E X T O X N E T
Pesticide Information Profiles
A Pesticide Information Project of Cooperative Extension Offices of Cornell
University, Oregon State University, the University of Idaho, and the University
of California at Davis and the Institute for Environmental Toxicology, Michigan
State University. Major support and funding was provided by the USDA/Extension
Service/National Agricultural Pesticide Impact Assessment Program.
EXTOXNET primary files maintained and archived at Oregon State University
TRADE OR OTHER NAMES: Imidacloprid is found in a
variety of commercial insecticides. The products Admire, Condifor, Gaucho,
Premier, Premise, Provado, and Marathon all contain imidacloprid as the active
REGULATORY STATUS: Imidacloprid is a General Use
Pesticide, and is classified by EPA as both a toxicity class II and class III
agent, and must be labeled with the signal word "Warning" or "Caution" (223).
There are tolerances for residues of imidacloprid and its metabolites on
food/feed additives ranging from 0.02 ppm in eggs, to 3.0 ppm in hops (328).
INTRODUCTION: Imidacloprid is a systemic,
chloro-nicotinyl insecticide with soil, seed and foliar uses for the control of
sucking insects including rice hoppers, aphids, thrips, whiteflies, termites,
turf insects, soil insects and some beetles. It is most commonly used on rice,
cereal, maize, potatoes, vegetables, sugar beets, fruit, cotton, hops and turf,
and is especially systemic when used as a seed or soil treatment. The chemical
works by interfering with the transmission of stimuli in the insect nervous
system. Specifically, it causes a blockage in a type of neuronal pathway
(nicotinergic) that is more abundant in insects than in warm-blooded animals
(making the chemical selectively more toxic to insects than warm-blooded
animals). This blockage leads to the accumulation of acetylcholine, an important
neurotransmitter, resulting in the insect's paralysis, and eventually death. It
is effective on contact and via stomach action (1).
Imidacloprid based insecticide formu-lations are available as dustable
powder, granular, seed dressing (flowable slurry concentrate), soluble
concentrate, suspension concentrate, and wettable powder (223). Typical
application rates range from 0.05 - 0.125 pounds/acre. These application rates
are considerably lower than older, traditionally used insecticides. It can be
phytotoxic if it is not used according to manufacturer's specifications, and has
been shown to be compatible with fungicides when used as a seed treatment to
control insect pests (329).
- Acute Toxicity: Imidacloprid is moderately toxic. The
oral dose of technical grade imidacloprid that resulted in mortality to half
of the test animals (LD50) is 450 mg/kg body weight in rats (223), and 131
mg/kg in mice (1). The 24-hour dermal LD50 in rats is >5,000 mg/kg. It is
considered non-irritating to eyes and skin (rabbits), and non-sensitizing to
skin (guinea pigs) (1). Some granular formulations may contain clays as inert
ingredients that may act as eye irritants. In acute inhalation toxicity tests
with rats, the airborne concentration of imidacloprid that resulted in
mortality to half of the test organisms (LC50) is > 69 mg/meters cubed air
in the form of an aerosol, and >5323 mg/meters cubed air in the form of
dust. These values represent the maximum attainable airborne concentrations
- Signs and Symptoms of Poisoning: Although no account of
human poisoning was found in the literature, signs and symptoms of poisoning
would be expected to be similar to nicotinic signs and symptoms, including
fatigue, twitching, cramps, and muscle weakness including the muscles
necessary for breathing (330).
- Chronic Toxicity: A 2-year feeding study in rats fed up
to 1,800 ppm resulted in a No Observable Effect Level (NOEL) of 100 ppm (5.7
mg/kg body weight in males and 7.6 mg/kg in females). Adverse effects included
decreased body weight gain in females at 300 ppm, and increased thyroid
lesions in males at 300 ppm and females at 900 ppm. A 1-year feeding study in
dogs fed up to 2,500 ppm resulted in a NOEL of 1,250 ppm (41 mg/kg). Adverse
effects included increased cholesterol levels in the blood, and some stress to
the liver (measured by elevated liver cytochrome p-450 levels) (331).
- Reproductive Effects: A three generation reproduction
study in rats fed up to 700 ppm imidacloprid resulted in a NOEL of 100 ppm
(equivalent to 8 mg/kg/day) based on decreased pup body weight observed at the
250 ppm dose level (331).
- Teratogenic Effects: A developmental toxicity study in
rats given doses up to 100 ppm by gavage on days 6 to 16 of gestation resulted
in a NOEL of 30 mg/kg/day (based on skeletal abnormalities observed at the
next highest dose tested of 100 ppm) (329). In a developmental toxicity study
with rabbits given doses of imidacloprid by gavage during days 6 through 19 of
gestation, resulted in a NOEL of 24 mg/kg/day based on decreased body weight
and skeletal abnormalities observed at 72 mg/kg/day (highest dose tested)
- Mutagenic Effects: Imidacloprid may be weakly mutagenic.
In a battery of 23 laboratory mutagenicity assays, imidacloprid tested
negative for mutagenic effects in all but two of the assays. It did test
positive for causing changes in chromosomes in human lymphocytes, as well as
testing positive for genotoxicity in Chinese hamster ovary cells (331).
- Carcinogenic Effects: Imidacloprid is considered to be of
minimal carcinogenic risk, and is thus categorized by EPA as a "Group E"
carcinogen (evidence of noncarcinogenicity for humans). There were no
carcinogenic effects in a 2-year carcinogenicity study in rats fed up to 1,800
ppm imidacloprid (328).
- Organ Toxicity: In short-term feeding studies in rats,
there were thyroid lesions associated with very high doses of imidacloprid
- Fate in Humans and Animals: Imidacloprid is quickly and
almost completely absorbed from the gastrointestinal tract, and eliminated via
urine and feces (70-80% and 20-30%, respectively, of the 96% of the parent
compound administered within 48 hours). The most important metabolic steps
include the degradation to 6-chloronicotinic acid, a compound that acts on the
nervous system as described above. This compound may be conjugated with
glycine and eliminated, or reduced to guanidine (1).
- Effects on Birds: Imidacloprid is toxic to upland game
birds. The LD50 is 152 mg/kg for bobwhite quail, and 31 mg/kg in Japanese
quail (223, 1). In studies with red-winged blackbirds and brown-headed
cowbirds, it was observed that birds learned to avoid imidacloprid treated
seeds after experiencing transitory gastrointestinal distress (retching) and
ataxia (loss of coordination). It was concluded that the risk of dietary
exposure to birds via treated seeds was minimal. Based on these studies,
imidacloprid appears to have potential as a bird repellent seed treatment
- Effects on Aquatic Organisms: The toxicity of
imidacloprid to fish is moderately low. The 96-hour LC50 of imidacloprid is
211 mg/l for rainbow trout, 280 mg/l for carp, and 237 mg/l for golden orfe.
In tests with the aquatic invertebrate Daphnia, the 48-hour EC50 (effective
concentration to cause toxicity in 50% of the test organisms) was 85 mg/l (1).
Products containing imidacloprid may be very toxic to aquatic invertebrates.
- Effects on Other Animals (Nontarget species):
Imidacloprid is highly toxic to bees if used as a foliar application,
especially during flowering, but is not considered a hazard to bees when used
as a seed treatment (1).
- Breakdown of Chemical in Soil and Groundwater: The
half-life of imidacloprid in soil is 48-190 days, depending on the amount of
ground cover (it breaks down faster in soils with plant ground cover than in
fallow soils) (334). Organic material aging may also affect the breakdown rate
of imidacloprid. Plots treated with cow manure and allowed to age before
sowing showed longer persistence of imidacloprid in soils than in plots where
the manure was more recently applied, and not allowed to age (335).
Imidacloprid is degraded stepwise to the primary metabolite 6-chloronicotinic
acid, which eventually breaks down into carbon dioxide (336). There is
generally not a high risk of groundwater contamination with imidacloprid if
used as directed. The chemical is moderately soluble, and has moderate binding
affinity to organic materials in soils. However, there is a potential for the
compound to move through sensitive soil types including porous, gravelly, or
cobbly soils, depending on irrigation practices (337).
- Breakdown of Chemical in Surface Water: The half-life in
water is much greater than 31 days at pH 5, 7 and 9. No other information was
- Breakdown of Chemical in Vegetation: Imidacloprid
penetrates the plant, and moves from the stem to the tips of the plant. It has
been tested in a variety of application and crop types, and is metabolized
following the same pathways. The most important steps were loss of the nitro
group, hydroxylation at the imidazolidine ring, hydrolysis to 6-
chloronicotinic acid and formation of conjugates (1).
- Analytical Methods: Methods are available for determining
imidacloprid residues (the 6-chloropicolyl moiety) in plant materials using
HPLC with u.v. detection (338).
PHYSICAL PROPERTIES AND GUIDELINES
- Appearance: Colorless crystals with a weak characteristic
- Chemical Name:
- CAS Number: 13826-41-3
- Molecular Weight: 255.7
- Water Solubility: 0.51 g/l (200 degrees C)
- Solubility in Other Solvents: @ 20 degrees C:
dichloromethane - 50.0 - 100.0 g/l; isopropanol - 1.0-2.0 g/l; toluene -
0.5-1.0 g/l; n-hexane - <0.1 g/l; fat - 0.061 g/100g
- Melting Point: 136.4-143.8 degrees C., 143.8 degrees C
(crystal form 1) 136.4 degrees C (crystal form 2)
- Vapor Pressure: 0.2 uPa (20 degrees C) (1.5 X 10 to the
minus 9 mmHg)
- Partition Coefficient: 0.57 (22 degrees C). (1)
- Adsorption Coefficient: Not Available
- ADI: Not Available
- MCL:Not Available
- RfD: 0.057 mg/kg/day (328)
- PEL: Not Available
- HA: Not Available
- TLV: Not Available
Bayer Agricultural Products
P. O. Box 4913
Kansas City, MO
References for the information in this PIP can be found in Reference List Number 10
DISCLAIMER: The information in this profile
does not in any way replace or supersede the information on the pesticide
product label/ing or other regulatory requirements. Please refer to the
pesticide product label/ing.