The influence of single and multiple applications of pyrene on the evolution of pyrene catabolism in soil.

The influence of pyrene added in a single application (0, 50, 100 and 200 mg kg(-1)) was investigated in multiple applications (1 x 50, 2 x 50 and 4 x 50 mg kg(-1)) on the evolution of catabolic activity in a pristine pasture soil. The microbial community's ability to degrade pyrene was assessed at 0, 4, 8 and 12 weeks by the mineralization of added 14C-pyrene. Significant mineralization (>5%) of added 14C-pyrene only occurred after 4 weeks soil-pyrene contact time in most of the pyrene-amended soils. Pyrene-amended soils showed statistically significantly shorter (P<0.05) lag times compared to the control soil after 8 and 12 weeks soil-pyrene contact time. Further, the rates of degradation increased in the presence of pyrene, peaking at 8 weeks. In terms of the overall extents of pyrene mineralization, there were statistically significant increases (P<0.05) between 4 and 8 weeks, with little difference between 8 and 12 weeks, with the general trend that an increase in pyrene concentration resulted in higher levels of mineralization. Increasing the concentration and number of pyrene additions can have a significant impact on the adaptation of the soil microflora to degrade pyrene over time.