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Liu Changling: Treating pesticides with fear is a prejudice.

Release Date:

2019-03-05

http://derui.ztouch-make-hn-16216.shushang-z.cn/news_detail/newsId=266.html “In the past, people had no choice but to rely on pesticides to secure their food supply, so they were indispensable. Today, with food readily available, we’ve begun to consider issues such as pesticide residues, risks, and environmental pollution—this is entirely justified. However, that doesn’t mean we should dismiss the essential role of pesticides in agricultural production,” said Liu Changling, Chief Scientist at Sinochem International’s Innovation Center, in a recent interview with a journalist. He added that people’s knee-jerk aversion to the word “pesticide” actually stems from a misunderstanding of agriculture…

http://derui.ztouch-make-hn-16216.shushang-z.cn/news_detail/newsId=266.html “In the past, people had no choice but to rely on pesticides to secure their food; today, with food readily available, we are beginning to consider issues such as pesticide residues, risks, and environmental pollution—this is entirely justified. However, this does not mean we should dismiss the essential role of pesticides in agricultural production,” said Liu Changling, Chief Scientist at Sinochem International’s Innovation Center, in a recent interview with a journalist. He added that the widespread fear surrounding “chemicals” often stems from deeply ingrained biases against pesticides.

　　Liu Changling was born in Henan in 1963. He formerly served as the Chief Engineer at the Shenyang Research Institute of Chemical Industry and currently holds the position of Chief Scientist at the Sinochem International Innovation Center. He also serves as the Chairperson of the Pesticide Professional Committee of the Chinese Chemical Society and the Director of the National Engineering Research Center for Pesticides (Shenyang). In 2014, his research team developed the “intermediate derivatization method” for green pesticide molecular design and variety creation, which was published in the top-tier chemistry journal Chemical Reviews.

　　Sinochem International (Holdings) Co., Ltd. originated from the rubber, plastics, chemical products, and storage-and‑transportation businesses of Sinochem Group. Established in Beijing in December 1998, the company currently focuses on intermediates and new materials, agrochemicals, polymer additives, natural rubber, and other related fields. In March 2000, Sinochem International was listed on the Shanghai Stock Exchange.

　　Agricultural chemicals refer to chemical agents used in agriculture to control pests, diseases, and weeds, as well as to regulate plant growth. Classified by type, they include insecticides, acaricides, fungicides, herbicides, and plant growth regulators, among others.

　　The public turns pale at the mention of “medicine,” a reaction rooted in highly toxic pesticides such as phorate.

　　Liu Changling believes that the public’s apprehension whenever “pesticides” are mentioned is largely shaped by past incidents involving highly toxic pesticides. In the early days, China’s pesticide portfolio consisted primarily of highly toxic organophosphate insecticides, leading people to equate insecticides with pesticides as a whole. However, in reality, those truly alarming “pesticides” have long since been phased out.

　　In the past, many insecticides produced in China belonged to the organophosphate class, including commonly used compounds such as parathion (1605), phorate (3911), demeton‑S‑methyl (1059), and dichlorvos. Among these widely employed organophosphate pesticides, based on the acute oral median lethal dose (LD50) in rats—where a lower value indicates greater toxicity—demeton‑S‑methyl exhibits an LD50 of 4 to 10 mg/kg, while phorate has an LD50 ranging from 2.1 to 3.7 mg/kg, both classified as highly toxic.

　　Based on the toxicity of commonly used agricultural pesticides (active ingredients), classified according to their acute oral LD50 values, they are divided into five categories: highly toxic, highly toxic, moderately toxic, slightly toxic, and practically non‑toxic. According to statistics, currently in China, 94% of approved pesticides fall into the low‑toxicity or practically non‑toxic categories, while 5% are classified as moderately toxic.

　　In 2002, the former Ministry of Agriculture issued an announcement prohibiting the use of highly toxic pesticides such as parathion‑methyl (1059) and phorate (3911) on vegetables, fruit trees, tea plants, and Chinese medicinal herbs.

　　Liu Changling noted that another pesticide once struck fear into people’s hearts: DDT. In the history of pesticides, DDT was the first artificially synthesized, broad-spectrum, and highly effective organochlorine insecticide. In 1939, a Swiss chemist first discovered that DDT could be used as an insecticide, and in 1948 he was awarded the Nobel Prize in Physiology or Medicine. From then on, organochlorine pesticides—led by DDT—became a crucial tool for boosting food production, reducing crop losses by roughly one-third of the world’s total grain output each year.

　　Around the 1970s, China introduced DDT. After decades of global use, it became clear that DDT‑based pesticides exhibit high stability and persistence; even six months after application, DDT residues can still be detected in agricultural soils. Moreover, DDT readily bioaccumulates in the adipose tissues of both humans and animals.

　　China banned DDT in 1982, but it continued to use the substance for emergency vector control, as well as in the production of dicofol and antifouling paints. In 2009, the former Ministry of Environmental Protection issued an announcement prohibiting the production, circulation, use, and import or export of DDT within China, while retaining the possibility of its use for vector control in emergency situations.

　　The toxicity of DDT‑type pesticides stems from bioaccumulation: when residues remain, the human body cannot metabolize and eliminate them, leading to their buildup within the organism and resulting in high toxicity. Liu Changling explained that, today, if a pesticide is found to exhibit bioaccumulative toxicity during pre‑market testing, its development is halted and it will not be approved for sale.

　　“We can never claim that pesticides are entirely non‑toxic, nor can we deny that they leave residues,” said Liu Changling. He emphasized that both the toxicity and residue issues of chemical substances require a proper understanding: whether harm occurs depends on the dose. “For example, the acute oral LD50 of sodium chloride in rats is approximately 3,750 mg/kg—yet sodium chloride is simply table salt; consuming more than 20 grams daily over the long term can be detrimental to health. In fact, the pesticides currently in use do not exhibit bioaccumulation, and the acute oral toxicity of some of them in rats is even lower than that of table salt, with residue levels in food far below 0.05 mg/kg.”

　　In addition, the issue of pesticide residues is also linked to the standardization of application practices. Liu Changling explained to reporters that if a particular pesticide requires only 1 gram per mu of land, researchers will typically use 100 grams during the experimental phase. Under “extreme‑application” conditions, residue limits—such as the maximum residue limit (the legally permitted maximum concentration of a pesticide in or on food or agricultural products, expressed in mg/kg) and the acceptable daily intake (the estimated amount of a substance that can be ingested daily over a lifetime without adverse health effects, expressed in mg/kg body weight)—are determined and established.

　　Secondly, there is a safety interval for pesticide application—just as, after taking medication, one must wait 30 minutes before consuming other foods. The same principle applies to pesticides: following the use of a particular product, a specific number of days is typically stipulated before it is safe to harvest.

　　Therefore, Liu Changling argues that, absent “excessive or improper use of pesticides” or “hasty harvesting,” there would be no human health concerns arising from pesticide residues in crops.

　　Pesticides remain the first choice for managing crop diseases, pests, and weeds.

　　“People around the age of 60 today all lived through times when there was not enough food to eat. When we were children, there were no pesticides at all, yet crop yields were extremely low,” said Liu Changling. He added that even without any chemical inputs, grain yields per mu back then still fell short of ensuring adequate food for everyone, let alone meeting the basic subsistence needs of China’s current population of 1.4 billion.

　　Today, the population continues to grow, while arable land is still shrinking relative to industrialization. Under these circumstances, ensuring food security can only be achieved by boosting crop yields per unit area.

　　Liu Changling noted that there are many ways to increase yield per unit area—such as using improved seeds, optimizing soil management, and implementing various crop protection measures—all of which are already in practice. However, the results are not immediate; particularly when it comes to controlling diseases, pests, and weeds, pesticides remain the first choice.

　　Liu Changling recounted an incident from 40 years ago: a severe insect infestation struck a wheat field. At the time, there were no pesticides available, so hundreds of students were mobilized to hand‑pick the pests. “With so many people wading into the fields to eradicate the insects, the pests were indeed wiped out—but the crops were almost entirely destroyed, and there was no harvest left.”

　　In addition, crop diseases such as cucumber downy mildew and potato late blight can spread through the air; in other words, if even a single cucumber or potato leaf becomes infected, the entire greenhouse can experience an outbreak simply by someone passing through or when the wind blows. “Like humans, crops need proper nutrition and preventive care when they’re healthy, but once they fall ill, they must be treated with medication.”

　　Cucumber leaves affected by downy mildew

　　Several scientists interviewed earlier also stated that, aside from biotechnology, chemical pesticides are another key approach to boosting food production. Liu Changling argues that biotechnology is one of the means to enhance crops’ resistance to pests and diseases; however, a single growing season can see crops afflicted by several or even dozens of pest and disease threats. At present, existing biotechnologies have not yet succeeded in enabling a single crop to withstand all such threats, which is why biotechnology and chemical methods must be used in combination.

　　According to Liu Changling, a statistic from the Food and Agriculture Organization of the United Nations (FAO) indicates that, through the rational use of pesticides, crop yield losses can be reduced by 40%, while also decreasing the toxins produced by crops as a defense against pests and diseases, thereby benefiting both human and animal health.

　　In addition, Liu Changling also discussed the pesticide market’s response. In 2018, environmental regulations led to production restrictions on certain pesticides, driving prices steadily higher. The fungicide flutriafol, which had previously been priced at around RMB 300,000 per ton, saw its price surge to RMB 680,000 per ton by August 2018.

　　“This simply illustrates one point: demand for pesticides is inelastic, so when supply falls, prices rise.”

　　The development of pesticides is similar to that of pharmaceuticals: it involves a long R&D period and has a low success rate.

　　Like the pharmaceutical industry, China’s pesticide sector also began with generic products. According to Liu Changling, among the roughly 600 to 700 commonly used pesticides today, about 98% are generics, while domestically developed pesticides with independent patents are extremely rare. Both the pesticide and pharmaceutical industries face challenges such as long R&D cycles, low success rates—resulting in high risks—and substantial capital investment. Liu Changling notes that, compared with pharmaceuticals, the pesticide industry imposes even stricter cost constraints.

　　“To take a very simple example, no one goes to the hospital and says, ‘This medicine is too expensive—I won’t use it.’ You’d naturally choose whichever drug works best, even if it’s pricier,” Liu Changling said. “But with pesticides, it’s different: if they’re too costly, there won’t be a market; at worst, farmers will simply opt for a smaller harvest this time around.”

　　In the past, due to generally rudimentary testing technologies, a new pesticide could be developed or replicated within three to five years and promptly brought to market, often without a thorough understanding of its potential impacts on the ecological environment.

　　As technology continues to advance, humans have gained the capacity to conduct an ever wider array of toxicological tests and environmental assessments, leading to increasingly stringent requirements for pesticide safety. Liu Changling explained that around 1956, it was possible to identify a single product from among 800 compounds; by 1970, this number had risen to 8,000; after 1980, roughly 20,000 compounds were needed to screen for one product; and today, it typically takes about 160,000 compounds to develop a single product.

　　Using a team of 30 people to synthesize 160,000 compounds—assuming each member synthesizes roughly 150 compounds per year—would take approximately 35 years. This significantly prolongs the drug‑development cycle for agrochemicals. Liu Changling notes that the commonly cited figure of 12 years per product development actually refers only to the development phase and does not account for the preliminary research stage.

　　In addition to the lengthy timeline, the low success rate is another major deterrent. During the compound‑discovery phase, researchers identify a candidate with promising activity that can be optimized, derivatized, or modified. If it proves functionally suitable, the next steps involve extensive toxicity testing, residue and metabolism studies, ecological risk assessments—evaluating whether the compound exhibits low toxicity, minimal residues, no carcinogenicity, no mutagenicity, no teratogenicity, and what impact it may have on pollinators, aquatic organisms, soil, water, and other environmental compartments. This research process typically takes six to eight years, during which most candidates are weeded out in this rigorous “natural selection” phase. Once the compound advances to industrial production, synthetic routes must be optimized; again, candidates with poor cost‑effectiveness are discarded. The process then moves through laboratory‑scale and pilot‑scale trials before scaling up to large‑scale manufacturing. As in the pharmaceutical sector, each stage entails very high attrition rates, resulting in a correspondingly low overall success rate.

　　In the 1980s, Liu Changling discovered that although certain pesticides differed in formulation, they shared the same raw materials or intermediates. Over the following 25 years, he published a series of related papers and developed the “intermediate‑derived‑functionalization method.”

　　In 1997, Liu Changling’s team published the paper “A Brief Discussion on the Commonality of Intermediates.” In 2014, they were invited to contribute a review article titled “Applications of Intermediate-Derivatization Strategies in the Discovery of New Pesticides” to Chemical Reviews, a top-tier journal in the field of chemistry. In 2017, Chemical Reviews had an impact factor of 52.613, ranking first among journals in the chemical and chemical engineering disciplines and surpassing both Nature and Science in the global journal impact‑factor rankings.

　　Liu Changling explained to reporters that the intermediate‑derived‑compound method was developed on the basis of retrosynthetic analysis and practical production feasibility. For example, when examining a house—whether it’s a single‑family home, an apartment building, or some other type—their appearances and functions may vary. Yet by tracing back to their underlying framework, design, and constituent materials, one ultimately discovers that they are composed of just a few basic ingredients: sand, cement, steel reinforcement, bricks, and the like.

　　The same holds true for pesticides: most are synthesized from a handful of starting materials, which undergo a variety of reactions to yield different end products. Selecting the right intermediate means choosing the right raw material; opting for safe, cost‑effective reagents in the reaction process equates to half the battle, increasing the likelihood of developing low‑toxicity, safe, and cost‑effective candidate compounds—and thereby boosting the overall success rate of R&D.

　　Natural products represent a crucial pathway toward the greening of agrochemicals. In this endeavor, Liu Changling’s team used natural products as templates and intermediates to develop fluopicolide, a fungicide belonging to the cinnamic acid derivative class, which became the first agrochemical in China to secure patent protection in China, the United States, and Europe. Subsequently, they invented cyprodinil, a fungicide containing only carbon, hydrogen, and oxygen that is effective against apple tree rot diseases, as well as azoxystrobin, which exhibits fungicidal, antiviral, and crop‑growth‑promoting activities. Furthermore, they established two international standards—one for the technical grade active ingredient azoxystrobin and another for its formulated products.

　　The Future of Pesticides: Low-Dose, High-Efficiency, and Environmentally Compatible

　　Regarding future research directions, Liu Changling believes that, much like the pharmaceutical industry, the enduring challenge in agrochemicals remains the emergence of new pests, diseases, and weeds, coupled with effective resistance management. Influenced by climate and environmental factors, novel pest and weed threats arise from time to time, while any pesticide, when used over the long term, will inevitably lead to resistance. Liu Changling notes that addressing these emerging challenges and managing resistance both require the continuous development of new products; meanwhile, a particularly thorny issue in the field of pesticides is the rapid evolution of target organisms.

　　In the pharmaceutical sector, humans typically produce a new generation every 20 to 30 years; although the mechanisms by which higher organisms develop resistance are complex, the changes from one generation to the next remain relatively modest. By contrast, pesticides confront lower‑order organisms that reproduce rapidly and mutate just as quickly. For instance, mites can generate more than 30 generations per year in higher‑latitude regions. Identifying which factors drive the emergence of resistance in pests, diseases, and weeds remains a critical challenge that pesticide research must urgently address.

　　Regarding the impacts on the ecological environment and human health, environmental compatibility must be taken into account, according to Liu Changling. He noted that current analytical techniques can readily achieve detection at the microgram level (ppm, parts per million by mass) and, in some cases, even at the nanogram level (ppb, parts per billion by mass). If a clear issue is detected at the nanogram level, the candidate will be eliminated during the research process.

　　On the other hand, there are cases where a particular drug may be harmful to a specific organism yet still receive marketing approval following an ecological‑environmental risk assessment. This is because, in the absence of a superior alternative, regulators may choose to retain such a product if its potential environmental impacts are deemed relatively low at this stage. Liu Changling cited an example: a certain wheat herbicide might exhibit high toxicity to fish, but since the affected fields are located far from aquatic habitats, a safety evaluation concluded that the risk is not significant. If the impact on fish falls below a specified threshold, the product can still be approved for market release.

　　“Everything involves a balance: we can’t do without pesticides, but when we use them, we hope their impact on the ecological environment is as minimal as possible,” said Liu Changling.

　　In 2015, the former Ministry of Agriculture issued the “Action Plan for Achieving Zero Growth in Pesticide Use by 2020.” By the end of 2017, the ministry announced that it had attained the goal of zero growth in pesticide use three years ahead of schedule.

　　As a pesticide researcher, Liu Changling argues that the so‑called “zero growth” in pesticide use merely imposes quantitative limits. With advances in technology, achieving “zero growth”—or even “negative growth”—in pesticide application while maintaining crop yields is entirely feasible.

　　“For example, the herbicide currently under industrial development requires only up to 4 grams per mu, whereas glyphosate typically needs about 100 grams per mu. If it successfully enters the market and replaces glyphosate, a substantial reduction in usage would be readily achievable.”

　　Thus, in Liu Changling’s view, regulating pesticide use entails more than merely maintaining a zero‑growth in application volumes; it also requires phasing out outdated products that fail to meet standards through increasingly comprehensive assessments of their ecological and environmental toxicity. In the future, highly efficient, safe, and environmentally friendly green pesticides will play an increasingly important role, with particular demand for green pesticide formulations that are compatible with the environment.

　　“Zero growth is the first step; the next stage is safety, environmental protection, and low risk. Although nothing is entirely risk-free, the ultimate goal—and the inevitable trend of development—is to create and apply green pesticides that are highly effective, environmentally compatible, and virtually risk-free,” said Liu Changling.

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