Methodological modifications for accurate and efficient determination of contaminant biodegradation in unsaturated calcareous soils

Maribeth E Watwood, C. S. White, C. N. Dahm

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15 Citations (Scopus)

Abstract

Many techniques for quantifying microbial biodegradation of 14C-labeled compounds use soil-water slurries and trap mineralization-derived 14CO2 in solution wells suspended within the incubation flashs. These methods are not satisfactory for studies of arid-region soils that are highly calcareous and unsaturated because (i) slurries do not simulate unsaturated conditions and (ii) the amount of CO2 released from calcareous soils exceeds the capacity of the suspended well. This report describes simple, inexpensive methodological modifications for quantifying microbial degradation of [14C]benzene and 1,2-dichloro[U-14C]ethane in calcareous soils under unsaturated conditions. Soils at 50% water holding capacity were incubated with labeled contaminants for periods up to 10 weeks, followed by acidification of the soil and trapping of the evolved CO2 in a separate container of 2 N NaOH. The CO2 was transferred from the incubation flask to the trap solution by a gas transfer shunt containing activated charcoal to remove any volatilized labeled organics. The amount of 14CO2 in the trap solution was measured by scintillation counting (disintegrations per minute). The method was tested by using two regional unamended surface soils, a sandy aridisol and a clay-rich riparian soil. The results demonstrated that both [14C]benzene and 1,2-dichloro[U-14C]ethane were mineralized to release substantial amounts of 14CO2 within 10 weeks. Levels of mineralization varied with contaminant type, soil type, and aeration status (anaerobic vs. aerobic); no significant degradation was observed in abiotic control samples. Methodological refinements of this technique resulted in total 14CO2 recovery efficiency of approximately 90%.

Original languageEnglish (US)
Pages (from-to)717-720
Number of pages4
JournalApplied and Environmental Microbiology
Volume57
Issue number3
StatePublished - 1991
Externally publishedYes

Fingerprint

calcareous soil
calcareous soils
biodegradation
Soil
unsaturated conditions
ethane
slurries
pollutant
traps
carbon dioxide
benzene
mineralization
soil
incubation
riparian soils
Aridisols
degradation
soil acidification
Ethane
activated carbon

ASJC Scopus subject areas

  • Environmental Science(all)
  • Biotechnology
  • Microbiology
  • Earth and Planetary Sciences(all)

Cite this

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title = "Methodological modifications for accurate and efficient determination of contaminant biodegradation in unsaturated calcareous soils",
abstract = "Many techniques for quantifying microbial biodegradation of 14C-labeled compounds use soil-water slurries and trap mineralization-derived 14CO2 in solution wells suspended within the incubation flashs. These methods are not satisfactory for studies of arid-region soils that are highly calcareous and unsaturated because (i) slurries do not simulate unsaturated conditions and (ii) the amount of CO2 released from calcareous soils exceeds the capacity of the suspended well. This report describes simple, inexpensive methodological modifications for quantifying microbial degradation of [14C]benzene and 1,2-dichloro[U-14C]ethane in calcareous soils under unsaturated conditions. Soils at 50{\%} water holding capacity were incubated with labeled contaminants for periods up to 10 weeks, followed by acidification of the soil and trapping of the evolved CO2 in a separate container of 2 N NaOH. The CO2 was transferred from the incubation flask to the trap solution by a gas transfer shunt containing activated charcoal to remove any volatilized labeled organics. The amount of 14CO2 in the trap solution was measured by scintillation counting (disintegrations per minute). The method was tested by using two regional unamended surface soils, a sandy aridisol and a clay-rich riparian soil. The results demonstrated that both [14C]benzene and 1,2-dichloro[U-14C]ethane were mineralized to release substantial amounts of 14CO2 within 10 weeks. Levels of mineralization varied with contaminant type, soil type, and aeration status (anaerobic vs. aerobic); no significant degradation was observed in abiotic control samples. Methodological refinements of this technique resulted in total 14CO2 recovery efficiency of approximately 90{\%}.",
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T1 - Methodological modifications for accurate and efficient determination of contaminant biodegradation in unsaturated calcareous soils

AU - Watwood, Maribeth E

AU - White, C. S.

AU - Dahm, C. N.

PY - 1991

Y1 - 1991

N2 - Many techniques for quantifying microbial biodegradation of 14C-labeled compounds use soil-water slurries and trap mineralization-derived 14CO2 in solution wells suspended within the incubation flashs. These methods are not satisfactory for studies of arid-region soils that are highly calcareous and unsaturated because (i) slurries do not simulate unsaturated conditions and (ii) the amount of CO2 released from calcareous soils exceeds the capacity of the suspended well. This report describes simple, inexpensive methodological modifications for quantifying microbial degradation of [14C]benzene and 1,2-dichloro[U-14C]ethane in calcareous soils under unsaturated conditions. Soils at 50% water holding capacity were incubated with labeled contaminants for periods up to 10 weeks, followed by acidification of the soil and trapping of the evolved CO2 in a separate container of 2 N NaOH. The CO2 was transferred from the incubation flask to the trap solution by a gas transfer shunt containing activated charcoal to remove any volatilized labeled organics. The amount of 14CO2 in the trap solution was measured by scintillation counting (disintegrations per minute). The method was tested by using two regional unamended surface soils, a sandy aridisol and a clay-rich riparian soil. The results demonstrated that both [14C]benzene and 1,2-dichloro[U-14C]ethane were mineralized to release substantial amounts of 14CO2 within 10 weeks. Levels of mineralization varied with contaminant type, soil type, and aeration status (anaerobic vs. aerobic); no significant degradation was observed in abiotic control samples. Methodological refinements of this technique resulted in total 14CO2 recovery efficiency of approximately 90%.

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