Assessment of the biodegradation potential of hydrocarbons in contaminated soil from a permafrost site

Abstract

Biodegradation of hydrocarbons in the Arctic and Antarctic has shown to be very slow, due to low temperatures combined with low contents of nutrients, organic matter and water. In this study, the degradation potential of diesel and hexadecane by indigenous microorganisms in a contaminated soil from a permafrost site was evaluated. Soil samples were taken from two profiles at a hydrocarbon-contaminated site at Svalbard, at depths of 0.5 m (active layer), 2.0 m (transition zone between active layer and permafrost) and 3.5 m (permafrost). The aerobe biodegradation potential was assessed using two different laboratory approaches: nutrient amended liquid cultures with arctic diesel as the carbon source, and soil microcosms with radiolabelled hexadecane. The experiments were performed at 5 °C. Biodegradation of hydrocarbons at 5 °C was obtained with both methods. In the liquid cultures 18–54% of the initial diesel concentration was degraded after 32 days. The total degradation increased with sampling depth such that the greatest degradation was observed in cultures inoculated with soil from the permafrost. In the soil microcosm experiments, 0.9–15.8% of the initial hexadecane concentration mineralised after 128 days, at rates from 0.4 to 6.2 mg hexadecane/kg/day. In the soil microcosms study, greatest total degradation was observed in soil from the transition zone, followed by the samples from active layer and permafrost, respectively. Both liquid cultures and soil microcosms can be used to study the biodegradation potential of contaminated arctic soil at 5 °C. The methods can be regarded as complementary, with the liquid cultures being qualitative and the soil microcosms quantitative in nature. The liquid cultures provide information regarding the indigenous microorganisms' capability to degrade different compounds under optimised conditions. The soil microcosm experiments result in mineralisation rates in the soil under the prevailing conditions.