• [热点科普] 通俗解读法国转基因玉米喂食白鼠实验 -湘西山民- ♂ 
(9096 bytes) (48 reads) 9/21/12
最近媒体热炒法国转基因玉米喂食白鼠实验.这样的实验本来应该很有意义,因为转基因食品的安全性是大家都关心的问题。但是这个实验的设计却有很大问题，因而得出的结论不可靠。
实验的设计有哪些问题呢？
1) 实验选用的白鼠品种,本身就容易长肿瘤。实验结果表明不喂食转基因玉米的白鼠，也长了肿瘤。
2）实验虽然用了200只白鼠，但每组只有10只。从统计上，这样的结果没有代表性。好比抛掷硬币，我们都知道得到正面的概率是50%。 但是这个结果要抛掷足够多的次数之后才能得到。抛1，2，3，4，5次，得到的结果可能与 50% 相差甚远。下图引自原始论文。大家可以看到喂食转基因玉米多（0，11%，22%，33%）的白鼠，反而死得晚（少）！这个结论当然不靠谱，原因是样本太少。
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Fig. 1. Mortality of rats fed GMO treated or not with Roundup, and effects of Roundup alone. Rats were fed with NK603 GM maize (with or without application of Roundup) at three different doses (11, 22, 33% in their diet: thin, medium and bold lines, respectively) compared to the substantially equivalent closest isogenic non-GM maize (control, dotted line). Roundup was administrated in drinking water at 3 increasing doses, same symbols (environmental (A), MRL in agricultural GMOs (B) and half of minimal agricultural levels (C), see Section 2). Lifespan during the experiment for the control group is represented by the vertical bar ± SEM (grey area). In bar histograms, the causes of mortality before the grey area are detailed in comparison to the controls (0). In black are represented the necessary euthanasia because of suffering in accordance with ethical rules (tumors over 25% body weight, more than 25% weight loss, hemorrhagic bleeding, etc.); and in hatched areas, spontaneous mortality.
3）论文中喂食白鼠草甘磷组的容许量，是饮水中人体的容许量。白鼠的体重多少？人的体重多少？对相关毒性的耐受量是什么关系？ 一般动物毒性试验的结果外推倒人身上，第一要考虑体重，第二要考虑物种差别。光从体重的角度，老鼠喝一两白酒和和人喝10斤白酒的结果大致一样（5两重的 老鼠和500两重的人比较）。
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参考文献：
[1] Claims of GM foods 'link to cancer' disputed by other researchers（http://www.nhs.uk/news/2012/09September/Pages/Claims-of-GM- foods-link-to-cancer-disputed-by-other-researchers.aspx）
[2] Séralini G, Clair E, Mesnage R et al. Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize. Food and Chemical Toxicology. Published online September 19 2012
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This study is reported to involve the highest number of rats regularly studied in a GM-diet study. The research also benefits from testing three different dietary concentrations of GM maize over a two-year period, along with GM maize treated with and without Roundup and Roundup alone diluted in water. All the rats in these groups were compared with rats fed only untreated, non-GM feed. The researchers also said that the Roundup concentration in water started at a dose below the range of levels permitted by regulatory authorities.
Animal research such as this is highly valuable for looking at the possible toxic effects. However, claims that GM food may have a similar toxic effect in humans cannot be justified using the results of this study, which many experts argue was poorly conducted.
There are several significant limitations to the research, including the following:
- Although the study did include a large number of rats overall, there were only 10 males and 10 females in each group. All comparisons were made with just one control group of 10 male rats and 10 females, and a larger group of control rats may not have given identical average lifespan and health data. Such a small control group makes it more likely that the results are due to chance.
- Humans are biologically different from rats, and we may not have identical susceptibilities to disease and illness.
- One expert argument was that the rats in this study were a breed already susceptible to tumours, especially if they are given unlimited access to food. This seems plausible as the rats are described to have been virgin albino Sprague-Dawley rats; however, their tumour susceptibility is not discussed in the paper.
- The method of statistical analysis used to assess the results was described by the researchers as being a "robust method for modelling, analysing and interpreting complex chemical and biological data", but is complicated and fairly impenetrable, even to those with training in statistics.
- The rats were fed a regular, concentrated diet of the test substance, and how this dose relates to any human intake is unclear.
- This two-year period roughly equated to a rat’s lifetime. It is difficult to equate this directly to humans. Does it represent lifelong, daily consumption of GM foods treated with herbicides, and at what age adverse effects – if any – may be expected to be seen in humans?
The very unusual way in which the trial was conducted makes it hard to lend much weight to its conclusions. In any case, given the public hostility to GM foods in the UK, it is unlikely that supermarkets are going to start stocking GM foods on the shelf any time soon.
Research and debate into the safe levels of GM foods and herbicides in the diet is likely to continue.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.
Links to the headlines
Cancer row over GM foods as French study claims it did THIS to rats... and can cause organ damage and early death in humans. Daily Mail, September 20 2012
GM crop enquiry launched by French government. The Daily Telegraph, September 19 2012
French GM-fed rat study triggers furore. BBC News, September 19 2012
Links to the science
Séralini G, Clair E, Mesnage R et al. Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize. Food and Chemical Toxicology. Published online September 19 2012
