Tolerance and phytoremediation potential of four tropical grass species to land-applied drill cuttings

This work evaluated the tolerance and phytoremediation potential of four tropical grasses over a 12-week period, with a view to assessing their suitability for land farming of oil-based drill cuttings. It considered four grass species, namely, guinea grass (Megathyrsus maximus), spear grass (Imperata cylindrica), gamba grass (Andropogon gayanus), and elephant grass (Pennisetum purpureum). The treatments involved growing each of the four grasses on a mixture of 3:1 soil/drill-cuttings ratio, after failed trials with mix ratios ranging from 1:3 to 2:1 soil/drill-cuttings ratio, and on uncontaminated soil. The TPH concentration dropped by 27-81% from 4805 mg kg(-1) in the 3:1 soil/drill-cuttings mixtures in the different treatments after 12 weeks. Better growth performance in the contaminated treatments, compared to uncontaminated controls, correlated with higher reduction in TPH and metals concentrations. The contaminated elephant grass treatment showed better plant height and leaf sizes than the uncontaminated control. The growth parameters of contaminated treatments with the other three grasses ranged from 29 to 75% of the corresponding uncontaminated controls. The results demonstrate that the relative suitability of the grasses for land farming of oil-based drill cuttings is in the order, elephant grass > guinea grass > gamba grass > spear grass.