EMEP Contribution to the Preparatory Work for the Review of the CLRTAP Protocol on POPs. New Substances: Model Assessment of Potential for Long-range Transboundary Atmospheric Transport and Persistence of Pentachlorobenzene

MSC-E Information Note 15/2005

N. Vulykh, E. Mantseva, V. Shatalov

ABSTRACT

Pentachlorobenzene (PeCB) is a widespread organochlorine compound. PeCB is always present in all chlorinated benzenes, which in their turn are widely known as:

- intermediate products at the production of many organic species;
- solvents in stain manufacturing;
- additions to transformer oils and lubricants.

Besides, there is information about the presence of chlorinated benzenes in emissions (flue gases) from pulp and paper mills. PeCB concentrations in pulp and paper mills in Finland are from 0.2 to 0.9 mg/m3 [HSDB, 2001]. This substance is also present as an admixture to pentachlorophenol, other chlorinated phenols and hexachlorobenzene therefore it can be found in places of their application. PeCB like others chlorinated aromatic compounds with one and more benzene rings are identified at different stages of solid domestic waste incineration [Wilkstrom and Marklund, 2000]. PeCB can be formed "de novo" at the combustion of ethane, ethylene and acetylene at the presence of hydrogen chloride and catalysts which are silicon, aluminium and copper oxides and flue soot particles [Frose and Hutzinger, 1996a,b]. PeCB was the original reagent for the manufacturing the fungicide quintozene or pentachloronitrobenzene (PCNB). Mainly PCNB is used as a fungicide against agents of diseases of cotton, grain-crops, vegetables and decorative cultures.

PeCB is within a scope of interest of the Task Force on POPs as a potential candidate for the inclusion into the Protocol on POPs. This year the European Commission has submitted a proposal for amendment to the Protocol with regard to this chemical. In accordance with a suggestion of the Working Group on Strategies and Review that during the 90-day period between the submission of dossier and the twenty-third session of the Executive Body, the preliminary dossier on PeCB prepared by national experts [van de Plassche et al., 2005] is available on the Convention's website for comment and submission of additional information by all interested persons or groups. Additional information for the evaluation of PeCB as a potential new POP in accordance with the two criteria: potential for long-range transboundary atmospheric transport (LRTP) and persistence can be provided by modelling.

A certain experience in the model assessment of the long-range transboundary atmospheric transport and persistence in the environment for a wide range of typical POPs already included in the Protocol on POPs and some potential new POPs [Shatalov et al., 2003; Dutchak et al., 2004; Mantseva et al., 2004; Vulykh et al., 2004, 2005] is accumulated in the Meteorological Synthesizing Centre-East of EMEP. For the evaluation of LRTP and persistence of pollutants, EMEP/MSCE-POP multicompartment hemispheric transport model is used. To estimate the considered parameters for PeCB, the model calculation of its atmospheric transport from a conventional emission point source located in Europe (10°Å; 47.5°N) is made for one-year period. Information on physical-chemical properties and degradation rates of PeCB used for modelling is included in Annex A.

To illustrate LRTP of PeCB, two numerical characteristics are calculated. The first one is residence time in the atmosphere (Half-life in aircalc (T1/2air)) obtained with allowance of all processes removing the considered pollutant from the atmosphere. The second is Transport Distance (TD) that is the distance from the source at which annual mean atmospheric concentration of a chemical in question drops 1000 times compared with the concentration near the source. Additional information on this criterion for PeCB is provided by the spatial distribution of air pollution caused by the considered conventional point source.

Persistence in the environment is evaluated by Half-life in the environment (T1/2env) estimated for PeCB on the basis of the model simulation of its atmospheric transport taking into account deposition and degradation processes, and exchange of the pollutant between main environmental media.

To diminish uncertainties in evaluating LRTP and persistence of PeCB with the help of the model dependent TD and T1/2env, a comparison of their numerical values calculated for the considered chemical against those obtained for B[a]P and HCB as adequately studied "benchmark substances" is presented.

In conclusion, the calculated numerical characteristics of LRTP and persistence of PeCB are given in relation to the indicative criteria outlined in Executive Body Decision 1998/2.

Detailed information on the structure of the model and parameterisation of the media processes can be found in the EMEP/MSC-E reports [Gusev et al., 2005]