| Chemical Abstract Number (CAS #) |
72435
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| Synonyms | p,p'-Methoxychlor |
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Benzene, 1,1'-(2,2,2-trichloroethylidene)bis[4-methoxy- | 1,1,1-Trichloro-2,2-bis(4-methoxyphenyl)ethane | Ethane, 1,1,1-trichloro-2,2-bis(p-methoxyphenyl)- | p,p'DMDT | Methoxcide | Dimethoxy DDT | Metox |
| Analytical Methods |
EPA Method 505 |
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EPA Method 508 |
EPA Method 525 |
EPA Method 608.2 |
EPA Method 617 |
EPA Method 625 |
EPA Method 8080A |
EPA Method 8081 |
EPA Method 8250A |
| Molecular Formula | C16H15Cl3O2 |
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| Use | VET: ECTOPARASITICIDE
AN EXCELLENT REPLACEMENT FOR DDT WHERE APPLICATION MAY
CONSTITUTE HAZARD TO WARM-BLOODED ANIMALS OR SUSCEPTIBLE PLANTS.
IT IS RARELY PHYTOTOXIC, & INJURY IS NEGLIGIBLE EVEN ON
DDT-SUSCEPTIBLE CROPS SUCH AS CUCURBITS.
IT IS APPROVED IN US FOR USE ON 78 AGRIC CROPS (INCL SEVERAL TYPES OF
SEEDS), WITH RESTRICTIONS ON USE OF TREATED SEEDS. FOR USE AS
INSECTICIDE ON BEEF CATTLE, DAIRY CATTLE, GOATS, SHEEP, & SWINE & FOR
SPRAY TREATMENT OF BARNS, GRAIN BINS, MUSHROOM HOUSES, & OTHER
AGRIC PREMISES .
Methoxychlor has been utilized extensively for the control of biting flies in both northern and
southern regions of Canada.
0.25-1.0% AS DIP; 0.5-1.0% AS AEROSOL SPRAY--CATS, DOGS, SWINE; 1.0-3.0% AS
AEROSOL SPRAY--CATTLE; 1.0-5.0% IN OIL BASE FOR BACKRUBBERS--CATTLE;
2.0-5.0% DUST BAGS--CATTLE HORN FLIES 5.0-50.0% AS SPOT TREATMENT
DUSTS ON LIVESTOCK; TABLESPOONFUL DOSES ONLY OF THE 50% CONCN ON
CATTLE; UP TO 2.0% DUSTS ON HAMSTERS, MICE, AND RATS; 2.0-5.0% AS A
PREMISE SPRAY
Insecticide effective against mosquito larvae and house-flies.
A contact & stomach insecticide effective against a wide range of pests, but not aphids, in field &
forage, fruit & vegetable crops.
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| Consumption Patterns | INSECTICIDE FOR LIVESTOCK & POULTRY, 43%; ALFALFA, 29%; CITRUS,
29% (1982)
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| Apparent Color | PURE METHOXYCHLOR FORMS COLORLESS CRYSTALS ; DIMORPHIC
CRYSTALS ; CRYSTALS FROM DIL ALCOHOL ; White to light yellow solid ; A white
crystalline solid ; Technical methoxychlor is a pale buff to gray flaky powder
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| Odor | Slightly fruity
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| Melting Point | 89 DEG C
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| Molecular Weight | 345.65
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| Density | 1.41 at 25 DEG C
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| Odor Threshold Concentration | 4.7 mg/kg in water
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| Sensitivity Data | SLIGHTLY IRRITATING TO SKIN.
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| Environmental Impact | Release of methoxychlor to the environment is expected to occur primarily due to its use
as an insecticide. Other sources of release may include loss during manufacturing, formulation,
packaging, and disposal of methoxychlor. If released to soil, methoxychlor is expected to remain
immobilized primarily in the upper layer of soil although a small percentage may migrate to lower
depths, possibly into groundwater as suggested by the detection of methoxychlor in some
groundwater samples. Under anaerobic conditions, biodegradation appears to be the dominant
removal mechanism; however, under aerobic conditions, biodegradation is expected to be less
rapid and possibly negligible. Rapid primary degradation of methoxychlor has been observed
under anaerobic conditions in flooded soils (half-lives 1 week to < 2 months). Major degradation
products under anaerobic conditions are dechlorinated methoxychlor (DMDD) and mono- and
di-hydroxy derivatives of methoxychlor and DMDD. Methoxychlor may undergo indirect
"sensitized" photolysis on the soil surfaces and it may undergo chemical hydrolysis in moist soils
(half-life > 1 year). If released to water, methoxychlor may be removed or transported by several
different mechanisms. Methoxychlor may adsorb to suspended solids and sediments or it may
bioaccumulate in certain aquatic organisms, although fish are reported to metabolize
methoxychlor fairly rapidly. Methoxychlor may undergo direct photolysis (half-life 4.5 months) or
indirect "sensitized" photolysis (half-life <5 hours) depending upon the presence of
photosensitizers. 1,1-Bis(p-methoxyphenyl)-2,2-dichloroethylene (DMDE) is a major photolysis
product of methoxychlor. Volatilization of methoxychlor may be significant (half-life 4.5 days
from a shallow river) and methoxychlor may also biodegrade under anaerobic conditions (half-life
< 28 days in sediments) or aerobic conditions (half-life >100 days in sediments). Oxidation and
chemical hydrolysis are not expected to be significant fate processes. If released to the
atmosphere, methoxychlor may exist in either vapor or particulate form. Methoxychlor may
undergo reaction with photochemically generated hydroxyl radicals (estimated vapor phase
half-life 3.7 hours) or physical removal by settling out or washing out in precipitation. The most
probable route of exposure to methoxychlor would be inhalation or dermal contact during home
use of this insecticide, inhalation of airborne particulate matter containing methoxychlor or
ingestion of food or drinking water contaminated with methoxychlor. The US Food and Drug
Administration (FDA) estimated average daily intake of methoxychlor Fiscal year 1981/1982
0.004 ug/kg body wt day.
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| Environmental Fate | Terrestrial Fate: The persistence and disappearance (washoff or dryfall) of methoxychlor
from mature soybean foliage was investigated in a small field plot study under natural rainfall
conditions in 1977 and 1978. Methoxychlor washoff rate was 8 or - 4% of the amount on plants
(prior to rain) per cm of rainfall, regardless of time after application. Total seasonal washoff for
1978 accounted for 33.5% of the applied pesticide; however, 30.5% of the total loss was removed
by washoff on the second day after application. Dryfall or dislodgeable residue accounted for less
than 1% of the amt applied. The amt of dryfall was greater in plots entered by workers than in
those where entry was avoided.
TERRESTRIAL FATE: If released to soil, methoxychlor is expected to remain immobilized
primarily in the upper layer of soil, although a small percentage may migrate to lower depths,
possibly into groundwater as suggested by the detection of methoxychlor in some groundwater
samples. Under anaerobic conditions, biodegradation appears to be the dominant removal
mechanism; however, under aerobic conditions biodegradation is expected to be less rapid. Under
anaerobic conditions major degradation products are dechlorinated methoxychlor (DMDD) and
mono- and dihydroxy- (dimethylated) derivatives of methoxychlor and DMDD. Methoxychlor
may undergo indirect "sensitized" photolysis on the soil surfaces and it may undergo chemical
hydrolysis in moist soils (half-life approx 1 year). Methoxychlor underwent rapid primary
degradation in 4 types of flooded soil under anaerobic conditions (half-life 1 week to 2 months),
but degraded less rapidly under aerobic conditions in 4 types of upland soil (half-life >3 months)
. After 100 days incubation in a soil, negligible degradation of methoxychlor was observed
under aerobic conditions and 73% degradation was observed under anaerobic conditions .
AQUATIC FATE: If released to water, methoxychlor may be removed or transported by several
different mechanisms. Methoxychlor may adsorb to suspended solids and sediments or it may be
taken up and bioaccumulate in some aquatic organisms, although fish are reported to metabolize
methoxychlor fairly rapidly. Methoxychlor may undergo direct photolysis (half-life 4.5 months) or
indirect "sensitized" photolysis (half-life= 5 hours) depending upon the presence of
photosensitizers. 1,1-Bis(p-methoxyphenyl)-2,2-dichloroethylene (DMDE) is a major photolysis
product of methoxychlor. Methoxychlor may volatilize significantly (calculated half-life 4.5 days
from a shallow river) and it may biodegrade under anaerobic conditions (half-life < 28 days) or
aerobic condition (half-life >100 days) in sediments. Under anaerobic conditions major
degradation products are dechlorinated methoxychlor (DMDD) and mono- and dihydroxy
derivatives of methoxychlor and dechlorinated methoxychlor. Oxidation and chemical hydrolysis
are not expected to be significant fate processes.
ATMOSPHERIC FATE: If released to the atmosphere, methoxychlor may exist in either vapor or
particulate form. It may undergo reaction with photochemically generated hydroxyl radicals
(estimated vapor phase half-life = 3.7 hours) or be physically removed by settling out or washing
out in precipitation.
ATMOSPHERIC FATE: Wind erosion of methoxychlor-contaminated earth is a route by
which the pesticide can enter the atmosphere.
TERRESTRIAL FATE: Methoxychlor is a moderately persistent compound. Residues have been
demonstrated to remain in the soil for up to 14 months.
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| Drinking Water Impact | Methoxychlor was added to the head waters of the Twin Falls Canal Co canal system
(0.3 ppm) and subsequently determined in water at a location approx 75 miles away by gas-liquid
chromatography. Methoxychlor residues peaked at the sampling site at 45-46 hr after most of the
applications. The highest residue level at that time was 1.4 ppb; the mean peak level was 1.1 ppb.
SURFACE WATER: During July 1981, methoxychlor was detected in subsurface water taken
from the Niagara River, 5 samples, 1 pos, 0.0010 ppb detected . During 1980-81, in surface
water taken from Niagara-on-the-Lake, 75 samples, 5 pos, 0.1 ppt mean concn detected .
During July 1976, in James River near Hopewell, VA, trace amounts (<8 ppt) detected . During
1974-75 in Lake Superior, 16 samples, 0.02 ppb max. concn detected, 0.015 ppb mean concn
detected . During 1971-72 in tributary of Lake Michigan, 2.9-89.1 ppt methoxychlor
detected . In 1983, methoxychlor was found in 11 of 14 samples taken from Lake Ontario, at a
maximum concn of 0.086 ng/L(6).
GROUNDWATER: Methoxychlor has qualitatively been identified in groundwater in NJ and
CA . During 1978, methoxychlor was identified in groundwater below irrigated farmland in
Nebraska at concn ranging from well below detection limits to 0.01 ppb . Methoxychlor was
detected in 0.7% of groundwater samples taken at CERCLA waste sites (<500 sites tested) and
0.8% of samples at RCRA sites (>1,500 sites) .
DRINKING WATER: Methoxychlor was detected in drinking water supplies in rural SC:
Chesterfield County, 45.8% pos, concn range ND-312 ppb, mean concn. 33 ppt, Hampton
County, 63.6% pos, concn range ND-100 ppb, mean concn 23 ppt .
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