Under the Stockholm Convention, countries are required to build and maintain detailed inventories of Persistent Organic Pollutants (POPs) to develop and update National Implementation Plans (NIPs). Customs import and export records often serve as a key source of information for these inventories. However, effective use of trade data requires a solid understanding of the Harmonized System (HS) of tariff codes, including how POPs are classified, which articles and products may contain them, and what are the existing gaps in HS coverage under the Convention.
Daniel Cardozo, a chemical engineer and international trade expert with extensive experience in customs classifications and chemicals management, including service as staff of the World Customs Organization (WCO), and Melisa Tin Siong Lim, Project Management Officer at BRS Secretariat/UNEP, answered a number of questions raised during a recent GGKP regional workshop for Latin America and the Caribbean “POPs and Border Control – HS Code Classification and Practical Application” held on 18 September 2025.
POPs: HS Codes Classification and CAS numbers
Q: When identifying chemicals, do they have the same CAS number and HS code? Or are these different?
Daniel Cardozo: A CAS number is a unique numerical identifier assigned to a specific chemical substance. Each chemical has only one CAS number, and no two substances share the same one.
An HS code, on the other hand, is used in customs and trade classification systems. Ideally, an HS code can also be assigned to a specific chemical, which is the most advisable approach. However, in practice, some HS codes cover groups of substances rather than a single chemical.
In other words:
- One chemical always has only one CAS number.
- One chemical may also have a designated HS code, but in some cases, an HS code can apply to several different chemicals.
Q: Why are there products that have two or more CAS numbers?
Daniel Cardozo: In theory, one chemical has only one CAS number. However, sometimes the Chemical Abstract Services assign a different CAS number to an isomer of the chemical. Isomers look similar, they share the same molecular formula and similar names, but different 3D chemical structure.
For example, Hexabromocyclododecanes have several CAS numbers, all of them share the same name, but they are isomers having different chemical structure in which the 6 bromines are distributed differently in the 3D chemical structure.
Q: The further breakdown to the 8-digit HS code helps to reduce confusion in classifying commodities. Here in The Bahamas, as in some other Caribbean countries, we apply the 8-digit level.
Daniel Cardozo: Yes, that is correct. At the international level, the Harmonized System is standardized only up to six digits, and many people expect the Convention to clarify everything at that level. But in practice, additional work must also be done nationally. Countries or regions can add further digits—typically two or more—to create their own tariff lines. For each six-digit subheading, this allows up to 99 additional national subdivisions when using 8-digits. This is the level where commodities, including POPs and related articles, can be more precisely distinguished. I will show you some practical examples of how this can be done.
Melisa Lim: Some countries already have 8-digit codes for identifying POPs and articles containing POPs, and others may want to introduce this type of code. That is the direction the work is heading. If you already have such codes in your national nomenclature, please share them with the Secretariat; or, if you think new ones could be developed, please also send us your ideas.
Q: Is it possible for one product to be classified under more than one heading or subheading?
Daniel Cardozo: Yes, sometimes the same product is classified differently according to how it was presented to Customs or according to its final use or function. For instance, hydrogen peroxide is classified in heading 28.47. According to Section VI Note 2, when the same product is packaged in measured doses or for retail sale, for example to be sold as medicament, then it is classified in heading 30.04.
Chemical Identification in Trade Data
Q: In official customs tariff publications, substances are identified by tariff codes or headings, but CAS numbers are not included. Could CAS numbers be incorporated into these publications to better define POP substances and avoid confusion?
Daniel Cardozo: This is true. In customs documents, the CAS number is not a standard requirement and therefore is usually not indicated directly. Customs declarations and shipping documents (such as invoices, packing lists, and bills of lading) typically rely on HS codes for classifying goods, not CAS numbers. I also agree that it would be good to include the CAS number as a unique identifier in the customs permit, not into the tariff per se. In the customs permit for import and export, you have a lot of data to introduce, the origin, the weight, one of the fields that could be introduced there is a CAS number. However, at this point, if not indicated by the exporter in the invoice and the packing list, it can be also found on the Safety Data Sheets.
Q: In Customs publications, the term DCI in Spanish or INN in English (Denominación Común Internacional or International Nonproprietary Name) appears. Could it be that a trade name is being confused with the ISO denomination? What does the INN (International Nonproprietary Name) nomenclature mean, and how does it differ from ISO?
Daniel Cardozo: ISO names are designations established under ISO standards. By contrast, INN (International Nonproprietary Names) are names assigned by the World Health Organization (WHO) to identify certain medicines. For example, instead of using the long chemical name for paracetamol, WHO designates the nonproprietary name “paracetamol” as a standard short form. These INNs are non-proprietary, internationally recognized names that can be used universally in medicine, research, and regulation, avoiding confusion with lengthy chemical names or commercial brand names.
The World Customs Organization (WCO), upon request by WHO, also classifies INN medicines once a year, and maintains a list of INNs in its database (WCO Six). This provides customs and regulatory authorities with an authoritative reference to ensure consistency in classification.
INN database link at the WCO: https://www.wcoomd.org/-/media/wco/public/global/excel/inn-dci-list.xlsx?db=web
Conventions Compliance and Enforcement
Q: Could you please repeat the import procedure under the Stockholm Convention?
Daniel Cardozo: The Stockholm Convention itself does not set out import/export procedures for POPs. Its core function is to ban or restrict the production and use of POPs. However, if a POP is also listed under the Rotterdam Convention, then the Prior Informed Consent (PIC) procedure must be applied. Similarly, if a POP falls under the Basel Convention, then the Basel procedures for transboundary movement of hazardous wastes apply.
For chemicals listed in Annexes A and B of the Stockholm Convention:
- Import is only permitted for the purpose of environmentally sound disposal, and this must be declared in advance.
- Export is only permitted for environmentally sound disposal, or to another Party that is allowed to use the chemical under specific exemptions listed in Annex A or B.
Melisa Lim: To complement,
- The Basel Convention regulates transboundary movement of hazardous wastes and other wastes, with detailed procedures that Parties must follow.
- The Rotterdam Convention regulates trade in certain chemicals listed in Annex III to the Convention through the PIC procedure.
By contrast, the Stockholm Convention’s main purpose is elimination or restriction of POPs. While some exemptions exist, over time, all Parties are expected to stop producing, using, importing, or exporting POPs altogether.
Q: If a pesticide is listed in the Rotterdam Convention but not in the Stockholm Convention, can it still be marketed even though it cannot be moved around the world?
Melisa Lim: Listing a chemical in Annex III of the Rotterdam Convention does not prohibit its use. Instead, it subjects the chemical to the Prior Informed Consent (PIC) procedure, which governs trade but does not ban it. National regulatory provisions must be consulted regarding whether the pesticide can still be used within a given country. In other words, trade is not prohibited, but it is controlled through the PIC mechanism.
Q: What should be done with products or equipment that are classified under unregulated tariff codes but contain controlled substances?
Daniel Cardozo: If such products or equipment are considered waste, the procedures of the Basel Convention must apply. For example, a transformer that contains PCBs would be classified as hazardous waste. If it is properly declared as containing PCBs, it can be managed and disposed of in an environmentally sound manner under the Basel Convention framework.
However, if these products are misdeclared (e.g., declared simply as “metallic scrap” when they in fact contain PCBs), this constitutes illegal trade. In such cases, the shipment is treated as illegal traffic under the Basel Convention. Depending on national legislation, this may require:
- Investigating the owner of the cargo;
- Returning the illegal shipment to the country of origin; or
- Managing it in another way consistent with environmental and legal requirements.
The key distinction is whether the goods are accurately declared for environmentally sound disposal or misdeclared, in which case enforcement and legal procedures apply.
Q: What institutional arrangements should be in place to share this information among regulators and other relevant agencies?
Daniel Cardozo: Preventing illegal trade and monitoring legal trade in controlled substances requires the cooperation of several enforcement and governmental agencies with competent, designated authorities or/and national focal points at national or international level and also a variety of stakeholders, such as traders, customs brokers, NGOs, etc.
It is preferable to set up institutional arrangements on a formal basis by signing of a memorandum of understanding, by establishing communication channels and adopting joint guidelines and procedures for action, clarifying the competences of each institution.
Q/Comment: In practice, when managing POPs wastes for safeguarding and disposal, several challenges arise. For example, in West Africa, POPs wastes are typically exported to Europe (e.g., France). In such cases, the waste management company handling the safeguarding usually manages the Basel Convention export procedure, including notifications to each country of transit. Only once all countries along the route approve the import or transit can the waste be shipped from country A to country B.
However, this is not possible in all regions. In Central Asia, for instance, many countries prohibit transit, as indicated on the Basel Convention website. This raises serious questions about options for environmentally sound disposal when transit is blocked. Exporting waste over long distances (e.g., 10,000 km) is not only uneconomical but also carries high risks of accidents during transport. Therefore, it is critically important to develop national or regional disposal options and to enhance cooperation among countries.
Melisa Lim: You have highlighted a well-recognized issue regarding the practical challenges of implementing the Prior Informed Consent (PIC) procedure under the Basel Convention. These challenges are regularly discussed among Parties, and there are ongoing processes to identify solutions and make the procedure more efficient.
Authors:
 | Daniel Cardozo, Chemical Engineer and International Trade Expert |
 | Melisa Tin Siong Lim, Project Management Officer, Basel, Rotterdam and Stockholm Conventions (BRS) Secretariat |
