Canadian Government Study finds Risks to Honeybees from Biggest Nicotine Pesticide

Canadian Council of Ministers of the Environment

Le Conseil canadian des ministres de l'environnement

CANADIAN WATER QUALITY GUIDELINES: IMIDACLOPRID
SCIENTIFIC SUPPORTING DOCUMENT

ABSTRACT
This scientific supporting document describes the development of Canadian Water Quality Guidelines for imidacloprid. It contains a review of technical background information on the chemical and physical properties of imidacloprid, a review of uses in Canada, the distribution and behaviour of imidacloprid in the environment, and the toxicological effects of imidacloprid in freshwater and marine aquatic life, terrestrial crops, mammals and birds. This information is used to derive ambient water quality guidelines for imidacloprid. The guidelines in this document are based on the best available toxicity data at the time of writing, June 2006.
Imidacloprid is an insecticide active ingredient used to control sucking insects, such as aphids, leafhoppers, psyllids and beetles in agricultural crops and turfgrass, as well as domestic pests such as fleas and cockroaches. It is most commonly applied as a soil and foliage treatment, and as a seed dressing. Crops to which this compound is applied include: various grains, maize, fruits, vegetables, potatoes, hops and turf. Imidacloprid is water soluble, persistent in soil and relatively non-volatile under field conditions. Imidacloprid is not expected to bioaccumulate. Imidacloprid residues may be measured in water and soil using High Performance Liquid Chromatography (HPLC), or gas chromatography-mass spectrometry (GC-MS).
Imidacloprid is a nicotinoid neurotoxin that acts by irreversibly blocking acetylcholine receptors. Although mammals and insects both have acetylcholine receptors that can be blocked by imidacloprid, insects are more sensitive than mammals. Symptoms of imidacloprid poisoning include staggering, trembling, immobility and lethargy. Sensitivites of non-target organisms to imidacloprid varies. Imidacloprid may be highly toxic to beneficial insects, such as the honeybee and it is recommended that imidacloprid application be limited in areas frequented by honeybees. Imidacloprid may also induce toxicity in aquatic invertebrates and juvenile fish at low levels and is considered acutely toxic to birds. Moderate concentrations of the insecticide may decrease growth of algae. Phytoxicity is not predicted for crops if the insecticide is applied post-emergence.
Canadian water quality guidelines for the protection of agricultural water uses were not derived for imidacloprid. Insufficient data were available at the time of writing to support the development of these guidelines.
Sufficient toxicity data were available to derive interim freshwater and marine water quality guidelines for imidacloprid for the protection of aquatic life. The interim freshwater guideline was based on a 28-day LOEC (EC15) of 2.25 μg a.i./L for reduced emergence of the midge Chironomus riparius. As this is a low effects level chronic study, a safety factor of 0.1 was applied, giving an interim freshwater quality guideline of 0.23 μg a.i./L.
The interim marine water quality guideline was based on a 48-hour LC50 of 13 μg a.i./L for larvae of the saltmarsh mosquito Aedes taeniorhynchus. As the study was acute, and imidacloprid is non- persistent in water, a safety factor of 0.05 was applied to this value, giving a guideline value of 0.65 μg a.i./L.
These guidelines are intended to protect all forms of aquatic life and all aspects of aquatic life cycles during an indefinite period of exposure to the water column (CCME, 1991).

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