What are pesticide residues?
Pesticide residues are the trace amounts of pesticides that remain in organisms, agricultural products (or food) and the environment after pesticide application; besides the pesticides themselves, they also include toxic metabolites and impurities, and are the collective term for pesticides and related substances. The amount of residue remaining is called the residue level and is expressed as milligrams per kilogram of sample (mg/kg). Pesticide residues are an inevitable consequence of pesticide application, but if they exceed the maximum residue limit (MRL), there is a risk of adverse effects on humans and livestock, or of harm to organisms in the ecosystem through the food chain.
Do all agricultural products contain pesticide residues?
Pests, diseases and weeds commonly occur in agricultural production, so pesticides are needed for control; only some organic farming uses natural biological pesticides, so almost all agricultural products may contain pesticide residues. This is true of Chinese agricultural products and of foreign ones. In fact, the higher the degree of agricultural modernization, the greater the amount of pesticides used, so developed countries generally use more pesticides than developing countries; according to FAO statistics for 2000, pesticide use per unit area in developed countries was 1.5-2.5 times that of developing countries. In practice, owing to limitations such as pesticide application technology, the actual utilization rate of pesticides is only 30%, and most pesticides are lost to the environment; pesticide residues on plants remain mainly on the crop surface, and the systemic part of a pesticide is absorbed into the plant. Through wind and rain, natural degradation and biodegradation, the pesticide residue at harvest is very small. But to ensure the safety of agricultural products, pesticide residue standards must be established to keep residues within a safe range. Zero residue is an ideal; no country can achieve it, but reducing pesticide residues and ensuring the safety of agricultural products is the goal of agricultural and pesticide management in every country.
Can we do without pesticides?
In recent years incidents affecting the quality and safety of agricultural products have occurred from time to time, and some members of the public ask, "can we stop using pesticides?". In fact, pesticides have been used worldwide for only about 200 years, but during this period pesticide use has kept increasing, because population growth requires vigorous development of agricultural production to guarantee a safe food supply, and because the development of modern agriculture increasingly depends on pesticides. Some studies indicate that losses caused by crop pests, diseases and weeds can reach 70%, and correct use of pesticides can recover about 40% of that loss. China is a country with a large population and scarce arable land; increasing grain output and farmers' income has always been the main goal of agricultural production, and using pesticides to control pests, diseases and weeds so as to reduce grain losses is a necessary technical measure. Without pesticides, China would certainly face famine! Modern agricultural techniques such as mechanization require pesticides for weeding, height control, defoliation and fruit setting to facilitate mechanized operations. For plants, pesticides are as important and indispensable as medicine is for humans. However, pesticide residues can be reduced through certain measures: first, comprehensively carry out integrated pest management to reduce the amount of pesticides used; second, use pesticides correctly and in a standardized way to reduce residue levels; third, vigorously promote biological pesticides to reduce the use of chemical pesticides and continuously lower residue levels. Agricultural departments have been working on these measures.
Are agricultural products containing pesticide residues safe to eat?
Whether eating agricultural products containing pesticide residues is safe depends on the residue level, the toxicity and the amount eaten. To ensure the safety of agricultural products, countries set pesticide residue limit standards according to the toxicological data of pesticides (mainly the acceptable daily intake and the acute reference dose) and the dietary structure of residents; residues below the standard are safe and can be eaten without concern, while products exceeding the standard carry a safety risk and should not be eaten. It should be added that a safety factor of at least 100-fold is built into residue standards, so residue standards have a large margin of safety; in theory, even accidental consumption of a product with residues above the standard may not cause a safety incident.
To ensure the safety of agricultural products, China strictly manages pesticide safety; pesticide registration requires two years of safety testing covering 18 items of acute, subchronic and chronic tests, and products with carcinogenic or teratogenic safety hazards are never approved for registration. China has also adopted the strictest management of highly toxic pesticides, successively banning and phasing out 33 highly toxic pesticides - including products such as methamidophos that are still widely used in the United States and some other developed countries - while vigorously developing biological pesticides. At present the proportion of highly toxic pesticides in China has fallen from 30% to less than 2%, and more than 72% of pesticides are low-toxicity products, so pesticide safety has greatly improved, poisoning incidents in rural production have decreased and the mortality rate from suicide by drinking pesticides has also fallen markedly. This does not mean that China's agricultural products are absolutely safe; what can be affirmed is that today's pesticides are safer than those of the past. If you are concerned about pesticide residues, when eating fresh vegetables and fruit you can also take measures such as soaking in water and peeling to remove possible residues.
Which agricultural products carry greater residue risk?
In general, organic agricultural products, green food and pollution-free agricultural products are relatively safer with smaller residues and fewer cases of exceeding the standard, because there are strict regulations on the pesticides used and how they are applied. For food crops such as wheat, rice and maize, because the growing period is long and the storage period is also long, most pesticide residues degrade, and they are further processed and cooked, which removes and degrades residues further, so they are relatively safe. Because vegetables and fruit are mostly eaten fresh, pesticide residues degrade little, so the state manages the pesticides used on vegetables and fruit more strictly; besides banning highly toxic pesticides, it strictly specifies the application technique and the pre-harvest interval for permitted pesticides, so normal production will not cause safety problems. For some fresh vegetables and fruit that are harvested continuously, the residue risk may be relatively greater. All agricultural products have pesticide residues; because countries strictly manage pesticides and their residues, agricultural products that meet residue standards are safe. Therefore, residues and the safety of agricultural products should be understood correctly. Awareness of safety should be strengthened, but there is no need to turn pale at the mention of pesticides. The amount of pesticide residue is very small, and its harm is far less than that of some pollutants and pathogenic microorganisms in the environment and the air.
How are pesticide residue standards set?
Pesticide residue standards include pesticide residue limit standards (i.e. maximum residue limits), pesticide residue testing method standards and so on; the one most directly relevant to consumers is the pesticide residue limit standard for food or edible agricultural products. Like developed countries such as those of Europe and America, Japan and Australia, China uses internationally accepted risk assessment techniques and methods and, on the principle of considering the greatest possible risk, sets national standards for pesticide residue limits. The specific method and steps are: first, according to the needs of each stage of production, processing, distribution, consumption and import/export of agricultural products and the actual situation of pesticide use, determine the combinations of agricultural products (or food) and pesticides for which residue limit standards need to be set; then carry out simulated dynamic degradation tests of pesticide residues, national dietary structure surveys and pesticide toxicology studies, to obtain respectively the residue values of a pesticide remaining in an agricultural product (or food) under normal use (including the median value, maximum residue value, etc.), the dietary data of Chinese consumers (the daily consumption of each edible agricultural product or food by different regions, ages and sexes) and the toxicity of the pesticide (including the acceptable daily intake, acute reference dose, etc.); on this basis, carry out a dietary intake risk assessment of pesticide residues, obtaining a recommended value for the pesticide residue limit standard; finally, after deliberation and approval by the National Food Safety Pesticide Residue Standard Review Committee, it is promulgated and implemented jointly by the Ministry of Health and the Ministry of Agriculture.
It should be particularly noted that when setting residue standards, the greatest possible risk is taken as the basis, that is, the strictest safety requirements are applied; on this basis, a safety factor of at least 100-fold is also added. For example, if a pesticide residue of 50 mg/kg in food might pose a safety risk, the standard is set at 0.5 mg/kg.
Are China's pesticide residue standards lower than those of Europe and the US?
People often like to compare China's standards with those of developed countries in Europe and America. In terms of the number of pesticide residue standards, because Europe and America have a longer history of pesticide management, they have set more residues than China. But in terms of the level of the standards, it is difficult to compare the levels of different countries' residue standards. Technically speaking, countries differ in agricultural production, pesticide use and food structure, so residue standards will differ to some extent. From a management perspective, although the main purpose of setting residue standards is to ensure food safety, countries increasingly treat pesticide residues as a technical barrier to international trade in agricultural products and, when necessary, as a political bargaining chip.
Differences in pesticide residue standards among countries are also affected by the following factors. First, for pesticides not produced or used in one's own country, the strictest standards are often set, while for pesticides used in one's own country - especially those used on exported agricultural products - residue standards are kept as lenient as possible within the safe range. For example, the US, the EU and Japan apply the default limit standard (i.e. 0.01-0.05 mg/kg) to pesticides not registered for use in their own countries, a concentration that the instruments of many developing countries cannot even detect; but for pesticides registered for domestic use, even if the pesticide is highly toxic, their standards are lenient. For example, the US sets a standard for the highly toxic pesticide methamidophos of 1 mg/kg on celery and 0.5 mg/kg on cauliflower, and Japan sets 5 mg/kg on celery and 1 mg/kg on cauliflower. Second, standards are strict for crops that a country does not grow or mainly imports. For example, chlorantraniliprole is a new insecticide; the EU's standard is 1 mg/kg on grapes but 0.01 mg/kg on rice and other grains and 0.02 mg/kg on tea. Logically grapes are eaten fresh, so the standard should be higher, but grapes are a competitive crop of Europe, so the standard set is lenient; likewise for the commonly used fungicide chlorothalonil, the EU standard is 1 mg/kg on apples and pears eaten directly, but 0.01 mg/kg on rice and other grains and 0.1 mg/kg on tea. Third, for the same crop, standards differ among countries: for example, for the fungicide captan, which is not very safe, the residue standard in rice grain is 5 mg/kg in Japan and 0.02 mg/kg in the EU, a 100-fold difference; and for the highly toxic pesticide methyl parathion, it is 1 mg/kg in Japan and 0.02 mg/kg in the EU, a 50-fold difference.
To coordinate and unify residue standards, the Codex Alimentarius Commission is responsible for setting international standards for pesticide residues, but even where international residue standards exist, most developed countries implement their own national standards, while most developing countries, having weak capacity to set residue standards, can often only implement international standards. China is the chair country of the Codex Committee on Pesticide Residues, so China's pesticide residue standards align as far as possible with Codex standards (rather than those of Europe, America or Japan); some standards are lower than developed countries' but some are higher. For example, for the new pesticide methoxyfenozide, China's standard in cabbage is 2 mg/kg, while the US and Japan set 7 mg/kg; malathion is an old pesticide, and China's standards are 2 mg/kg in citrus, apple and snap bean, 1 mg/kg in brown rice and 0.5 mg/kg in radish, all stricter than the US standard of 8 mg/kg; metribuzin's standard in soybean is 0.05 mg/kg, while the US sets 0.3 mg/kg and the EU and Japan 0.1 mg/kg; for the commonly used fungicide thiabendazole, China's standard in mushroom is 5 mg/kg, while the US sets 40 mg/kg, the EU 10 mg/kg and Japan 60 mg/kg, i.e. 8, 2 and 12 times stricter respectively. China sets pesticide residue standards mainly with safety in mind and rarely involves trade protection. It can thus be seen that, whatever the differences in the level of residue standards among countries, residue standards are all set on the basis of safety risk assessment; as long as a product meets the residue standard, it is safe, and one cannot use another country's standard to judge whether it is safe, nor use one country's standard to negate another's - that would lack scientific basis. This is because pesticide residue standards are set not only on the basis of safety risk assessment results, but also by comprehensively considering factors such as industry development and international trade.
What is the current status of pesticide residues in Chinese agricultural products?
The current status of pesticide residues in Chinese agricultural products can be summed up in three sentences: it has been improving continuously in recent years, the overall situation is relatively good, but hidden risks still exist. Specifically, first, the routine quality and safety monitoring of agricultural products carried out 3-5 times a year nationwide shows results that have improved year by year and greatly improved - not only is the rate of exceeding residue standards falling continuously year by year, from over 50% a decade ago to below 10% now, but the detected residue values are also markedly lower; a decade ago there were relatively many vegetables with detected pesticide residues above 1 mg/kg, but this is now rare, with only occasional detections above 1 mg/kg. Second, the current pass rate of pesticide residue monitoring of agricultural products is generally high: for example, rice and fruit reach above 98%, and vegetables and tea also reach above 95%. Third, the current residue situation is not yet stable and some hidden risks remain - for example, in the south or other regions in summer, because pests and diseases are severe and pesticide use is high, agricultural products easily exceed residue standards; also, under protected off-season cultivation, because pesticide doses are large and degradation is not easy, residues easily exceed the standard; moreover, as domestic and foreign residue limit standards are raised or the variety of monitored pesticides increases, products that previously did not exceed the standard become non-compliant; in particular, because the scale of China's agricultural production is too small, with tens of thousands of scattered farmers producing and operating independently, and production techniques are relatively backward, base-level exit control and market access are hard to truly implement, making supervision more difficult. At the same time, the number of China's residue standards is still relatively small compared with developed countries, so accelerating the formulation and improvement of pesticide residue standards is a very important task.
How can pesticide residues be removed?
Pesticide residues in agricultural products can be removed or reduced by certain methods; commonly used simple methods include standing (leaving to sit), washing, cooking and peeling. First, standing: because pesticide residues degrade continuously over time, some storable products such as potato, Chinese cabbage, cucumber and tomato can be left for a few days after purchase - on the one hand this allows the produce to continue ripening, and on the other the pesticide degrades so residues decrease. Second, washing: pesticide residues that remain on or outside the surface of agricultural products are also relatively easily rinsed off by water or dishwashing liquid, so before cooking, soak vegetables in water for half an hour and then rinse with a little dishwashing liquid, which can basically remove surface pesticide residues. Third, cooking: high temperature generally makes pesticide residues degrade faster. Fourth, peeling: pesticide residues on the skin of agricultural products such as apple, pear and citrus are generally higher than in the internal tissues, so peeling is a very good method.
However, it should be explained that, whatever method is used, it is difficult to completely remove pesticide residues from agricultural products - especially the small amount of residue that has already entered the internal tissues; and if other substances are used in the process of removing residues, such as dishwashing liquid, bacterial agents or enzyme agents, the safety to the human body of the residues of these substances after use must also be considered, because although dishwashing liquid can remove pesticide residues, it is itself a chemical or biological contaminant and may also cause secondary contamination of agricultural products (or food), and the toxicity of some detergents may be greater than that of many pesticides. It is fine to consciously treat agricultural products appropriately, but there is no need for excessive worry and treatment; as long as residues do not exceed the standard, there will be no safety problem - just as we may breathe in germs every day but do not fall ill.