- 期刊
基轉植物之生物安全性評估及管理
Experiments for Studies on the Management of the bio-safety of Transgenic Plants
摘要
基轉植物栽培面積日益擴大，種類也日漸增多，為澄清對基轉植物安全性之疑慮，世界主要已開發國家及部份開發中國家都已制定了對基轉生物（包含動植物）的管理法規，以期在上市前進行必要安全評估工作。 各國所訂定之管理法包含二大方向：一是作為食品之安全性；二是對環境衝擊之風險評估。不論是進行那一方面的評估，對轉殖基因之來源、轉殖基因之特性、轉殖基因之功能機制及表現方式、該基因調控產物之理化特性、基因載體、基因之殖入方式、該基因在受體植物細胞內之位置及其表現之穩定度等都必需先要能完全的掌握。在作為食品時之安全評估方面，最重要的是要証明源自基轉植物之產品與傳統產品有實質之同等性。換句話說，轉入之外源基因或基因產物對人畜無毒，轉入之基因應不屬可調控過敏源產生者，另外還要考慮營養物質和基因產物之含量等。這些評估因子都可藉動物毒理試驗及化學分析等已成熟之標準試驗規範來進行，所以困難度不高。這類的資料可以通用，而不受國家或地區之不同而有差異。在對環境的衝擊風險評估方面，受體植物之一般特性、繁殖方式、栽培管理方式以及栽培地區都有密切的關係。評估的結果可能會有地區性的差異，某國家所得的結果可能不適用於另外的國家。對環境衝擊的風險評估包括有下列數點：一、受體植物對生態之影響，其內容包括對病害、蟲害或其他昆蟲、動物族群消長之影響。二、轉殖基因植物野化而演變成雜草之可能性或機率。三、轉殖基因流佈到近緣野生種或環境微生物之可能性及機率。受體植物對病害、蟲害或其他昆蟲、動物族群消長影響之風險評估試驗可根據農藥效果試驗規範之方法作為借鏡，並可將這些影響量化作為評估之用。唯不同地區關鍵病蟲害、有益昆蟲生態以及動物之食物鏈都不一樣，所以測試之對象也會不同，這在準備開拓國際市場時宜特別注意。轉殖基因植物演變成農田雜草之可能性或機率方面，可以室內控制下的試驗來比較受體在獲得新的基因後會不會增加其生存競爭力，在生長勢、抗逆境、種子產量和生命力等方面是否比非轉殖植株強。若轉基因植物可以在自然生態條件下生存，勢必會改變自然的生物相，打破生態的平衡，尤其其母本植物原本就是普遍存在的野生種。在轉殖基因流佈到近緣野生種或環境微生物之可能性及機率方面，首先必需先作詳細的調查，在該轉殖植物環境釋放區鄰近有無近緣野生種的分佈，有些栽培植物會和周圍生長的近緣野生種發生天然雜交，而將轉入基因流佈到野生種中，並在野生種中傳播。若基因的產物具有生物活性，可能會增加野生種的競爭力而造成對環境的衝擊，若僅為改善品質者可能影響較少。 上述風險評估工作數據的收集，似都可先就單一因子按標準操作規範先作室內的試驗以取得量化的結果，再在模擬自然環境的控制條件下作複合因子的試驗，最後才進入田間觀察試驗。基轉植物對環境衝擊的風險評估與農用化學品的風險評估一樣，包含有五個步驟：一、基因及受體植物特性必須徹底瞭解；二、根據其要栽培的環境，近緣野生植物之種類、生態等資料進行可能產生之危害分析，可能的話應擬定評估的標準；三、進行此基轉植物在環境中流佈(含野化，基因流佈等)以及其生物效應之分析；四、根據上述資料進行風險評估，說明風險的特徵及可能產生危害的機率；五、進行風險管理，包含風險／利益比、本/益比、公眾評價、研究、監控以及減少風險策略之擬訂等。基改植物之食品安全評估應無地域上的差異，但基改植物對環境衝擊之風險評估則有地域上的差異，每個國家的管理辦法雖大同小異，但因栽培的環境不一樣，其要求的試驗資料也會不同，因此基轉植物應視市場個案準備環境風險評估之資料。現階段如何積極培養風險評估及風險管理人才，推動風險溝通制度，慎選基轉植物研發對象是當前之首務。
並列摘要
In recent years, the cultivation acreage of genetically modified (GM) crops has sharply increased. To ensure the safety of GM plants, most developed and some developing countries have established criteria to manage the risk before those products are released to the environment and are consumed as foods. The criteria for the safety evaluation of transgenic plants contain 2 main aspects: the first is the safety of GM plants as foods, and the other is the impact of transgenic plants on the environment. Regardless of what kinds of safety evaluations are going to be carried out, the most important step is to fully understand the characterization of the GM plant and the function and mechanism of the transgenes. The concept of substantial equivalence is an important component of the safety evaluations of foods and food ingredients derived from GM plants. This concept embodies a science-based approach in which a GM food is compared to its existing appropriate counterpart. The approach is not intended to establish absolute safety, which is an unattainable goal for any food. Rather, the goal of this approach is to ensure that the food and any substances that have been introduced into the food as a result of genetic modification are as safe as its traditional counterpart. Main factors taken into account in the safety assessment include: the toxicity and allergenicity of foods derived from genetically engineered plants. The methodology for toxicological studies and existing chemical analytical methods for food quality control could be adopted to evaluate the safety of transgenic foods. Other countries commonly accept the data obtained from evaluations based on the international standard of ”good laboratory practice”. The second aspect concerns evaluation of the impacts of genetically modified plants on ecosystems. In order to reduce risks of environmental impacts of transgenic plants, there are 3 primary categories which might be considered: the weediness of transgenic plants and/or their filial generations, the transfer of transgenes to crop relatives (gene flow), and adverse effects of transgenic plants on non-target organisms. Different genetically engineered plants will present different problems depending on the new genes are inserted, the characteristics of the parent crops, and the locales in which they are grown. For future risk assessments, a rational stepwise approach is necessary. First of all, knowledge of the crop and its wild relatives, knowledge of the biogeographical situation, and knowledge of the transgene have to be taken into account. An impact analysis for examining the likely effects on non-target organisms should consider: (1) those species reliant on the crop itself, whether through using it for food or shelter; (2) those plants and animals that live within the field and which might be damaged if changes are made to the crop that modifies their habitat or their ability to survive; (3) plants and animals living in the field margin or hedges and walls, if the management of the crop modifies the size, extent, or susceptibility to herbicides and pesticides of this field area; and (4) those soils and soil organisms which may be affected by changes in plant varieties or management. According to the US-EPA suggestions, we can follow the guidelines concerning evaluation of the adverse effects on non-target organisms of biopesticides. For the risk assessment of the weediness of transgenic plants, it is necessary to understand the competition of transgenic plants with other members in the ecosystem before they are released to the environment. Those agronomic characterization studies usually have to be carried out under controlled conditions or in semi-field conditions. For the risk assessment of the transfer of transgenes to crop relatives (gene flow), it is necessary to determine whether there are any close relatives in the environment in which the transgenic plants are going to be released and the possibility of transfer of inserted genes by any form of vector. The principles and procedures for ecological risk assessment of transgenic plants are based on experience for predictive risk assessment of chemicals or agrochemicals. Five stages in the ecological risk assessment should be considered. (1) Characterization of transgenic plant and the inserted gene. General information on the receiver plant and the inserted trait should be collected, the information evaluated, and additional data needs of the receiver plant should be identified. (2) Hazard identification. This stage in a predictive risk assessment of transgenic plants is to identify and analyze the hazards involved including measurement variables (i.e., endpoint definition), description of the environment, and the terms for the release. The main questions are: What is at risk in the environment? And how should the effects be defined? If possible, it is necessary to draw up standards for risk assessment. (3) Analysis of occurrence and effect. For transgenic plants, the concept of ”occurrence” could refer to the product of relevant probability factors, e.g., the probability for gene transfer, hybridization, and dispersal of plants into new areas over time. Studies of effects in ecological risk assessment have mainly been done at the species level, but tests of effects at population and ecosystem levels are needed and would be of perhaps greater use. (4) Risk estimation. Estimates of risks can be derived from data on occurrence probabilities and data from tests on effects of the release. Hence, occurrence probabilities for different scenarios (e.g., gene-flow, invasion) and level of effects should be given. (5) Risk management. Risk management involves the decision making which attempts to minimize the undesired effects of a hazard. It involves political issues as well as practical precautions and restoration measures. Valuation of the ecological resources at risk depends on different considerations, which must be balanced. Analytic procedures such as cost-benefit may be included. Testing of the transgenic crop should follow a step-by-step procedure evaluating data of the first phase before continuing into the next phase. The more risky the crop and/or the transgene, the more stringent the testing scheme should be before the transgenic crop can be allowed to be grown commercially on a large scale. But in the end, 1 dilemma will remain: even after the most-careful risk assessment process, only a mass release will bring all effects to the surface. Small-scale field trials do not allow investigation of the ecological risks of widespread commercialization. Therefore in order to achieve sustainability in cultivating transgenic crops, the focus should be on long-term monitoring of several years in the same field where the transgenic crop is planted. Risk assessments of the impacts of transgenic plants on the ecosystem should be carried out on a case-by-case basis depending on the eco-environment to which the plant is going to be released. For the time being, standard operating procedures (SOPs) must urgently be established for the risk assessment of transgenic plants, specialists must be trained concerning risk assessment and risk management, and appropriate communication channels among researchers should be strengthened. Finally, determining how to select target plants for transgenic studies to avoid complications of regulatory requirements is also important work.