Three different wood preservative products, their eluates produced by leaching tests, mixtures of some of their ingredients and some of their ingredients as single substances were tested for growth inhibition of green algae as well as acute and chronic toxicity to Daphnia magna. The tests were conducted according to ⁠OECD⁠ standard guidelines and supported by analytical
chemistry. The model deviation ratio (MDR) was used as quantitative measure for the compliance between observed mixture toxicity and the toxicity predicted by concentration addition. An MDR considerably larger than 2 may indicate synergistic interactions or the necessity to include so-far neglected substances into the prediction. For the here investigated wood preservative products and their eluates, the importance of taking formulation additives and transformation products into account has been clearly demonstrated. Acute as well as chronic toxicity could be reliably predicted with less than 2fold deviation when all relevant ingredients were known and included in the prediction. Yet, there was a tendency to overestimate mixture toxicity for endpoints of sub-lethal toxicity at low effect levels.