Benzo(a)pyrene shows low toxicity to three species of terrestrial plants, two soil invertebrates, and soil-nitrifying bacteria.

We examined the toxicity of benzo(a)pyrene (BaP) to several standard test organisms including the seed emergence and early life-stage growth of three terrestrial plants (Trifolium pratense, Lolium perenne, and Brassica alba), the survival and reproduction of enchytraeids (Enchytraeus crypticus), and the nitrifying ability of soil bacteria. To also have a look at possible food-chain effects, we included a two-species reproduction test with predatory mites (Hypoaspis aculeifer) and collembolan (Folsomia fimetaria) prey. No effect or only weak effects even at very high BaP concentrations were observed for all tests. None of the soil invertebrates were affected within the concentration range tested (up to 947 mgkg(-1)). For soil-nitrifying bacteria, significant effects were recorded at 977 mgkg(-1), leaving a no observable effect concentration (NOEC) of 293 mgkg(-1). BaP did not affect seed emergence for any of the plants, but the growth of B. alba was significantly reduced at the highest concentration tested (375 mgkg(-1)), leaving a NOEC of 69 mgkg(-1). Compared to a number of other polycyclic aromatic compounds previously tested in the same soil type, BaP is generally less toxic.