2007 Progress Report: Aquatic Toxicity of Carbon-Based Nanomaterials at Sediment-Water InterfacesEPA Grant Number: R833316
Title: Aquatic Toxicity of Carbon-Based Nanomaterials at Sediment-Water Interfaces
Investigators: Deng, Baolin , Ingersoll, Chris , Li, Hao , Wang, Ning
Institution: University of Missouri - Columbia
EPA Project Officer: Hahn, Intaek
Project Period: April 1, 2007 through June 30, 2010
Project Period Covered by this Report: April 1, 2007 through June 30, 2008
Project Amount: $399,506
RFA: Exploratory Research: Nanotechnology Research Grants Investigating Environmental and Human Health Effects of Manufactured Nanomaterials: a Joint Research Solicitation-EPA, NSF, NIOSH, NIEHS (2006) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Health Effects , Nanotechnology , Health , Safer Chemicals
This study aims to investigate toxicity of carbon-based one-dimensional (1-D) nanomaterials toward aquatic organisms that inhabit sediment-water interfaces and to identify factors controlling the toxicity to sediment-dwelling organisms. Because of their extraordinary properties, carbon nanotubes, nanofibers, and silicon carbide nanowires may find wide applications as catalyst supports, hydrogen storage devices, electrodes and sensors, reinforcing fibers, insulating materials, and flat panel display, etc. These nanomaterials often contain heavy metals (e.g., Fe, Co, Ni, Cu, and Cr), mostly introduced as catalysts for their manufacturing. There is little doubt that some of these manufactured nanomaterials will be released into the environment. Our knowledge on their environmental impact, however, is extremely limited. We hypothesize that the aquatic toxicity of metal-containing carbon-based nanomaterials is contributable to three aspects: (i) soluble metals released from metal-loaded nanomaterials, (ii) toxicity due to metal-free nanomaterials, and (iii) metals bound to the nanomaterials. This project will test these hypotheses with a goal of elucidating whether the interaction between heavy metals and carbon-based nanomaterials will neutralize or promote the aquatic toxicity, or have no effect to sediment-dwelling organisms.
During the first year of this project, our research focused on the following three aspects: (1) Acquisition, Manufacturing, and Characterization of Testing Materials. Various single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) were obtained from commercial sources. Other nanomaterials, including silicon carbide nanofibers with controlled metal contents were manufactured at the University of Missouri. Materials were characterized by scanning electron microscopy and energy dispersive spectroscopy (EDS), and major metal impurities in the examined carbon nanotubes were identified to be Ni, Fe, and Cr. The metal impurities could be partially solubilized in 3.5 M nitrate acid (~49% for Ni, 34% for Fe, and ~0% for Cr), suggesting that significant amounts of metal impurities may reside inside the nanomaterials that are non-extractable or non-releasable to the aqueous phase. (2) Establishment of the Standard Operation Procedure for Toxicity Testing. Toxicity and health effects of many nanomaterials are unknown. A Standard Operating Procedure (SOP) was established for the safe handling, storage, use, and disposal of the nanomaterials in the laboratory to maintain a healthy working environment and to avoid contaminating water and soils. (3) Development of Short-term Methods for Estimating the Chronic Toxicity of Nanotubes to amphipods (Hyalella azteca), midge (Chironomus dilutus), oligochaetes (Lumbriculus variegatus), and juvenile freshwater mussels (Villosa iris). The Phase I tests conducted in the first year of the current study aimed to refine a 14-d static-renewal sediment toxicity test method and evaluate the potential effect of nanomaterials to the four sediment-dwelling species. Multiple 14-d water-only tests have been successfully completed with control survival of ≥80%. Three types of nanomaterials (two MWCNT samples and one SWCNT sample) were used for the 14-d exposures (200 mg of sonicated or non-sonicated nanomaterials in 200 ml of water). In the tests with the two MWCNT samples, mean survival of amphipods was 3-8% (sonicated or non-sonicated materials), mean survival of mussels 23-35% (non-sonicated) and 3-43% (sonicated), mean survival of midge 60% (non-sonicated) and 43% (sonicated), mean ash-free biomass of oligochaete was 15-54% of the mean biomass in the controls. In the tests with the SWCNT sample, mean survival amphipods was 20% (non-sonicated SWCNTs) and 0% (sonicated SWCNTs), mean survival of midge was 10% (non-sonicated) and 0% (sonicated), and mean ash-free biomass of oligochaete was 15-50% of the mean biomass in the controls. These results indicated that the three nanomaterials were toxic to the sediment-dwelling organisms. Surviving organisms from the exposure of the test materials were also examined by light microscopy and substantial amounts of the nanomaterials were observed in the guts of test organisms, indicating that one of the mechanisms causing the toxicity of these materials is by either smothering the organisms or by reducing their consumption of food.
For the second year, we plan to focus on the toxicity of nanomatierisals in the presence of sediments and examine whether the toxicity to the four sediment-dwelling organisms is due to nanomaterials or from the metal impurities. Effort will also be devoted to publish research results through conference presentations and in archived journals.