Virtually all of the "scary" work on endocrine disruptors has been based on overblown findings in rodent studies. Although many of us think we know some human rats, the fact is that:
Rodents are not good models for human fetal germ cell development and, in view of the contrasting effects of phthalates on certain fetal characteristics in rats and mice, it is unclear whether the rat is a suitable model for the human. {Mitchell R, Cowan G, Morris KD, Anderson RA, Fraser HM, Mckenzie KJ, Wallace WHB, Kelnar CJH, Saunders PTK, Sharpe RM. Germ cell differentiation in the marmoset (Callithrix jacchus) during fetal and neonatal life closely parallels that in the human. Hum Reprod 2008; 23:2755-2765.}
As such, the marmoset, a non-human primate, was used in a recent study to investigate if phthalate exposure can affect testis development. { McKinnell C, Mitchell RT, Walker M, Morris K, Kelnar CJ, Wallace WH, Sharpe RM. Effect of fetal or neonatal exposure to monobutyl phthalate (MBP) on testicular development and function in the marmoset. Hum Reprod 2009 Jun 2. [Epub ahead of print] }
This study comprised two portions, one in which pregnant marmosets were dosed with monobutyl phthalate (MBP), and another in which newborn males were dosed with the same amount of MBP per body weight.
No measurable effects were observed in either portion of the study.
That's right: Despite doses of 500 mg/kg of body weight per day, nothing happened.
I wonder what Freddie vom Saal, Shanna Swan, and the Mount Sinai School of Medicine crew (all charter members of the endocrine disruptor gang) have to say about this?Listen to Chris Bryant, managing director of the American Chemistry Council:
"This new research adds significantly to earlier work, and increases the overall weight of scientific evidence that suggests primates, which include humans, are more resistant to the effects of phthalates than are lab rodents. Japanese research published in 2006 by Tomonari et al showed that huge doses of a phthalate that can affect rodents showed no testicular effects in developing infant marmosets. It is worth noting that there are significant differences even between rats and mice in the way they react to phthalates. So it is not at all surprising that there would be significant differences between rodents and primates."
Rodents, of course, have long been favored by researchers since they are cheap, don't take up too much space, and are easy to care for—and kill, for that matter. The problem is that rodents are not humans.
Sad to say, non-applicable rodent endocrine disruptor results are only the tip of the iceberg. Untold billions have been spent on cancer therapies that cure mice, but not humans.
It's long past time that we leave the rats and mice on the sinking ship of useless rodent results.
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