Hexadecane mineralization and denitrification in two diesel fuel-contaminated soils

The effect of nitrate, ammonium and urea on the mineralization of [C-14]hex adecane (C16H34) and on denitrification was evaluated in two soils contamin ated with diesel fuel. In soil A, addition of N fertilizers did not stimula te or inhibit background hexadecane mineralization (4.3 mg C16H34 kg(-1) da y(-1)). In soil B, only NaNO3 stimulated hexadecane mineralization (0.91 mg C16H34 kg(-1) day(-1)) compared to soil not supplemented with any nitrogen nutrient (0.17 mg C16H34 kg(-1) day(-1)). Hexadecane mineralization was no t stimulated in this soil by NH4NO3 (0.13 mg C16H34 kg(-1) day(-1)), but th e addition of NH4Cl or urea suppressed hexadecane mineralization (0.015 mg C16H34 kg(-1) day(-1)). Addition of 2 kPa C2H2 did not inhibit the minerali zation process in either soil. Denitrification occurred in both soils studi ed when supplemented with NaNO3 and NH4NO3, but was not detected with other N sources. Denitrification started after a longer lag in soil A (10 days) than in soil B (4 days). In soil A microcosms supplemented with NaNO3 or NH 4NO3, rates of denitrification were 20.6 and 13.6 mg NO3- kg(-1) day(-1), r espectively, and in soil B, they were 18.5 and 12.5 mg NO3- kg(-1) day(-1), respectively. We conclude that denitrification may lead to a substantial l oss of nitrate, making it unavailable to the mineralizing bacterial populat ion. Nitrous oxide was an important end-product accounting for 30-100% of t otal denitrification. These results indicate the need for preliminary treat ability studies before implementing full-scale treatment processes incorpor ating commercial fertilizers. Crown copyright (C) 2000 Published by Elsevie r Science B.V. All rights reserved.