Persistent organic pollutants (POPs) are organic compounds of natural or anthropogenic origin that resist photolytic, chemical and / or biological degradation (UNEP, 1999). They are characterised by low water solubility and high lipid solubility, which gives then high potential for bioaccumulation in fatty tissues of living organisms. POPs are semi-volatile, allowing them to be transported via the atmosphere, long distances from their original source. POPs are also distributed via the aquatic environment. As a consequence of their environmental transport, POPs have been distributed throughout the planet, including regions where they have never been used.
APIS contains records on three major POPs, covering organochlorine pesticides (e.g. DDT), industrial chemicals (e.g. PCBs) and by-products (e.g. PAHs). An overview of their sources and fate is available (Jones & de Voogt 1999). The full list is as follows:
- DDT & analogs (DDT, TDE etc)
- HCH compounds (alpha-, beta & gamma- isomers of HCH)
- Cyclodienes & related compounds (dieldrin, aldrin, endrin, chlordane, heptachlor)
- Toxaphene & related compounds (toxaphene)
- Compounds with Caged Structures (mirex & chlordecone)
Industrial Chemical Groupings:
- Polychlorinated biphenyls (PCBs)
By-products or contaminants:
- dioxins /furans (PCDDs/Fs)
- Polycyclic aromatic hydrocarbons (PAHs)
POPs are toxic, persistent and tend to bioaccumulate. Toxic effects in water and soil are unlikely, except near a point source or as the result of an accident, although there is little direct information available. It is likely that the concentration of PAHs in some lake sediments is high enough that sediment-dwelling organisms (midge larvae, oligochaetes, crustacea) may be affected (Sanders et al. 1996; Rippey 1990).
The tendency of POPs to bioaccumulate means that it is top predators that are affected, in particular, birds (raptors, piscivors and marine) and marine mammals (seals and whales). Well-known examples of the effects of bioaccumulation are egg shell thinning by OCs in birds of prey (Pearse et al. 1979) and reproductive impairment by OCs, PCBs and PCDDs/Fs in fish-eating birds (Bosveld & van den Berg 1994; Munro et al. 1994). More recently, organochlorines (OCs) and PCBs are now though to be responsible for endocrine disruption in freshwater fish.
Some PAHs are known or suspected carcinogens, although the ecological consequences have not been established, as most organisms will be predated before they develop carcinomas. However tumours in fish can present a problem for the human food chain.
The Stockholm Convention on Persistent Organic Pollutants
The Stockholm Convention on Persistent Organic Pollutants was adopted on 22 May 2001 in Stockholm, Sweden. The Convention entered into force on 17 May 2004.
This is a global treaty 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 on the environment. Exposure to Persistent Organic Pollutants (POPs) can lead to serious health effects including certain cancers, birth defects, dysfunctional immune and reproductive systems, greater susceptibility to disease and damages to the central and peripheral nervous systems. Given their long range transport, no one government acting alone can protect its citizens or its environment from POPs. In response to this global problem, the Stockholm Convention, which was adopted in 2001 and entered into force in 2004, requires its parties to take measures to eliminate or reduce the release of POPs into the environment.
As set out in Article 1, the objective of the Stockholm Convention is to protect human health and the environment from persistent organic pollutants. Among others, the provisions of the Convention require each party to:
•Prohibit and/or eliminate the production and use, as well as the import and export, of the intentionally produced POPs that are listed in Annex A to the Convention (Article 3). Annex A allows for the registration of specific exemptions for the production or use of listed POPs, in accordance with that Annex and Article 4, bearing in mind that special rules apply to PCBs. The import and export of chemicals listed in Annex A can take place under specific restrictive conditions, as set out in paragraph 2 of Article 3.
•Restrict the production and use, as well as the import and export, of the intentionally produced POPs that are listed in Annex B to the Convention (Article 3). Annex B allows for the registration of acceptable purposes for the production and use of the listed POPs, in accordance with that Annex, and for the registration of specific exemptions for the production and use of the listed POPs, in accordance with that Annex and Article 4. The import and export of chemicals listed in Annex B can take place under specific restrictive conditions, as set out in paragraph 2 of Article 3.
•Reduce or eliminate releases from unintentionally produced POPs that are listed in Annex C to the Convention (Article 5). The Convention promotes the use of best available techniques and best environmental practices for preventing releases of POPs into the environment.
•Ensure that stockpiles and wastes consisting of, containing or contaminated with POPs are managed safely and in an environmentally sound manner (Article 6). The Convention requires that such stockpiles and wastes be identified and managed to reduce or eliminate POPs releases from these sources. The Convention also requires that wastes containing POPs are transported across international boundaries taking into account relevant international rules, standards and guidelines.
•To target additional POPs (Article 8). The Convention provides for detailed procedures for the listing of new POPs in Annexes A, B and/or C. A Committee composed of experts in chemical assessment or management - the Persistent Organic Pollutants review Committee, is established to examine proposals for the listing of chemicals, in accordance with the process set out in Article 8 and the information requirements specified in Annexes D, E and F of the Convention.
•Other provisions of the Convention relate to the development of implementation plans (Article 7), information exchange (Article 9), public information, awareness and education (Article 10), research, development and monitoring (Article 11), technical assistance (Article 12), financial resources and mechanisms (Article 13), reporting (Article 15), effectiveness evaluation (Article 16) and non-compliance (Article 17).