Date of Award

8-2007

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Biochemistry

Advisor

Gregory D. Mayer

Second Committee Member

Clarissa Henry

Third Committee Member

Anja Nohe

Abstract

Semiconductors and semiconductor nanoparticles have become a popular component of many new manufactured products. The molecular properties of semiconductors allow the manipulation of electrical conductivity, which can be utilized for the development of numerous electronics (1;2). The increasing use has become an environmental concern with a predicted increase in semiconductor waste upon product expiration (3). Waste regulation agencies correlate semiconductor contamination with heavy metal pollution due to the composition of semiconductors consisting of at least one heavy metal and one metalloid (4). The focus of the concern is on semiconductor contamination of aquatic environments, as heavy metal pollution is arguably more prevalent in fresh water lakes, rivers and streams (3;4). Current allowable contamination levels mirror those of their heavy metal constituents (5). Recent studies investigating semiconductor nanoparticle toxicity observe acute toxicity at levels far below that of salts containing identical heavy metals (6;7). Exact modes of toxicity are not yet fully understood, but implications of heavy metal liberation, free radical formation and membrane disruption have been suggested (4;8;9). Here we investigate the toxicological effects semiconductor nanoparticles impart on aquatic organisms. Semiconductor nanoparticle toxicity was assessed through the monitoring of known heavy metal-responsive pathways, the use of toxicity assays, the observation of nanoparticle uptake and the use of counteractive reagents. Our experiments demonstrate semiconductor nanoparticles do not stimulate the same genes associated with heavy metal homeostasis and are significantly more toxic than equivalent concentrations of heavy metal salts. Other findings include that semiconductor nanoparticles do share some toxicological characteristics with heavy metal salts such as liver damage and bioaccumulation, but are definitively dissimilar in terms of overall toxicity. Our conclusions supply noteworthy evidence against the present administrative guidelines regulating allowable semiconductor release into aquatic environments and support the need for the reevaluation of these regulations.

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