K0763216 041007

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UNITED

NATIONS SC

UNEP/POPS/POPRC.3/INF/7

United Nations

Environment

Programme

Distr.: General

25 September 2007

English only

Stockholm Convention on Persistent Organic Pollutants 

Persistent Organic Pollutants Review Committee

Third meeting

Geneva, 19–23 November 2007

Item 7 of the provisional agenda*

The OECD screening tool for overall persistence and long-range 

transport potential

Presentation on environmental transport and modelling

Note by the Secretariat

1. Potential for long-range environmental transport is one of the screening criteria set out in 

paragraph 1 of Annex D of the Stockholm Convention that must be satisfied if a chemical is to be listed 

in annexes A, B or C of the Convention. According to subparagraph (d) of Annex D, it is evidenced for 

a given chemical by:

“(i) Measured levels of the chemical in locations distant from the sources of its 

release that are of potential concern;

(ii) Monitoring data showing that long-range environmental transport of the

chemical, with the potential for transfer to a receiving environment, may have 

occurred via air, water or migratory species; or

(iii) Environmental fate properties and/or model results that demonstrate that the 

chemical has a potential for long-range environmental transport through air, 

water or migratory species, with the potential for transfer to a receiving 

environment in locations distant from the sources of its release. For a chemical 

that migrates significantly through the air, its half-life in air should be greater 

than two days”.

2. At the second meeting of the Persistent Organic Pollutants Review Committee, it was noted that 

the Organisation for Economic Cooperation and Development (OECD), working with the 

United Nations Environment Programme (UNEP), had developed a model to predict the environmental 

fate and long-range transport of persistent organic pollutants. The Chair of the Committee suggested 

 * UNEP/POPS/POPRC.3/1/Rev.1.
UNEP/POPS/POPRC.3/INF/7

2

that an expert who had been involved in that work might be invited to attend the Committee’s third 

meeting to demonstrate the model.

3. In response to the Chair’s suggestion, Dr. Martin Scheringer from the Swiss Federal Institute of 

Technology Zurich was invited to provide a presentation at the third meeting of the Committee on the 

OECD screening tool for overall persistence and long-range transport potential. A summary of the 

presentation is contained in the annex to the present note. It is presented as received and has not been 

formally edited by the Secretariat.

4. A side event on environmental transport and modelling will be organized during the lunch 

period on Tuesday, 27 November, at which Professor Michael McLachlan from Stockholm University 

and Dr. Scheringer will give further presentations regarding long-range transport models. Their 

presentations will be followed by discussion on the topic.
UNEP/POPS/POPRC.3/INF/7

3

Annex

The OECD screening tool for overall persistence and long-range 

transport potential

Martin Scheringer, Matthew MacLeod, Fabio Wegmann, Swiss Federal Institute of Technology Zurich 

(ETH Zurich), scheringer@chem.ethz.ch.

Overall persistence (Pov) and long-range transport potential (LRTP) are indicators describing the 

potential of chemicals to be present in the environment for a long time and to be transported over long 

distances (Scheringer 1996). High Pov and LRTP are unwanted properties of chemicals because, if a 

chemical with high Pov and LRTP causes health effects in humans or wildlife, these effects will cover a 

large area and can persist for a long time. In October 2001, a workshop on the “Use of Multimedia 

Models for Estimating Overall Environmental Persistence and Long-Range Transport in the Context of 

PBTs/POPs Assessment”, organized by UNEP and OECD, was held in Ottawa, Canada. 

Recommendations from the workshop were that different multimedia models should be compared and 

that a core set of multimedia models should be available and accessible at no cost to the public.

Based on these recommendations, the developers of nine multimedia fate and transport models 

performed a comparison of their models with respect to the ranking of chemicals in terms of Pov and 

LRTP (Fenner et al. 2005). They used a set of 3175 hypothetical chemicals covering a broad range of 

chemical properties to investigate how closely the nine models would rank them in terms of Pov and 

LRTP. Whereas absolute Pov and LRTP values differed considerably among the models, the rankings 

of the 3175 chemicals were highly similar for Pov and still considerably similar for LRTP. This 

indicates that the models yield similar results for the purpose of identifying chemicals with high Pov 

and LRTP. On this basis, the model developers agreed that a consensus model representing the 

essential features of the different models should be developed. The OECD agreed to support the 

development of the consensus model and to make it available from the OECD web site. The model was 

developed in 2005 by a team of researchers at ETH Zurich (Wegmann et al. 2007) and presented at 

international workshops in Switzerland, Canada and Japan. The main purpose of the model is to 

provide estimates of Pov and LRTP of organic chemicals and to present these estimates in an intuitive 

way. It is included in a single MS Excel spreadsheet that can easily be used on any personal computer. 

The model has been applied to the POP candidates that have been proposed for inclusion in the list of 

POPs of the Stockholm Convention. These were γ-HCH, pentabromodiphenyl ether (BDE-99), 

hexabromobiphenyl, and chlordecone in 2006 (PFOS was excluded) and penta-chloro-benzene, α- and 

β-HCH, octabromo-diphenylether, and short-chain chlorinated paraffin in 2007. Results for Pov and 

LRTP of these substances will be presented and discussed in the talk, and the application of the model 

will be illustrated. 

1. Fenner, K., Scheringer, M., MacLeod, M., Matthies, M., McKone, T.E., Stroebe, M., Beyer, A., 

Bonnell, M., Le Gall, A.C., Klasmeier, J., Mackay, D., Pennington, D.W., Scharenberg, B. (2005) 

Comparing Estimates of Persistence and Long-Range Transport Potential among Multimedia Models, 

Environmental Science & Technology 39, 1932–1942.

2. Scheringer, M. (1996) Persistence and Spatial Range as Endpoints of an Exposure-Based 

Assessment of Organic Chemicals, Environmental Science & Technology 30, 1652–1659. 

3. Wegmann, F., Cavin, L., MacLeod, M., Scheringer, M., Hungerbühler, K. (2007) The OECD 

Software Tool for Screening Chemicals for Persistence and Long-Range Transport Potential, under 

review for Environmental Modeling and Software. Available on request from the authors.

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