Phytoremediation of Crude Oil-Contaminated Soil by Medicago sativa (Alfalfa) and the Effect of Oil on its Growth

Abstract

In oil producing countries, crude oil is one of the main organic pollutants of soil and water. The use of plants to phytotreatment of crude oil contaminated soil has been a particular interest in environmental cleansing. Some plants such as grasses and legumes have been demonstrated to have better capacity in biodegradation of oil in the soil. In this study, the effect of different concentrations of light crude oil (up to 10 %) on the growth and germination of Medicago sativa (alfalfa) was studied. Our results showed that the germination number and the number of leaves per plant decreased by increasing light crude oil concentration in the soil. About 75 % of germination was observed in control while it was 15 % in high concentration of crude oil in soil (10 %). Total dry biomass of plant was higher in control (2 g) sample while it was lower in 7 and 10 % sample. Number of leaves was higher in control but it was lower in 7 and 10 % oil-polluted soil. The presence of high concentration of oil in soil caused chlorosis of leaves and there were no green plants at the end of experiment (120 days). Total colony and oil-degrading colony counts in soil showed that in all vegetated samples, the microbial population was higher than non-vegetated samples. In vegetated samples, the total microbial population in 7 % samples was higher than control and also higher than that in low concentrations of crude oil (1 and 3 % samples). The effect of plants on reduction of oil in soil was also investigated. In all vegetated samples, the reduction of crude oil was higher than that in non-vegetated samples. The higher reduction occurred in 1 % sample (70 %), while the lower reduction observed in 10 % sample (20 %). In conclusion, Medicago sativa as a plant in legume family could not tolerate high concentration of crude oil and crude oil could severely affect its growth and germination and cause untimely chlorosis. Our results propose that Medicago sativa is not a good option for removal of oil from the soil by the method of phytoremediation.