Herbicides, dinitroaniline

Considerable research has been conducted to investigate the soil sorption and mobiUty of dinitroaniline herbicides. In general, these herbicides are strongly sorbed by soil (354), and sorption has been correlated to both soil organic matter and clay content (355). Dinitroaniline herbicides are not readily leached in most soils (356), although leaching of triduralin is enhanced by addition of surfactants (357). 

Health advisories have been issued for the phenol dinoseb and trifiuralin health advisories have not been issued for the remaining dinitroaniline herbicides, eg, profluralin [26399-36-0]. 

The detection limits for 2,6-dinitroaniline herbicides are between 20 and 200 ng substance per chromatogram zone (Table 1). Similar results are also obtained with methyl and ethyl parathion (pink-colored zones). 

Table 1 Absorption maxima and detection limits for some 2,6-dinitroaniline herbicides on silica gel layers after treatment with the reagent sequence and after additional exposure to ammonia vapor.

Fig I Chromatogram of 2,6-dinitroaniline herbicides after treatment with the reagent sequence (A) and after additional treatment with ammonia vapor (B) 1 = oryzalin, 2 = nitralin, 3 = dinitramin, 4 = pendimethalin, 5 = butralin, 6 = fluchloralin, 7 = isopropalin, 8 = trifluralin, M = mixture. 

DimethyItin dichloride lb 319 Dimetinden lb 354 Dinitramine lb 110-112 Dinitroaniline derivatives lb 111 Dinitroaniline herbicides lb 110,112... 

Dinitroaniline Herbicides. Another major contamination problem was that of treflan, which was contaminated with over a hundred ppm of NDPA ( ). Mechanistic sleuthing led to the postulate that the nitrosamlne was produced during Treflan... 

The N -Ditroso derivatives of the dinitroaniline herbicides bu-tralinSa and pendimethalin were quite stable in aerobic soils, persisting over several months. An aerobic actinotnycete of the Streptonyces genus was isolated from soil that metabolized N -ni-trosopendimethalin in laboratory culture.e... 

The discovery of nitrosamines in pesticide formulations, Ross et al (1976), led to remarkable public and regulatory reaction. The widely used herbicide, trifluralin, because of the inadvertent nitrosamine impurity, received the most attention. All dinitroaniline herbicides have similarities therefore, trifluralin, with appropriate exceptions, will serve as a suitable exan le. 

Dinitroaniline herbicides have an unusual property of serving both as an amine contributor and nitrosating agent. The phenomenon (Grove, 1979) was observed when solid or liquid dinitroanilines are subjected to heat. For exan le, when trifluralin is heated to 70 0, N-nitrosodipropylamine (NDPA) is formed. Figure 1 shows the accumulation of NDPA with time. Increased nitrosamine formation is a function of temperature and time. 

The reaction occurs with technical material only, and, once formulated, the nitrosamine content is not altered as a function of time at ambient formulation temperatures. This intra-molecular rearrangement requires careful attenticn to conditions in the formulation of dinitroaniline herbicides. 

Biggs and Williams (1976) have studied denitrosation over a wide range of acidities. They demonstrated that rate constants for denitrosation and rearrangements could be measured by limiting experimental conditions for N-alkyl-N-nitrosoanilines which is applicable to N-nitroso-dinitroaniline herbicides such as pendimethalin and butralin. 

Dinitroaniline herbicides, in general, are very lipophilic, hence they are insoluble in water. They are stable under acidic or alkaline conditions. Dinitroaniline herbicides are potentially dissipated in the environment via photodegration and volatilization. 

Owing to its low water solubility and high octanol/water partition coefficients, dinitroaniline herbicides adsorb and bind to soil macromolecules and show minimal leaching potential. Dinitroanilines herbicides show good soil residue activities with soil half-lives ranging from 30 days for benfluralin and oryzalin to 6-7 months for trifluralin. Al-Dealkylation (aerobic conditions) and reduction of the nitro group to an amino moiety (anaerobic conditions) have been reported as major soil degradation pathways. 

Dinitroaniline herbicides show minimal plant systematic translocation properties with the majority of the absorbed residues in the root tissues. Metabolites identified include traces of Al-dealkylation, alkyl and aryl hydroxylation and nitro reduction products. Low levels of dinitroaniline herbicide residues have been reported in raw agricultural commodities according to Good Agricultural Practice. 

Residual pendimethalin in various crops was determined as follows." A 10-20-g amount of fruits or vegetables was extracted by blending twice with 200 mL of methanol. Grasses and mint were extracted with 200 mL of methanol-water (1 1, v/v). Nuts were extracted with 200 mL of n-hexane-2-propanol (3 1, v/v). For the residue analysis of the dinitroaniline herbicides butralin, dinitramine, ethalfluralin, pendimethalin, and trifluralin, a tomato sample (5 g) was extracted twice with 20 mL of methanol in a Sorvall homogenizer and filtered through filter paper. Benfluralin and trifluralin residues in the sample (10 g) were extracted with 100 mL of acetonitrile-water (99 1, v/v) in 250-mL screw-cap jars with Teflon liners rotated for 1 h on an end-over-end shaker (40 rpm). ... 

To determine the residue levels of dinitroaniline herbicides, GC/NPD or GC/ECD is used in general. An aliquot of GC-ready sample solution is injected into the gas chromatograph under the conditions outlined below. Further confirmatory analysis is carried out using gas chromatography/mass spectrometry (GC/MS) in the selected-ion monitoring (SIM) mode. 

The amount of dinitroaniline herbicide residue (7 ,mgkg ) in the sample is calculated with the following equation ... 

Wi = amount of dinitroaniline herbicide for y read from the calibration curve (ng)... 

Dinitroaniline herbicides are generally stable in soil. Residue methods were developed for both the parent molecule and selective soil degradates. 

Residual dinitroaniline herbicides are generally extracted from 10-25 g of air-dried soil samples using organic solvents such as ethyl acetate, acetonitrile, methylene chloride and acetone by sonication, mechanical shaking or Soxhlet extraction. If necessary, the extract is then cleaned by a Florisil column or SPE. The extract is allowed to evaporate completely to dryness and the residue is dissolved in an appropriate volume of the solvent for GC or HPLC analysis. 

The fate of the dinitroaniline herbicides in soil is extremely complex and many metabolites have been identified. Golab and Althaus reported 28 metabolites identified in a degradation study of trifluralin in soil. Major degradation products of dinitroaniline herbicides were formed by nitro reduction, A-dealkylation (mono-dealkylated and completely dealkylated) and the ring formation of benzimidazole. 

Dinitroaniline herbicides have low soil mobility potential. Herbicide residues in the treated field are usually incorporated into the upper layers of the soil mainly as unextractable bound residue therefore, the movement of dinitroaniline herbicides from soil to the water compartment is minimal. Run-off is the principal route, which could lead to the contamination of surface waters. Residue methods were developed to measure the parent concentration in water samples. 

Cabras et al reported an HPLC residue method for dinitroaniline herbicides. A water sample was analyzed after purification and concentration on a Bond-Elut Ci8 cartridge (500-mg/2.8-mL). The cartridge was treated with 10 mL of methanol... 

Di-re-dodecylamine, melting point, 2 52 It Di-re-hexadecylamine, melting point, 2 52 It Di-re-hexadecyl percarbonate, 6 303 Dinitraniline Orange, 1.9 434 Dinitroaniline herbicides, 43 318-319 Dinitroanilines, 13 303 1,5 -D initro anthr aquinone, 9 315-316 a,a -Dinitroanthraquinones, 9 315-316 Dinitrochlorobenzenes, 17 262 Dinitrogen, 17 311. See also N2 oxidation complexes, 17 273-274 fixation of, 17 290... 

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