Birch tar oil (BTO) is a by-product of processing birch wood in a pyrolysis system. Accumulating evidence suggests the suitability of BTO as a biocide or repellent in terrestrial environments for the control of weeds, insects, molluscs and rodents. Once applied as biocide, BTO may end up, either through run-off or leaching, in aquatic systems and may have adverse effects on non-target organisms. As very little is known about the toxicity of BTO to aquatic organisms, the present study investigated acute toxicity (LC 50 /EC 50 ) of BTO for eight aquatic organisms. Bioassays with the Asellus aquaticus (crustacean), Lumbriculus variegatus (oligochaeta worm), Daphnia magna (crustacean), Lymnea sp. (mollusc), Lemna minor (vascular plant), Danio rerio (fish), Scenedesmus gracilis (algae), and Vibrio fischeri (bacterium) were performed according to ISO, OECD or USEPA-guidelines. The results indicated that BTO was practically nontoxic to most aquatic organisms as the median effective BTO concentrations against most organisms were > 150 mg l -1 . In conclusion, our toxicity tests showed that aquatic organisms are to some extent, invariably sensitive to birch tar oil, but suggest that BTO does not pose a severe hazard to aquatic biota. We deduce that, unless BTOs are not applied in the immediate vicinity of water bodies, no special precaution is required.

The use of birch tar oil (BTO) is a new innovation in plant and animal protection working against various weeds, harmful insects and rodents. Due to its novelty as a biocide/repellent/plant protection product, no comprehensive information on the effects of BTO on non-target soil organisms is available. In this study we examined the impact of BTO on non-target soil organisms (enchytraeids, nematodes and soil microbes) and plants using laboratory toxicity tests and field experiments. In addition, we determined the LC 50 value of BTO to the earthworm Aporrectodea caliginosa and the EC 50 value of BTO to the offspring production of the collembolan Folsomia candida. The effects of BTO on soil fauna were mostly insignificant. BTO seemed to be detrimental to the growth of plants directly after application, but this effect was short-term; after a period of 2.5 months, the growth of most of the plant species recovered completely from the application. The LC 50 for A. caliginosa was 6560 mg BTO kg -1 dry soil and EC 50 for juvenile production of F. candida was 5100 mg BTO kg -1 dry soil. The results indicate that the risk caused by BTOs (concentration 500−1360 l ha -1 ) to the soil environment is insignificant and short-term as compared to the many chemical products applied for similar purposes.