Pesticide Residues Are Highly Harmful: A Detailed Explanation of Detection and Prevention Methods

The use of pesticides is an unavoidable step in modern agriculture, but pesticides that remain on agricultural products due to improper pesticide use or ineffective detection will bring serious harm to the human body, agricultural products, and the production environment. Understanding the detection standards, causes, and hazards of pesticide residues can help us better remove and prevent pesticide residues.

1. Standards for pesticide residues

In order to address the limit standards for vegetables, fruits, and China's specialty agricultural products and to improve the detection methods supporting pesticide residue limit standards, the National Health and Family Planning Commission, the Ministry of Agriculture, and the China Food and Drug Administration jointly formulated the 2016 edition of the National Food Safety Standard Maximum Residue Limits for Pesticides in Food, which was officially promulgated and implemented on January 18, 2017. This new national standard for pesticide residues made major breakthroughs in the number of standards and coverage rate, specifying 4,140 residue limits for 433 pesticides in 13 major categories of agricultural products, an increase of 490 items over the 2014 edition, basically covering commonly used pesticides already approved for use in China and the main agricultural products consumed daily by residents.

The newly released pesticide residue limit standards have three major features:

First, 184 maximum residue limits were set for 24 banned and restricted pesticides such as fenamiphos, providing a basis for judging and regulating the illegal use of banned and restricted pesticides;

Second, in accordance with international practice, for 33 pesticides with no dietary risk, the formulation of maximum residue limit standards in food was exempted, enhancing the scientific nature, practicality, and systematicness of China's pesticide residue standards in food.;

Third, in addition to recommending supporting detection methods for the limits involved in the standards, 106 national standards for pesticide residue detection methods were also released simultaneously.

As the chair country of the Codex Committee on Pesticide Residues, China is one of the few countries participating in the formulation of international standards. During the "12th Five-Year Plan" period, China's capacity and influence in participating in the formulation of international standards gradually increased, and the number of international limit standards formulated using China's residue data has reached 11. At present, China's principles, methods, and data volume requirements for dietary risk assessment of pesticide residues are already in line with international practices. According to reports, during the "13th Five-Year Plan" period, the formulation of pesticide residue standards has laid out clear tasks and plans: formulate 6,000 pesticide residue limit standards, focus on resolving limit standards for vegetables, fruits, and China's specialty agricultural products, and improve detection methods supporting pesticide residue limit standards; gradually implement "import limit standards" and "uniform limit standards" to expand the coverage of China's limit standards; at the same time, focus on pesticides independently innovated in China, actively participate in formulating Codex Alimentarius standards, and promote China's independent pesticide innovation.

2. Causes of pesticide residues

There are many causes leading to and affecting pesticide residues. Among them, the properties of the pesticide itself, environmental factors, and pesticide application methods are the main factors affecting pesticide residues.

(1) Pesticide properties and pesticide residues

Currently banned pesticides such as organic arsenic and mercury pesticides remain in the environment and plant bodies because their metabolites, arsenic and mercury, ultimately cannot be degraded.

Organochlorine pesticides such as BHC and DDT and their metabolites have stable chemical properties, degrade slowly in crops and the environment, and easily accumulate in the fat of humans and animals. Therefore, although the toxicity of organochlorine pesticides and their metabolites is not high, their residual toxicity problem still exists.

Organophosphorus and carbamate pesticides have unstable chemical properties and are easily decomposed under the influence of external conditions after application. However, among organophosphorus and carbamate pesticides, there are some highly toxic and extremely toxic varieties, such as methamidophos, parathion, aldicarb, carbofuran, and isocarbophos. If they are applied to vegetables with short growing periods and continuous harvesting, it is difficult to avoid poisoning of humans and livestock due to excessive residues.

In addition, although some pesticides themselves have low toxicity, their production impurities or metabolites have high residual toxicity, such as impurities produced during the production of dithiocarbamate fungicides and their metabolite ethylene thiourea, which is a carcinogen, DDT as an impurity in dicofol, and carbofuran and 3-hydroxycarbofuran as the main metabolites of carbosulfan and benfuracarb.

The systemic property, volatility, water solubility, and adsorptivity of pesticides directly affect their residues in plants, the atmosphere, water, soil, and other surrounding environments. Environmental factors such as temperature, light, rainfall, soil pH and organic matter content, vegetation conditions/microorganisms also affect the degradation rate of pesticides to varying degrees and affect pesticide residues.

(2) Application methods and pesticide residues

Generally speaking, formulations used for direct spraying such as emulsifiable concentrates and suspension concentrates cause relatively greater contamination of crops. Powders, because they easily drift, are more harmful to the environment and the applicator. Any pesticide variety has its suitable target pests and crops for control, as well as its reasonable application time, number of applications, application amount, and pre-harvest interval (the safe interval from the last application to harvest).

Lacking basic knowledge of correct pesticide use, the vast majority of farmers use pesticides only for control. The reason is simple: good insecticidal effect and quick results. Some farmers also do not pay attention to application techniques (such as applying to the upper side of leaves for powdery mildew and the underside of leaves for downy mildew, and not applying pesticides at noon on sunny days). Once they believe the control effect is poor, they increase the dosage, resulting in pests and diseases developing resistance. When resistant pests and diseases harm vegetables in the field again, even larger doses are applied for control. In this vicious cycle, pesticide residues in vegetables greatly increase. More seriously, some farmers also illegally use banned and restricted pesticides on vegetables. After application, before the safe pre-harvest interval has been reached, they rush to market them, causing even greater harm to the human body.

(3) Structural errors

Insufficient awareness of the use of pollution-free pesticides also affects vegetable quality. The pesticides affecting vegetable quality are mainly insecticides, and among these pesticides, organophosphorus insecticides are dominant, namely the three 70%s: 70% of pesticides used are insecticides; 70% of insecticides are organophosphorus insecticides; 70% of organophosphorus insecticides are highly toxic, extremely toxic, and high-residue pesticides. Some farmers believe that pesticides that take effect immediately after application are good pesticides, while low-toxicity and pollution-free biological pesticides are expensive and slow-acting, wasting manpower and material resources. This also has a certain impact on vegetable quality.