Aging effect of petroleum hydrocarbons in soil under different attenuation conditions

In this paper, aging process of petroleum-contaminated soil was characterized during 210 d of attenuation under different conditions: clean soil spiked with petroleum (Run 1), clean soil spiked with petroleum and humic acid (Run 2), quartz sand spiked with petroleum (Run 3) and petroleum-contaminated saline soil from an oil field (Run 4). An initial increase of pH was found before 60 d of aging. Total petroleum hydrocarbon (TPH) content decreased with the process of aging and the degradation rates for the 4 runs were 61%, 60%, 24% and 20% after 210 d of aging, respectively. The saturated fraction of petroleum hydrocarbons was most degraded in Run 1 in clean soil; while addition of humic acid enhanced the degradation of aromatic fraction and asphaltene and polar fraction. Addition of TPH in soil resulted in the increase of the dehydrogenase activity at the initial period of aging. A significant negative correlation was found between bacteria count and TPH content during aging process and fungi number was only increased at certain time of aging. The biological toxicity increased at the middle of aging process of 30–60 d as determined by plant growth and luminescent bacteria experiment. The result suggested that proper regulation on the influencing factors such as particle size and salinity was important for the management of contaminated soils and could enhance the natural attenuation of the petroleum pollutants.