Fate of benefin in soils, plants, artificial rumen fluid, and the ruminant animal

Abstract

Benefin, a selective, preemergence, soil-incorporated herbicide, decomposed rapidly in soil under defined anaerobic conditions, with approximately 5% detectable after 16 days; whereas, under defined aerobic conditions, 50% of the originally incorporated benefin was detectable after 120 days and only 12.1 % after 352 days. Identifiable degradation products were the dealkylated, reduced, and oxidized derivatives of benefin, and an unidentified polar mixture. Soil-incorporated 14C-labeled benefin was not readily absorbed into growing peanut plants and alfalfa. Most of the radioactivity absorbed by plants was not extractable. In the extractable portion, the identifiable degradation products were similar to those found in soil. Artificial rumen fluid destroyed benefin rapidly; only 0.1 % of the original benefin remained after 12 hr incubation. Identifiable degradation products were reduced forms of benefin and nonidentifiable polar substances. Radioactivity from 14C-labeled benefin orally administered to the lactating ruminant animal was excreted in the urine (10.8%) and feces (89.1%) within 5 days after ingestion. No radioactivity residue was found in milk.Benefin (a,a,a-trifluoro-2,6-dinitro-Abutyl -Nethyl -ptoluidine) is a chemical analog of trifluralin (a,a,atrifluoro-2,6-dinitro-./V,/V-dipropyl-p-toluidine) possessing similar herbicidal properties, and is marketed under the trade name Balan. It is a selective, soil-incorporated, preemergence herbicide for many agronomic and horticultural crops, some of which may be consumed as forage. The herbicidal spectrum, which complements trifluralin, includes annual grasses and broadleaf weeds. The fate of trifluralin in soils (Probst et al., 1967), plants , and artificial rumen fluid and ruminant animals (Golab et al., 1969) has been extensively investigated. A similar investigation, based on the experimental methodology employed with trifluralin, was undertaken to determine benefin's persistence, pathway of degradation, and the nature of degradation products. MATERIALS AND METHODSGeneral Methods. Labeled Benefin. Benefin, used in this investigation, was a mixture of 14C uniformly ringlabeled and trifluoromethyl-labeled species. Degradation studies conducted in our laboratories, subsequent to this investigation, revealed that the purchased 14C-labeled p-chlorobenzoic acid, used in the synthesis of uniformly ring-labeled trifluralin (Marshall et al., 1966) and benefin, is a mixture of 15% uniformly ring-labeled and 85% carboxyl-labeled pchlorobenzoic acids rather than a single molecular species. Its specific activity was 14.04 pCi per mg (3.12 107 dpm per mg), and radiochemical purity, as determined by thin-layer chromatography using silica gel GF developed with carbon tetrachloride, was greater than 99 %.Labeled benefin used in these experiments, except in the ruminant animal (goat study), was diluted with nonlabeled material. The specific activity of I4C-benefin after dilution was 0.20 ^Ci per mg in the soil, 1.40 pCi per mg in soil with plants, and 0.92 pd per mg in arti...

Morphological and Anatomical Effects of Benefin Vapors on Tobacco (Nicotiana tabacum)

“…Much of the 14 C material was retained by the wax and cutin layers, but a small fraction apparently penetrated into the internal tissues (15). Benefin and trifluralin are not actively metabolized by plants, and unaltered herbicides are the major source of the radioactivity in plants, including tobacco, when treated with 14 C-benefin or -trifluralin (4,5,6,11). The objectives of this study were to determine some of the morphological and anatomical changes that occurred in tobacco as a result of exposure to vapors from benefintreated soil.…”

Degradation of Benefin and DCPA in Thatch and Soil from a Kentucky Bluegrass (Poa pratensis) Turf

“…Several processes including volatilization, photodecomposition, and microbial decomposition are involved in its dissipation. Golab et al (6) postulated that under anaerobic conditions, benefin is rapidly degraded by a sequence of reductive reactions, while under aerobic conditions, benefin is metabolized more slowly by oxidative dealkylation reactions. Both pathways result in the formation of polar products from aromatic amine precursors.…”

Persistence of benfluralin in soil and its uptake by carrots

“…The herbicide benfluralin (N-butyl-N-ethyl-2,6-dinitro-4-trifluoromethy~ani~ine) has been introduced for the control of a wide variety of annual grasses and broadleaved weeds, a serious nuisance in many agronomic and horticultural crops. 1 Residue analyses have indicated that benfluralin, which is relatively persistent in the soil,2 does not become incorporated in the leaves, seeds or fruits of a wide variety of plants. Roots from plants grown in soil containing this herbicide are likely to contain a residue only in the region of contact with the treated soil.…”