Chlorpyrifos may be listed under the Stockholm Convention on Persistent Organic Pollutants—what implications will this have for China’s pesticide industry?

The seventeenth meeting of the Persistent Organic Pollutants Review Committee was held in Geneva earlier this year.

At this meeting, the proposal submitted by the European Union to list chlorpyrifos in Annex A of the Stockholm Convention on Persistent Organic Pollutants (hereinafter referred to as “the Convention”), pursuant to Article 8, paragraph 1, of the Convention, was reviewed. Under the Convention as amended in 2019, inclusion in Annex A would require Parties to “eliminate” the production and use of chlorpyrifos. Whether China may grant specific exemptions for the use of chlorpyrifos in certain crop–target pest combinations remains subject to further review and will depend on China’s final position.

China is a major producer and exporter of chlorpyrifos; if chlorpyrifos were listed in Annex A, it would inevitably have a significant impact on the industries involved in its production and sale. Accordingly, this paper provides a brief overview of the process by which chlorpyrifos may be designated as a POP, based on the relevant documents issued at the Seventeenth Conference, for the reference of stakeholders.

1 The European Union’s conclusion on chlorpyrifos, in accordance with the criteria set out in Annex D.

1.1 Conclusions Regarding Persistent Pollution

In the water‑degradation studies evaluated, the half‑life of chlorpyrifos ranged from 21 to 75 days across different temperatures. Under temperate environmental conditions, when the temperature is standardized to 12°C, the half‑life falls within the range of 6.8 to 124 days. Consequently, chlorpyrifos exhibits a half‑life in water exceeding two months, thereby meeting the persistence criterion.

In soil, the longest degradation half-life of chlorpyrifos is observed at high application rates (100–1,000 mg/kg). Chlorpyrifos remains approved in some countries for termite control; at elevated application levels, its degradation rate decreases, a consequence of reduced biodegradation due to its toxicity to microorganisms. When applied for agricultural use at rates below 100 mg/kg, literature and patent abstracts report wide-ranging half-lives across different temperatures, ranging from 6 to 224 days. At a standardized temperature of 12°C, these values span 12.7 to 483 days. Among the numerous soil studies evaluated here, approximately half yield half-lives that exceed the 6-month threshold for soil persistence.

The laboratory study on the degradation of aerobic sediments (sludge) reported a half-life for chlorpyrifos that is below the 180-day (6-month) threshold stipulated by the Stockholm Convention for the entire system. In most cases, it is not possible to calculate its half-life in sediments independently. For studies conducted under aerobic conditions, the reported half-lives are longer and may even exceed the threshold. Chlorpyrifos exhibits strong adsorption onto sediments; the fraction that is adsorbed may remain unavailable to microbial degradation, which also helps explain why chlorpyrifos has been detected in well water and marine sediments. Its frequent detection can be partly attributed to widespread use, but it may also reflect its enhanced persistence associated with sediments, as well as lower temperatures and other factors.

The environmental half-life of chlorpyrifos ranges from a few days to several years, depending on the application rate, ecosystem type, soil or sediment characteristics, and other environmental factors, including temperature. Monitoring data from the Arctic indicate that chlorpyrifos can undergo long-range transport to remote regions. Given that chlorpyrifos degradation is temperature‑dependent, it is expected to persist in these areas for considerable periods. The frequent detection of chlorpyrifos across all environmental media in the Arctic provides corroborating evidence. Furthermore, chlorpyrifos has been identified in archived sediment cores from lakes in both the Arctic and sub-Arctic.

Accordingly, in accordance with the definition set forth in the Stockholm Convention, chlorpyrifos may be regarded as exhibiting characteristics of persistent organic pollution in certain environmental contexts.

1.2 Conclusions on Bioaccumulation

Log of chlorpyrifos K _ow Indicates that it has the potential for bioaccumulation. When Log K _ow >2 and log K _oa > A BCF greater than 5 indicates that chlorpyrifos can bioaccumulate in oxygen‑consuming organisms. To date, chlorpyrifos has been detected across different trophic levels in remote regions, and it has also been found in top predators worldwide as well as in human breast milk, with concentrations whose effects on offspring drawing significant concern. Based on the available data, it is not yet possible to conclude that the bioconcentration factor exceeds 5,000. Many fish species exhibit moderate bioaccumulation. However, if toxicity is likewise high, even moderate bioaccumulation can lead to elevated internal concentrations and adverse effects, making this a matter of serious concern. Given chlorpyrifos’ high toxicity to fish, invertebrates, amphibians, birds, mammals, and other taxa, combined with its moderate bioconcentration factor (BCF) in soil organisms and a bio‑sediment accumulation factor (BSAF) exceeding 6 in soil microorganisms, it satisfies criterion 2 of Annex D: chlorpyrifos can bioaccumulate in other species, exhibits high toxicity, and possesses ecotoxicity. For these reasons, the European Union considers that chlorpyrifos generally meets the criteria for bioaccumulation.

1.3 Conclusions Regarding the Potential for Long-Distance Dispersal

The gaseous half-life of chlorpyrifos in air is estimated to be 1.4–14 hours, which is relatively short—significantly shorter than the two-day threshold specified in the Stockholm Convention for long-range transport potential (LRTP). In contrast, the particulate form of chlorpyrifos has a much longer half-life of up to 66.5 hours and can persist in both air and water, although it constitutes only a minor fraction of the total atmospheric chlorpyrifos.

Although modeling results cannot predict long-range transport, chlorpyrifos has been detected in various abiotic and biotic media in remote areas far from point sources, including Arctic reindeer, seals, and polar bears, as well as in sea‑ice meltwater and Antarctic air. Consequently, chlorpyrifos is considered to meet the Stockholm Convention’s criteria for long-range environmental transport (SSC, 2018).

1.4 Conclusion Regarding Adverse Effects

Laboratory studies have clearly demonstrated that chlorpyrifos is highly toxic to aquatic communities, exerting adverse effects on aquatic invertebrates at concentrations of approximately 0.1 μg a.s./L or lower. Chlorpyrifos also exhibits high acute toxicity to terrestrial vertebrates, particularly birds; for example, the median lethal concentration for Japanese quail is 13.3 mg a.s./kg body weight. In mammals, the median lethal concentration in mice ranges from 64 to 71 mg a.s./kg body weight. Chronic toxicity values for chlorpyrifos are relatively low; for instance, a no-observed-adverse-effect level of 0.1 mg/kg body weight per day was observed in a two-year dietary study in rats.

Based on these studies, the available data on the ecotoxicity of chlorpyrifos indicate that it may pose risks to the environment. In vivo animal studies have demonstrated that, even at doses below those that induce cholinesterase inhibition, chlorpyrifos can adversely affect the developing nervous system, including alterations in cognition, motor control, and behavior in rats and mice. Taken together with these findings and epidemiological evidence, chlorpyrifos is considered to be neurotoxic to the developing nervous system.

Finally, the European Union stated the following regarding its concerns about chlorpyrifos and the necessity of global action:

The environmental degradation half-life of chlorpyrifos ranges from a few days to several years, depending on application rates, ecosystem type, soil or sediment characteristics, and other environmental factors. Chlorpyrifos can persist in seawater, certain soils, and deeper sediment layers. Monitoring data from the Arctic and Antarctic indicate that chlorpyrifos can be transported over long distances to remote regions. Given that chlorpyrifos degradation is temperature‑dependent, it is expected to remain persistent in these areas for extended periods, as evidenced by its frequent detection across all environmental media in the Arctic. Furthermore, chlorpyrifos has been identified in old sediment cores from Arctic and subarctic lakes. Accordingly, it can be concluded that chlorpyrifos exhibits sufficient persistence to warrant consideration under the Convention.

Although many studies have demonstrated moderate bioconcentration, high toxicity in conjunction with this raises serious concerns. Given that chlorpyrifos has been detected at concentrations sufficient to affect offspring in Arctic organisms across different trophic levels, in global top predators, and in human breast milk, it follows that its potential for bioaccumulation provides ample grounds for its consideration under the Convention.

Chlorpyrifos has a short atmospheric half-life, estimated at 1.4 to 14 hours; however, it has been detected in various abiotic matrices in remote regions of the Arctic and Antarctic, as well as in Arctic top predators—including polar bears—demonstrating its capacity for long-range transboundary transport. Potential transport pathways include atmospheric transport in the gas phase or particulate phase, and transport via water in rivers and/or ocean currents.

Epidemiological evidence, together with animal studies, demonstrates that chlorpyrifos exhibits developmental neurotoxicity in humans.

Furthermore, chlorpyrifos exhibits both acute and chronic toxic effects at very low environmentally relevant concentrations. It is highly toxic to aquatic communities, fish and aquatic invertebrates, as well as to the early life stages of bees, birds, and mammals. The ecotoxicological and toxicological properties of chlorpyrifos can have adverse impacts on human health and the environment.

Given that chlorpyrifos exhibits persistent contamination, bioaccumulative potential, and toxicity to aquatic organisms and terrestrial animals, including humans, and is widely detected in environmental media—even in remote areas—its use is deemed likely to have significant adverse effects on human health and the environment, thus necessitating global action.

In accordance with decision POPRC‑17/4 of the Committee, the European Union’s proposal to list chlorpyrifos in Annexes A, B and/or C of the Convention has been reviewed. Applying the screening criteria set out in Annex D of the Convention and pursuant to paragraph 4(a) of Article 8 of the Convention, it was determined that chlorpyrifos meets those criteria. The Committee established an intersessional working group to conduct a further review of the proposal and to prepare a draft risk profile for chlorpyrifos in line with Annex E of the Convention.

The Committee requests that Parties and observers submit to the Secretariat, by 14 March 2022, the information on chlorpyrifos listed in Annex E.

To date, 14 Parties have submitted Annex E information and related materials to the Committee. Some countries have also provided one or more additional types of information; for example, Canada has submitted its 2003 review report on chlorpyrifos. In addition, seven other countries, participating as observers, have likewise submitted the information required under Annex E, including China—represented by the China Pesticide Industry Association—and India—represented by the Indian Association of Pesticide Producers and Processors—both of which are major producers of chlorpyrifos.

At its seventeenth meeting, the Committee prepared a draft work plan for the intersessional preparation of the “Risk Profile” and the “Risk Management Evaluation” for the seventeenth and eighteenth meetings (Table 1).

2 Can chlorpyrifos be listed in Annex A?

Pursuant to paragraph 7 of Article 8 of the Convention (on the addition of chemicals to Annexes A, B, and C), if the Review Committee, on the basis of the risk profile prepared in accordance with Annex E, determines that: (a) chlorpyrifos may, owing to its long-range environmental transport, give rise to adverse effects on human health and/or the environment, thereby justifying global action, it shall proceed with the consideration of the proposal. Even in the absence of sufficient scientific evidence, such a lack shall not preclude further consideration of the proposal. The Committee shall, through the Secretariat, invite all Parties and observers to submit information relevant to the various considerations set out in Annex F. Thereafter, the Committee shall prepare a risk management evaluation report, including an analysis of possible control measures for the chemical in accordance with Annex F; or (b) the proposal should not be further considered, in which case it shall, through the Secretariat, make the risk profile available to all Parties and observers and set the proposal aside.

Pursuant to paragraph 8 of Article 8 of the Convention, any proposal that has been deferred under paragraph 7(b) above may be subject to a request by a Party to the Conference of the Parties to consider whether the Review Committee should invite the proposing Party and other Parties to submit additional information within a period not exceeding one year. Following that period, the Committee shall, on the basis of any information received and in accordance with the priority order determined by the Conference of the Parties, reconsider the proposal pursuant to paragraph 6 of Article 8 of the Convention. If, after this procedure, the Review Committee again defers the proposal, the Party concerned may challenge the Committee’s decision, and the matter shall be considered by the Conference of the Parties at its next session. The Conference of the Parties may, on the basis of the risk profile prepared in accordance with Annex E and taking into account the Review Committee’s assessment as well as any supplementary information submitted by Parties and observers, decide to continue consideration of the proposal. Should the Conference of the Parties decide to proceed with the consideration of the proposal, the Review Committee shall then prepare a risk management evaluation report.

In accordance with paragraph 9 of Article 8 of the Convention, the Review Committee shall, on the basis of the risk profile referred to in paragraph 6 and the risk management evaluation referred to in paragraph 7(a) or paragraph 8, recommend whether the Conference of the Parties should consider chlorpyrifos for inclusion in Annex A. The Conference of the Parties, after duly taking into account the Committee’s recommendations, including any scientific uncertainties, and in line with the precautionary principle, shall decide whether to list the chemical in Annex A and prescribe the corresponding control measures.

All of the above are standard procedures. At present, the process of listing chlorpyrifos in Annex A is in its final one or two stages, and the final decision is expected to be reached within the next one to two years.

3 International Restrictions and Bans on Chlorpyrifos

Chlorpyrifos has long been a controversial pesticide. In recent years, calls to ban or restrict its use have grown louder, and countries around the world have taken corresponding measures—reassessing it, banning it, or imposing usage restrictions. However, owing to the product’s critical role in agricultural production, progress on these measures has been slow.

Surprisingly, in 2020 the European Union decided not to renew the registration of chlorpyrifos (nor its methyl‑substituted analogue). Because existing data do not rule out the potential genotoxicity of chlorpyrifos and because no toxicological reference values are available, it is impossible to conduct risk assessments for applicators, workers, consumers, bystanders, and residents. Furthermore, based on evidence of delayed neurotoxicity and epidemiological findings, chlorpyrifos has been classified as reproductive toxicity category 1B, and the European Food Safety Authority (EFSA) concluded that it does not meet the regulatory approval criteria. Effective January 1, 2021, chlorpyrifos was also banned in the United Kingdom.

The United States, Canada, and Australia have already revoked the registration of chlorpyrifos for residential and home‑garden use. On February 25, 2022, the U.S. EPA further confirmed that it will phase out all food‑use registrations for chlorpyrifos; several U.S. states, including Hawaii, California, Louisiana, New York, and Connecticut, have either banned or plan to ban the pesticide. In Australia and Canada, agricultural uses are still under ongoing evaluation. India, Thailand, Myanmar, and Malaysia have also proposed banning chlorpyrifos.

4. Potential Impacts on China of Listing Chlorpyrifos on the POPs List

Chlorpyrifos has long been one of China’s key insecticides, widely registered for use on a variety of crops, vegetables, and fruit trees to control numerous pest species. Due to concerns about its residues, Ministry of Agriculture Announcement No. 2032, issued on December 9, 2013, mandated that chlorpyrifos be banned for use on vegetables effective December 31, 2016. Subsequently, chlorpyrifos was included in the Ministry of Agriculture’s “List of Restricted‑Use Pesticides (2017 Edition),” though no specific measures were imposed to regulate its sale and use through designated outlets.

In 2021, the Hainan Provincial Department of Agriculture and Rural Affairs issued a notice announcing the “List of Pesticides Prohibited from Production, Transportation, Storage, Sale, and Use in the Hainan Economic Special Zone (2021 Revised Edition),” under which Hainan has imposed a comprehensive ban on 73 pesticides, including chlorpyrifos. This decision may also have a certain impact on the use of chlorpyrifos‑containing products in other provinces and across the country.

If chlorpyrifos is further listed in Annex A of the Convention by the United Nations Environment Programme (UNEP), it will have an even greater impact on China’s production, use, and export of chlorpyrifos.

4.1 Factors Affecting the Export of Chlorpyrifos

China is a major producer, user, and exporter of chlorpyrifos. According to data from AgroPages, in 2019 China exported 28,900 tonnes of chlorpyrifos (expressed as 100% active ingredient), valued at US$147 million. The top five destination countries were Vietnam, Brazil, Indonesia, Thailand, and Pakistan, which together accounted for 50% of the total value of China’s chlorpyrifos exports.

If chlorpyrifos is listed in Annex A, Chinese companies concerned will undoubtedly be significantly affected, and the domestic pesticide market’s product mix will also face substantial disruption.

4.2 It is conducive to reducing the number of registrations for pesticide emulsifiable concentrate products in China.

As of March 28, 2022, China had registered a total of 1,127 chlorpyrifos products, including 69 technical-grade formulations and 1,058 formulated products. In addition, five methyl‑chlorpyrifos products were registered, comprising three technical-grade formulations and two emulsifiable concentrates.

Among chlorpyrifos formulations, emulsifiable concentrates account for 681 products, representing approximately 30% of all organophosphorus products and roughly 64% of the total chlorpyrifos formulation volume. If chlorpyrifos were banned, China’s emulsifiable concentrate market would shrink by about 7%, thereby increasing the share of environmentally friendly formulation types.

4.3 Promoting the Development of Low-Risk Alternative Pesticides

Among the chlorpyrifos formulations registered domestically, there are 1,037 products for field use and 21 products for public health use.

Since China has banned the use of chlorpyrifos on vegetables, its field‑applied formulations are now primarily registered for controlling pests in rice, as well as in crops such as cotton, peanuts, apple trees, citrus trees, lychee trees, wheat, and sugarcane. As shown in Table 2, most crops have registered alternative pesticides for their target pests; however, for a few specific crops, further development of low‑risk new products or new applications will be necessary to meet demand.

Note: In the “Registered Crops” column, the figures following each crop represent the percentage of chlorpyrifos registrations for that crop relative to the total number of chlorpyrifos formulations registered for field use. In the second column, “Target Pests,” the figures following each target indicate the percentage of chlorpyrifos registrations for that specific target on the crop, relative to the total number of chlorpyrifos registrations for that crop.

Due to the neurotoxicity of chlorpyrifos, its indoor application poses safety risks; it must not be used in sensitive indoor areas where it could be easily accessed by humans or children, and should instead be formulated into bait stations that are out of children’s reach. In practice, chlorpyrifos is primarily employed for termite control. Following the phase-out of organochlorine pesticides, China has a limited selection of registered products for soil and wood treatment to manage termites in buildings, though numerous alternative formulations have now been approved. By contrast, there is a relatively wide array of alternative pesticides and products available for cockroach‑control baits (see Table 3).

Note: Under the “Registered Location” column, the figures following each location represent the percentage of chlorpyrifos registered at that location relative to the total number of chlorpyrifos‑based formulations registered for public health use.

5 Reflections and Prospects

Restricted and prohibited pesticides are a double-edged sword, posing risks to relevant enterprises while also creating opportunities for industrial upgrading.

The possible inclusion of chlorpyrifos in Annex A of the Convention inevitably prompts regulatory authorities to reconsider how registered pesticide products should be supervised. We must study and master international pesticide safety‑assessment methodologies, as well as the principles and criteria for establishing bans or restrictions on pesticide use; we should also adopt a life‑cycle perspective and elevate the standards of pesticide re‑evaluation. China is gradually transitioning from a country that relies on the imitation and production of pesticides to one that emphasizes independent research, development, and manufacturing. To achieve this, we must not only acquire cutting‑edge R&D and production technologies but also establish robust risk‑assessment and phase‑out mechanisms. In doing so, we will not only fulfill our obligations under international conventions but also actively participate in and help shape initiatives aimed at safeguarding human health and enhancing global environmental governance.

It is recommended that relevant authorities and enterprises promptly prepare for the implications of chlorpyrifos being added to the POPs list, opt for alternative low-risk pesticides, and rise to the new challenges.

Source: Pesticide Market Information – New Media World

Authors: Wang Yyan, Shen Jizhong