Abstract
Microcosm experiments were conducted to determine the fractionation of stable carbon isotopes during biodegradation of naphthalene. The microcosms were performed under aerobic conditions, anaerobic (amended with sulfate, amended with nitrate and with no amendments) and sterile controls. The liquid phase was analyzed to determine naphthalene concentration and stable carbon isotope signature. Aerobic microcosm showed that naphthalene degraded aerobically within 60 hours. The δ13C increased from -25.5‰ to -25.1‰ (enrichment of 0.4‰ ± 0.08‰) in a single sample in which 95% of the naphthalene was biodegraded. Anaerobic microcosms show that after 288 days, the microcosms with no amendments, amended with nitrate and amended with sulfate had consumed respectively 30%, 50% and 60% of naphthalene on average, compared to control microcosms. Under the denitrifying conditions, the δ13C of naphthalene increased from -25.2‰ to -23.9‰ (enrichment of 1.3‰ ± 0.3‰) after a 95% of naphthalene biodegradation. For the unamended microcosms, a slight enrichment on δ13C napththalene was detected, from -25.2‰ to -24.5‰ (enrichment of 0.7‰ ± 0.3‰) after a biodegradation of approximately 65% of naphthalene (after 288 days). For sulfate reducing microcosms, no significant changes were detected on the δ13C during naphthalene biodegradation.
Highlights
Contamination of groundwater by hydrocarbons has been widely documented in literature [1,2]
Aerobic microcosm showed that naphthalene degraded aerobically within 60 hours
Biodegradation rates obtained under aerobic conditions were: λ1 = 2.4 d‒1 and λo= 0.72 d‒1
Summary
Contamination of groundwater by hydrocarbons has been widely documented in literature [1,2]. Naphthalene is the simplest polynuclear aromatic hydrocarbon (PAH) consisting of two benzene rings [1]. It is produced mainly by the refining of petroleum and is found mostly in creosote [3]. Several studies have shown a change in this stable carbon isotope ratio during biodegradation of chlorinated carbon solvents [18,19,20]. The BTEX compounds produce very small stable carbon isotopic fractionation during biodegradation [20,21,22]. The gasoline additive, MTBE, produces a very small stable carbon isotopic fractionation during biodegradation [23]. Richnow et al [24] found a very low carbon isotopic fractionation on naphthalene in a field study
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