Assessment and bioremediation of heavy metals from crude oil contaminated soil by earthworms

Abstract

The assessment of the levels of heavy metals present in crude oil contaminated soil and the application of the earthworm - Hyperiodrilus africanus with interest on the bioremediation of metals from the contaminated soil was investigated within a 90-days period under laboratory conditions. Selected heavy metals such as zinc, manganese, copper, nickel, cadmium, vanadium, chromium, lead, mercury and arsenic were determined using AAS. The physicochemical conditions showed an increase in pH, but a decrease in conductivity, total nitrogen and chloride. Assessment of heavy metals indicated that heavy metals are present in crude oil at elevated levels beyond national regulatory guidelines. There was a significant (P < 0.05) decreasing trend in percentage of heavy metals present in soil after inoculation with earthworm in zinc (57.66%), manganese (57.72%), copper (57.64%), nickel (57.69%), cadmium (57.57%), vanadium (57.68%), chromium (57.67%), lead (57.64%), arsenic (1.36%) and mercury (57.41%) after 90 days period. Bioaccumulation factor showed that zinc, manganese, copper, cadmium, vanadium, chromium and lead had a factor of 1.36, while nickel, arsenic and mercury had 1.37, 0.01 and 1.35 respectively. The results showed that the earthworms H. africanus can be effectively used to bioremediate heavy metals from crude oil polluted soil.

 Key Words: Heavy metals, Bioremediation, Vermiremediation, Crude oil, Hyperiodrilus africanus