Trifluralin degradation

Figure 5. Postulated pathway of trifluralin degradation in an anaerobic soil from...

Figure 13. Trifluralin degradation with time. , amount in soil and water o, amount in water.

Wheeler WB, Stratton GD, Twilley RR, Ou LT, Carlson DA, Davidson JM (1979) Trifluralin degradation and binding in soil. J Agr Food Chem 27, 702-706. 

Klupinski TP, Y-P Chin (2003) Abiotic degradation of trifluralin by Fe(II) kinetics and transformation pathways. Environ Sci Technol 37 1311-1318. 

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. 

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. 

Degradation of Trifluralin in Submerged Soil. The redox potential of the soil became negative after only 3 days and reached a low of -450 mv after 32 days (Table II). There was little difference in the measurements between the 1 and 3 cm soil depths. We therefore assume that all soil samples (except possibly at Day 2) were anaerobic. 

Table III. Degradation of [14C]trifluralin in a flooded soil (expressed as percent of extracted radioactivity). ...

Degradation of Trifluralin in Water. The amount of 14c recovered from water with time is shown in Table IV. About half of the total 14c (direct count analysis) in water was recovered by extracting twice with ethyl acetate hexane (7 3), indicating that polar metabolites rapidly formed. Also, the concentration of 14c in water increased most rapidly during the first 22 days, after which the rate decreased. Analysis of the water extracts by TLC is shown in Table V. Trifluralin disappeared very rapidly, decreasing to nondetectable levels between 9 and 22 days. Even as early as 2 days only 46% of the recovered 14C was trifluralin. 

Table VI. Degradation of [ C]trifluralin in bluegill fish (expressed as percent...

Although previous applications of this technique in our laboratory had been concerned with aquatic animal metabolism of pesticides such as DDT, parathion, carbaryl, and trifluralin (14, 15), we also became interested in comparing metabolic routesljy means of a "metabolic probe". Such a compound ideally should be stable to nonbiological degradation, of low toxicity to maximize the dose, and subject to as many major routes of metabolism as possible without undue analytical complexity. 

Zayed et al. (1983) studied the degradation of trifluralin by the microbes Aspergillus carneus, Fusarium oxysporum, and Thchoderma viride. Following an inoculation and incubation period of 10 d in the dark at 25 °C, the following metabolites were identified a,a,a-trifluoro-2,6-dinitro-A -propyl-jO-toluidine, a,a,a-trifluoro-2,6-dinitro-p-toluidine, 2-amino-6-nitro-a,a,a-trifluoro-p-toluidine, and 2,6-dinitro-4-trifluoromethylphenol. The reported half-life in soil is 132 d (Jury et al., 1987). 

Parr, J.F. and Smith, S. Degradation of trifluralin under laboratory conditions and soil anaerobiosis. Soil ScL, 115(l) 55-63, 1973. 

Studies were initiated at Iowa State University in 1977 to determine if pesticides would be contained and degraded when deposited in water/soil systems. Although the addition of known amounts of the selected pesticides was controlled, the physical environment was not temperature, humidity, wind speed, etc. were normal for the climate of Central Iowa. Four herbicides and two insecticides were chosen on the basis of three factors. Firstly, they represented six different families of pesticides. The four herbicides, alachlor, atrazine, trifluralin, and 2,4-D ester, represent the acetanilides, triazines, dinitroanilines, and phenoxy acid herbicides, respectively. The two insecticides, carbaryl and para-thion, represent the carbamate and organophosphorus insecticides, respectively. Secondly, the pesticides were chosen on the basis of current and projected use in Iowa Q) and the Midwest. Thirdly, the chosen pesticides were ones for which analytical methodology was available. 

Under field conditions trifluralin has been predicted to degrade to nonphytotoxic levels within a growing season when soil conditions are moist and warm (12). After three years, less than 1.5% of C-trifluralin was detected in test plots maintained under natural conditions (18). 

The analytical data for the added pesticides and two of the hydrolysis products, 2,4-D acid and 1-naphthol, were used to formulate the degradation graphs shown in Figures 3-14. Atrazine underwent no degradation either alone or in mixtures and alachlor and trifluralin underwent no degradation in mixtures, so the graphs for these pesticides under these conditions are not shown. 

Figure 16. Degradation of alachlor (ALA), trifluralin (TRI), parathion (PAR), 2,4-D ester (2,4-D), carbaryl (CAR), 2,4-D acid (acid) and 1-naphthol (NAP) at high concentration and ambient conditions. , amount in soil and water o, amount in water.

Mixtures had an inhibitory effect with the most dramatic being the degradation of 2,4-D ester, trifluralin and parathion. 

Several bench-scale degradation experiments were completed. The data from these studies of 2,4-D butoxyethanol ester, alachlor, trifluralin and atrazine under a variety of aerobic and anaerobic conditions were used for the following preliminary observations ... 

Those degradation products which have been identified in our investigations are 1-naphthol from carbaryl, 2,4-D acid and 2,4-dichlorophenol from 2,4-D ester, 2-chloro-2, 6 -diethylacetanilide from alachlor, o,o,oe-trifluro-2-nitro-6-amino-N,N-dipropyl-p-tolu-idine and o,o,o-trifluro-2,6-diamino-N,N-dipropyl-p-toluidine from trifluralin, and a variety of phenols and acids from the degradation of the aromatic solvents used in the formulation of the liquid pesticides as emulsifiable concentrates (41,42). 

Oxidation is, of course, the dominant reaction. For example, vaporized trifluralin ( a, a, < -trifluoro-2,6-dinitro-ll,ll-dipropyl-p-toluidine) was demethylated (Figure 7) (26), and its atmospheric half-life was found to be 8 minutes (27). However, the reaction occurred to a small extent even at night, and oxidation by ozone was implicated. In fact, there is evidence (28) that parathion photooxidation actually required the presence of ozone or other highly reactive oxidants. Degradation not requiring external reagents also may proceed rapidly trifluralin was cyclized to a substituted benzimidazole (11, 26), and dieldrin again formed photodieldrin (29). 

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