Effects of birch tar oils on soil organisms and plants

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.