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NCER Grantee Research Project Results

Enzymatic Degradation of Carbon Nanotubes To Mitigate Potential Toxicity

EPA Grant Number: FP917138
Title: Enzymatic Degradation of Carbon Nanotubes To Mitigate Potential Toxicity
Investigators: Kotchey, Gregg Peter
Institution: University of Pittsburgh - Main Campus
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: September 1, 2010 through August 31, 2013
RFA: STAR Graduate Fellowships (2010)
Research Category: Academic Fellowships , Fellowship - Pesticides and Toxic Substances

Description:

Objective:

Due to their unique properties, vast research has been conducted on nanomaterials, especially carbon nanotubes (CNTs). As the resulting electronic, composite, and sensor applications become commercialized, the demand for CNTs of all varieties has increased. The current output for large-scale production of CNTs has been given as 10,000 tons per manufacturing plant per year. With such a large amount of CNTs being produced and the associated handling involved in processing these nanomaterials, not only do the workers increase their risk of point-source exposure through inhalation, but also the general public is at risk of the toxic effects of CNTs, when this material is introduced into non-point source aquatic environments such as rivers and streams. This research project will develop a mechanistic understanding and manipulation of the enzymatic degradation of CNTs that can be employed for future environmental remediation that aims to mitigate possible toxicological effects of CNTs before these materials enter the human body.

Synopsis:

Due to their unique properties, carbon nanotubes (CNTs) have been integrated in numerous applications. Toxicological studies, however, have demonstrated that CNTs induce inflammatory responses and cellular apoptosis. As production of CNTs increase to meet the growing demand, the risk of environmental contamination increases. This project aims to develop a mechanistic understanding of the enzymatic degradation of CNTs that can be applied in future environmental remediation schemes.

Approach:

The basis for this research project is rooted in the findings by our research group that the enzyme, horseradish peroxidase (HRP), can degrade carboxylated CNTs in the presence of low concentrations (~40 ┬ÁM) of hydrogen peroxide (H2O2). The focus of this project is to obtain a fundamental mechanistic understanding of this enzymatic degradation process, which will be accomplished by three approaches. First, the environmental and structural factors affecting the kinetics of CNT degradation using HRP will be identified. Next, to promote the degradation of pristine CNTs, HRP will be modified, and the CNTs will be noncovalently functionalized. Finally, the intermediate products of HRP-degradation of CNTs and their potential toxicity will be determined.

Expected Results:

The factors impacting the mechanism of HRP catalyzed degradation of CNTs will be ascertained during this comprehensive study. By performing the research outlined in the first approach, the optimal pH, temperature, and concentration of H2O2 for maximizing the kinetics of in vitro HRP degradation of carboxylated CNTs will be ascertained. Second, modifying the cofactors of HRP to create a more hydrophobic active site should enhance its interaction with pristine CNTs resulting in their degradation. In addition, a precedent has been established for the coating of CNTs with natural organic matter (NOM), which enables CNTs to disperse in aqueous media. This increased hydrophilicity should promote favorable interaction between HRP and the coated-CNT conjugate, resulting in the degradation of pristine material that was functionalized through noncovalent approaches. Finally, because HRP is known to facilitate the heterolytic cleavage of H2O2 to form Compound I and water, it is expected that the majority of products from this reaction will consist of highly oxidized aromatic hydrocarbons and oxidized aliphatic hydrocarbons. Moreover, we expect to see CO2 gas production as an indication of complete degradation. By examining the literature, the toxicity of the products of degradation will be ascertained.

Potential to Further Environmental/Human Health Protection:

While production companies increase their output of CNTs to meet growing demand, the risk of environmental contamination of this toxic material is increased. Such contamination can subsequently diffuse through aquifers and residential drinking water. As a result, necessary precaution will have to be taken to insure that the public, as well as the manufacturers, are safe from the toxic effects associated with CNTs. This project comprehensively outlines a method to safely degrade CNTs employing the enzyme HRP. Armed with the findings of this work, environmental engineers will be well equipped to develop in situ remediation schemes for environmental systems to mitigate CNT toxicity.

Supplemental Keywords:

carbon nanotubes, toxicity, enzymes, horseradish peroxidase, degradation, environmental contamination, environmental remediation,

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The 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.

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