Organophosphate Insecticides with Active EPA Registration (as of 2002)

The oral LD₅₀ is 500 mg/kg body wt in goats and 97 mg/kg in rats. In comparison with calves, steers, and cows, bulls (particularly of the exotic breeds) are highly susceptible to a single dose of chlorpyrifos.

Coumaphos:

Coumaphos is used against cattle grubs and a number of other ectoparasites and for treatment of premises. The maximum concentration that may be safely used on adult cattle, horses, and pigs is 0.5%. Young calves and all ages of sheep and goats must not be sprayed with concentrations >0.25%; 0.5% concentrations may be lethal. Adult cattle may show mild toxicity at 1% concentrations.

Diazinon:

Young calves appear to tolerate 0.05% spray but are poisoned by 0.1% concentrations. Adult cattle may be sprayed at weekly intervals with 0.1% concentrations without inducing poisoning. Young calves tolerate 0.44 mg/kg body wt, PO, but are poisoned by 0.88 mg/kg. Cattle tolerate 8.8 mg/kg, PO, but are poisoned by 22 mg/kg. Sheep tolerate 17.6 mg/kg but are poisoned by 26 mg/kg.

Dichlorvos:

Dichlorvos has many uses on both plants and animals. It is rapidly metabolized and excreted, and residues in meat and milk are not a problem if label directions are followed. It is of moderate toxicity, with a minimum toxic dose of 10 mg/kg body wt in young calves and 25 mg/kg in horses and sheep. The LD₅₀ in rats is 25-80 mg/kg, PO. A 1% dust was not toxic to cattle. Flea collars containing dichlorvos may cause skin reactions in some pets.

Dimethoate:

When administered PO, the minimum toxic dose for young dairy calves was ~48 mg/kg body wt, while 22 mg/kg was lethal for cattle 1 yr old. Daily doses of 10 mg/kg for 5 days in adult cattle lowered blood cholinesterase activity to 20% of normal but did not produce poisoning. Horses have been poisoned by doses of 60-80 mg/kg, PO. When applied topically, 1% sprays have been tolerated by calves, cattle, and adult sheep.

Disulfoton:

The maximum nontoxic oral dose is 0.88 mg/kg body wt for young calves, 2.2 mg/kg for cattle and goats, and 4.8 mg/kg for sheep. Poisoning has occurred in cattle after consuming harvested forages previously sprayed with this insecticide.

Fenthion:

Minimum toxic dose, PO, is 25 mg/kg body wt for cattle; 50 mg/kg is lethal to sheep.

Malathion:

Malathion is one of the safest organophosphates. Young calves tolerate 0.5% but not 1% sprays; adult cattle tolerate 2% sprays. Given PO, it is toxic at 100 mg/kg but not 55 mg/kg body wt; young calves tolerate 11 mg/kg but are poisoned by 22 mg/kg. Malathion is excreted in cow’s milk.

Methyl Parathion:

The LD₅₀ in rats from a single oral dose is 9-25 mg/kg body wt compared with 3-13 mg/kg for ethyl parathion. Microencapsulation of this compound decreases its toxicity, and the lethal dose in cattle has been increased from a 0.5% to a 2% spray.

Naled:

The oral LD₅₀ in rats is 430 mg/kg body wt.

Oxydemeton-methyl:

The maximum nontoxic oral dose is 0.88 mg/kg body wt for young calves, 2.2 mg/kg for cattle, and 4.8 mg/kg for sheep and goats.

Parathion:

Parathion (diethyl parathion) is widely used for control of plant pests and is approximately one-half as toxic as TEPP (see below). It is used as a dip and spray for cattle in some countries (not in the USA). Most cases of occupational insecticide poisonings in humans have been attributed to parathion or its degradation products. As a 0.02% spray, it produces signs of poisoning in young calves and occasional transitory signs at 0.01%. Parathion is lethal to sheep at 22 mg/kg body wt, PO, but not at 11 mg/kg. Young dairy calves are poisoned by 0.44 mg/kg, while 44 mg/kg is required to poison older cattle. Parathion is used extensively to control mosquitos and insects in orchards and on market garden crops. Normally, because so little is used per acre, it presents no hazard to livestock. However, because of its potency, care should be taken to prevent accidental exposure. Parathion does not produce significant residues in animal tissues.

Phorate:

The minimum toxic dose PO is 0.25 mg/kg body wt in calves, 0.75 mg/kg in sheep, and 1 mg/kg in cattle.

Phosmet:

The minimum oral toxic dose PO is 25 mg/kg body wt in cattle and calves and 50 mg/kg in sheep.

Temephos:

The oral LD₅₀ for rats is 1 g (or more)/kg body wt, while the dermal LD₅₀ is >4 g/kg.

Tetrachlorvinphos:

Tetrachlorvinphos has low toxicity in dogs; chronic feeding studies indicate the lowest effect level (LEL) was 50 mg/kg/day and the no observed effect level (NOEL) 3.13 mg/kg/day. The minimum toxic dose in pigs is 100 mg/kg.

Trichlorfon:

As a spray, trichlorfon at a 1% concentration is tolerated by adult cattle; given PO, it is tolerated by young dairy calves at 4.4 mg/kg body wt but produces poisoning at 8.8 mg/kg. Adult cattle, sheep, and horses appear to tolerate 44 mg/kg, while 88 mg/kg produces poisoning. Dogs were unaffected when fed 1,000 ppm of trichlorfon for 4 mo. Trichlorfon is metabolized rapidly.