Crude Oil Hydrocarbon Bioremediation and Soil Ecotoxicity Assessment

Abstract

In this study, we determined the limits and extent of hydrocarbon biodegradation, earthworm and plant toxicity, and waste leachability of crude oil-containing soils. Three oils (heavy, medium, and light of API gravity 14, 30, and 55, respectively) were mixed into silty loamy soils containing low (0.3%) or high (4.7%) organic carbon at 4000−27 000 mg/kg TPH. Hydrocarbon bioremediation in these artificially weathered oily soils usually followed first-order removal rates in which 50−75% and 10−90% of the total petroleum hydrocarbons (TPH) were degraded in 3−4 months for the low and high organic soils, respectively. Gas chromatographic profiles (simulated boiling point distillation of saturates and aromatic compounds) showed that, after bioremediation, hydrocarbons in oily soils decreased from 70 to 90%, from 40 to 60%, and from 35 to 60% for those carbon number species in the range of C11−C22, C23−C32, and C35−C44, respectively. Most oily soils were initially toxic to earthworms in which few animals survived 14-day bioassays. In a solid phase Microtox test, most oily soils had EC50 values that were ≤50%. Seed germination and plant growth (21-day test, wheat and oat but not corn) were also significantly reduced (0−25% of controls) in untreated soils containing the medium and light crude oils but not the heavy oil. Bioremediated soils were neither toxic to earthworms, inhibitory in the Microtox assay, nor inhibited seed germination after 5 (high organic soil) or 10−12 (low organic soil) months of treatment. Water-soluble hydrocarbons (e.g., O&G and BTEX) could leach from pretreated soils (medium and light crude oily soils) in column or batch extraction experiments. However, after bioremediation, most of the aromatic compounds were no longer leachable from the soils. These data demonstrate that treated oily soils lose their toxicity and potential to leach significant amounts of BTEX. These nontoxic soils contain 1000−8600 mg/kg residual hydrocarbons as TPH. Furthermore, these data suggest that the remaining petroleum compounds may be bound or unavailable in that they are not (a) biodegraded further, (b) toxic to soil-dwelling species (earthworms and plants), and (c) susceptible to leaching and subsequent impact to groundwater. These findings provide a basis for a framework in which petroleum hydrocarbon-containing soils can be evaluated by ecological assessment methods such as biodegradability, ecotoxicity, and leaching potential of regulated substances.

Impact of hydrocarbons from a diesel fuel on the germination and early growth of subantarctic plants

“…Lowered hydrocarbon bioavailability is attributed to increased hydrocarbon sequestration onto organic matter and therefore, decreased bioavailability, which is consistent with equilibrium partitioning for neutral organics based on sorption coefficients [29][30][31][32].…”

Multi-Species Ecotoxicity Assessment of Petroleum-Contaminated Soil

“…The lack of synchrony by different groups of organisms in response to the loss of hydrocarbons that we saw has been observed in other studies (Hund and Traunspurger, 1994;Salanitro et al, 1997;Sayles et al, 1999). In general, the inhibition of plant growth persisted longer than the effects on invertebrate viability or toxicity measured by Microtoxâ (Salanitro et al, 1997;Hund and Traunspurger, 1994).…”

“…In general, the inhibition of plant growth persisted longer than the effects on invertebrate viability or toxicity measured by Microtoxâ (Salanitro et al, 1997;Hund and Traunspurger, 1994). Hund and Traunspurger (1994) also found that nematodes and nitrification were very sensitive to petroleum contamination: nematodes were not found in heavily contaminated soils and were still at much reduced densities after 4 months, ammonium oxidation showed partial recovery after 7 months, and nitrite oxidation after 10 months of bioremediation.…”

“…It has been shown repeatedly that after an initial lag period, the rate of bioremediation first increases then slows, with most activity taking place within a 2-to 5-month span or in 10 to 12 months for a soil low in organic matter, and little mineralization after that (Bossert et al, 1984; Salanitro et al, 1997;Fisher and King, 1994;Duncan et al, 1998). Bossert et al (1984) noted an increase in humification after the active mineralization phase.…”

Prepared bed bioremediation of oily sludge in an oilfield in northern China

“…There are no universal TPH cleanup standards for soils contaminated with crude oils [23]. Some guidelines have been developed for oil content.…”