Trichoderma POTENTIAL INTO POLLUTED SOILS DETOXIFICATION

Oil dispersion is nowadays one of the most severe environmental issue. Petroleum hydrocarbon pollution may arise from oil well drilling production operations, transportation and storage in the upstream industry, and refining, transportation, and marketing in the downstream industry. Due to the diversity of hydrocarbon compounds a range of remediation technologies may be applicable. Among these, microbial biodegradation is one of the most important processes involved in the eventual removal of petroleum from the environment, particularly of the non-volatile components. Bioremediation technologies that take advantages on these microorganisms’ natural activities appear to be among the most promising methods for dealing with a wide range of organic contaminants, particularly petroleum hydrocarbons. In this context, a Trichoderma atroviride strain able to grow on media contaminated with hydrocarbons was investigated. Trichoderma species are widespread and highly competitive soil-borne fungi. They display a successful antagonism against soil-borne plant pathogens. Moreover they produce extracellular enzyme systems including cellulolytic and chitinase activity (1), and extracellular laccases (2). In this context this strain was supposed to be able to produce enzymes able to detoxify the soils (3). In order to test the detoxifying capacity of the Trichoderma strain we have proceeded as follows. The germination index of Lepidium sativum on a low sulphur crude oil (LSCO) polluted medium at various concentrations was evaluated, in order to find out the LD50. L. sativum seeds were distributed on the paper and left for germinating. After three days a LSCO concentration of 5% w/v led to inhibit the germination of half of the seeds (LD50). Gardening soil samples were, than, artificially polluted with a LSCO concentration of 5% w/v, by mixing the soil with hydrocarbons, solved into dichloromethane as solvent, and distributing in 40 jars of 50 ml. Twenty of the jars were inoculated with fresh culture of Trichoderma atroviride suspended into sterile water, and left for forty days at room temperature in sterile plastic bag. The other twenty jars were left without the fungus at the same condition. After that time three seeds of L. sativum for each jars were sown and the germination index was recorded each three-four days for two weeks. A significantly different germination index was observed between the soil treated by Trichoderma and the control, after 6 days. In the jars with the fungus the germination index was 20% higher than the untreated soil (p value <0,05) (4). The germination index reached the plateau after 6 days in the treated jars and after 11 days in the control jars, reaching the same values (70%). Taking the time of the germination index for reaching the plateau as a parameter the polluted soil treated with Trichoderma atroviride was less toxic compared with the untreated one of about the 45%.The strain of Trichoderma atroviride utilized in these tests was able to halve the toxicity of LSCO after forty days of growth and activity.