Introduction
In our daily lives, some seemingly harmless chemicals may hide significant environmental and health risks. These substances, known as Persistent Organic Pollutants (POPs), pose a long-term threat to human health and ecosystems because they are difficult to break down, can accumulate in living organisms, and magnify through the food chain. To address this global challenge, the Stockholm Convention on Persistent Organic Pollutants (hereinafter referred to as the "Stockholm Convention") was established.
The Stockholm Convention on POPs: A Global Treaty for Chemical Elimination
The Stockholm Convention is a global treaty aimed at protecting human health and the environment from the dangers of POPs. It was officially adopted at a diplomatic conference in Stockholm, Sweden, in 2001, signed by an initial 128 parties, and entered into force in 2004. Its core objective is to eliminate or restrict the production and use of POPs and to reduce their unintentional release. Initially, the Convention listed 12 POPs, including DDT and polychlorinated biphenyls (PCBs). As scientific research has advanced, the Convention's annexes have been continuously updated to include more chemicals with POPs characteristics. As of July 2025, 37 substances have been identified as POPs and are regulated under the Stockholm Convention.
The Convention is centered around its three annexes, which act as three lines of defense, classifying and managing different POPs and setting clear legal obligations for the parties:
Annex A - Elimination: This is the most stringent list. Chemicals listed in this annex must be eliminated, meaning parties must take measures to cease all production and use, with exemptions only for specific cases, such as laboratory-scale research.
Representative substances: Aldrin, Dieldrin, Endrin, Polychlorinated biphenyls (PCBs), DDT, Hexachlorobutadiene (HCBD), and Short-chain chlorinated paraffins (SCCPs).
Annex B - Restriction: The production and use of chemicals on this list are strictly limited. The Convention permits their continued use for specific, acceptable purposes, but parties must implement measures to prevent their release into the environment.
Representative substances: Perfluorooctane sulfonic acid (PFOS), its salts and perfluorooctane sulfonyl fluoride (PFOSF) are key substances in this annex. While their primary uses have been banned, exemptions still exist for critical applications, such as specific photolithography processes and metal plating.
Annex C - Unintentional Production: This annex targets byproducts generated unintentionally during industrial processes (such as dioxins), requiring measures to continuously reduce and ultimately eliminate their emissions wherever possible.
Representative substances: Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and hexachlorobenzene (HCB).
The EU POPs Regulation: A Stricter and More Comprehensive Regional Practice
If the Stockholm Convention sets the global guiding principles, then the EU's Regulation (EU) 2019/1021 (hereinafter the "EU POPs Regulation") is the region's legally binding implementation of those principles and the core tool for fulfilling its international commitments. It not only fully adopts the Convention's lists but, in some respects, establishes even stricter standards and faster phase-out schedules.
The annex structure of the EU POPs Regulation is similar to the Convention's but more detailed:
Annex I - Prohibition: This corresponds to the Convention's Annexes A and B. It lists all substances whose production, placing on the market, and use are prohibited. It is noteworthy that the EU often places substances from Annex B (Restriction) of the Stockholm Convention, such as PFOS, directly into Annex I of its regulation. This annex provides highly limited and specific conditional exemptions, reflecting the EU's more stringent control standards. It also specifies Unintentional Trace Contaminant (UTC) limit values for substances in products, which serve as a key basis for enforcement.
Annex II - Restriction: This annex is currently empty. Substances requiring restriction have been incorporated into Annex I along with their exemption clauses, creating a more unified and clear management system.
Annex III - List of substances subject to release reduction provisions: This directly corresponds to the Convention's Annex C, listing substances like dioxins, furans, and PCBs that require control of unintentional emissions. It also mandates that member states develop and implement action plans to minimize the release of these substances.
Annex IV - Waste Management: This is a significant addition in the EU regulation, setting specific concentration limits for waste containing POPs listed in the first three annexes. If the POPs content in waste exceeds these limits, it must be disposed of in a way that destroys or irreversibly transforms the pollutants, strictly prohibiting recycling or landfilling. This approach effectively cuts off the pathway for POPs to re-enter the environment through the waste cycle.
Looking Ahead: Substances Soon to Be Added to the Lists
The list of POPs is not static; as scientific research progresses, new chemicals with POPs characteristics are continuously identified.
In May 2025, at the twelfth meeting of the Conference of the Parties to the Stockholm Convention (COP-12), Chlorpyrifos, medium-chain chlorinated paraffins (MCCPs) and long-chain perfluorocarboxylic acids (LC-PFCAs) were officially added to Annex A. These substances are now in the process of being formally incorporated into the EU POPs Regulation. Currently, the UN POPs Review Committee (POPRC) has placed new chemical substances on its review agenda. These substances are in various stages of evaluation and are potential candidates for future inclusion in the Convention:
• Polybrominated dibenzo-p-dioxins (PBDDs): Similar to dioxins (PCDDs), PBDDs are considered highly toxic and persistent pollutants. They are primarily generated unintentionally during the combustion of materials containing bromine, such as certain flame retardants.
• Polybrominated dibenzofurans (PBDFs): Similar to PCDFs, PBDFs are not only produced during combustion but are also often present as impurities in commercial brominated flame retardant products.
• Mixed polybromo/chloro-dioxins and furans (PBCDDs/PBDFs): These are dioxin and furan molecules that contain both bromine and chlorine atoms. These highly toxic substances are easily formed unintentionally when different types of waste containing both elements, such as bromine-containing electronic waste and chlorine-containing PVC plastics, are incinerated together.
Once these substances are formally included in the Stockholm Convention, the EU will quickly initiate its internal legislative process to add them to the annexes of the EU POPs Regulation and establish corresponding limit values and control measures.
Conclusion
The Stockholm Convention acts as a global "blacklist" for POPs, while the EU POPs Regulation is a key instrument for its implementation. The EU often acts as a "front-runner," with a list of restricted substances that may be broader and limit values that may be stricter than the Convention's. These annexes are not just working documents for scientists and legislators; they are directly linked to global trade, industrial supply chains, and consumer safety.
Understanding the changes to these lists, especially paying attention to newly added substances, can help companies plan ahead, develop safer alternatives, and drive society toward a non-toxic, sustainable future.
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