Anatomical Response of Digitaria horizontalis and Eluesine indica Grown in Waste Engine Oil Contaminated Soil

The ability of Digitaria horizontalis and Eluesine indica grass species to phytoremediate waste engine oil contaminated soil was investigated. Four (4) kg of air dried soil was measured into four (4) kg perforated plastic buckets. Waste engine oil was added to four (4) kg different soil samples to obtain different concentrations on weight basis: 0 % (control), 2 %, 4 %, 7 % and 10 % v/w oil-in-soil and allowed to stand for seven days before transplanting. At the end of 8 weeks of transplanting, the plants were harvested. There were observed changes in some anatomical structures of the two grass species, which could be attributed to the effects of the waste engine oil in the soil in which they were grown. Epidermal cells of the leaves showed that both all the two grass species exhibited irregular epidermal cell shape and sinuous cell walls. In stem anatomy, there was reduction in cell size, the increase in cell shape irregularity, increased thickness of cell wall of the parenchyma tissues and breakdown of vascular bundles as the waste engine oil concentration increased. Similarly, there was reduction in root cell size, the increase in cell shape irregularity and increased thickness of cell wall of the parenchyma tissues and break down of cortex region as the waste engine oil concentration increased. In conclusion, the two grass species studied were sensitive to the toxic effects of waste engine oil in the soils and their sensitivity varied with different concentrations of waste engine oil used.