Chlorinated Hydrocarbon Compounds (Toxicity)

Aldrin is a potent insecticide similar to dieldrin with the same order of toxicity (see Dieldrin). It is no longer registered in the USA but was used for termite control. The oral LD₅₀ in rats is 39 mg/kg, and the dermal LD₅₀ in rabbits is 65 mg/kg. In farm animals, the toxic dose is ~15–30 mg/kg.

Benzene hexachloride (BHC) is composed of 12%–45% γ isomer. BHC was a useful insecticide for large animals and dogs but is highly toxic to cats in the concentrations necessary for parasite control. Only the γ isomer (γ−BHC, lindane) is a useful insecticidal agent; the other isomers are stored for excessively long periods in body tissues. Lindane, which contains >99% of the γ isomer, should be used in preference to the technical grade of BHC, which contains several isomers. The oral LD₅₀ of lindane in rats is 76 mg/kg, and the dermal LD₅₀ in rabbits is 500 mg/kg. Presently, BHC is not sold in the USA.

Cattle in good condition have tolerated 0.2% lindane applications, but stressed, emaciated cattle have been poisoned from spraying or dipping in 0.075% lindane. Horses and pigs appear to tolerate 0.2%–0.5%, and sheep and goats ordinarily tolerate 0.5% applications. Emaciation and lactation increase the susceptibility of animals to poisoning by lindane; such animals should be treated with extreme caution. Young calves are very susceptible to lindane and are poisoned by a single oral dose of 4.4 mg/kg. Mild signs appear in sheep given 22 mg/kg, and death occurs at 100 mg/kg. Adult cattle have tolerated 13 mg/kg without signs. BHC is stored in body fat and excreted in milk.

Chlordane is no longer registered as an insecticide in the USA. Exposure occurs when livestock consume treated plants or when they come in direct contact through carelessness and accidents. The lethal dose of chlordane for most species is in the range of 200–300 mg/kg. Very young calves have been killed by doses of 44 mg/kg, and the minimum toxic dose for cattle is ~88 mg/kg. Cattle fed chlordane at 25 ppm of their diet for 56 days showed 19 ppm in their fat at the end of the feeding. Topical emulsions and suspensions have been used safely on dogs at concentrations up to 0.25%, provided freshly diluted materials were used; dry powders up to 5% have been safe. The no-effect level in dogs in a 2-yr feeding study was 3 mg/kg. Pigeons and Leghorn cockerels and pullets suffered no effects after 1–2 mo exposure to vapors emanating from chlordane-treated surfaces. The oral LD₅₀ in rats is 283 mg/kg, and the dermal LD₅₀ in rabbits is 580 mg/kg.

Dieldrin is not a registered pesticide in the USA. Residues limit its application, and it is one of the most toxic chlorinated hydrocarbon insecticides. The oral LD₅₀ in rats is 40 mg/kg, and the dermal LD₅₀ in rabbits is 65 mg/kg. Young dairy calves are poisoned by 8.8 mg/kg, PO, but tolerate 4.4 mg/kg, whereas adult cattle tolerate 8.8 mg/kg and are poisoned by 22 mg/kg. Pigs tolerate 22 mg/kg and are poisoned by 44 mg/kg. Horses are poisoned by 22 mg/kg. Because of its effectiveness against insect pests on crops and pasture and the low dosage per acre, dieldrin is not likely to poison livestock grazing the treated areas. Diets containing 25 ppm of dieldrin have been fed to cattle and sheep for 16 wk without harmful effects other than residues in fat, which are slow to disappear. Great care must be exercised in marketing animals that have grazed treated areas or consumed products from previously treated areas. There is a zero tolerance level for residues in edible tissues.

Statements pertaining to dieldrin also apply, in general, to endrin, the most toxic of the three chlorinated cyclodiene insecticides.

Endosulfan is widely used to control insect and mite pests on a variety of crops and orchards. It is heavily used on tobacco. Endosulfan is very toxic to mammalian species. The oral LD₅₀ in rats is 18 mg/kg, and the dermal LD₅₀ in rabbits is 74 mg/kg. The LD₅₀ of endosulfan in dogs is 77 mg/kg. Its lethal dose in cattle is 8 g. Generally, cattle are poisoned by accidental exposure, and dogs are poisoned by malicious intent. Exposure of cattle to endosulfan produces residues in the liver, kidneys, muscle, and milk.

Heptachlor is not currently registered in the USA and is not recommended for use on livestock in the USA. Among its few agricultural applications, heptachlor is used for residual control of subterranean termites. The oral LD₅₀ in rats is 40 mg/kg, and the dermal LD₅₀ in rabbits is 119 mg/kg. Because it is very effective against certain plant-feeding insects, it is encountered from time to time in some geographic areas grazed by livestock. Young dairy calves tolerate dosages as high as 13 mg/kg but are poisoned by 22 mg/kg. Sheep tolerate 22 mg/kg but are poisoned by 40 mg/kg. Diets containing 60 ppm of heptachlor have been fed to cattle for 16 wk without harmful effects other than residues in fat. Heptachlor is converted to heptachlor epoxide by animals and stored in body fat. For this reason, a specific analysis performed for heptachlor usually yields negative results, while that for epoxide is positive.

Methoxychlor is one of the safest chlorinated hydrocarbon insecticides and one of the few with active registration in the USA. The oral LD₅₀ in rats is 5,000 mg/kg, and the dermal LD₅₀ in rabbits is 2,820 mg/kg. Young dairy calves tolerate 265 mg/kg; 500 mg/kg is mildly toxic. While 1 g/kg produces rather severe poisoning in young calves, sheep are not affected. One dog was given 990 mg/kg/day for 30 days without showing signs. Six applications to cattle of a 0.5% spray at 3-wk intervals produced fat residues of 2.4 ppm; ~0.4 ppm of methoxychlor is found in milk 1 day after spraying a cow with a 0.5% concentration. Methoxychlor sprays are not approved for use on animals producing milk for human consumption. Cattle and sheep store essentially no methoxychlor when fed 25 ppm in the total diet for 112 days. If methoxychlor is used as recommended, the established tolerance in fat will not be exceeded. Commercial products are available for garden, orchard, and field crops, and for horses and ponies.

Numerous reports suggest that methoxychlor has negative reproductive effects in laboratory animal experiments, but this has not been seen in the field.

Toxaphene is no longer under active registration in the USA. It has been used with reasonable safety if recommendations were followed, but it can cause poisoning when applied or ingested in excessive quantities. The oral LD₅₀ in rats is 40 mg/kg, and the dermal LD₅₀ in rabbits is 600 mg/kg. Dogs and cats are particularly susceptible. Young calves have been poisoned by 1% toxaphene sprays, while all other farm animals except poultry can withstand 1% or more as sprays or dips. Chickens have been poisoned by dipping in 0.1% emulsions, and turkeys have been poisoned by spraying with 0.5% material. Toxaphene is primarily an acute toxicant and does not persist long in the tissues. Adult cattle have been mildly intoxicated by 4% sprays and severely affected by 8%. Adult cattle have been poisoned from being dipped in emulsions that contained only 0.5% toxaphene (an amount ordinarily safe) because the emulsions had begun to break down, allowing the fine droplets to coalesce into larger droplets that readily adhere to the hair of cattle. The resultant dosage becomes equivalent to that obtained by spray treatments of much higher concentrations. Toxaphene is lethal to young calves at 8.8 mg/kg but not at 4.4 mg/kg. The minimum toxic dose for cattle is ~33 mg/kg, and for sheep between 22 and 33 mg/kg. Spraying Hereford cattle 12 times at 2-wk intervals with 0.5% toxaphene produced a maximum residue of 8 ppm in fat. Cattle fed 10 ppm of toxaphene in the diet for 30 days had no detectable toxaphene tissue residues, whereas steers fed 100 ppm for 112 days stored only 40 ppm in their fat (this amount was eliminated 2 mo after the toxaphene was discontinued).