REMOVAL OF TOLUENE FROM TWO CONTRASTING SOILS, AN AGRICULTURAL SOIL AND AN ALKALINE SOIL

Among the most serious environmental disasters that threaten biodiversity in soil are oil spills. Different factors control the removal of hydrocarbons from soil, e.g., soil characteristics, composition of the contaminant, and the composition of the microbial population. Toluene is highly volatile, toxic and soluble in water so its removal from soil is important to limit the damage to the environment. Two soils, a arable soil from Otumba, State of Mexico, Mexico, and an alkaline soil from the former Texcoco lakebed, were spiked with three concentrations of toluene (C7H8) and incubated aerobically for 20 days. The CO2 emission and the contaminant in the headspace of the microcosm and the soil were monitored. The CO2 emission increased with increased application of toluene, but showed a lag of two days. After one day, volatilization of toluene was substantial from both soils, 34 % from the Texcoco soil and 58 % from the Otumba soil, but most of it was removed from the headspace within two days. Overall, 98 % of the toluene added to soil was recovered. No abiotic factor affected the removal of toluene from soil. Nearly all toluene was removed from the TExcoco soil within one day independent of the amount applied, but it took more than three days in the arable soil. A lag of two days between dissipation and mineralization was detected, as toluene first has to be incorporated in the microbial cell before it can be degraded. The removal of toluene was faster from the Texcoco soil than from the arable soil.