Rapid Environmental Impact Screening for Engineered Nanomaterials: A Case Study Using Microarray Technology
|Principal Investigator||Eva Oberdorster|
|Institution||Southern Methodist University|
|Relevance to Implications||High|
|Class of Nanomaterial||Engineered Nanomaterials|
|Broad Research Categories||
|Anticipated Total Funding||$30,000.00|
|Funding Source||Project on Emerging Nanotechnologies|
|Anticipated End Year||2006|
The goal of this project was to use both the existing standard tests approved by the US EPA, and to develop new technologies based on gene-expression changes to more thoroughly assess the toxicity of one type of engineered nanomaterial, Reactive Nano-Iron Particles (RNIP). RNIP has already received EPA approval and is currently being used to remediate superfund sites.
The standard ecotoxicity tests used in this study involved acute toxicity testing with the zooplankton crustacean, Daphnia magna. Daphnia are used in testing since these animals are the basis of aquatic food chains and therefore are ecologically important, they are small (1 mm length), and they have short (3-week) life cycles, which means that they can be tested rapidly and inexpensively. The daphnids were used to produce “kill curves”, which are used to calculate the concentration at which 50% mortality occurs after 2 days (termed the 48-hour LC50). The LC50 concentration can then be compared to a large database, and RNIP can be classified as to it’s toxicity. This is the standard number used by EPA to make regulatory decisions. In this case, the 48-hour LC50 of 55 ppm is considered moderately toxic’. The drawback of this type of testing is that sub-lethal effects, such as physiological changes (ex: altering reproduction or growth), initiation of non-specific defenses (ex: inflammation) and specific defenses (ex: metabolic enzymes) are not considered.
To assess the potential for RNIP to cause sub-lethal effects, another standard model, the fathead minnow, Pimephales promelas, was used. These fish are small, easy to culture, and their genome has been well characterized. Recent development of a fathead minnow gene chip (microarray) by EcoArray in collaboration with the US EPA makes this species even more useful for screening and testing. After a 5-day exposure to high levels of RNIP (50 ppm), the minnows were sacrificed and their tissues assessed for up- or down- regulation of 2000 different genes. A single high-dose was used in this study to maximize the gene expression changes, but without causing mortality (sub-lethal effects). The genes that were differentially expressed help us assess how the animal responds to RNIP, for example by initiating tissue repair. A future goal is to develop a database of gene expression changes for a variety of toxicants; essentially creating a toxicant fingerprint. This fingerprint can be used in the field to determine whether fish have been exposed to contaminants, and to identify those contaminants. Fingerprints have already been created for a number of compounds, increasing the utility of the gene chip assay.