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
Effects of natural organic matter on the bioavailability and environmental mobility of NAPL compounds: As reported previously, Dr. Walt Weber’s lab found that the sorption capacities of a number of natural organic materials for organic compounds increased greatly after treatment with superheated water under conditions designed to mimic but sharply accelerate natural diagenesis processes in the environment. These treated organic materials were then applied to soil as engineered natural organic sorbents (ENOS) to determine their effects on the environmental mobility and bioavailability of selected organic contaminants. Two representative NAPL compounds, i.e., trichloroethylene (TCE) and tetrachloroethylene (PCE), were aged in a soil amended with treated and untreated MI peat, pine needles, and maple leaves for 75 days, and their recoveries from aged soil samples, their bioavailabilities and their environmental mobilities were determined.
The recovery of TCE from the soil samples amended with the above organic markedly increased, ranging from 20.3 to 36.3% for untreated ENOSs, and from 54.5 to 79.3% for treated ENOSs, and only about 3% of initially applied TCE remained in the soil samples without amending any organic sorbents. The recovery of PCE increased from 15.6 to 78.9% in the soil amended with 0 to 20% of treated MI peat. The data showed that natural organic materials, especially ENOSs, significantly increased retention of TCE and PCE in soil samples.
Their bioavailabilites were assessed by exposing TCE or PCE aged soil samples to earthworms for 10 days followed by determinations of their concentrations in worm tissue. The uptake of residual TCE and PCE was greatly decreased in the soil samples amended with organic materials, especially ENOSs. Based on the percentages taken up by worms, the availability of TCE from the untreated soil sample is a factor of 1.7 to 9.3 higher from soil samples amended with untreated organic materials and a factor of 6.3 to 15.2 higher than that from soil samples amended with treated organic materials. For the soil samples amended with different amount of the treated MI peat, the concentrations in worm tissues and percentages of PCE decreased as the amount of treated MI peat increased.
The environmental mobilites of aged TCE and PCE were determined by measuring their aqueous desorptions. The results showed that desorption percentages and rates of TCE and PCE decreased from soils containing the organic amendments.
Removal of estrogenicity from water through enzymatic coupling reactions: Estrogenic phenolic compounds comprise an important class of endocrine disrupting chemicals of increasing public concern. Dr. Weber’s group found that these chemicals can be effectively transformed through catalyzed oxidative coupling reactions. They studied bisphenol A (BPA) as a surrogate estrogenic chemical, examined its transformation in horseradish peroxidase mediated oxidative coupling reactions, and proposed a detailed reaction pathway map with the help of product identification and ab initio molecular modeling.
Combined NOM reconfiguration and ultrafiltration for the reduction of DBP formations: Natural organic matter (NOM) causes problems in water treatment systems by reacting with disinfectants (eg. chlorine) to form disinfection byproducts (DBPs) that are carcinogenic, mutagenic or hepatotoxic. Dr. Weber’s group has found that aquatic NOMs can be effectively reconfigured through induced oxidative coupling reactions to yield stable species of greater molecular sizes, thus rendering them more readily removable by ultrafiltration. Such molecular reconfigurations also significantly reduce the role of NOMs in forming DBPs by effectively reducing the number of halogen-reactive groups.
Mechanisms for horseradish peroxidase inactivation and its mitigation: Horseradish peroxidase (HRP) catalyzes redox reactions of a wide spectrum of substrates, and has great potential in pollution control and remediation applications. HRP is, however, susceptible to rapid inactivation, limiting its catalytic efficiency. Dr. Weber’s group evaluated HRP inactivation behavior and mechanisms during the catalytic oxidation of phenol under a variety of conditions, and characterized the protein structural changes using Raman and FTIR. These data provide the first experimental support for HRP inactivation by phenoxyl radical attack, involving destruction of the heme (the catalytic center of HRP) and deprivation of the heme iron.