|Environmental Impact|| Fluchloralin's use as a pre-plant or pre-emergence herbicide releases the compound
directly to the environment through applications in sprays and other routes of application. If
released to the atmosphere, fluchloralin will degrade rapidly in the vapor-phase by reaction with
photochemically produced hydroxyl radicals (half-life of about 5 hr). If applied to soil surfaces,
fluchloralin can dissipate rapidly through photodecomposition and volatilization; half-lives of
1.5-4.0 days have been observed following surface application; however, immediate soil
incorporation greatly increases soil persistence. Various persistence studies have reported
fluchloralin soil half-lives ranging from several weeks to several months. Within soil systems,
biodegradation is the probable route of disappearance, but it appears to be much slower than
surface photolysis or volatilization. Under field conditions, fluchloralin has not been found to
leach. If released to water, fluchloralin can degrade through photodecomposition and
biodegradation. Volatilization may contribute to its loss from water. Occupational exposure
occurs through dermal contact and inhalation of sprays, especially to workers applying the
compound as a herbicide. Since fluchloralin has been detected infrequently in U.S. foods,
exposure to the general population through consumption of foods containing fluchloralin residues
would appear to be slight.
|Environmental Fate|| C-Fluchloralin was degraded in a loamy sand soil. Degradation products were
identified by TLC and GLC and comparison with standard compounds whose structure was
confirmed by IR and MS. Degradation products included the following compounds:
2,6-dinitro-N-propyl-4-trifluoromethylaniline. Some CO was formed and a part of the (l4)C
was found in humic acids.
TERRESTRIAL FATE: Fluchloralin can dissipate readily from soil surfaces through
volatilization and photodegradation. One study found a half-life of 1.5-4.0 days following surface
application . Screening studies have demonstrated that fluchloralin photolyzes(2-3) and
volatilizes readily from near surface soil(4-5). Within soil, fluchloralin appears to biodegrade; grab
sample tests have shown that fluchloralin degrades faster in nonsterile soil than in sterile soil(6);
however, the rate appears to be much slower than surface photodecomposition or volatilization.
For example, at recommended rates of application, low levels of fluchloralin residues can persist
for more than one season after application(7). Under field conditions, fluchloralin has not been
found to leach(7).
TERRESTRIAL FATE: The results of field and laboratory studies conducted over a 3-yr period
found that delaying soil incorporation of herbicidal applications of fluchloralin caused important
herbicide losses through volatilization and photodecomposition ; avg losses for delayed
incorporation for 1, 3 and 7 days were 11, 29, and 69% respectively . In greenhouse studies
using a silt loam and a clay loam soil, fluchloralin had a half-life of 3.3 to 5.1 months . In
laboratory soil metabolism studies, fluchloralin metabolites were found to include a benzimidazole
derivative, a quinoxaline derivative and various fluchloralin dealkylation derivatives . A field
study in Arkansas found half-lives of 12.2-17.6 weeks ; a laboratory study at 25 deg C found
half-lives of 8.4 weeks (field capacity) and 2.9 weeks (flooded conditions) ; at 4 deg C,
half-lives were 28.7 weeks (field capacity) and 19.5 weeks (flooded conditions) . In 2-yr
Wisconsin field tests, initial half-lives of about 60-75 days were observed ; in greenhouse tests,
persistence was much greater in dry soil (half-life >29-55 days) than in wet soil (63% dissipation
in 29 days) .
AQUATIC FATE: Fluchloralin can degrade in natural water through photodecomposition and
biodegradation. In one aqueous photolysis study , 84% of initial fluchloralin photolyzed after 13
days of natural sunlight exposure ; other aqueous photolysis tests have also found rapid
photodegradation . Biological screening tests have found fluchloralin to be biodegradable ;
however, sufficient data are not available to predict the rate or its relative environmental
importance in water. Volatilization may contribute to fluchloralin/s!dissipation from water;
in the absence of strong adsorption to sediment, volatilization half-lives of 35 hr and 16 days can
be estimated for a model river (1 m deep) and a model pond (2 m deep), respectively(4-5,SRC).
Koc values ranging from 200 to 3600(6-7,SRC) indicate some adsorption to sediment may occur
which will decrease volatilization rates.
ATMOSPHERIC FATE: Based upon a reported vapor pressure of 2.1X10-5 mm Hg at 20 deg
C , fluchloralin can exist in both the vapor and particulate-phases in the ambient atmosphere,
although the vapor-phase will dominate(2,SRC). It will degrade rapidly in the vapor-phase by
reaction with photochemically produced hydroxyl radicals with an estimated half-life of about 5
hr(3,SRC). Particulate-phase fluchloralin and aerosols released to air during applications of
fluchloralin herbicides will be physically removed from air by dry and wet deposition.