Grantee Research Project Results
2001 Progress Report: The Effects of Aging and Sorbent Decomposition on the Bioavailability of Toluene and Xylene in Solid Waste
EPA Grant Number: R827131Title: The Effects of Aging and Sorbent Decomposition on the Bioavailability of Toluene and Xylene in Solid Waste
Investigators: Barlaz, Morton A. , Knappe, Detlef R.U.
Institution: North Carolina State University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1998 through September 30, 2001 (Extended to March 31, 2002)
Project Period Covered by this Report: October 1, 2000 through September 30, 2001
Project Amount: $425,000
RFA: EPA/DOE/NSF/ONR Joint Program on Bioremediation (1998) RFA Text | Recipients Lists
Research Category: Land and Waste Management , Hazardous Waste/Remediation
Objective:
This research project hypothesizes that kinetically limited sorption/desorption processes and humification control the bioavailability and leaching of organic contaminants in landfills and that humification may be an endpoint in the fate of toluene and o-xylene. The overall objective of this research project is to develop an understanding of factors controlling the bioavailability and fate of organic contaminants sorbed to components of municipal solid waste (MSW). Specific objectives are to: (1) estimate the expected distribution of sorbed contaminants in MSW by measuring the sorptive capacity of the dominant organic refuse components in fresh and biodegraded form; (2) determine whether the sorptive uptake of organic contaminants in MSW is reduced in the presence of leachate as a result of organic contaminant binding by dissolved organic macromolecules; (3) determine the impacts of aging and leachate composition on contaminant desorption rates; (4) compare rates of desorption and biodegradation to determine whether desorption limits bioavailability; (5) determine the effects of refuse decomposition on bioavailability; and (6) identify whether humification is an important sequestration mechanism for aromatic xenobiotics in solid waste.Progress Summary:
This project is being conducted with individual components of MSW [polyvinyl chloride (PVC), high-density polyethylene (HDPE), newsprint, office paper, model food, and yard waste (rabbit food)]. Each of the biopolymer composites (office paper, newsprint, rabbit food) is tested in both fresh and anaerobically decomposed form. Batch isotherm data were collected in phosphate-buffered organic-free water as well as in acidogenic and methanogenic leachate. Flame-sealed glass ampules were used to minimize volatilization losses, and sodium azide was added to the liquid phase to prevent aerobic biological activity. Acidogenic leachate was prepared by recirculating water through fresh residential MSW, and methanogenic leachate was generated from decomposed refuse. The isotherm data showed that alkylbenzene sorption to plastics was greater than to biopolymer composites, and differences in sorbate/sorbent solubility parameter compatibility explained this observation. Alkylbenzene sorption to biopolymer composites yielded linear isotherms, and sorption capacities [log (Koc/Kow)] decreased linearly with increasing sorbent polarity as expressed by the O-alkyl/alkyl ratio. Leachate composition had little effect on alkylbenzene sorption with one exception; volatile fatty acids in acidogenic leachate appeared to convert PVC from a glassy to a rubbery polymer. The results of the isotherm study showed that sorbent organic matter affinity for hydrophobic organic contaminants (HOCs) increases with increasing extent of MSW decomposition because of the recalcitrance of plastics and the preferential degradation of polar biopolymers. Furthermore, the plasticizing effect of volatile fatty acids in acidogenic leachate may enhance the bioavailability of HOCs sorbed to glassy organic matter in MSW or in soils contaminated with acidogenic leachate.To determine the effects of aging on alkylbenzene desorption rates, abiotic batch desorption tests were performed in both acidogenic and methanogenic leachates. Prior to desorption testing, sorbents were exposed to 14C-labeled toluene for 30, 180, and 360 days in flame-sealed ampules. To assure sterility during aging, flame-sealed ampules were g-irradiated. Selected samples containing 14C-labeled o-xylene also were analyzed after an aging time of 1 year. Desorption tests showed that alkylbenzene desorption rates varied significantly among different MSW components (PVC slowest, fresh rabbit food fastest). Furthermore, desorption rates decreased as aging time increased, suggesting that the bioavailability of HOCs in landfills decreases over time as HOCs are physically sequestered or undergo humification. A single-parameter polymer diffusion model successfully described PVC and HDPE desorption data, but it failed to simulate desorption rate data for biopolymer composites such as rabbit food, newsprint, and office paper. Current efforts focus on the development of a three-parameter biphasic polymer diffusion model to describe desorption rate data from biopolymer composites.
For bioavailability tests, 14C-toluene was aged under abiotic conditions in the presence of individual waste components for periods ranging from 1 to 180 days. After aging, Pseudomonas putida F1, a well-characterized toluene degrader, was added to the aged toluene-sorbent mixture and toluene bioavailability was determined by monitoring 14CO2 production over time. 14CO2 production also was monitored in sorbent-free positive controls, and all tests were conducted in triplicate. For all sorbents, there was a phase of rapid biodegradation after which the 14CO2 production rate decreased and ultimately stopped, despite the presence of residual toluene sequestered in the solid phase. The extent of biodegradation varied markedly among sorbents and was correlated with the sorbents' chemical characteristics. 14CO2 recovery ranged from 66.7 percent for toluene aged on degraded office paper for 1 day to 45.6 percent for toluene aged on PVC for 180 days. In general, toluene bioavailability was reduced by aging. Analysis of the solid phase at the termination of bioavailability tests revealed that 14C was present in all three major forms of humic substances: humic acid, fulvic acid, and humin. High-performance size exclusion chromatography showed that 14C in humic and fulvic acid fractions was present in molecular size fractions greater than that of free toluene. Further research is required, however, to determine whether the 14C in these fractions was physically sequestered or covalently bound. Overall, 14C mass balances of 95 to 101 percent were measured.
Future Activities:
Future activity will be focused on the completion of bioavailability tests and the description of desorption and bioavailability data by appropriate models.Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 7 publications | 1 publications in selected types | All 1 journal articles |
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Type | Citation | ||
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Wu BY, Taylor CM, Knappe DRU, Nanny MA, Barlaz MA. Factors controlling alkylbenzene sorption to municipal solid waste. Environmental Science & Technology 2001;35(22):4569-4576. |
R827131 (2001) R827131 (Final) |
not available |
Supplemental Keywords:
landfills, solid waste, toluene, o-xylene, humic substances., RFA, Scientific Discipline, Toxics, Waste, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Environmental Chemistry, HAPS, chemical mixtures, Bioremediation, 33/50, fate and transport, Toluene, landfills , Xylenes, kinetic studies, aging, contaminant release, desorption rates, solid waste, humification, Xylene, municipal solid waste, Xylenes (isomers and mixture), leachateRelevant Websites:
http://www4.ncsu.edu:8030/~knappe/bio.html
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.