Appendix D - Dossier (PDF) - Tera

date: 20–JUL–2005
3. Environmental Fate and Pathways Substance ID: 71–43–2
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Type: aerobic
Inoculum: other
Year: 1998
GLP: no
Remark: Aerobic biodegradation of gasoline and its constituents,
benzene, toluene and ethylbenzene were studied using an
enrichment from soil indigenous microbial population.
Gasoline–contaminated soil (obtained from a site in
Montreal, Canada) was used to develop an enriched culture
over 28 weeks by succesive transfer of 10% (v/v) inoculum,
amended at each transfer w/ 75 mg/L gasoline (obtained from
commercial gas station).
Result:
Appendix D: Benzene SIDS Dossier
Growth kinetics and gasoline biodegradation were evaluated
in 1L culture flasks containing enriched inoculum (10% v/v)
and gasoline (16.1 – 660 mg/L) in 120 mL medium during a 4
day period. Liquid or gas samples were removed and analyzed
by GC/FID for gasoline component concentrations and
potential metabolites (GC/MS). Microbial growth was based on
biomass dry weight and absorbance (spectrophotometry at 550
nm) of liquid samples.
Mineralization of 14C benzene and toluene (initial
concentrations 50–200 mg/L) using the enriched culture was
investigated individually by analyzing KOH solutions used to
trap 14CO2 produced from closed test systems. Maximum
duration approx 35 days. Test systems containing >100 ppm
benzene or toluene were amended 2x/week w/ 2 mLs of oxygen
to avoid oxygen deficiency.
Results: The enrichment culture completely degraded 16.1–660
mg/l gasoline in 2.5–16 days respectively, without
accumulation of any by–products. Toluene and ethylbenzene
showed no lag period in biodegradation, whereas benzene
showed a delay in degradation and only began degradation at
an increased rate after toluene and ethylbenzene were nearly
exhausted. When benzene and toluene were used as sole
substrates, the maximum specific rates of their
biodegradation were 62.9 and 16.4 times greater than the
corresponding values for a mixture (gasoline). The microbial
culture was able to mineralize up to 200 mg/l pure toluene
and benzene. Maximum mineralization efficiencies of pure
benzene and toluene were 76.7 +/– 5.1% and 76.8 +/– 1.3%
respectively. Self–inhibition of pure benzene and toluene
biodegradation at concentrations above 14.4 and 24.8 mg/L
(respectively) is expected to have occurred as
biodegradation rates declined at and above these
concentrations. Competitive inhibition of specific chemical
biodegradation is concluded to have occurred in the gasoline
mixture since the maximum specfic biodegradation rate
decreased when liquid–phase concentrations were above 0.5
mg/L.
Maximum specific biodegradation rate (mg/mg biomass/day)
– 195/957 –