans isomerization were evaluated. The time scales for this isomerization at room temperature are seconds for the parent herbicides and several hours for the metabolites. Rotation of the phenyl ring with respect to the amide moiety was not observed. CZE allows the determination and quantification of the different isomers of ESA and OXA metabolites and will facilitate the investigation of the probable stereoselective degradation of acetanilide herbicides in the environment.

Identification of ionic chloroacetanilide-herbicide metabolites in surface water and groundwater by HPLC/MS using negative ion spray.

Solid-phase extraction (SPE) was combined with high-performance liquid chromatography/high-flow pneumatically assisted electrospray mass spectrometry (HPLC/ ESP/MS) for the trace analysis of oxanilic and sulfonic acids of acetochlor, alachlor, and metolachlor. The isolation procedure separated the chloroacetanilide metabolites from the parent herbicides during the elution from C18 cartridges using ethyl acetate for parent compounds, followed by methanol for the anionic metabolites. The metabolites were separated chromatographically using reversed-phase HPLC and analyzed by negative-ion MS using electrospray ionization in selected ion mode. Quantitation limits were 0.01 microgram/L for both the oxanilic and sulfonic acids based on a 100-mL water sample. This combination of methods represents an important advance in environmental analysis of chloroacetanilide-herbicide metabolites in surface water and groundwater for two reasons. First, anionic chloroacetanilide metabolites are a major class of degradation products that are readily leached to groundwater in agricultural areas. Second, anionic metabolites, which are not able to be analyzed by conventional methods such as liquid extraction and gas chromatography/mass spectrometry, are effectively analyzed by SPE and high-flow pneumatically assisted electrospray mass spectrometry. This paper reports the first HPLC/MS identification of these metabolites in surface water and groundwater.

Multiresidue Method for the Chromatographic Determination of Triazine Herbicides and Their Metabolites in Raw Agricultural Products

A method is described for the determination of 19 triazine herbicides and 4 metabolites in 6 agricultural products that represent diverse matrixes. In addition, a modification of this method to determine the more water-soluble metabolite, desethyldesisopropylatrazine, is described. In both these procedures, residues are extracted with methanol, and the product coextractives are removed using solvent partition and cation-exchange solid-phase extraction chromatography. A nitrogen phosphorus detector and DB-17 megabore column are used for the temperature-programmed chromatographic determination of samples fortified at 0.02-1.0 ppm levels. Average recoveries ranged from 81.1 to 106.2% for the parent herbicides and from 59.6 to 87.5% for the metabolites on all crops. An average recovery of 101.1% was obtained for desethyldesisopropylatrazine.

Bioremediating herbicide-contaminated soils.

Combinations of landfarming and biostimulation were evaluated for remediating pesticide wastes. Various amounts of soil contaminated with alachlor and trifluralin (> or = 100 mg/kg each) and metolachlor and atrazine (> or = 20 mg/kg each) were applied to field plots, and sewage sludge or corn meal was incorporated into designated plots. Plots were also treated with fresh spray mixtures in amounts similar to those applied as contaminated soil. Soil bioactivity and dissipation of parent herbicides were monitored after the treatments. During 100 d, soil dehydrogenase activities were highest in organic-material-amended plots. During the same period, the levels of alachlor had declined by 85-95% in amended, contaminated soil-treated plots and by 75-85% in corresponding unamended plots. In freshly sprayed plots, 95-100% of the initial doses of alachlor had dissipated in amended plots, and 85-95% was lost in corresponding unamended plots. The levels of trifluralin had declined by 70-80% in corn-meal-amended plots and by 60-75% in unamended plots. There were no significant differences between dissipation of trifluralin applied as contaminated soil or fresh sprays.

Gas chromatographic analysis of phenylurea herbicides following catalytic hydrolysis on silica gel

A method is described for the rapid catalytic hydrolysis of phenylurea herbicides on silica gel at elevated temperatures. After derivatisation of the anilines produced with heptafluorobutyric acid anhydride final analysis is done on a gas chromatograph equipped with an electroncapture detector. Detection limits are in the 1–5 picogram range. The method has successfully been applied to residue analysis of water samples at the 1 ppb level. The determination of free anilines present in water samples and the potential of various techniques to be used to discriminate between free anilines and parent herbicides are also discussed.

INTERACTION OF PESTICIDE-DERIVED CHLOROANILINE RESIDUES WITH SOIL ORGANIC MATTER1

Herbicide-derived chloroaniline residues are immobilized by physical absorption to both the organic and the inorganic fraction of the soil and, in addition, by chemical binding to the soil organic matter. In contrast to the polymerization reactions, the binding of the chloroanilines is strictly a physicochemical process; microbial activity is involved only in the liberation of the chloroanilines from the parent herbicides. The chemical attachment of chloroanilines to humic substances occurs by at least two mechanisms, in a hydrolyzable (probably anil and anilinoquinone) and in a nonhydrolyzable (probably heterocyclic rings and ether bonds) manner. In the test soil (Nixon sandy loam) these two types of bonds immobilized roughly equal amounts of chloroanilines. Free radicals have little or no role in these reactions. The binding of chloroanilines to the soil organic matter greatly increases the persistence of these herbicide-derived residues in the environment.