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Ecosystems and Human Health - Chapter 9

Thuốc trừ sâu Vì vậy, các nhà tự nhiên quan sát, trời có bọ chét nhỏ hơn mà trên ông con mồi; này có nhỏ hơn vẫn cắn 'em; Và như vậy tiến hành vô cùng tận. - Jonathan Swift Giới thiệu Thuốc bảo vệ thực vật hạn đề cập đến một cơ quan lớn của các hóa chất đa dạng bao gồm thuốc trừ sâu, thuốc diệt cỏ, thuốc diệt nấm, thuốc diệt loài gặm nhấm, và fumigants sử dụng để kiểm soát một hoặc nhiều loài được coi là không mong muốn từ quan điểm con người. . | chapter nine Pesticides So naturalists observe a flea has smaller fleas that on him prey And these have smaller still to bite em And so proceed ad infinitum. Jonathan Swift Introduction The term pesticides refers to a large body of diverse chemicals that includes insecticides herbicides fungicides rodenticides and fumigants employed to control one or more species deemed to be undesirable from the human viewpoint. Pesticides are of environmental concern for two main reasons. Although considerable progress has been made with respect to their selective toxicity many still possess significant toxicity for humans and many are persistent poisons so that their long biological t1 2 allows bioaccumulation and biomagnification up the food chain see Chapter 3 . Thus there is the possibility that besides constituting an ecological hazard they may enter human food supplies. By their very nature pesticides must have an impact on any ecosystem because they are designed to modify it by their selective elimination of certain species. As is always the case in considering chemicals used in the service of humankind there is a complex risk-benefit equation that must be taken into account when making decisions regarding the use of pesticides. There is no question that they have increased agricultural production when used properly and they have in the past been highly effective in controlling the insect vectors of human diseases such as malaria and yellow fever spread by mosquitoes and African sleeping sickness which affects both humans and animals and is spread by the tse-tse fly. As will be seen however these gains have not been without their problems. Efforts to control agricultural pests probably evolved in parallel with cultivation techniques. Early methods included manual removal of weeds and insects rigorous hoeing to prevent weed growth and the use of traps for animal and insect pests. The first chemical controls to be used against agricultural pests were the arsenical compounds.