| Chemical Abstract Number (CAS #) |
2921882
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| Synonyms | Chlorpyrifos |
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Dursban | Phosphorodithioic acid, O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) ester |
| Analytical Method |
EPA Method 8141A |
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| Molecular Formula | C9H11Cl3NO3PS |
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| Use | ACARICIDE
It has a broad range of insecticidal activity and is effective by contact, ingestion and vapor action,
but is not systemic. Used for control of flies, household pests, mosquitoes (larvae and adults) and
of various crop pests in soil and on foliage; also used for control of ectoparasites on cattle and
sheep.
EFFECTIVE AGAINST CATTLE & SHEEP TICKS & PSOROPTIC MANGE IN SHEEP BY
DIPPING (0.1%) & TURKEY CHIGGERS BY SOIL TREATMENT (4 LB/ACRE OR 448
MG/SQ M ).
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| Consumption Patterns | INSECTICIDE USED ON CORN, 39%; ALFALFA, 6%; COTTON, 3%; SORGHUM,
1%; OTHER FIELD CROPS-EG, CITRUS & DECIDUOUS FRUITS/NUTS, 21%;
NON-AGRICULTURAL USES, 31% (1982)
(1978) 4.00X10 9 G (CONSUMPTION)
(1982) 3.27X10 9 G (CONSUMPTION)
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| Apparent Color | WHITE GRANULAR CRYSTALS ; Colorless crystals
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| Odor | MILD MERCAPTAN ODOR
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| Melting Point | 41-42 DEG C
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| Molecular Weight | 350.59
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| Density | 1.398 at 43.5 deg C (liquid)
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| Sensitivity Data | May be irritating to skin and eyes.
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| Environmental Impact | Chlorpyrifos is released into the environment primarily from its application as an
insecticide. If released to soil, chloropyrifos can degrade by a combination of chemical hydrolysis
and microbial degradation. The chemical hydrolysis is clay catalyzed and yields a primary
degradation product of 3,5,6-trichloro-2-pyridinol. Volatilization from soil surfaces, is expected
to contribute to its loss from soil. Chlorpyrifos is tightly absorbed by soil and not expected to
leach significantly. Although a general soil persistence of 60-120 days has been reported, the
persistence can vary greatly depending on soil type, climate, and conditions and has been
experimentally measured to range from as little as 2 weeks to over 1 year. If released to water,
chlorpyrifos partitions significantly from the water column to sediments. The measured hydrolysis
half-life at 25 deg C at (or near) neutral conditions is 35-78 days. The hydrolysis rate is relatively
independent of pH from pH 1 to pH 7, increases significantly under alkaline conditions, decreases
2.5-3 fold with 10 deg C temperature decrease, is markedly enhanced by the presence of Cu( 2)
ions in sufficient concentration, and is not affected by adsorption to sediments in acidic or neutral
water. The hydrolysis products include 3,5,6-trichloro-2-pyridinol and various trichloropyridyl
phosphorothioates. The photolysis half-life at the water surface in the US during the mid summer
is about 3 to 4 weeks, however, photolysis is not expected to be a very significant removal
mechanism in relatively deep waters, in the winter-time, or in any natural waters containing
sufficient light attenuating material. Microbial degradation may contribute to removal in some
natural waters. The volatilization half-life from a river one meter deep flowing 1m/sec with a wind
velocity of 3 m/sec is estimated to be 5.7 days; however, the significance of volatilization may be
greatly decreased by aquatic sediment adsorption. Experimental and estimated log BCF values
ranging from 2.50 to 3.54 indicate potential significant bioconcentration. The desorption from
sediments can contribute to long term residual concentration in the water column (low ppb). If
released to air, chlorpyrifos will react in the vapor-phase with photochemically produced hydroxyl
radical half-life of 13.74 hours, but it is not expected to react with ozone. Photolysis in air may
contribute to its transformation. Major general population exposure to chlorpyrifos will occur
through consumption of contaminated food and inhalation of contaminated air. Occupational
exposure by dermal and inhalation routes may be significant.
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| Environmental Fate | MODERATELY RESIDUAL ON PLANT SURFACES, QUITE RESIDUAL ON
INERT SURFACES SUCH AS WOOD/. VOLATILE ENOUGH TO FORM RESIDUES ON
NEARBY SURFACES
HALF-LIFE OF CHLORPYRIFOS IN SEDIMENT-WATER STUDIES RANGED FROM 1.2
TO 34 DAYS & WERE IN THE FOLLOWING ORDER OF INCREASING PERSISTENCE:
METHYL PARATHION, PERMETHRIN, BENTHIOCARB, AC 222,705, CHLORPYRIFOS,
& FENVALERATE. AFTER TERMINATION OF THE EXPOSURE, EACH INSECTICIDE
WAS DEPURATED BY OYSTERS TO NONDETECTABLE CONCENTRATIONS WITHIN
1 WK.
TERRESTRIAL FATE: When released to soil, chlorpyrifos can degrade by a combination of
chemical hydrolysis and microbial degradation. The chemical hydrolysis, which is catalyzed by
clay and yields a primary degradation product of 3,5,6-trichloro-2-pyridinol, occurs in both dry
and moist soils. Microbial degradation may be significant in various soils as indicated by
significantly faster degradation rates in non-sterile versus sterile soil. Laboratory experiments have
indicated that volatilization from soil surfaces under field conditions is expected to contribute to
its loss from soil. Photodegradation on soil surfaces may occur, but is not expected to be
competitive with other fate processes. Measured Koc values ranging from 4381 to 13600 and
various field studies indicate that chlorpyrifos is tightly absorbed to soil and not expected to leach
significantly. A general soil persistence of 60-120 days has been reported . An initial half-life of
10 days was measured in a paddy soil with residual chlorpyrifos remaining after 60 days . The
initial half-lives in field plots of sandy and muck soils were 2 and 8 weeks, respectively, with 4%
and 9% remaining after one year, respectively . A persistence of 2-4 weeks was measured in a
sandy loam soil . Persistence of 180 days was measured in a field soil receiving normal
application rates . A field study with silt loam soil showed that chlorpyrifos disappeared 2-3
times faster from generally dry surfaces than when incorporated or applied beneath the soil
surface(6,SRC). Dislodgeable residue of chlorpyrifos dissipates rapidly from turfgrass from 0.15
ug/sq m 2 hrs after application to approximately 0.015 ug/sq m at 96 hrs after application(7).
AQUATIC FATE: When released to water, chlorpyrifos partitions significantly from the water
column to sediments. It hydrolyzes in water at a rate which is relatively independent of pH from
pH 1 to pH 7 and has a measured hydrolysis half-life of 35 to 78 days at 25 deg C at (or near)
neutral conditions. The hydrolysis rate increases significantly under alkaline conditions, decreases
two-and-half to three-fold with a 10 deg C decrease in temperature, is markedly enhanced by the
presence of Cu( 2) ions in sufficient concentration, and is not affected by adsorption to sediments
in acidic or neutral water. The hydrolysis products include 3,5,6-trichloro-2-pyridinol and various
trichloropyridyl phosphorothioates. The photolysis half-life in the US during the mid summer is
about 3 to 4 weeks at surface-water conditions, but decreases significantly with increased water
depth, the presence of material in natural water which lessened light intensity, and decreased
hours of sunlight exposure. Microbial degradation may contribute to chlorpyrifos removal from
natural water as indicated by faster degradation rates in various non-sterile versus sterilized
waters. The volatilization half-life from a river one meter deep flowing 1 m/sec with a wind
velocity of 3 m/sec is estimated to be 5.76 days; however, the potential significance of
volatilization may be lessened greatly by adsorption to sediments. Experimental log BCF values of
2.88 and 3.54 indicates that chlorpyrifos will bioconcentrate significantly in various aquatic
organisms. The desorption of chlorpyrifos from sediment can contribute to long term residual
concentration in the water column(1,SRC).
ATMOSPHERIC FATE: If released to the atmosphere in vapor-phase, chlorpyrifos will react
with photochemically produced hydroxyl radicals at an estimated half-life of 13.7 hours , but is
not expected to react with ozone. Photolysis may also contribute to its transformation.
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| Drinking Water Impact | SURFACE WATER: Chlorpyrifos was detected in 3 of 949 water samples taken from 11
agricultural watersheds in southern Ontario during 1975-1977 at concentrations ranging from less
than 0.01 ppb to 1.6 ppb(1,2). Chlorpyrifos was qualitatively identified in waters from Lake Erie
and Lake St. Clair .
Waters from 21 wells and 2 springs located in a typically farmed, mostly agricultural PA
watershed (the Mahantango Creek Watershed) were analyzed for 11 pesticides, including
chlorpyrifos. Pesticides were selected according to a farm use survey, and samplings were made
during Dec 1985, Aug 1986, and Mar/Apr 1987. Chlorpyrifos was applied in 1985 but not in
1986. No chlorpyrifos was found in any sampling (< 4 ng/l).
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