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methoprene (Altosid) EPA R.E.D. Facts 3/91

United States Environmental Protection Agency
Pesticides And Toxic Substances (H-7508W)
21T-l003, March 1991



Pesticide Reregistration

All pesticides sold or used in the United States must be registered by EPA, 
based on scientific studies showing that they can be used without posing 
unreasonable risks to people or the environment. Because of advances in 
scientific knowledge, the law requires that pesticides which were first 
registered years ago be reregistered to ensure that they meet today's more 
stringent standards.

In evaluating pesticides for reregistration, EPA obtains from pesticide 
producers and reviews a complete set of studies showing the human health and 
environmental effects of each pesticide. The Agency imposes any regulatory 
controls that are needed to effectively manage each pesticide's risks. EPA 
then reregisters pesticides that can be used without posing undue hazards to 
human health or the environment.

When a pesticide is eligible for reregistration, EPA announces this and 
explains why in a Reregistration Eligibility Document, or RED. This fact sheet 
summarizes the information in the RED for methoprene.


Methoprene, which is sold under the trade name Altosid, is an insect growth 
regulator. It is considered a biochemical pesticide because rather than 
controlling target pests through direct toxicity, methoprene interferes with 
an insect's life cycle and prevents it from reaching maturity or reproducing. 
Methoprene is used in the production of a number of foods including meat, 
milk, eggs, mushrooms, peanuts, rice and cereals. It is also used in aquatic 
areas to control mosquitoes and several types of flies, moths, beetles and 
fleas. All pesticide products that contain methoprene as the sole active 
ingredient are eligible for reregistration except the briquette or slow-
release formulation.

Regulatory History

Methoprene was first registered by EPA as a conventional, chemical pesticide 
in 1975. EPA issued a Registration Standard for methoprene in February 1982. 
Subsequently, the Agency reclassified methoprene as a biochemical pesticide.

Health Effects

Methoprene is a biochemical pesticide, and its health-related data base 
consists mainly of a group of screening studies designed to show its toxicity 
and developmental effects in people and other nontarget organisms. If these 
studies indicated potential adverse effects, further studies on environmental 
fate, ecological effects and food residues would have been required.

The results of these screening tests and other available studies on methoprene 
indicate that it is of low toxicity and poses little risk to people and other 
nontarget species, with one exception. Methoprene is highly acutely toxic to 
estuarine invertebrates. Use of the briquette or slow-release formulation of 
methoprene in aquatic environments could pose an undue risk to these species. 
Further study of this formulation is being required, as described further 

Methoprene showed no significant adverse toxicological effects in any human 
health effects screening studies. The pesticide has very low acute oral and 
inhalation toxicity potential, and is not an eye or skin irritant (it has been 
placed in toxicity category IV, the least toxic category, for these effects). 
It also is not a human skin sensitizer. Methoprene is of low acute dermal 
toxicity (it has been placed in toxicity category III).

In subchronic studies, methoprene showed some evidence of causing increased 
liver weights in test animals, at high dose levels. However, in chronic 
effects and oncogenicity studies, no effects were observed even at the highest 
dose levels. Other studies show that methoprene does not cause developmental 
or reproductive effects, is not mutagenic, and metabolizes rapidly and 
completely in mammals.

Routes Of Exposure

     Through the Diet
People may be exposed to small amounts of methoprene through the food supply. 
However, the amount of methoprene in the U.S. consumer's diet is well below 
the level at which any adverse health effects could occur.

Tolerances, or legal residue limits, have been established for residues of 
methoprene in or on a number of raw agricultural commodities (also see 40 CFR 
180.359). Several international Codex Maximum Residue Levels (MRLs) and 
Canadian tolerances also have been established, as listed below:

Methoprene Tolerances

                             U.S.          Codex          Canadian
Commodity                 Tolerance         MRL           Tolerance
                            (ppm)          (ppm)            (ppm)

Cattle, fat                  0.3
Cattle, meat                 0.1
Cattle, meat byproducts      0.1
Eggs                         0.05          0.05
Goats, fat                   0.3
Goats, meat                  0.1
Goats, meat  byproducts      0.1
Hogs, fat                    0.3
Hogs, meat                   0.1
Hogs, meat byproducts        0.1
Horses, fat                  0.3
Horses, meat                 0.1
Horses, meat  byproducts     0.1
Milk                         0.05
Mushrooms                    1.0            0.2              0.1
Peanuts                      2.0            2.0 
Peanut hulls                40.00
Poultry, fat                 0.5
Poultrv, meat                0.5
Poultry, meat byproducts     0.5
Sheep, fat                   0.3
Sheep, meat                  0.1
Sheep, meat byproducts       0.1
Meat, fat                                   0.1
Cattle milk                                 0.05
Edible offal (mammalian)                    0.1

EPA has reassessed the existing tolerances and finds that they are set at 
appropriate levels. Although the U.S. tolerances for mushrooms and meat fat 
are higher than the Codex and Canadian limits, EPA is not lowering the U.S. 
tolerances at this time. These tolerances are set at levels that accommodate 
current methoprene use practices in this country. No changes are needed to 
adequately protect the public health.

No new tolerances are required to cover the existing methoprene uses. (Please 
note that a petition is pending to establish additional methoprene tolerances 
for cereal grains, grain milled fractions and rice hulls.)

     During Application
People can be exposed to methoprene while mixing, loading or applying the 
pesticide, and while working among treated crops. However, since methoprene is 
of such low acute toxicity, and poses no risk of oncogenic, reproductive, 
developmental or neurotoxic effects, EPA is satisfied that methoprene poses no 
risks to people who are occupationally exposed to the pesticide.

Environmental Hazards

All the environmental fate data requirements for methoprene are satisfied. The 
information available to EPA indicates that methoprene win not result in 
unreasonable adverse effects to the environment. However, the ecological 
effects studies on methoprene suggest that use of the briquette or slow-
release formulation in estuarine areas may cause undue risks to estuarine 
invertebrates, since the pesticide is highly acutely toxic to these organisms. 
EPA is therefore requiring further study of this methoprene use.

     Environmental Fate
Methoprene degrades rapidly in sunlight, both in water and on inert surfaces. 
The pesticide also is metabolized rapidly in soil and does not leach. Thus, it 
should not persist in soil or contaminate ground water.

     Ecological Effect
Methoprene has been shown to be practically non-toxic to mallard ducks, and 
had no effect on quail reproduction. However, the pesticide is moderately 
toxic to warm water, freshwater fish, and is slightly toxic to cold water, 
freshwater fish.

Methoprene is very highly toxic to freshwater invertebrates, as seen in 
studies with crayfish and Daphnia magna. The pesticide also can be very highly 
acutely toxic to estuarine and marine invertebrates, as seen in studies with 
grass shrimp and mud-crabs. Marine organisms are not likely to be exposed to 
methoprene, but estuarine organisms are likely to be exposed as a result of 
the use of methoprene as a mosquito larvicide.

Methoprene degrades rapidly in water so the use of most formulations in 
estuaries is not of concern. However, the slow-release briquette formulation 
is of concern to EPA because it causes estuarine organisms to be exposed to 
methoprene over an extended period of time. An estuarine invertebrate life 
cycle toxicity study is being required to adequately characterize the chronic 
toxicity of methoprene to estuarine

Additional Data Required

EPA has a sufficient battery of studies to support the reregistration of most 
uses of methoprene. The only use of concern is the aquatic, mosquito larvicide 
use involving the briquette formulation. An estuarine invertebrate life cycle 
study is being required to determine whether long term exposure of these 
species to methoprene through the briquette formulation poses adverse effects. 
In addition, an octanol/'water partition coefficient study is being required 
to complete the product chemistry data
base for methoprene.

Product Labeling Changes Required

End-use products containing methoprene must bear a statement warning the 
applicator that improper use could harm aquatic invertebrates. These products 
also must bear an updated water contamination warning. Please see the 
Reregistration Eligibility Document for a detailed list of labeling 

Regulatory Conclusion

- The studies available to EPA indicate that the biochemical insect growth 
regulator methoprene is of low toxicity and poses very little hazard to people 
and most other nontarget species.

- Methoprene is highly acutely toxic to estuarine invertebrates, however, and 
these organisms may be exposed to sufficient amounts of methoprene through its 
aquatic, slow-release, briquette formulation to experience adverse effects. An 
estuarine invertebrate life cycle toxicity study must be completed before the 
briquette formulation of methoprene will be eligible for reregistration.

- All other registered methoprene products can be used without causing 
unreasonable adverse effects in people or the environment Therefore, all 
pesticide products containing methoprene as the sole active ingredient, except 
the briquette formulation, are eligible for reregistration.

- EPA will reregister individual products containing methoprene once product 
specific data and revised product labeling are submitted to and accepted by 
the Agency.

For More Information

EPA requests public comments on the Reregistration Eligibility Document for 
methoprene, and will consider comments received during the next several 
months. To obtain a copy of the RED, or to submit written comments, please 
contact the Public Response and Program Resources Branch, Field Operations 
Division (H-7506C), Office of Pesticide Programs, U.S. EPA, Washington, D.C. 
20460. Call 703-557-4436, or FAX to 703-557-1884.

To obtain a copy of the Registration Standard for methoprene, please contact 
the National Technical Information Service (NIIS), 5285 Port Royal Road, 
Springfield, VA. 22161. Call 703-487-4650, and request document #PB87-109443.

For more information about methoprene or about EPA's pesticide reregistration 
program, please contact the Special Review and Reregistration Division (H-
7508W), Office of Pesticide Programs, U.S. EPA, Washington, D.C. 20460. Call 
703-808-8000, or FAX your request to 703-308-8005.

For information about the health effects of pesticides, or for assistance in 
recognizing and managing pesticide poisoning symptoms, please contact the 
National Pesticides Telecommunications Network NPIN). Call toll-free 1-800-
858-7378, 24 hours a day, seven days a week, or FAX your inquiry to 806-743-