Polychlorinated Dibenzodioxins - Toxic Effects in Animals

Toxic Effects in Animals

While it has been difficult to establish specific health effects in humans due to the lack of controlled dose experiments, studies in animals have shown that dioxin causes a wide variety of toxic effects. In particular, TCDD (see this) has been shown to be teratogenic, mutagenic, carcinogenic, immunotoxic, and hepatotoxic. Furthermore, alterations in multiple endocrine and growth factor systems have been reported. The most sensitive effects, observed in multiple species, appear to be developmental, including effects on the developing immune, nervous, and reproductive systems. The most sensitive effects are caused at body burdens relatively close to those reported in humans.

Among the animals for which TCDD toxicity has been studied, there is strong evidence for the following effects:

• Birth defects (teratogenicity)

In rodents, including rats, mice, hamsters and guinea pigs, birds, and fish.

• Cancer (including neoplasms in the mammalian lung, oral/nasal cavities, thyroid and adrenal glands, and liver, squamous cell carcinoma, and various animal hepatocarcinomas)

In rodents and fish

• Hepatotoxicity (liver toxicity)

In rodents, chickens, and fish

• Endocrine disruption

In rodents and fish

• Immunosuppression

In rodents and fish.

The LD50 of dioxin also varies wildly between species with the most notable disparity being between the ostensibly similar species of hamster and guinea pig. The oral LD50 for guinea pigs is as low as 0.5 to 2 μg/Kg body weight, whereas the oral LD50 for hamsters can be as high as 1 to 5 mg/Kg body weight, a difference of as much as thousandfold or more, and even among rat strains there may be thousandfold differences.