For this study, we used sunflower (

For this study, we used sunflower (H. annuus L. cv. PR 63A90)
seeds from the University of California that were certified for agronomic crop production. The greenhouse experimental design consisted of 5 pots with 2 kg of soil per treatment. The treatments included uncontaminated soil planted with seeds (as a positive control for plant growth) and contaminated soil with or without seeds. Five seeds were used per planted pot. The experiment was carried out in a greenhouse at 23 ` 1 C and 20% field capacity. After 45 and 90 days, soil samples were collected in each of three randomly chosen pots for each treatment for measurements of residual PAH contents and microbiological determinations. Soil samples (20 g) were carefully extracted from the rhizosphere zone with the aid of a glass tube (150 25 mm) used as a bore. Care was taken to avoid damaging the plants. Samples for the PAH analyses were stored at 20 C, and samples for the microbio- logical analyses were stored at 4 C. In both cases the samples were analyzed separately. At the end of the experimental period, the percentage of germination was evaluated for each treatment, and the fresh and dry weights of stems and roots were deter- mined separately. Dried stems and roots were generated by incubating the separated plant materials in a desiccation oven (70 C) for 72 h.