Speaking of pesticides, many people may directly associate with a “toxic” and “harmful” liquid medicine image. Of course, people who eat melons are afraid to avoid the pesticide ingredients in melons. < / P > < p > but what if there were no pesticides in the world? Then, according to a 2001 study in the Japanese Journal of crop science, total global crop production will be reduced by about 10%. This will not only lead to a sharp rise in food prices, but also increase the global famine. < / P > < p > most intuitively, pesticides left on agricultural products or accidentally contacted by farmers’ uncles are toxic. Taking a small amount of pesticide can make people feel dizzy and diarrhea, and taking a small sip may make doctors all over the world cry back. On the other hand, pesticides can also poison animals and plants, and destroying the ecology and soil is another major problem. < / P > < p > in 2009, the Ministry of environmental protection of China issued a joint announcement jointly with ten administrative departments, banning the pesticide “DDT”, which would cause great damage to the environment; in 2016, it was highly toxic to human beings and animals, and paraquat, a herbicide with a lethal rate of 90% if ingested more than 3 ml orally, was also banned. However, what we can not imagine now is how exaggerated the abuse of highly toxic pesticides is in the “wild age” of lack of relevant knowledge and backward technology. Arsenic, lead, sulfur Many harmful substances to human body are the pits that human beings have stepped on, some of which have even affected up to now. Since the 15th century, toxic chemicals such as arsenic, mercury and lead have been used in crops to kill pests. In the spirit of the fearless spirit of killing ten thousand enemies and losing three thousand, the western peasants and uncles freely sprayed all kinds of poisonous substances on the farmland and fruit trees. In contrast, the slow development of chemistry is a blessing in disguise. For thousands of years, “insect control pesticides” are nothing more than natural extracts such as mangrove, orpiment and oil. Of course, in the 19th century, the West also introduced pyrethrum from the Middle East, as well as natural and safe insecticides such as rotenone from Japan. (rotenone is also moderately toxic, and excessive intake can cause death) < / P > < p > the peak of human abuse of toxic pesticides occurred in the late 1800s. At that time, the west of the United States developed rapidly, and farms and orchards sprang up like mushrooms, covering the entire western territory. At the same time, the widespread invasion of codling moth has become the biggest headache for fruit growers, whose larvae will burrow into the fruit and cause it to rot rapidly. In order to combat the invasion of the moth, the U.S. Department of agriculture has vigorously promoted lead arsenate, a dangerous pesticide. Lead arsenate can kill all kinds of moths and even mosquitoes in orchards, but it can also do harm to humans and livestock. The harm of arsenic and lead has been discovered for a long time, but there was no better way to deal with pests at that time. So there was a very common common sense in the United States at that time – to wash the fruit with vinegar before eating it. However, we soon discovered an unfortunate fact: the resistance of pests is becoming stronger and stronger, and the fruit growers can only increase the dosage of drugs to drive away the “powerful pests”. < / P > < p > another problem brought about by the increase of pesticide dosage is that the pesticide residues on the surface of fruits can not be cleaned with vinegar. In 1919, researchers began to look for alternatives to lead arsenate. The search for < / P > < p > goes back to 1945. As a substitute for lead arsenate, DDT (disambiguation), which has been banned, is mentioned at the beginning of this paper. DDT is a kind of organochlorine insecticide. It was synthesized by Othmar Zeidler, an Austrian chemist, in 1874. However, it was not until 1939 that Swiss chemist Paul Hermann Muller discovered its insecticidal effect. In 1945, DDT began to be used as an agricultural insecticide in agricultural production, gradually replacing lead arsenate, which is very harmful to human body. DDT played an important role during World War II until the 1970s. It eliminated mosquitoes and helped humans control diseases such as malaria and dengue fever. It also eliminates pests and helps increase food production. It is a powerful assistant for farmers. < / P > < p > but soon, researchers who were constantly observing the environment discovered the problem – although DDT does little harm to humans, it does great harm to the environment. First of all, it almost indiscriminately kills insects, so many small animals like bees, which are beneficial to flower pollination, are also “poisoned”. Secondly, the modern method of spraying pesticide by airplane will make it fall into the pond and forest. Statistics show that all kinds of fish and birds also have the problem of reproductive decline and even direct death due to the accumulation of excessive DDT in their bodies – the biological chain has been seriously damaged. In 1971-1972, the United States held a seven month hearing, and scientists debated on the basis of their research results, and finally decided to abolish the use of DDT in most areas. The Stockholm Convention, which entered into force in 2004, banned the use of several persistent organic pollutants (POPs) worldwide, including the limitation of DDT’s application in agriculture. < p > < p > back to the original lead arsenate, although this pesticide was basically stopped in the United States as early as 1940s, the heavy metals contained in it were deposited on the surface of the earth’s surface – the impact is still today. Until the beginning of this year, a testing agency had detected different levels of lead and arsenic on more than 100000 acres in central Washington. With the support of contemporary scientific research, we have developed pesticide application to a relatively advanced level. Under the premise of effective weeding, insect repellent and sterilization, how to reduce the harm of pesticides to soil, other organisms and human beings as far as possible is an ideal direction that we pursue unremittingly. However, from the logical analysis of the natural operation of the earth, it seems to be an impossible proposition. Insects eat grass, birds eat insects, big fish eat small fish, human eat all The food chain is right in front of us. It seems that any toxic substances that human beings put into nature will eventually come back to us. However, it seems that we can solve this problem with the help of technology. One way is to create “molecular food”. As long as we ensure adequate intake of essential elements such as glucose and vitamins, we may find ways to make our own food, independent of the food chain.