Acute toxicity studies with oxamyl.

The acute toxicity of oxamyl, an insecticide and nematicide, has been evaluated to establish proper handling guides. The material is highly toxic when given as a single oral dose; its LD50 is in fasted rats 2.5 to 3.1 mg/kg, 2.3 to 3.3 mg/kg in fasted mice, and 7 mg/kg in guinea pigs. A beagle dog given 30 mg/kg died, while 15 mg/kg was not lethal. In all species, clinical signs of cholinesterase inhibition (lacrimation, salivation, tremors) were observed. Cholinesterase activity was depressed in rats treated with a single oral dose. Atropine, when given immediately after oxamyl, was antidotal. When given by intraperitoneal injection, oxamyl was highly toxic to rats, mice, and guinea pigs. The material is a mild eye irritant with the reaction limited to the conjunctiva and iris, but systemic absorption via eye contact makes use of protective equipment essential. Oxamyl produces mild skin irritation and the dermal absorption toxicity in rats (LD50 is greater than 1,200 mg/kg) and rabbits (740 mg/kg) is relatively high suggesting limited absorption. No sensitization was produced when tested in guinea pigs. Oxamyl is highly toxic via inhalation with the 1-hr LC50 value in rats being 0.17 mg/liter (male) and 0.12 mg/liter (female). The corresponding 4-hr value is 0.064 mg/liter for male rats which indicates that concentration X time is a constant through the time periods tested. Repeated-dose studies, orally in rats and dermally in rabbits, showed oxamyl to be noncumulative, with the target system being the nervous system mediated through cholinesterase inhibition. No specific tissue or organ pathology was seen in either species tested.