Further description:-  Persistent Organic Pollutants 

Glossary Entry
Persistent organic pollutants (POPs) are extremely toxic substances for environment and human 
health at a world scale. Their physical and chemical properties, particularly their high stability,
give them ubiquity and capacity of accumulation in the leaving organisms and nature. POPs are man-
made compounds (not naturally found) such as PCB, some pesticides, insecticides and contaminants
of paper and hydrocarbon industries, and substances which delay fire. They may also result of combustion
(dioxin, furan). Governmental organisations get on togather to focus action on 12 or 16 selected
Level 1: Diffuse Pollution:

Persistent Organic Pollutants (POPs)



Some of the persistent organic pollutants (POPs) have been deliberately produced by the industry for a wide variety of applications (i.e. pesticides, polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs). Others are accidentally formed or eventually released as a byproduct from various activities, such as industrial or combustion processes (i.e., polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polycyclic aromatic hydrocarbons (PAHs). Since 1995, the international community was working on legal instruments to eliminate POPs. Different organisations initiated an assessment process, which in December 2000 resulted in the resolution of the POP Convention. Initial action is taken towards twelve POPs: Aldrin, Chlordane, DDT, Dieldrin, Endrin, Heptachlor, Hexachlorobenzene, Mirex, Toxaphene, PCBs, PCDDs and PCDFs (Tab. 1).


Table 1: Comparative lists of POPs selected for environmental and toxicological studies.

POPs selected on the Stockholm Convention (2001)

Organic pollutants (or proposed POPs) with an assigned TEF* or REP**

Emerging POPs











































* Toxic Equivalent Factor; ** Relative Potency


Further information:



In the last decades, emphasis has been put on the evaluation of the dioxin toxic potency of different environmental samples. The commonly named dioxin-like compounds (DLCs), such as PCDDs, PCDFs, PCBs and PCNs, were studied in order to determine their relative toxic potency. Recently, some studies indicated that if samples contain both PAHs and DLCs, the PAHs can dominate equivalent estimations. Other emerging contaminants, such as brominated flame retardants, also exhibited dioxin-like activities. The knowledge of the relative contribution of each contaminant to the total dioxin-like activity associated with environmental samples could aid in identifying the most important contributory pollutants.

Although consensus values for the relative potencies of the most active PCDDs, PCDFs and PCBs have been established, the database of relative potency values for other DLCs is currently limited.

The contribution of each contaminant to the total toxicity of environmental samples depends on the relative order of potency along with the contamination levels in the environment. Dioxins are the most potent contaminants. Their levels in soils and sediments, however, are much lower than those presented by other POPs, such as PCBs, PCNs, PBDEs or PAHs. For this reason, greater toxicity contributions of less potent contaminants with higher concentrations could be found. A number of studies have reported PCDD, PCDF and PCB levels from sediments and sludge in North America, Europe and Asia. Regarding the PCB data, a number of studies have reported levels expressed as total PCBs or as a sum of seven indicator PCBs; however, the literature on the dioxin-like PCBs is very scant.

The relative order of potency, along with the wide distribution of PAH, PCN or PBDE contamination in the environment, suggests that monitoring programmes should be extended to include these persistent substances besides the PCDDs, PCDFs and PCBs regularly analysed at present. Quality objectives for TEQs have been formulated in order to assess the quality of freshwater and coastal sediments, resulting in a safe sediment value of 20 pg TEQ/g. Fig. 1.1 shows the concentration levels of each contaminant group needed to reach this safe value. These levels were calculated using the most potent congener of each contaminant group. Moreover, the concentration levels normally found in different sediment samples were depicted. As can be seen, the monitoring of PCDDs, PCDFs and PCBs is important, but other contaminants like PCNs, and esspecially PAHs, need further control.

Furthermore, data on brominated dioxin, as well as mixed brominated-chlorinated dioxins are needed in order to determine their environmental impact. However, chemical analysis of mixed halogenated compounds is very difficult in environmental samples due to the large number of possible combinations (there are 4600 potential mixed congeners). In order to achieve this goal it is necessary to develop analytical procedures that permit the determination of different groups of halogenated contaminants.













Figure 1: Comparison between the concentration levels needed to reach the safe sediment value and the concentration levels generally found in sediment samples (values expressed in pg/g).




Key publications

E. Eljarrat, D. Barcelo (2003): Priority lists for persistent organic pollutants and emerging contaminants based on their relative toxic potency in environmental samples. Trends in Analytical Chemistry  22/10, 655-665




Policy and regulations


Stockholm convention on Persistent Organic Pollutants (POPs)

The Stockholm Convention is a global treaty to protect human health and the environment from persistent organic pollutants (POPs). POPs are chemicals that remain intact in the environment for long periods, become widely distributed geographically, accumulate in the fatty tissue of living organisms and are toxic to humans and wildlife. POPs circulate globally and can cause damage wherever they travel. In implementing the Convention, Governments will take measures to eliminate or reduce the release of POPs into the environment.





Stockholm, 22 May 2001 - The International Council of Chemical Associations, ICCA, also speaking on behalf of the World Chlorine Council (WCC) today welcomes the adoption in Stockholm, Sweden, of the UNEP Convention on Persistent Organic Pollutants (POP).


The Convention is a legally binding instrument for persistent organic pollutants that undergo long-range transport, so called POPs.  The Convention will require phase-outs or restrictions of listed POPs products and the continuing minimisation and/or, when technically and economically feasible, ultimate elimination of releases of POPs listed as byproducts. The Convention presently covers twelve POPs, including eight pesticides (aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, and toxaphene), two industrial chemicals (PCBs and hexachlorobenzene, which is also a pesticide), and four unwanted by-products of combustion and industrial processes (dioxins, furans, hexachlorobenzene and polychlorinated biphenyls).  A science-based process for adding additional POPs and determining appropriate risk management measures is also part of the Convention. Governments are to promote the best available technologies and practices for minimizing POPs emissions and destroying POPs waste while preventing the development of new POPs. They will draw up national legislation and develop action plans for carrying out their commitments.

Initial action

What are the criteria for POP in the Stockholm Convention on POPs (Procedure to add new POPs)?

·        PERSISTENCE: half life of 2 months in water

·        BIOACCUMULATION: BCF in aquatic species greater than 5000 or KO/W greater han 5

·        ADVERSE EFFECTS: evidence of adverse effects to human health or to the environment

·        POTENTIAL FOR LONGE-RANGE ENVIRONMENTAL TRANSPORT: measured levels of the chemical in locations distant from the sources of its release that are of potential concern


POPs selected for environmental and toxicological studies



Decision support / management tools




Country information / Library



D. Barcelo, P. Grathwohl, K. Jones, K.-U. Totsche




Who does what?

SOWA – Integrated Soil and water Protection: Risks from diffuse pollution






SOWA Working Group “Inventory: “Identification of priority compound classes”

Lead: Damiá Barcelò (dbcqam@cid.csic.es)

The most relevant organic compounds such as persistent organic pollutants POPs, i.e. polycyclic aromatic hydrocarbons (PAHs) are inventored and discussed. The relevance of emerging and new compounds and their impact on soil, water, and ecosystems is adressed and as a main future task, the following future research needs are identified:

·        the urgent need of a European list of emerging contaminants,

·        the interaction of chemicals between soil and water as a key issue

·        the lack of studies to assess the functioning of the water/soil system.





No Author information available