“…Eschenbach et al (1991) studied the effects of 1, 5, and 10 mg kg −1 of benzo[a]pyrene on the respiration and dehydrogenase activity of the soil, but observed no effects in any of the treatments after 1-10 d. Similarly, Park et al (1990) found no change in the bacterial or fungal communities in two different soils after more than 100 d of exposure to benzo[a]pyrene with a starting concentration of 33 mg kg −1 . Similarly, Dörr (1970) reported a lack of benzo[a]pyrene toxicity to rye when grown in soil with a concentration of 3.3 mg kg −1 . After 2 wk of exposure, they found an EC 50 value for acenaphthene of 25 mg kg −1 .…”