|Chemical Abstract Number (CAS #)||
||EPA Method 638|
Link to the National Library of Medicine's Hazardous Substances
Database for more details
on this compound.
|Use|| Selective pre-emergence herbicide
Control of many annual grasses and broad-leaved weeds in cotton, fruit trees, nut trees, vines,
ornamentals, soya beans, groundnuts, oilseed rape, sunflowers, lucerne, peas, sweet potatoes,
mint, and non-crop areas.
At recommended rates, oryzalin is effective for controlling many annual grass and broadleaf
weeds such as: barnyardgrass (Echinochloa crusgalli), annual bluegrass (Poa annua), brachiaria
(Brachiaria sp.), browntop panicum (Panicum fasciculatum), crabgrasses (Digitaria sp.),
crowfootgrass (Dactyloctenium aegyptium), Southwestern cupgrass (Eriochloa gracilis), fall
panicum (Panicum dichotomiflorum), foxtails (Setaria sp.), goosegrass (Eleusine indica), seedling
johnsongrass (Sorghum halepense), wild oat (Avena fatua), Texas panicum (Panicum texanum),
carpetweed (Mollugo verticillata), common purslane (Portulaca oleracea), Florida purslane
(Richardia scabra), lambsquarters (Chenopodium album), pigweeds (Amaranthus sp.), chickweed
(Stellaria media), and prostrate spurge (Euphorbia supina).
Surface-applied herbicide for established bermudagrass turf, and established ornamentals. C-327]
|Apparent Color|| Yellow-orange crystals
|Odor|| No appreciable odor
|Melting Point|| 137-138 deg C
|Molecular Weight|| 346.36
|Sensitivity Data|| Slightly to moderately irritating to skin, eyes, and mucous membranes.
|Environmental Impact|| Oryzalin's use as a pre-emergence herbicide releases the compound directly to the
environment through applications in sprays and other routes of application. If released to the
atmosphere, oryzalin will degrade rapidly in the vapor-phase by reaction with photochemically
produced hydroxyl radicals (half-life of about 3.7 hr). Particulate-phase oryzalin and aerosols
released to air during spray applications of oryzalin herbicides will be physcially removed from air
by dry and wet deposition. If released to soil or water, oryzalin may degrade through microbial
degradation and photodecomposition. The results of one biological screening study (which
demonstrates the role of microorganisms) have shown that oryzalin degrades much slower in
sterilized soil as compared to nonsterile soil. Sunlight exposure studies have shown that oryzalin
photodecomposes after application to soil surfaces and exposure to sunlight. Delaying soil
incorporation increases oryzalin's degradation in soil. Oryzalin leaches to a limited extent under
natural rainfall conditions. The soil persistence half-life can range from 15 days to several months.
Occupational exposure to oryzalin occurs through dermal contact and inhalation of sprays,
especially to workers applying the compound as a herbicide.
|Environmental Fate|| TERRESTRIAL FATE: Microbial degradation and photodecomposition contribute to
the degradation of oryzalin in soil . The results of one biological screening study, which
demonstrates the role of microorganisms, have shown that oryzalin degrades much slower in
sterilized soil as compared to nonsterile soil . Sunlight exposure studies have shown that
oryzalin photodecomposes when oryzalin (applied to soil surfaces) is exposed to sunlight(3-4). In
one photodegradation study , oryzalin was applied to air dried clay loam and exposed to
unfiltered solar radiation for 7 days in July ; comparison with 7 day dark controls indicated that
26.2% of initially applied oryzalin had photodecomposed . Koc values of 75 to 150 indicate a
medium to high mobility in soil(5,SRC); however, results of field, greenhouse and laboratory
studies have shown that oryzalin does not leach appreciably in soil, especially when the moisture
content is low(5-6). Limited leaching can occur under natural rainfall conditions .
TERRESTRIAL FATE: In greenhouse studies using Drummer silty clay loam and Cisne silt
loam soils, oryzalin was observed to have a persistence half-life ranging from 1.6 to 4.3
months . In laboratory studies using Weld loam soil, oryzalin had half-lives of 1.4 and 4.35
months at respective temperatures of 30 and 15 deg C under aerobic conditions ; under
anaerobic conditions, the half-life fell to 0.34 months . In 1974 and 1975 Wisconsin field
studies, oryzalin was observed to have an initial half-life of approximately 15 to 40 days .
Presumably due to surface photodegradation, delaying the time between soil application and soil
incorporation will increase oryzalin's degradation in soil ; in one test, a 7 day delay reduced the
oryzalin concn by nearly 20% . The US Dept of Agric's Pesticide Properties Database lists a soil
half-life of 20 days for oryzalin .
AQUATIC FATE: Using (14)C labelled oryzalin and a terrestrial aquatic laboratory model
ecosystem, an oryzalin BCF value of 50 was determined for fish (Gambusia affinis) ; this BCF
value suggests that bioconcentration in aquatic organisms may not be an important fate
process. The relative importance of individual degradation processes has not been
determined for natural water. Since photodegradation and microbial degradation have been
identified as important mechanisms for soil systems(2-4), they may also be important in
water. Adsorption to aquatic sediments is not likely to be important based upon
experimentally-derived Koc values of 75 to 180(5,SRC). Aquatic volatilization is not expected to
be an important fate process.
ATMOSPHERIC FATE: Based upon a reported vapor pressure of <1X10-8 mm Hg at 25 deg
C , oryzalin can exist in both the vapor and particulate-phases in the ambient
atmosphere(2,SRC). It will degrade rapidly in the vapor-phase by reaction with photochemically
produced hydroxyl radicals with an estimated half-life of about 3.7 hr(3,SRC). Particulate-phase
oryzalin and aerosols released to air during applications of oryzalin herbicides will be removed
from air physically by dry and wet deposition.