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 Dicofol

MSC-E Information Note 13/2005

N. Vulykh, E. Mantseva, V. Shatalov

ABSTRACT

Dicofol is an organochlorine pesticide of widespread occurrence. Chemicals with different trade names (Kelthane, Hifol, Milbol et al.) and different content of dicofol were used in agriculture. In addition mixtures of dicofol with other pesticides were used. Dicofol is a miticide and broad-spectrum non-systematic acaricide with little insecticidal activity. It is used on terrestrial food crops and non-food sites [RED Dicofol, 1998].

Dicofol is included into the OSPAR List of Chemicals for Priority Action (Update 2004) [Meeting of the OSPAR Commission (OSPAR), 2004]. As a potential candidate for the inclusion into the UN-ECE Protocol on POPs this chemical was addressed by the Ad Hoc Expert Group on POPs [Lerche et al., 2002]. This year the Netherlands has re-submitted the dossier on dicofol [van de Plassche and Rasenberg, 2003] for technical review by the Task Force on POPs. Additional information for the evaluation of dicofol 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 dicofol, the model calculation of its atmospheric transport from a conventional emission source located in Europe is made for one-year period. Since dicofol is a pesticide its emissions to the atmosphere occur as a result of its application on crop areas. In this connection, a conventional diffusive emission source covered the use area of approximately 200 by 200 km is considered. Information on physical-chemical properties and degradation rates of dicofol used for modelling is included in Annex. Of note, in this model assessment dicofol was treated not as one compound - p,p'-isomer but as the technical product - a mixture of two isomers (p,p'- and o,p'-dicofol).

To illustrate LRTP of dicofol, 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 dicofol is provided by the spatial distribution of air pollution caused by the considered conventional diffusive source.

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

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

In conclusion, the calculated numerical characteristics of LRTP and persistence of dicofol 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]