Emission of N2O from Polycyclic Aromatic Hydrocarbons Contaminated Soil at Different Water Contents Added with Vermicompost

Vermicompost is typically applied to improve soil quality, but can be used to remediate hydrocarbon-contaminated soils. Little information is available on how contamination and subsequent bioremediation with vermicompost affects emissions of N2O and CO2, important greenhouse gases. A sandy loam soil with different water contents (40%, 60%, 80% and 100% of water holding capacity (WHC)) was contaminated with phenanthrene, anthracene and benzo(a)pyrene and amended with or without vermicompost to stimulate remediation of soil. Emissions of N2O and CO2, and concentrations of inorganic N (ammonium (NH4⁺), nitrite (NO2⁻) and nitrate (NO3⁻)) were determined in a laboratory incubation experiment after 0h, 5h, 24h, 72h and 168h. The cumulative CO2 production rate was significantly larger in soil incubated at 60%WHC and 80%WHC compared to soil incubated at 40% and 100%WHC. Addition of vermicompost increased production of CO2 and N2O. Addition of PAHs increased production of CO2 when water content of soil was at 60%WHC and production of N2O when water content of soil was at 80% WHC. Addition of PAHs induced immobilization of inorganic N and inhibited nitrification as the concentration of NH4⁺ and NO2⁻ in soil contaminated with PAHs was larger than in unamended soil while the concentration of NO3⁻ was lower. It was found that contamination of soil with PAHs increased emissions of N2O and CO2 and biostimulation of autochthonous microflora with organic material to remediate those soils further increases production of N2O and CO2. These findings indicate that trace gas emissions should be included in estimations of the environmental impact of contamination of soil and their subsequent bioremediation.