The effect of hydroxycinnamic acids (caffeic, ferulic and p-coumaric acids) on the microbial mineralisation of phenanthrene in soil slurry by the indigenous microbial community has been investigated. The rate and extent of 14C–phenanthrenemineralisation in artificially spiked soils were monitored in the absence of hydroxycinnamic acids and presence of hydroxycinnamic acids applied at three different concentrations (50, 100 and 200 μg kg-1) either as single compounds or as a mixture of hydroxycinnamic acids (caffeic, ferulic and p-coumaric acids at a 1:1:1 ratio). The highest extent of 14C–phenanthrene mineralisation (P< 0.001) was obtained in soils amended with 50 μg kg-1 ferulic acid (52.9% ± 0.45) compared to that obtained in unamended soils (37.2% ± 0.23). In addition, mineralisation of 14C–phenanthrene was monitored in pre–incubated artificially spiked soils at various time intervals (0, 16, 32 and 48 d) following amendment with hydroxycinnamic acids at a concentration of 100 μg kg-1. After 16 d of pre-exposure, artificially spiked soils amended with 100 μg kg-1 ferulic acids had the highest extents of 14C–phenanthrene mineralisationcompared to those obtained soils with other treatment conditions. The results obtained showed enhanced mineralisation of 14C–phenanthrene in freshly spiked soils amended with hydroxycinnamic acids and the extents of 14C–phenanthrene mineralisation range in the order of 50 ≥ 100 > 200 μg kg-1. Depending on its concentrationin soil, hydroxycinnamic acids can either stimulate or inhibit mineralisation of phenanthrene by indigenous soil microbial community. Therefore, effective understanding of phytochemical–microbe–organic contaminant interactions is essential for further development of phytotechnologies for remediation of PAH–contaminated soils.
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