imidacloprid is rated as moderately toxic on an acute oral basis to mammals and low toxicity on a dermal basis by the World Health Organization (WHO) and the United States Environmental Protection Agency (EPA or USEPA) was class II or III, requiring a warning or caution label.
Imidacloprid disrupts the nerve's ability to send a normal signal, and the nervous system stops working the way it should. Imidacloprid is much more toxic to insects and other invertebrates than it is to mammals and birds because it binds better to the receptors of insect nerve cells.
Imidacloprid is a systemic insecticide, which means that plants take it up from the soil or through the leaves and it spreads throughout the plant's stems, leaves, fruit, and flowers. Insects that chew or suck on the treated plants end up eating the imidacloprid as well. Once the insects eat the imidacloprid, it damages their nervous system and they eventually die
Animal toxicity is moderate when ingested orally and low when applied dermal. It is not irritating to eyes or skin in rabbits and guinea pigs although some commercial preparations contain clay as an inert ingredient, which may be an irritant. The acute inhalation LD50 in rats was not reached at the greatest attainable concentrations, 69 mg/m4 of air as an aerosol, and 5,323 mg a.i./m3 of air as a dust. In rats subjected to a two-year feeding study, no observable effect was seen at 100 ppm. In rats, the thyroid is the organ most affected by imidacloprid. Thyroid lesions occurred in male rats at a LOAEL of 16.9 mg a.i./kg/day. In a one-year feeding study in dogs, no observable effect was seen at 1,250 ppm, while levels up to 2,500 ppm led to hypercholesterolemia and elevated liver cytochrome p-450 measurements