The objective of this project was to investigate the influence different exposure directions – North, East, South and West on the cumulative quantity of a biocide leached from painted wood surfaces due to rainfall and the consequences for the risk assessment. The study included a solvent-borne primer without biocides and a topcoat protected with a biocidal active substance. Both products were applied by brushing at DTI in Denmark. Duplicate test set-ups for leachate collection were constructed, each consisting of 20 wood panels. Leachate was collected during 751 consecutive days. During the study period, 1147 mm of rainfall was registered. The leaching data was used as input to the House scenario in the Emission Scenario Document for wood preservatives as stipulated in the European Biocidal Products Regulation. The leaching from all other directions were less than from south. If using the actual measured leaching rates from each direction to calculate the leaching in the House scenario, the total amount of biocide leached is about half the amount compared to the result where the leaching data from the test set-ups exposed to the South were used to calculate the leaching from the whole house. Because of this, a “hidden” safety factor is introduced – in this case of about 2.

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