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Trong nửa cuối của thế kỷ XX, người ta phát hiện rằng một số các chất ô nhiễm hữu cơ có tác dụng phụ có hại trong hệ sinh thái tự nhiên, nổi bật trong số đó có hóa chất độc tính cao (gây chết người hoặc sublethal) kết hợp với sự bền bỉ sinh học được đánh dấu. Ví dụ như dieldrin, DDT, TBT và methyl thủy ngân là một phần chính của phần thứ hai của văn bản này. Sau khi những phát hiện, hạn chế và cấm khi phát hành của họ vào môi trường đã được. | CHAPTER 15 The environmental impact of organic pollutants future prospects 15.1 Introduction During the second half of the twentieth century it was discovered that a number of organic pollutants had harmful side-effects in natural ecosystems prominent among them chemicals that combined high toxicity lethal or sublethal with marked biological persistence. Examples such as dieldrin DDT TBT and methyl mercury constitute a major part of the second section of the present text. After these discoveries restrictions and bans upon their release into the environment were introduced in many countries. Persistent organochlorine insecticides for example were withdrawn from many uses and replaced by less persistent OP and carbamate insecticides. More stringent legislation was brought in to control the production and marketing of new chemicals with clearer guidelines for environmental risk assessment. Particularly strong rules were applied to new pesticides something of a double-edged weapon. More stringent regulations may be expected to reduce the risk of new persticides causing further problems but they also make the discovery and registration of newer more environmentally friendly compounds a more costly and time-consuming business. Thus they can discourage the development of more environmentally safe pesticides than those currently in use. 2001 C. H. Walker 246 Further issues and future prospects Looking ahead two major issues present themselves. 1 What changes may be expected in environmental risk assessment practices to evaluate new pesticides and industrial chemicals 2 What improvements are likely in the techniques and strategies used to investigate existing complex pollution problems As explained earlier in the text section 4.5 the central concern is about effects at the level of population or above but this can be very difficult to establish let alone to predict. These issues will be discussed in the sections that follow. 15.2 The design of new pesticides It is not .
