Stockholm Convention on Persistent Organic Pollutants
27 April 2023
The Stockholm Convention on Persistent Organic Pollutants is a global treaty between 186 countries to protect human health and the environment from chemicals that remain intact in the environment for long periods, become widely distributed geographically, accumulate in the fatty tissue of humans and wildlife, and have harmful impacts on human health or the environment. It is the youngest of the Basel, Rotterdam, and Stockholm Conventions, which together tackle the life cycle of global chemicals and waste.
Brief by Pamela Chasek, PhD
What are Persistent Organic Pollutants?
Persistent organic pollutants (POPs) are a class of highly hazardous chemical pollutants that are a serious, global threat to human health and to ecosystems. POPs are substances that specifically:
- remain intact for exceptionally long periods of time (many years);
- become widely distributed throughout the environment as a result of natural processes involving soil, water and, most notably, air;
- accumulate in living organisms including humans, and are found at higher concentrations at higher levels in the food chain; and
- are toxic to both humans and wildlife.
Many POPs were developed after World War II, when thousands of synthetic chemicals were introduced into commercial use. Some POPs are pesticides, some are industrial chemicals, and some are unintentionally produced by-products that form during certain combustion and chemical processes. Many of these chemicals benefit pest and disease control, crop production, and industry. Examples include polychlorinated biphenyls (PCBs), which have been useful in a variety of industrial applications, such as in electrical transformers and large capacitors, as hydraulic and heat exchange fluids, and as additives to paints and lubricants. DDT is a well-known POP that is still used to control mosquitoes that carry malaria. Unintentionally produced chemicals include dioxins, which result from some industrial processes and from combustion, such as municipal and medical waste incineration and backyard burning of trash.
Why was the Stockholm Convention developed?
In the 1980s and early 1990s, scientific evidence grew about the dangers from POPs. For example, when people eat POPs-contaminated foods, the POPs accumulate in their fatty tissue. Mothers pass POPs from their own bodies to their offspring. POPs contamination can lead to cancers and tumours, neurological disorders, immune suppression, reproductive disorders, and other diseases, including increased incidence of type 2 diabetes, endometriosis, hepatitis, and cirrhosis.
In May 1995, the United Nations Environment Programme’s (UNEP) Governing Council in decision 18/32 called for an international assessment process of an initial list of 12 POPs and that the Intergovernmental Forum on Chemical Safety (IFCS) develop recommendations on international action for consideration by the Governing Council and the World Health Assembly no later than 1997. The 12 POPs, sometimes called the “dirty dozen,” include:
- pesticides: aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, and toxaphene;
- industrial chemicals: hexachlorobenzene and PCBs; and
- unintentionally produced POPs: dioxins and furans
In June 1996, the IFCS concluded international action, including a global legally binding instrument, was required to minimize the risks from the 12 POPs through measures to reduce and/or eliminate their emissions or discharges. So, in February 1997, the UNEP Governing Council in its decision 19/13C established an intergovernmental negotiating committee (INC), with a mandate to prepare an international legally binding instrument to implement international action beginning with the 12 POPs. The INC met five times between June 1998 and December 2000. The Stockholm Convention was adopted and opened for signature at a Conference of Plenipotentiaries held from 22 to 23 May 2001 in Stockholm, Sweden. The Convention entered into force on 17 May 2004.
How does the Stockholm Convention work?
The Stockholm Convention lists chemicals in three annexes: Annex A lists chemicals to be eliminated; Annex B lists chemicals to be restricted; and Annex C calls for minimizing unintentional production and release of listed chemicals.
Beyond the first 12 POPs, the Stockholm Convention established specific scientific criteria and a step-by-step procedure for identifying, evaluating, and adding chemicals to the treaty. At the first meeting of the Conference of the Parties (COP-1) in 2005, the COP established the Persistent Organic Pollutants Review Committee (POPRC) to consider additional substances for listing under the Convention.
The Committee is comprised of 31 government-designated experts who review nominated chemicals in three stages. The Committee first determines whether the substance fulfils the screening criteria detailed in Annex D of the Convention, relating to the chemical’s persistence, bioaccumulation, potential for long-range environmental transport, and adverse effects on human health or the environment. If a substance fulfils these requirements, the Committee drafts a risk profile according to Annex E to evaluate whether the substance is likely, because of its long-range environmental transport, to lead to significant adverse human health and/or environmental effects and therefore warrants global action. Finally, if the POPRC finds global action is warranted, it develops a risk management evaluation according to Annex F, reflecting socio-economic considerations associated with possible control measures. Based on this, the POPRC decides whether to recommend the COP list the substance under Annexes A, B, and/or C.
Under the treaty, any party may nominate a chemical for evaluation. Each stage (criteria, risk profile, risk-management evaluation) typically takes one year, but some chemicals progress more slowly if the POPRC requires additional time to gather and review relevant information. Since 2005, the COP has added 19 POPs to the original dirty dozen that are now controlled under the Convention (See Table 1).
| Chemical | Annex | Use |
|---|---|---|
| Alpha hexachlorocyclohexane; Beta hexachlorocyclohexane | A | Byproduct of the production of the insecticide lindane |
| Chlordecone | A | Pest control |
| Decabromodiphenyl ether (commercial mixture, c-decaBDE) | A | Flame retardant; applications including in plastics/ polymers/composites, textiles, adhesives, sealants, coatings and inks. DecaBDE containing plastics are used in housings of computers and TVs, wires and cables, pipes and carpets. |
| Dicofol | A | Organochlorine miticide/pesticide used for foliar applications, mostly on cotton, apples, and citrus and other crops |
| Hexabromobiphenyl | A | Industrial chemical that has been used as a flame retardant |
| Hexabromocyclododecane (HBCD) | A | Used as a flame retardant additive on polystyrene materials in the 1980s as a part of safety regulation for articles, vehicles, and buildings |
| Hexabromodiphenyl ether and heptabromodiphenyl ether (commercial octabromodiphenyl ether) | A | Main components of commercial octabromodiphenyl ether (c-octaBDE) used as a flame retardant in the plastic industry for polymers used for housings of equipment containing electronics |
| Hexachlorobutadiene (HCBD) | A and C | Unintentionally formed and released from the production of certain chlorinated hydrocarbons, magnesium, polyvinyl chloride, ethylene dichloride and vinyl chloride monomer and incineration of acetylene, chlorine residues |
| Lindane | A | Broad-spectrum insecticide for seed and soil treatment, foliar applications, tree and wood treatment and against ectoparasites in both veterinary and human applications |
| Pentachlorobenzene | A and C | Used in PCB products, in dyestuff carriers, as a fungicide, a flame retardant and as a chemical intermediate; also produced unintentionally during combustion, thermal and industrial processes |
| Pentachlorophenol and its salts and esters | A | Fungicide and wood preservative |
| Perfluorohexane sulfonic acid (PFHxS), its salts and PFHxS-related compounds | A | A chemical used as a surfactant in a variety of industrial and commercial products such as food packaging, stain and water-resistant materials, fire-fighting foams and paint additives |
| Perfluorooctane sulfonic acid (PFOS), its salts and perfluorooctane sulfonyl fluoride (PFOSF) | B | Used in stain-resistant fabrics, fire-fighting foams, food packaging, and as a surfactant in industrial processes. |
| Perfluorooctanoic acid (PFOA), its salts and PFOA-related compounds | A | Used in a wide variety of applications such as in the fluoropolymer and fluoroelastomer production, as surfactants in fire-fighting foams, and in textile and paper production to provide water, grease, oil and/or dirt repellency. |
| Polychlorinated naphthalenes | A and C | Used in lubricants and electrical insulation |
| Short-chain chlorinated paraffins (SCCPs) | A | Primarily used in metalworking applications and in polyvinyl chloride (PVC) processing |
| Technical endosulfan and its related isomers | A | Pesticide used mainly on cotton, tea, coffee, soybean, sunflower, vegetables, rice, pulses and fruit |
| Tetrabromodiphenyl ether and pentabromodiphenyl ether (commercial pentabromodiphenyl ether) | A | Used as commercial flame retardants |
What are the Challenges in Dealing with “Live” Chemicals?
While the process of adding new substances works well, there are some obstacles. By creating the POPRC, the Stockholm Convention attempted to separate the scientific and technical consideration of nominated POPs—the purview of the POPRC—from the political concerns of parties, which are discussed by the COP. In essence, the POPRC addresses whether the convention can control a substance and how it would do so. Then the COP decides if it should.
However new challenges emerged, as the convention shifted to the evaluation of toxic chemicals still in widespread production and use (“live” chemicals), especially with regard to socio-economic considerations in the risk-management evaluation phase. This transition from “dead” to “live” chemicals illustrates the challenges of recommending policy responses to protect human health and the environment from chemicals that are still being used in applications such as fire-fighting foams, which are important for human safety.
With live chemicals, the POPRC is forced to consider both the science and the socio-economic implications of its recommendations to eliminate or reduce chemicals, including recommendations to allow some uses of the chemical to continue for a limited time, when use of safe alternative chemicals is not economically or technically feasible. At the political level, however, the COP has sometimes agreed to allow additional uses of these live chemicals, for longer time periods than the POPRC recommended, which delays the elimination or reduction of POPs production and use.
Fire-fighting foams, for example, presented a particularly difficult conundrum when weighing the dangers to human health and the environment, with the public safety risks posed by fires at places like airports and oil refineries (so-called “class B” fires) where PFOA-containing fire-fighting foams are used. The POPRC considered the dangers of future releases of PFOA from fire-fighting foams, particularly given their widespread use and the large amounts of foam dispersed when fighting a fire, which can cause both local contamination and global dispersion of PFOA. But, on the socio-economic side, an estimated USD 80 billion would be required to replace these foams, which led to a call for exemptions. PFOA was ultimately added to the Stockholm Convention in 2019, with specific exemptions.
What Other Challenges does the Stockholm Convention face?
According to the second effectiveness evaluation of the Stockholm Convention completed in 2022, there are some continuing implementation challenges that should be addressed. For example, many governments still need to strengthen the legal, administrative, and other domestic measures to control POPs, including through the development or revision of national legislation and regulations on POPs and their waste. Governments need to strengthen environmentally sound management of POPs waste, by taking appropriate measures to manage stockpiles and wastes, particularly obsolete pesticides, in an environmentally sound manner to ensure they do not enter recycling streams. Governments also need to strengthen awareness-raising and information exchange, including engaging with populations most at risk to the exposure of POPs.
The Stockholm Convention also needs to establish compliance procedures and mechanisms, and strengthen information collection, especially on national inventories of the production, use and releases of POPs. In addition, a perennial problem for all multilateral environmental agreements is the need to provide technical assistance and financial resources to developing country parties and parties with economies in transition. This is particularly important under the Stockholm Convention because these parties need assistance for the management and elimination of the POPs listed under the Convention.
Overall, the second effectiveness evaluation showed that regulations targeting POPs have succeeded in reducing levels of POPs in humans and the environment. For the initial POPs, concentrations measured in air and in human populations have declined and continue to decline or remain at low levels due to restrictions on POPs, some of which predated the Stockholm Convention and are now incorporated in it. For the newly listed POPs, concentrations are beginning to show decreases, although in a few instances, increasing and/or stable levels are observed. But the Convention cannot afford to rest on its laurels as these “forever chemicals” will take years to eliminate. And while they are still in the environment, human health and ecosystems remain at risk.