Toxic relationships

Citation: Gestational and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin affects social behaviors between developing rhesus monkeys (Macaca mulatta). T Negishi, H Shimomura, T Koyama, K Kawasaki, Y Ishii, S Kyuwa, M Yasuda, Y Kuroda, and Y Yoshikawa Toxicol Lett, Jan 2006; 160(3): 233-44.

Summary of Experiment: Forty-nine pregnant monkeys were injected with different doses of dioxin every thirty days from the third week of pregnancy until 3 months after delivery. From 1-2 ears of age, the babies performed tests to assess learning ability, social skills and response to novel and stressful events. Social skills were the only variable affected, and differences decreased over time. The dioxin monkeys seemed not to be afraid of things that elicited fear in normal monkeys. This same phenomenon had already been documented in earlier papers (Schantz AND Bowman, 1989; Schantz et al., 1992). They claim that the differences between those results and their own were due to differences in the behavioral tests used.

My Notes:

• Dioxin is the most potent animal carcinogen ever tested, as well as the cause of severe weight loss, liver problems, kidney problems, birth defects, and death. We already know that dioxin causes damage to development, reproduction, and the immune and endocrine systems at infinitesimally low doses (in the low parts per trillion). Toxicological studies have not been able to establish a "threshold" dose below which dioxin does not cause harmful effects.


• The authors indicate that monkeys may be able to overcome the toxic effects of dioxin during development, because some social behaviors changed. However, it’s equally possible that the initial effect was due to novelty, and continued tests with novelty may have revealed persistent effects.


• Experiments were done at an SNBL facility. Female are housed individually most of the time, but with a male 3 days per month if they are not already pregnant.
  Babies were weaned at 13-14 months (much better than 5 months of age in the prior test), but thereafter were housed individually.


• Some of the methods were funky – they didn’t count non-responses to the test environment as a “trial,” which could lead to habituation, etc. In some tests, they are using groups of 3 and 4 monkeys, in others 28…you can’t just pick and choose like that and then argue that the statistics mean anything.


• Their conclusions are wacky:
  

  “However, the results might serve as a warning to humans of potential alterations by perinatal exposure to TCDD in developing social behaviors, and these alterations might not be necessarily considered as apparently negative effects such as learning disability and psychological disorders.”

Author affiliations: University of Tokyo

Funding acknowledged: Core Research for Evolutional Science and Technology (CREST) program of the Japan Science and Technology Agency.