Intellectual Merit. With the projected market for nanomaterial-based products approaching in the trillions of dollars annually, management of these products and their waste will inevitably pose challenges to environmental health, particularly when nanomaterials are released through product disposal or industrial waste streams. This study is a plan to describe quantum dot fate in representative aquatic settings subjected to broad chemical conditions while exploring specific degradation mechanisms and environmental factors that influence these processes. Quantum dots (QDs) are semiconducting nanocrystals with core/shell structures often less than 20 nm and employed in fluorescent measurements and energy applications, and, like other metallic nanoparticles studied over the past decade, may undergo physical (aggregation) and chemical (dissolution) transformations that influence their overall bioavailability upon release to receiving water bodies. While the toxicity of CdSe/ZnS QD and their leached metals have been examined closely for a variety of microorganisms, more mechanistic details of their degradation processes is needed for the various classes of QDs subjected to diverse aquatic chemistries in order to better predict their overall fate. The overall goal of this proposal is to determine how different types of QDs, both conventional and next-generation, degrade in aquatic environments and waste streams. Specific objectives are (1) to develop a robust, rapid analytical procedure for identifying and quantifying QD elements in their particulate, complexed, and dissolved forms with almost no sample pre-treatment using single-particle inductively coupled plasma mass spectrometry (SP-ICPMS) and size exclusion chromatography (SEC-ICPMS), (2) to identify the ligand groups of various types of organic matter that promote QD degradation and element release, (3) to determine influence of UV and visible light in promoting QD degradation, (4) to evaluate other inorganic geochemistry factors such as dissolved hydrogen, oxygen, and sulfide that may influence QD degradation, and (5) to determine whether physicochemical properties of QD coatings can be altered to prevent QD degradation. Reaction rates and product distributions will be determined within batch reactors containing various combinations of QDs and geochemical constituents. The results will provide fundamental information on the roles of geochemical solution conditions, dissolved organic compounds, and UV and visible light exert on the dissolution of a variety of QDs. The SP-ICPMS developed here will have application to other metallic nanoparticle measurements in waters.
Broader Impacts The laboratory investigations into QD degradation processes will lead to a deeper understanding of QD longevity to be expected upon release into aquatic environments, and this information will lead to improved designs of QD coatings. This work will provide education for one graduate student per year and several undergraduate students in environmental engineering. The research opportunity provides diverse experimental and analytical instrumentation training in water quality, inorganic synthesis chemistry, and mineralogical techniques. Broadened participation of underrepresented groups will be addressed by providing experiential learning opportunities through hands-on laboratory engagement to undergraduate students, Massachusetts state teachers, and local high school students. Their research experiences will be integrated into the PI's Research Program by supporting QD synthesis, reaction, and characterization methods as well as the Educational Program by assisting development of educational materials for the instruction of broad audiences about the principles of environmental science and engineering. These materials are intended to foster systems thinking education using WWW-based multimedia modules comprised of graphical, video, and systems modeling tools. The results of this Educational Program will reach local middle school, high school, and undergraduate students through field trip demonstrations and curriculum modules.
