Phytoremediation of petroleum contaminated soils in the tropics

Phytoremediation, i. e. the use of plants to recover contaminated soils, water and sediments, is a non-destructive and cost-effective in situ technology. In the tropics, it is particularly promising for the clean-up of petroleum-contaminated soils (plant-assisted rhizodegradation), since climatic conditions favour plant growth and microbial activity in the soil. The present work studied the potential of tropical species found in contaminated soil in the savannah of eastern Venezuela for their use in phytoremediation. The research comprised field studies for the pre-selection of potential phytoremediation species, the effect of crude oil on plant growth and root morphology, and greenhouse experiments for the evidence of enhanced crude oil degradation in planted soil. The tropical pasture grass Brachiaria brizantha, showing best degradation results, was chosen for detailed studies on phytoremediation mechanisms. Different fertiliser levels were tested with the aim to optimise growth of B. brizantha, and to enhance microbial degradation of heavy crude oil in soil. The effect of B. brizantha on the number and activity of soil microorganisms in the rhizosphere compared to non-rhizosphere soil was studied. Furthermore, substrate utilization patterns were used to determine the influence of B. brizantha on the microbial community structure. The present study identified a tropical grass species for the phytoremediation of petroleum hydrocarbon-contaminated soils that is interesting not only for Venezuela but also other tropical and subtropical countries.