Current knowledge and evaluation of potential toxicity for soil organisms

Wood preservatives are biocidal products used to protect wood building materials from wooddestroying or wood-disfiguring organisms. Active ingredients such as metallic salts, quaternary ammonium salts, carbamates and azoles are frequently employed. Solid timber or wood based products are used for diverse service situations and are therefore classified according to different "Use Classes", as defined by the European standard EN 335: 2013. Situations for which wood product is above ground and exposed to the weather or in direct contact with ground are classified under use class 3 and 4, respectively. In this case, the chemical substances employed are likely to reach the soil compartment either by leaching from the treated wood surface or by direct contact between the wood and the soil. They may then pose a potential risk for the soil organisms, the essential functions they performed and thus for the soil ecosystem in general. Currently, the available toxicity data for terrestrial organisms regarding the active ingredients present in wood preservatives are still scarce. The aim of this project was to synthesize the available knowledge regarding the toxicity for terrestrial organisms of representative active ingredients contained in wood preservatives and authorized for use in Switzerland, and to provide missing data where necessary. Therefore, a market analysis was performed to determine the active ingredients the most frequently used (calculated as the number of entries of active ingredients registered in wood preservatives authorized in Switzerland) and present on the Swiss market. More than 60% of the number of entries of active ingredients were represented by only 4 substances, i.e. IPBC, Propiconazole, Permethrin, and Tebuconazole, all belonging to use class 3. Boric acid, quaternary ammonium salts and copper based salts represented more than 15% of the number of entries for use class 4. Four wood preservatives containing the selected active ingredients, either present as a single substance or in a mix, were chosen for the ecotoxicological evaluation. They contained: 1) IPBC, 2) Propiconazole, 3) Boric acid and Copper(II)hydroxide, with Chromium as fixing agent; referred to as "CuCrB" 4) Copper(II)carbonate-Copper(II)hydroxide, Didecylpolyoxethylammoniumborat (DPAB) and Boric acid; referred to as "Quats". A review of the toxicity data available for terrestrial organisms for the chosen active ingredients was made. Literature was also searched for mixture toxicity data regarding the active ingredient combinations present in the corresponding wood preservatives. The literature search showed a lack of information regarding the toxicity of IPBC, Propiconazole and DPAB for terrestrial organisms. Toxicity of Boric acid and Copper based salts was better documented but no information on mixture toxicity was found for the active ingredient combinations. Therefore, collembolan reproduction tests and earthworm avoidance tests were performed in order to determine effect concentrations, either for the single active substance or for the active ingredient mixture contained in the wood preservatives. For IPBC, similar range of toxicity were obtained for collembolans and earthworms, with EC50s of 40 mg a.i./kg d.w. and of 33 mg a.i./kg d.w., respectively. Earthworms seemed to be more sensitive to Propiconazole than collembolans with EC50s of 52 mg a.i./kg d.w. and 192 mg a.i./kg d.w., respectively. The 2 wood preservatives containing a mix of active ingredients showed a quite high toxicity for collembolans but even greater for earthworms taking into account that 2 or more active ingredients were present in the biocidal products. For CuCrB, EC50s of 239 mg/kg d.w. and of 11 mg/kg were found for collembolans and earthworms, respectively. For Quats, the EC50 was of 873 mg/kg for collembolans and of 47 mg/kg d.w. for earthworms. The toxicity data found in the literature for the individual active ingredients themselves were much greater than the corresponding concentrations of these substances present in the wood preservative for which a toxicity was observed. Leaching data in field situation for the selected active ingredients contained in wood preservatives are nearly unavailable and data on measured environmental soil concentrations were not found. This project will provide the basis for future studies aiming at characterizing the impact of wood preservatives on soil organisms in microcosms or in field conditions