| Chemical Abstract Number (CAS #) |
298000
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| Synonyms | Methyl parathion |
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Parathion-methyl | Metaphos | Phosphorothioic acid, O,O-dimethyl O-(4-nitrophenyl) ester | O,O-dimethyl O-p-nitrophenyl phosphorothioate | Nitrox-80 |
| Analytical Method |
EPA Method 8141A |
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| Molecular Formula | C8H10NO5PS |
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| Use | INSECTICIDE USED ON OVER 50 CROPS (PRIMARILY COTTON) & ON
SEVERAL ORNAMENTALS
IT CONTROLS APHIDS, BOLL WEEVILS, & MITES ESP WELL, ALTHOUGH ITS
SPECTRUM FOR CONTROL OF INSECTS IS NEARLY AS BROAD AS PARATHION.
RECOMMENDED AS BROAD SPECTRUM INSECTICIDE FOR RICE, FRUIT, &
VEGETABLES.
EMULSIONS OR DUSTS FOR CONTROLLING PLANT LICE, THRIPS, & BUGS
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| Consumption Patterns | 83% FOR COTTON; 8% FOR SOYBEANS; 2% FOR WHEAT; 5% FOR OTHER
GRAIN CROPS INCLUDING CORN; 2% FOR ORNAMENTALS AND MISC
AGRICULTURAL COMMODITIES INCLUDING TOBACCO, PEANUTS, ALFALFA,
ASSORTED VEGETABLES, AND CITRUS FRUITS (1971)
Applied to alfalfa, 15.6%; Artichokes, 7.5%; Cotton, 7.8%; Lettuce, 7.9%; Onions, 3%; Rice,
32%; Sugarbeets, 7.4%; Tomatoes, 8.1%; Most of remainder applied to vegetable crops (1984);
/California use, calculated from table (1984) 1.04X10 6 g Used in California
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| Apparent Color | WHITE CRYSTALLINE SOLID OR POWDER ; CRYSTALS FROM COLD
METHANOL
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| Melting Point | 37-38 DEG C
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| Molecular Weight | 263.23
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| Density | 1.358 AT 20 DEG C/4 DEG C
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| Odor Threshold Concentration | 0.1328 mg/cu m odor low and high.
1.23X10-2 ppm (detection in water; purity not specified)
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| Sensitivity Data | Since methyl parathion does not irritate or burn the skin, no warning of skin exposure is
likely to occur.
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| Environmental Impact | Methyl parathion is likely to enter the atmosphere from production of the pesticide, or its
application as an insecticide. It should degrade in soil and water over the course of several months
primarily by photolysis and biodegradation. The major exception is for spills, where degradation
will occur only after many years. Methyl parathion metabolizes rapidly in plants and animals and is
not expected to bioconcentrate in food products. Human exposure is primarily occupational, or
from contact with spills; however some intake may result from fruits and vegetables as well as air
and water in agricultural areas where methyl parathion is used during the growing season.
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| Environmental Fate | TERRESTRIAL FATE: Methyl parathion is rapidly degraded in soil at the low
concentrations which are associated with its use as an insecticide. Loss is primarily due to
biodegradation (half life 10 days - 2 months) . Degradation increases with temperature and
exposure to sunlight . Methyl parathion will mineralize; intermediate products are amino methyl
parathion and O-methyl-O'-p-nitrophenylthiophosphoric acid . At very high concentrations such
as might be associated with a spill, degradation is exceedingly slow and may be primarily due to
photodegradation . Since methyl parathion demonstrates moderate soil adsorption and
biodegrades rapidly, it is unlikely to leach into ground water under most circumstances(1,2).
Evaporation should not be an important transport mechanism(4,SRC). In a terrestrial ecosystem
the majority, 65%, of the (14)C residue from ring labeled methyl parathion was found in the air,
15 days after application which indicates that volatile degradation products such as CO2 are
formed . Degradation was more rapid under flooded conditions than under non-flooded
conditions in soil(6,7). Hydrolysis was implicated under non-flooded and to a minor extent in
flooded(6,7); degradation under flooded conditions proceeded essentially by nitro group
reduction(7,8). Mineralization of methyl parathion proceeded more rapidly in moist soils (which
have lower soil-water tension values) than in dry soils(8).
AQUATIC FATE: Rapid degradation in seawater, lake water, and river water primarily by
biodegradation and photolysis (100% degradation in 2 weeks to 1 month or more)(3,4).
Degradation appears to be more rapid in the presence of sediment and in fresh water rather than
salt water . Mineralization occurs (5-11% in 4 days) in rivers and more slowly in marine
systems . Amino methyl parathion is an observed product . The rate of degradation is a
function of the presence and acclimation of microbial populations in the body of water . Methyl
parathion degrades by direct photolysis in natural water (half life 8 days summer and 38 days
winter) producing p-nitrophenol and O-methyl-O'-p-nitrophenylthiophosphoric acid . This
might be the major degradative pathway in oligotrophic systems. Evaporation is not
significant. Methyl parathion was not biodegraded in seawater from two Gulf Coast
estuaries(6).
Methyl parathion should degrade fairly rapidly in the atmosphere by photolysis . Methyl
parathion has a vapor pressure of 9.6X10-6 mm Hg at 20 degC ; organic compounds having
vapor pressure of this magnitude are expected to exist in combination of vapor-phase and
pariculate-phase in the ambient atmosphere . Vapor-phase methyl parathion will react with
sunlight produced hydroxyl radicals at an estimated half-life rate of 3.6 days(4,SRC). The
detection of methyl parathion in fogwater suggests that physical removal from the atmosphere is
possible via dissolution and subsequent rainfall.
TERRESTRIAL FATE: Simulated spillage of emulsifiable concentrate and microencapsulated
formulations of methyl parathion on soil were studied. Persistence of residues from both
formulations spilled as concn and as simulated drum rinses were followed for up to 45 mo.
Spillage of encapsulated formulation resulted in the formation of a solid cake-like deposit on the
soil surface. At 45 mo, soil residues had decr by 64% for emulsifiable concentrate spills, and 68%
for the soil beneath the cake. Residue in the cake itself only decr by 31%. Soil residue levels from
simulated drum rinses were essentially innocuous by 45 mo for the emulsifiable concentrate and
by 1 yr for the microencapsulated material.
AQUATIC FATE: The half life of methyl parathion in untreated estuarine sediment water studies
was 1.2 days (95% confidence limit 0.60-2.0 days).
TERRESTRIAL FATE: 73 acres of alfalfa in Vernal, Utah, were sprayed with an emulsifiable
concentrate (EC) containing 6 lb/gal ethyl parathion and 3 lb/gal methyl parathion. The material
was applied at 4.15X10-2 gal/acre. Wind conditions were negligible. Samples were taken from the
sprayed plot (sites A and B) and from an adjoining non-target pasture (site C). Immediately after
treatment, methyl parathion residues averaged 40% of ethyl parathion levels at the 3 sampling
stations. Foliar residues of the parent cmpd dissipated rapidly with time. At Site A, the residues
dropped below 1.25 mg/kg within 28 hr for methyl parathion. First order half life of methyl
parathion was 12 hr.
Methyl parathion, it is believed, does not bioaccumulate has little or no potential to contaminate
ground water was not included on the list of potential ground water contaminators.
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| Drinking Water Impact | SURFACE WATER: Cape Fear River Basin, NC 0-468 parts/trillion (20.2 parts/trillion
avg, 29% positive) dissolved phase . 0-123 parts/trillion (5.8 parts/trillion avg, 28% positive)
particulate phase . Ioannina basin and Kalamas River Greece 1984-85, 61 samples, not detected
(detection limit not specified) - 42 parts per trillion methyl parathion, 64% pos .
Drinking water: Methyl parathion has not been identified in drinking water in the United
States.
DRINKING WATER: Methyl parathion was postively detected in a drinking water of unspecified
origin .
RAIN/SNOW: For water samples collected at the USDA Agricultural Research Center in
Beltsville, MD in 1984 contained methyl parathion levels of 1210 ng/l .
EFFL: 15 ppb in initial runoff in rain following foliar application . Low potential for runoff .
10-190 parts/trillion in < 10% of samples - drain effluent in California .
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