The EPA's plan to bypass normal validation procedures for animal tests is especially troubling given the scientific concensus that there are enormous differences between animal and human endocrine systems. Dr. Robert Combes, scientific director of the Fund for Replacement of Animals in Medical Experiments in England, states, "[T]here are fundamental concerns about the validity of modeling human hormonal effects by using rodents. The endocrine system is extremely complex and there are many important species-specific differences between humans and rodents. For example, in contrast to humans, rodents do not produce sex hormone-binding globulin following parturition, resulting in reduced hormonal clearance. Other problems include strain and species differences in sensitivity, high levels of intralaboratory and interlaboratory variability, lack of suitable positive and negative controls, and responses detected with chemicals acting via mechanisms considered to be irrelevant to endocrine disruptors.” There are problems of "nonspecificity, lack of reproducibility, and lack of relevance."
The U.S. National Academy of Sciences echoes these concerns:
"There are important differences among species and between adult and developing organisms in their responses [to endocrine disruptors]. These differences could have important implications when assessing toxicity studies or extrapolating data from one species to another."
Since this statement was issued by the National Academy of Sciences, a number of reports have cast serious doubt on the relevance and reliability of animal experiments to predict potential human endocrine effects. Some of the concerns include:
- Different strains of rats and mice purposely bred for laboratory toxicity tests have displayed drastically different effects in preliminary endocrine disruptor testing. For example, one recently published study found a particular mouse strain to be 100 times more resistant to endocrine effects than other strains. This means that the results of endocrine disruptor testing may in large part be determined by which strain of animal the tests are conducted on.
- At a recent toxicology forum held in London, England, a prominent endocrine disruptor researcher reported that the housing conditions of animals used in endocrine disruptor experiments substantially affect test results. As one would expect, animals housed individually have much different hormone levels (including testosterone) than animals housed in large groups or in mixed-sex cages. These varying conditions have led to skewed results when researchers examine the animals' reproductive organs. For example, submissive male mice in a mixed sex cage develop smaller prostate glands than the dominant male, a phenomenon that can be mistakenly reported as an endocrine disruptor effect.
- The results of endocrine disruptor tests are substantially influenced by the position of animals when they are still in their mother’s womb. As a result, scientists who study possible developmental effects of endocrine disruptors in animals must deliver litters by Caesarian section while taking detailed notes on the relative positions of all the animals in the womb. A male animal positioned between two other male animals will have much different hormone levels than a male animal positioned between two females. The uncertainties surrounding this issue have already been cited by scientists who recently declared that some studies on bisphenol A, an industrial chemical, are not relevant to humans because of the particular way the animals were positioned in the womb.
- Some animal tests required in the endocrine disruptor program are based on measuring the relative weight of animals' organs after they have been dosed and killed. One of the tests, known as the "uterotrophic assay" requires the experimenter to cut out and weigh the uterus of the animal. Scientists have raised concerns with this test, stating that it is very likely that researchers in different laboratories will cut out the uterus in slightly different ways, thereby compromising the test results. In fact, the former chair of the EPA’s Scientific Advisory Board, Dr. Genevieve Matanoski, raised this issue at a recent meeting, stating, "You can’t go across labs because each lab tends to be unique—I find that a big problem."
More Problems With the Proposed Animal Tests
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