Superfund Research Program

Factors Controlling the Environmental Mobility, Microbial Transformation and Toxicity of Mixed Non-Aqueous Phase Liquids and Exposed Soils/Sediments

Project Leader: Walter J. Weber (University of Michigan)
Grant Number: P42ES004911
Funding Period: 1995 - 2006

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Final Progress Reports

Year:   2004  1999 

The bioavailability and environmental mobility of pyrene in mixed non-aqueous phase liquids (NAPLs) were investigated under a number of conditions; i.e., different NAPLs, different NAPL concentrations, different aging time, different soils and soils amended with organic sorbents.  The bioavailability of aged pyrene was determined by its mineralization with a bacterial consortium and its uptake by the earthworm (Eisenia foetida), and its environmental mobility and sorption by soil were determined via aqueous desorption and methanol extraction.

Pyrene was aged with two soils for 2 (fresh soil no NAPL), 30 (no NAPL), 30, 110, and 167 (with NAPL) days.  Hexadecane (HEX) was used as a representative NAPL.  The results show that its availability to both earthworms and bacteria was greatly reduced for both NC soil and Chelsea soil as a result of aging and the presence of HEX.  The concentrations of pyrene in the worms were 1012.7 μg/g for fresh NC soil or 526.3 μg/g for fresh Chelsea soil based on dry weight of worm tissue mass.  After being aged in soils for 30 days with or without HEX, pyrene concentrations in worms decreased to 786.3 μg/g (no NAPL) and 290.4 μg/g (with NAPL) for NC soil and 386.6 μg/g (no NAPL) and 211.6 μg/g (with NAPL) for Chelsea soil, respectively.  After being aged for 110 and 167 days with HEX, pyrene concentrations in worm decreased to 219.8 4 and 226.8 μg/g for NC soil and 174.5 and 126.9 μg/g for Chelsea soil.  These aged and unaged soils were inoculated with a bacterial consortium for another114 days to monitor pyrene mineralization.  More than 57% of pyrene was mineralized into CO₂ from the fresh NC soil and 38.4% of pyrene from fresh Chelsea soil.  For the aged NC soils, the percentages of mineralized pyrene were 49.8, 19.2, 16.7 and 15.5%, respectively.  For aged Chelsea soil, there were 29.1%, 15.0%, 13.9%, and 12.6% of pyrene that was mineralized.  Aging and NAPL also decreased the desorption of pyrene into aqueous phase, although the effect were not remarkable comparing to its bioavailability.  

To assess the effects of different NAPLs on the bioavailability and desorption of pyrene, this compound was dissolved in four different NAPLs, i.e., HEX, heptamethylnonane (HMN), dimethyl phthalate (DMP) and toluene (TOL), and aged in NC soil for 126 days.  Both HEX and HMN reduced the uptake of pyrene by earthworms.  DMP and TOL were toxic to earthworms and all worms died.  Their effects on the availability of pyrene to the bacteria varied different among the four NAPLs.  Nearly 40% of pyrene was mineralized into CO₂ in aged NC soil without any NAPL, and only 11.7% of pyrene was mineralized in the presence of HEX.  For the soil with DMP, about 1.31% pyrene was mineralized in the first week of incubation, it then completely stopped, which suggested DMP was also toxic to bacteria.  Both HMN and TOL increased biodegradability of pyrene with mineralization percentages of 50.1% and 53.7%, respectively, which suggested that both HMN and TOL may increase the availability of pyrene to bacteria or co-metabolize with pyrene in soil slurry. All NAPLs increased the aqueous desorption of aged pyrene.

The effects of organic amendments on the bioavailability and mobility of pyrene in the presence and absence of NAPL were also determined.  Pyrene with and without HEX was aged in both NC soil and Chelsea soil amended with treated and untreated MI peat and soybean stalks.  Both HEX and organic amendments reduced the bioavailability of pyrene to both earthworms and bacteria, especially for treated MI peat and soybean stalks.  The availability of pyrene in the soil samples to human heath was measured by physiological extraction using an artificially synthetic stomach solution. Both HEX and treated MI peat reduced the pyrene concentrations in the stomach solution.  These aged soil samples were also sequentially extracted using water, mixture of methanol and water, methanol and the non-extractable pyrene residues were determined by combustion and fractionated into humic/fulvic acids and humin. HEX increased the aqueous desorption of aged pyrene and reduced its non-extractable fractions from the soil.  MI peat reduced the desorption of aged pyrene by both water and methanol and increased its non-extractable fractions.

The effects of biosurfactants on the solubilization of PAHs from a NAPL that comprised of five PAHs (i.e., naphthalene, 1-methylnaphthalene, phenanthrene, fluoranthene, and pyrene) were also investigated.  The results showed that biosurfactant rhamnolipids increased solubilization of all five PAHs, especially for more hydrophobic pyrene and fluoranthene, which may lead to their higher environmental mobility and availability to organisms.