Due to financial and logistical constraints, researchers usually use only a few hundred rats to test a particular carcinogen. They typically determine which dose causes about 10% of rats to develop cancer. Then they extrapolate down several orders of magnitude to estimate what dose would cause acceptable above-background cancer rates in people, leaving much room for error.
Since the cost of caring for trout is about 5% of the cost of caring for rats, researchers can use many more trout to test carcinogens. For example, George Bailey of Oregon State University (Corvalis) and his team tested the carcinogen Dibenzol [a, l] pyrene (DBP) at ultra-low doses of 0-225 ppm in 40,800 rainbow trout for 4 weeks and then fed them a normal diet for 9 months (Chem. Res. Toxicol. published online 18 May 2009; doi: 10.1021/tx9000754). They found that a DBP dose of 0.45 ppm caused an additional 0.02% of trout to develop liver cancer.
Bailey’s team then estimated the dose of DBP that would cause an additional one liver tumor in 1,000,000 people and found it was 500-1,500 times higher than that predicted from higher-dose DBP experiments in rats. This means that some carcinogens could be safe at levels far higher than currently thought. Additionally, researchers might need to re-evaluate how to best assess carcinogen toxicity. Exactly where trout fit into the picture remains to be seen.
Taken from LabAnimal Magazine, Vol.38 No.8 / August 2009
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