消費者聯盟(Consumers Union)報導04.21.00

　　基因工程食品　-　你聽過它，但你可能不知道你是否正在食用它。它們是遺傳工程下的產物，靠著特別的技術，來自動物或植物遺傳物質中控制著特殊性狀的DNA小片段得以相接合，並被插入其他生物的遺傳物質中。生物科技公司正在運用各種技術，改變作物的遺傳訊息，以發展出號稱能長得更好、更營養或產量更大的作物。但這些技術所能帶來的利益仍令人存疑，此外，其對環境的衝擊及對食物來源的安全性亦漸受到關切。

　　目前，經改造過的玉米、馬鈴薯與棉花已可自行生產殺蟲劑(指已具有抗蟲基因) ; 在嵌入來自病毒的基因後，南瓜與木瓜已能抵抗病害 ; 大豆、玉米、油菜籽與棉花也已發展出對某些殺草劑的免疫力。除了農作物之外，基因工程尚被用來改造細菌，使之能夠生產出牛的成長荷爾蒙，以提升牛奶產量。加拿大的科學家將特定的老鼠基因給了豬隻，使豬糞中的含磷量降低，以減少養豬場對環境的衝擊。基因改造過的鮭魚能更有效的利用自身的成長荷爾蒙，成長速度因而提升了四到六倍。 在1999年，基因工程食品的大量生產才三年的時間，消費者聯盟就發現轉殖基因植物的產品以充斥市面，從嬰兒處方到玉米片，都有轉殖基因植物的存在。我們會到雜貨店和速食店購買的食品中，有許多是玉米或大豆的製品，而這兩種作物是轉殖基因之成品的可能性最大。目前已有方法可偵測樣品中是否含有某計量以上的基因工程產品。我們以此技術分析了食品中的DNA。即使商品上沒有任何這方面的標示，我們還是在以下的食品中發現了基因工程改造過了成份 : 

• 阿華田麥粉飲品速烹食品
• 貝寇斯培根調味片
• 布拉佛玉米片
• 老帕索12炸玉米餅
• 傑飛玉米鬆餅速烹食品
• 三種粉狀嬰兒食品 - 英菲蜜豆類營養品，席蜜拉愛思蜜大豆營養品與鵲　巢康乃馨添加品
• 七種品牌的豆製夾餅 - Boca Burger, Chef Max's Favorite, Morningstar Farms Better 'n Burgers, Green Giant Harvest Burger (現在稱為Morningstar Farms Harvest Burgers)，與紐約市部份麥當勞的Mc Veggie Burgers。

　　我們並非指稱食用這些產品是不安全的。然而，基於以下幾點原因，消費者聯盟仍對這些自然界中所不存在之基因工程食品抱持著疑慮的態度。

　　第一，基因工程會使得一種食物（如堅果）的過敏原轉移到另一種作物（如大豆）上。1990年代中期發現，經胡桃基因修飾的大豆帶有原先會使人對胡桃過敏的過敏原。還好，這個問題在大豆能賣入市場前就被發現。然而，現在卻沒有一套強制監控系統，以監測基因轉植作物中是否有其它的過敏原，並避免其流入市面。

　　另一個原因是基因工程可能會無意中增加了某些食物中天然毒素的含量，或是減低了其養份含量。目前，我們尚未完全瞭解不同基因在染色體中的角色，以及基因與基因間的關係。在染色體的某一位置上插入特定的基因，可能會影響控制其他功能之基因的表現，由此啟動一個正常情況下不會作用的機制，或者關閉一個對生物健康十分重要的機制。再加上現今的遺傳工程技術，並無法準確地將基因插入染色體的特定位置。這些事實使我們很難，或更常是不可能，完全預測在生物的染色體中插入的新基因會帶來什麼樣的衝擊。

　　一項想藉由轉殖一個可關閉寄主色素基因的人工合成基因，來抑制煙草與牽牛花顏色表現的研究，正是這種不確定性的經典案例。研究人員預期所有的轉殖基因植物會長出同一種顏色的花。然而，真正的結果卻是，這些植物不只花的顏色變了，連花色的分布也有所改變，其中一些改變更是不合時宜的。因此，我們對某個被插入的外來基因可能會增加植物的某種自然毒素，或是減低其養份的憂慮，也不是不可能的。

　　即使基因工程食品不會危害健康，但仍有有些徵兆顯示基因工程作物可能會傷害環境中的其他物種、減低生物多樣性、或造成骨牌效應而影響食物的供應，並可能因此影響到我們的健康。歐洲科學家的實驗發現，由基因工程作物所自行生產的殺蟲劑(由抗蟲害基因產生)可能踰越食物鏈，而傷害到如瓢蟲與草蜻蛉等肉食性的益蟲。康乃爾大學的一項研究顯示，經改造過而含有來自Bacillus thuringensis (Bt)菌之天然殺蟲基因的玉米，其花粉對實驗室中的帝王蝶(moncarch butterfly)是有毒的。由於這種轉殖基因玉米的花粉含有Bt毒，因此若是推廣此種玉米，任其花粉隨風飄散到世界各處，將會危害到環境中的帝王蝶與其他益蟲。

　　另一項疑慮是，基因轉殖作物中的抗病毒基因有可能會轉疑到野生種植物上，使雜草也具有抗病性，而變得難以防治。抗生素基因如果轉移到野生細菌上，將使微生物抗藥性的問題更加嚴重，對大眾健康造成威脅。其中最麻煩的是，一旦這些基因被釋放出來，就沒辦法再把它們收回來。

　　對於那些因宗教或其他因素而避免食用某些特殊植物或動物製品的人而言，基因工程也引起重要的倫理與文化問題。比如說，素食主義者可能會想避免取食帶有比目魚耐寒基因的蕃茄。把人類基因轉殖到動物體內（這在實驗室內已成功了），則會引起更嚴重的倫理問題。

　　你可能會懷疑，既然問題這麼多，那麼會什麼還要汲汲營營地把轉殖基因食物推向商業市場？生物科技的提倡者說基因工程會降低殺草劑的使用量、增加產能、拯救世界饑荒。但目前的研究顯示，生物科技離這些高尚的目標還遠得很。1996年到1998年的研究顯示生物科技用於作物改良上的成效因地而異。某些地方因此科技而增加產量，但在某些地方卻適得其反。降低對除草劑之需要量上的成效也是因例而異的，在某些例子上，控制標的性雜草（指轉殖基因所能抑制的雜草）的除草劑用量雖因基因轉殖而得以降低，但防制其它非標的性有害生物之化學藥劑的用量卻不降反升。

　　在有適當的防護措施之下，基因工程可能真的能為農人與消費者提供莫大的好處，但當今的防護系統卻未臻完備。消費者聯盟相信基因工程食品在打進市場前必須強制性接受由聯邦政府制定的人類安全檢驗。然而，目前這些檢驗都是自發性的。此外，這些食品還應該受到完整的環境安全檢驗。

　　最後，所有的基因工程食品都應該在包裝上標識清楚，讓消費者知道他們所選購的產品為何。現在的標籤只能告訴消費者柳橙汁是新鮮的或是濃縮的。要求製造商據實標識他們產品的基因是否經過人工操作應是項合理的要求。

更多有關基因工程食品的資訊可以在1999年9月的消費者報導中找到。
原文詳見 : http://www.gristmagazine.com/grist/possessions/cu042100.stm
版權歸屬 Earth Day Network，環境信託協會 (謝洵怡 譯，吳海音審校)

Do we know enough about genetically modified foods?

Consumers Union 04.21.00 

Genetically modified foods -- you've heard about them, but you probably don't know whether you're eating them. They're produced by splicing genes, those little segments of DNA that code for particular traits, from one plant or animal species and inserting them into another. Biotechnology companies are cooking up all sorts of techniques to engineer organisms in ways that they claim could make crops easier to grow, foods more nutritious, and production more efficient. But the jury is still out on the actual benefits these techniques will bring and there is growing concern about their impact on the environment and the security of our food supply.

Corn, potatoes, and cotton have been made to produce their own pesticides; squash and papaya can fight disease thanks to genes from a virus; and soybeans, corn, canola, and cotton have been rendered immune to certain weed-killing chemicals. Beyond crops, genetic engineering has been employed to make bacteria that produce bovine growth hormone to boost milk production in cows. Canadian scientists have given pigs a mouse gene to reduce the phosphorus in their manure in order to lessen the environmental impact of farm runoff. Salmon have been modified to use more of their own growth hormone to increase in size 400 to 600 percent faster than their natural counterparts.

In 1999, just three years after the first large-scale harvest of genetically engineered crops, Consumers Union found transplanted genetic material cropping up in a wide variety of products from infant formula to nacho chips. We went to grocery stores and fast food restaurants and bought a number of foods made with corn or soybeans, the two crops most likely to be genetically engineered. Using a methodology powerful enough to detect engineered ingredients present at more than trace levels, we had the DNA of these foods analyzed. Even though none were labeled to indicate it, we found genetically engineered ingredients in the following products:

• Ovaltine Malt powdered beverage mix 
• Bac-Os Bacon Flavor Bits 
• Bravos Tortilla Chips Nacho Nacho! 
• Old El Paso 12 Taco Shells 
• Jiffy Corn Muffin Mix 
• three powdered infant formulas -- Enfamil ProSobee Soy Formula, Similac Isomil Soy Formula, and Nestle Carnation Alsoy 
• several brands of soy burgers, including Boca Burger, Chef Max's Favorite, Morningstar Farms Better 'n Burgers, Green Giant Harvest Burgers (now called Morningstar Farms Harvest Burgers), and McDonald's McVeggie Burgers, sold in select outlets in New York City 

We don't suggest that it is unsafe to eat these products. However, Consumers Union believes there are other reasons to be concerned about new hybrid products that nature could never produce on its own.

For one thing, genetic engineering makes it possible to transfer allergenic properties of one food, like nuts, to another food product, like soybeans. In the mid-1990s soybeans that were modified with the gene of a Brazil nut were found to contain the allergen that makes some people allergic to the nuts. Fortunately, this problem was identified before the soy went to market. However, there is currently no mandatory screening process to guarantee that other, perhaps less anticipated, allergens are detected and kept off the market.

Another concern is that genetic engineering could inadvertently increase natural toxins or decrease nutrient levels in some foods. The exact role of different genes in a chromosome and the importance of the relationship of one gene to another are not well understood. The location on a chromosome where genetic material is inserted may affect the expression of other genes that control other functions, turning on a process that otherwise wouldn't occur, or turning off a process critical to the health of the organism. This, coupled with the fact that modern genetic engineering techniques are fairly imprecise in terms of where the genes get placed within a chromosome, makes it difficult, and in many cases impossible, to fully predict the impact of inserting new genetic material.

A classic example of this unpredictability involved an attempt to suppress the color of tobacco and petunia flowers via the transfer of a synthetically created gene designed to turn off a host pigment gene. The expected outcome was that all the transformed plants would have the same color flowers. The actual result, however, was that the plants' flowers varied not only in color but in color pattern, and some changed color or color pattern unexpectedly with the seasons. It's not too far-fetched to imagine a similar scenario whereby an inserted gene could cause an increase in levels of a naturally occurring toxin generated by a plant, or a decrease in levels of nutrients.

But even if foods aren't engineered in ways that present health risks, there are emerging signs that genetically engineered crops may harm other species in the environment and decrease biodiversity, potentially creating a domino effect that could threaten our food supply and possibly harm our health in other ways. Laboratory studies by European scientists have found that pesticides made by genetically modified crops can be passed up the food chain and harm ladybugs and green lacewings, two beneficial predatory insects. Findings from Cornell University show that, in the laboratory, pollen from corn engineered to contain a natural pesticide from Bacillus thuringiensis (Bt) bacterium is toxic to the monarch butterfly. Because every grain of pollen produced by the engineered corn contains the Bt toxin, the risk to the monarch and other beneficial insects is dispersed into the environment as the pollen blows in the wind.

Other concerns relate to the possible transfer of virus-resistance genes from cultivated plants to their wild relatives, potentially creating weeds that are even more difficult to control. The transfer of antibiotic genes into wild bacteria could increase the growing problem of antibiotic-resistant microbes that would in turn pose an even greater threat to public health. What's most troubling is the knowledge that once these genes have been released into the world, there's no way to take them back.

Genetic engineering also raises important ethical and cultural concerns for those who seek to avoid eating particular plants or animal food products for religious or other reasons. Vegetarians might want to avoid tomatoes engineered to resist cold with flounder genes, for example. The potential for inserting human genes into animals, as has been accomplished in laboratory experiments, raises even more serious ethical questions for many people.

So with all these problems, you might wonder what's driving the rush to get genetically modified foods on the market. Biotech proponents say genetic engineering will reduce the need for weed-killing chemicals, improve yields, and help curb world hunger. But research has thus far failed to show that biotechnology is capable of achieving such lofty goals. Studies from 1996 through 1998 show different results for different regions. In some cases yields increased, whereas in others they declined. The need for herbicide treatments also varied and in some cases where treatments for "target" organisms declined, greater amounts were needed to fight non-target pests.

With proper safeguards, genetic engineering could offer potential benefits to farmers and consumers, but the current safeguards simply aren't sufficient. Consumers Union believes that genetically modified foods must be subject to mandatory federal human-safety reviews before they hit the market. Today such reviews are voluntary. The foods should also go through comprehensive environmental-safety reviews.

Finally, all genetically modified foods should be labeled so consumers can make informed choices about what they eat. Labeling is now required to tell consumers whether orange juice is fresh or from concentrate. It's only logical to require food producers to disclose whether the genes in their products have been artificially manipulated.

More information on genetically modified foods can be found in the September 1999 issue of Consumer Reports.
http://www.gristmagazine.com/grist/possessions/cu042100.stm