Pesticide Residue Limits Relaxed 24-Fold: Can We Still Eat Chinese Chives Safely?

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From 11 May this year, a newly updated national food safety standard has come into effect. The maximum residue limit for procymidone in Chinese chives has been raised from 0.2mg/kg to 5mg/kg – a 24-fold increase.

●Procymidone-related provisions in GB 2763.1—2022 National Food Safety Standard: Maximum Residue Limits for 112 Pesticides Including 2,4-DB Sodium Salt in Foods.
Although procymidone is classified as a low-toxicity pesticide, long-term exposure may still pose certain health risks. Experiments on rabbits and rats have confirmed that procymidone causes reproductive toxicity. Prolonged maternal exposure to procymidone may lead to malformation of the offspring’s reproductive organs or impair their skeletal and neural development. Furthermore, long-term procymidone intake may harm the visual organs, thyroid and pancreas. On 29 March, the National Committee for the Review of Pesticide Residue Standards specifically addressed the background behind the increase in the procymidone residue limit. The notice stated that this revision followed the principle of “the most rigorous standards”, and cited risk assessment findings to indicate that not only is 5mg/kg safe, but even raising the limit to 30mg/kg would not pose a safety risk.

But is this really the case?

I. The High Acceptable Daily Intake

First, we need to know how much procymidone consumed per day constitutes a health risk. China’s stated Acceptable Daily Intake (ADI) for procymidone is 0.1mg/kg bw/d, meaning 0.1mg per kg of body weight per day. This standard refers to the one set by the Joint FAO/WHO Meeting on Pesticide Residues (JMPR) in 2007. In reality, China’s standard is among the most lenient compared with those of other countries.

The EU does not permit the use of procymidone products, and its ADI is 0.0028mg per kg of body weight per day – just 2.8% of China’s figure.

Even in countries where procymidone is permitted for agricultural use, the ADI is significantly lower than the new national standard. Australia’s ADI for procymidone is 0.05mg per kg of body weight per day – half of China’s standard; Japan’s ADI is 0.038mg per kg of body weight per day – just 38% of China’s figure.

ADIs are generally derived from animal experiments by dividing the dose proven harmful in testing by a fixed safety factor, ensuring safety for all population groups. The standards of the countries above have essentially all been revised based on more recent toxicological research. China’s higher ADI figure may be because it has not updated its assessment in line with newer toxicological evidence, as those countries have.

II. Procymidone Is Everywhere

Let us take a step back and assume we accept China’s current maximum ADI of 0.1mg/kg bw/d. Even then, the issue is not as simple as Chinese chives alone. Under the existing standard, a person weighing 50kg has a maximum daily intake of 5mg. If they ate only Chinese chives, at the chive residue limit of 5mg/kg, they would need to eat 1kg of chives every single day to exceed the ADI. Of course, a normal person is unlikely to eat that many chives in one day. Perhaps this is why the national standard raised the procymidone MRL for chives to 30mg/kg – a nod to the low consumption volume.

But is it sound logic to relax pesticide residue limits simply because the quantity consumed of a particular food is small?

Procymidone, as a broad-spectrum fungicide, is currently widely used to control diseases across a range of fruits and vegetables. Under the national standard, residue limits for procymidone in various fruits and vegetables range from 2 to 10mg/kg. We must therefore consider the cumulative intake of procymidone from all sources.

●Procymidone residue limits for selected vegetables under GB 2763-2021.

In a 2019 paper by Zhou Yong et al. titled “Residue Detection of Procymidone in Chinese Chives and Long-Term Dietary Exposure Assessment”, the National Estimated Daily Intake (NEDI) for procymidone was calculated at 2.5562mg, based on residue levels across food categories and average daily food consumption figures for Chinese residents.

This means that an average adult weighing around 63kg, consuming on average 275g of vegetables and 45g of fruit, would be taking in a dose equivalent to 40.6% of the maximum daily intake. However, as living standards rise, the total quantity of fruit and vegetables many people eat daily is likely well above these figures.

The Dietary Guidelines for Chinese Residents (2022) recommends that each person consume 300–500g of vegetables per day (half of which should be dark-coloured varieties) and 200–350g of fruit. If an average-weight person ate at the upper limits recommended by the guidelines – 500g of vegetables and 350g of fruit – the calculated figure would rise to 7.089mg, equivalent to 113% of the maximum daily intake – a substantial amount.

●Recommended daily intakes in the 2022 Dietary Guidelines.
If the situation is this concerning for adults, toddlers with lower body weights are even more vulnerable to procymidone exposure. A 2020 paper by Liu Yuhong et al. noted that children aged 2–7 may face greater risk because they tend to consume proportionally more vegetables. If the saying goes that “discussing toxicity without considering dosage is nonsense”, then ignoring the widespread application of procymidone and assessing safety based solely on one vegetable – Chinese chives – is clearly flawed. From the analysis above, we can see that regardless of whether the national standard for chive residues is revised or not, the risk of excessive procymidone intake remains.

III. Procymidone and Grey Mould of Chinese Chives

As early as when the standard was first published this year, media outlets raised the suspicion that the revision was intended to reduce the number of failed spot checks, boost the pass rate for agricultural product inspections, and ultimately “eliminate” inspection failures altogether. According to incomplete statistics from the Department of Quality and Safety Supervision of Agricultural Products, Ministry of Agriculture and Rural Affairs, of the 14,295 batches of edible agricultural products sampled throughout 2020, 3,799 batches failed inspection – 26.57%. Among these, 352 batches exceeded the procymidone residue limit, ranking first among all pesticide residue exceedances, and every single one was detected in Chinese chives.

According to statistics compiled by the public-interest organisation Nature Field, even after the procymidone limit was raised to 5mg/kg, numerous test samples would still exceed the new threshold.

Their survey of regulatory records from 15 provinces and municipalities across China in 2022 found 223 instances where procymidone in Chinese chives exceeded the original limit. After the limit was raised to 5mg/kg, 31 instances of exceedance remained – with the highest residue level reaching 35.5mg/kg, seven times the new national standard.

●Nature Field also pointed out that this kind of limit relaxation is not unique to Chinese chives. In the 2022 revision of the National Food Safety Standard Maximum Levels of Contaminants in Foods, the cadmium limit for sea crabs and mantis shrimp was relaxed from 0.5mg/kg in the 2017 edition to 3mg/kg. As with chives, this change coincided with frequent cadmium exceedances found in swimming crab testing.

Why do procymidone residue levels in Chinese chives remain so persistently high? To understand this, we need to look at the production side.

In Chinese chive production, procymidone is applied primarily to control grey mould. In 1985, Li Mingyuan and Liu Jie at the Beijing Plant Protection Station identified the pathogen responsible for grey mould of Chinese chives for the first time in China. They also found that the fungus thrives between 15–20°C and in conditions of high humidity. When grey mould strikes, chive leaves are prone to tip desiccation or white spots; in severe cases, grey mycelium develops and the entire leaf dies back.

●Grey mould of Chinese chives is a fungal infection caused by Botrytis squamosa.
A technical director at a farm in the North China Plain told Foodthink that Chinese chives are prone to disease when cold weather coincides with heavy rain. In the north, therefore, the chilly spring is peak season for grey mould. Even when the infection is not severe, once white spots appear on the leaves, the chives lose all commercial value and can no longer be sold. On the other hand, changes in cultivation practices can also alter the growing environment of Chinese chives, triggering grey mould.

As early as 1985, Li Mingyuan and colleagues found that grey mould was the principal disease affecting Chinese chives over winter and spring, when plastic film is draped over beds for insulation. As high tunnels and solar greenhouses gradually became more common, these poorly ventilated, high-humidity agricultural structures often turned into hotspots for grey mould of Chinese chives.

A five-year survey conducted by a grassroots technician in a region of Henan province found that grey mould severity was greater in solar greenhouses than in plastic tunnels; among the plastic tunnels, low tunnels were worse affected than high tunnels; and open-air Chinese chives had a comparatively lower incidence of grey mould.

IV. How Can Grey Mould Be Controlled?

Yang Jingyong, head of the Wuhan Little Farmer Ecological Farm, previously worked in plant protection. Drawing on that experience, he suggests that growers of high-tunnel Chinese chives can ventilate the tunnels before nine in the morning to reduce humidity. Beyond this, he believes several other measures help prevent disease – scattering sawdust and wood ash; introducing beneficial microorganisms such as Bacillus subtilis to colonise the environment and compete with pathogens; enriching the soil with organic matter; and balancing the ratio of nitrogen to phosphorus fertiliser. Chinese chives also require crop rotation every two to three years to prevent diseases from intensifying.

These measures may strengthen plant resilience or improve growing conditions, but with the scale of contiguous Chinese chive cultivation expanding and more agricultural infrastructure being built, unless proactive steps are taken to promote plant health, rising grey mould incidence is an almost inevitable trend. For ordinary smallholders, applying pesticides once disease has broken out has become standard practice.

● Many regions across the country are developing similar “ten-thousand-mu Chinese chive cultivation bases”. Large-scale monocultures of this kind make crop rotation difficult, and diseases spread more easily.
Most pesticide trials conducted in laboratory conditions aim to demonstrate that, when pesticides are applied using standard methods, residues can be kept within acceptable limits. Zhou Yong et al.’s research noted that applying procymidone to Chinese chives could reduce residue levels to between 0.04 and 1.06 mg/kg after thirty days. In practice, however, many growers do not follow the standard operating protocol.

For the mainstream formulations – procymidone smoke agents and wettable powders – the spraying interval is thirty days in both cases, which is also the standard procedure used in experimental trials. However, the growing cycle of a typical Chinese chive crop is likewise around thirty days, meaning that procymidone can only be applied once per cycle, and only immediately after the previous cut.

Growers are unlikely to adhere to this schedule. Take the application of procymidone smoke agents in high tunnels: in winter and spring, the usual practice is preventive spraying every seven days, because once the disease takes hold it is very difficult to control. Yet at harvest, growers do not wait for the pre-harvest interval to expire – if they wait too long, the chives grow tough and become unsellable.

Decades of continuous procymidone application have caused the grey mould fungus to gradually develop resistance, undermining the pesticide’s efficacy and forcing producers to keep increasing doses.

In 2022, Hu Bin and colleagues tested nine different fungicides against grey mould strains isolated from Chinese chives in a region of Shandong province. The results showed the strongest resistance to procymidone, making its efficacy far inferior to that of the other fungicides tested.

V. From “The Most Stringent Supervision” to “The Most Rigorous Standards”?

In 2019, the revised Implementation Regulations of the Food Safety Law were issued, stipulating adherence to the “Four Stricteests”: “the most rigorous standards, the most stringent supervision, the harshest penalties, and the strictest accountability”. It is the clauses on “the most stringent supervision” and “the harshest penalties” that explain why, over the past few years, alarming headlines have appeared time and again: sellers of “poisonous” Chinese chives fined thousands, even tens of thousands, of yuan. In most such cases, the cause of the penalty was procymidone residue exceedance.

●Under the Food Safety Law, hailed as “the strictest ever”, the minimum penalty was abruptly raised to 50,000 yuan, and in recent years a string of bizarre regulatory rulings has surfaced. Yet relying on fines to tackle residue exceedances is merely scratching an itch through a boot. In the conventional food distribution system, Chinese chives pass through multiple hands before reaching consumers; market vendors simply have no idea where their produce came from or why it exceeded limits. Regulators are even less able to reach the growers, and so they can only penalise the sellers.
●Many markets are now equipped with pesticide residue testing rooms of this kind, but rapid tests generally lack sufficient accuracy to serve as a definitive basis for determining pesticide residue exceedances. Photograph taken by the author at a market in Guangzhou.

Now that the maximum residue limit for procymidone in Chinese chives has been relaxed twenty-four-fold, such headlines will grow ever rarer. Yet the safety of Chinese chives themselves has not changed – the long-term overuse of low-toxicity pesticides like procymidone still carries uncertain risks.

On a macro level, pesticide use has lowered the barriers to production, enabled high-tunnel growers to supply Chinese chives year-round, and helped large-scale operations resist disease. These year-round, large-scale production models are admittedly better suited to the market, but they have also bred a dependence on pesticides. This is why, despite two thousand years of growing Chinese chives in China, farmers today can be heard saying, “Without pesticides, we simply cannot grow vegetables.”

We worry that, with pesticides as a safety net, ever fewer growers will invest in ecologically friendly, plant-health-conscious cultivation methods, ultimately finding themselves trapped in an escalating cycle of pesticide use driven by resistance, until the chemicals cease to work altogether.

At its core, the issue of pesticide residues still hinges on tackling overuse at the production stage – a problem that extends well beyond Chinese chives. Yet because regulation cannot reach the growers, there exists a long-standing contradiction between the logic of oversight and production practices that rely on excessive pesticide use. The notorious reputation of “poisonous chives” stems simply from the fact that Chinese chives’ chronic residue exceedances have been laid bare precisely because of this contradiction, and the severity of the penalties has amplified the issue in the public eye.

The revision under the banner of “the most rigorous standards” may well ease this contradiction, but it will not alter the state of agriculture. It also sends a message to the public: the most important thing in safeguarding food safety is not stringent market supervision but a fundamental overhaul of unsustainable agricultural production practices.

●A “Blockchain + Chinese Chives” initiative launched by a local authority in 2021 was designed from the outset to address pesticide residue exceedances in Chinese chives. Yet it may well prove just another failed attempt at pesticide regulation.
References
Scientific Rigour Ensures Safe Consumption in the Revision of GB 2763.1—2022 National Food Safety Standard: Maximum Residue Limits for 112 Pesticides Including 2,4-DB Sodium Salt in Foods – Responses by Officials of the National Committee for the Review of Pesticide Residue Standards to Press Questions on the Revision of the Procymidone Residue Limit in Chinese Chives

http://www.moa.gov.cn/gbzwfwqjd/xxdt/202303/t20230329_6424229.htm?eqid=b5fb2f2a001793490000000364263d50

Zhou Yong, Park Su-yeong, Liao Xianjun, Liu Jia, Zhu Hang, Ma Haihao, Zhou Xiaomao, Li Fugen. “Residue Detection of Procymidone in Chinese Chives and Long-Term Dietary Exposure Assessment” [J]. Chinese Journal of Pesticide Science, 2021, 23(2): 373–379.

[Quality and Safety Work Bulletin on Agricultural Products, Issue 5] Analysis Summary of Failed Inspections of Edible Agricultural Products by Market Regulation Authorities in 2020 http://www.jgs.moa.gov.cn/gzjb/202102/t20210218_6361714.htm

Liu Yuhong. “Residue Detection of Procymidone in Chinese Chives and Long-Term Dietary Exposure Assessment”

Hu Bin, Huang Zhongqiao, Liu Xili, et al. “Control Efficacy of Nine Fungicides Against Grey Mould of Chinese Chives” [J]. Chinese Agricultural Science Bulletin, 2014, 30(4): 6.

Liu S, Che Z, Chen G. Multiple-fungicide resistance to carbendazim, diethofencarb, procymidone, and pyrimethanil in field isolates of Botrytis cinerea from tomato in Henan Province, China[J]. Crop Protection, 2016, 84: 56-61.

Xing Yanwei. “Occurrence and Integrated Control of Grey Mould of Chinese Chives” [J]. Friend of Farmers’ Prosperity, 2014, No. 495(22): 95.

Reconsideration of Procymidone: Human health risk assessment report (including Toxicology and Work Health Safety), Australian Pesticides and Veterinary Medicines Authority, 2017

GHS Classification Results by the Japanese Government

https://www.nite.go.jp/chem/english/ghs/20-meti-0055e.html

Foodthink Contributor
Wang Hao
Foodthink editor, a science-and-engineering graduate with a keen interest in food and agriculture issues, and a devoted enthusiast of Chinese chive-filled dumplings.

 

 

 

Editor: Ze’en

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