| Chemical Abstract Number (CAS #) |
21609905
|
|---|
| Synonyms | Leptophos |
|---|
Phosvel | Phosphorothioic acid, phenyl, O-(4-bromo-2,5-dichlorophenyl) O-methyl ester |
| Analytical Method |
EPA Method 8141A |
|---|
| Molecular Formula | C13H10BrCl2O2PS |
|---|
| Use | NOT PERMITTED FOR USE IN THE USA; EXPERIMENTAL REGISTRATION &
TEMPORARY TOLERANCE IN THE US WAS CANCELLED IN LATE 1975 DUE TO
DELAYED NEUROTOXIC EFFECTS (1976)
|
|---|
| Consumption Patterns | NOT PERMITTED FOR USE IN THE USA; EXPERIMENTAL REGISTRATION &
TEMPORARY TOLERANCE IN THE US WAS CANCELLED IN LATE 1975 DUE TO
DELAYED NEUROTOXIC EFFECTS (1976)
|
|---|
| Apparent Color | WHITE CRYSTALLINE SOLID; COLORLESS AMORPHOUS SOLID; Tan waxy
solid
|
|---|
| Melting Point | 70.2-70.6 DEG C
|
|---|
| Molecular Weight | 412.07
|
|---|
| Density | 1.53 @ 25 DEG C
|
|---|
| Environmental Impact | When used as an insecticide, leptophos is released directly to the environment through
applications in sprays, dusts and other routes of application. However, in the US its' registration
has been withdrawn. If released to the atmosphere, leptophos will degrade rapidly in the
vapor-phase by reaction with photochemically produced hydroxyl radicals (half-life of about 5 hr).
Particulate phase leptophos will be removed from air physically by wet and dry deposition. If
released to water, leptophos will partition from the water column to sediment and suspended
material. The results of one screening study indicate that chemical degradation is more important
in natural water than biodegradation. Aqueous hydrolysis rates increase with increasing pH; at 25
deg C, aqueous hydrolysis half-lives of 35, 5.5 and 2.3 weeks have been measured at respective
pHs of 6, 7 and 8. A measured BCF value of 6058 in topmouth gudgeon fish indicates that
aquatic bioconcentration may be an important fate process. If released to soil, leptophos will
adsorb strongly and will not leach. Hydrolysis may be an important transformation process in
moist, alkaline soils. Insufficient data are available to assess the relative importance of
biodegradation in soil. Based upon the results a laboratory study and a review of other leptophos
persistence studies, it has been concluded that leptophos is one of the most persistent
organophosphorus compounds in the environment. Occupational exposure to leptophos may
occur through dermal contact and inhalation of dust and sprays, especially to workers applying
the compound as an insecticide.
|
|---|
| Environmental Fate | LEPTOPHOS HAD SHORT-LIVED EFFECTS ON PROCESSES & NUMBERS OF
SOIL MICROORGANISMS.
TERRESTRIAL FATE: Laboratory studies have shown that leptophos is adsorbed strongly by
soil and will not leach ; log Koc values of 3.97-5.07 have been experimentally determined(1-2).
Aqueous hydrolysis studies have shown that leptophos degrades more rapidly with increases in
pH ; aqueous hydrolysis half-lives of 35, 5.5 and 2.3 weeks have been measured at respective
pHs of 6, 7 and 8 at 25 deg C ; therefore, hydrolysis may be an important transformation
process in moist, alkaline soils. Insufficient data are available to assess the relative
importance of biodegradation in soil. A foliar half-life of 4.0 days has been reported for endive
plants . In field studies conducted in Israel, foliar residue levels of leptophos (as applied to
tomato and grape plants) had dropped by 40-75%, from initial levels, after three weeks ; the
phenol derivative was a major degradation product . Based upon the results a laboratory study
and a review of other leptophos persistence studies, it was concluded that leptophos is one of the
most persistent organophosphorus compounds in the environment(6).
AQUATIC FATE: The results of various screening studies indicate that chemical degradation of
leptophos may be more important in water than biodegradation(1-3). Hydrolysis studies have
shown that degradation rates increase with increasing pH ; at 25 deg C, aqueous hydrolysis
half-lives of 35, 5.5 and 2.3 weeks have been measured at respective pHs of 6, 7 and 8 . Direct
photolysis tests of methanol solutions of leptophos exposed to sunlight (half-life of about 50
days) have shown that direct photolysis may contribute to transformation in water. In
water, leptophos will partition from the water column to sediment and suspended material and
can be expected to remain largely in the sediment. Laboratory studies with various Egyptian
natural waters have suggested the degradation rate may decrease in the presence of solids and
sediment . A measured BCF of 6058 in topmouth gudgeon fish(6) indicates that
bioconcentration in aquatic organisms may be an important environmental process.
ATMOSPHERIC FATE: Based upon a measured vapor pressure of 2.3X10-8 mm Hg at 20 deg
C , leptophos can exist in both the vapor and particulate phases in the ambient atmosphere,
although the particulate phase may 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 leptophos and aerosols released to air during spray applications of
leptophos insecticide can be removed from air physically by dry and wet deposition.
|
|---|
| Drinking Water Impact | SURFACE WATER: Leptophos has been qualitatively detected in open waters of Lake
St Clair of the Great Lakes ecosystem .
|
|---|
