The influence of a NAPL on the loss and biodegradation of 14C-phenanthrene residues in two dissimilar soils.
This study was carried out to assess the influence of diesel, applied over a log concentration range, on the loss and extractability of phenanthrene (measured as putative 14C-phenanthrene residues) in two different soils. The influence of diesel on the ability of a cyclodextrin based extraction method to predict the microbial bioavailability of 14C-residues was also assessed. An increase in loss of 14C-residues with increasing diesel concentration from 0 to 2000 mg kg-1 was generally observed with time in both soils. It is suggested that this trend is attributable to competitive sorption for soil sorption sites and to a lesser extent to displacement of 14C-residues from soil sorption sites by diesel resulting in greater compound availability and therefore greater loss by degradation via the actions of indigenous microorganisms. However, in the 20000 mg kg-1 diesel treatments of both soils, results indicated a delayed loss. It is suggested that this retarded loss was due to the formation of a discrete NAPL-phase into which 14C-phenanthrene residues partitioned, thereby decreasing their availability and as a consequence their degradation. Furthermore, it is suggested that nutrient limitation may have slowed down degradation rates as diesel concentrations increased. Comparison between cyclodextrin-extractability and microbial mineralisation supported the use of cyclodextrin to assess microbial bioavailability of 14C-residues after 50 d or more ageing up to diesel concentrations of 2000 mg kg-1. However, results suggested that at high diesel concentrations (specifically 20000 mg kg-1) co-extraction of 14C-phenanthrene residues may have occurred as a result of the combined solvation powers of both the cyclodextrin and the diesel. Furthermore, mineralisation of 14C-phenanthrene residues may have been affected by extreme nutrient limitation in this treatment.
Swindell
A L
AL
School of Environmental Sciences, University of East Anglia, Norwich, UK.
Reid
B J
BJ
D001673:Biodegradation, Environmental; D002250:Carbon Radioisotopes / Q000032:analysis; D003505:Cyclodextrins / Q000737:chemistry; D004784:Environmental Monitoring / Q000379:methods; D005742:Gasoline; D010616:Phenanthrenes / Q000032:analysis* / Q000378:metabolism; D012987:Soil / Q000032:analysis*; D012988:Soil Microbiology; D012990:Soil Pollutants, Radioactive / Q000032:analysis* / Q000378:metabolism
D002250:Carbon Radioisotopes; D003505:Cyclodextrins; D005742:Gasoline; D010616:Phenanthrenes; D012987:Soil; D012990:Soil Pollutants, Radioactive; C031181:phenanthrene