Dynamics of nitrogen in a PAHs contaminated soil amended with biosolid or vermicompost in the presence of earthworms

Nitrogen mineralization in PAHs contaminated soil in presence of Eisenia fetida amended with biosolid or vermicompost was investigated. Sterilized and unsterilized soil was contaminated with PAHs, added with E. fetida and biosolid or vermicompost and incubated aerobically for 70 days, while dynamics of inorganic N were monitored. Addition of E. fetida to sterilized soil increased concentration of NH₄⁺ 100 > mg N kg^-1, while concentrations in unsterilized remained <60 mg N kg^-1 except for soil amended with biosolid plus PAHs where it increased to >80 mg kg^-1. Addition of PAHs had no significant effect on concentration of NH₄⁺ compared to the unamended soil, except in the soil added with biosolid. Addition of E. fetida to sterilized soil increased concentration of NO₂^- 15 > mg N kg^-1 while concentrations in unsterilized soil remained <7.5 mg N kg^-1 except for soil amended with biosolid where it increased to >20 mg kg^-1. Addition of PAHs had no significant effect on concentration of NO₂^- compared to the unamended soil. Addition of biosolid and vermicompost increased concentration of NO₃^-, while addition of E. fetida decreased concentration of NO₃^- in biosolid amended soil. It was found that NH₄⁺ and NO₂^- oxidizers were present in the gut of E. fetida, but their activity was not sufficient enough to inhibit a temporarily increase in concentrations of NH₄⁺ and NO₂^-. Contamination with PAHs induced immobilization of N in biosolid or vermicompost amended soil, as did feeding of E. fetida on biosolid or vermicompost.