Intellectual Merit: The use of engineered metal nanoparticles (NP) in consumer products such as washing machines and cosmetic products is becoming widespread. As an example, ZnO NPs have the ability to absorb ultraviolet (UV) light when below the size of 100 nm, and are commonly found in sunscreens. Considered to be the richest family of nanostructures, ZnO NPs are also used as rubber additives, pigments, and in photoelectrodes. Environmental exposure to nanoparticles is not a new concept and organisms have adapted to natural exposures; the concern lies with the recent influx of manufactured nanoparticles that may have a detrimental effect on the environment. With the majority of NPs being released to the environment through municipal waste water and sewage sludge mediums, aquatic and terrestrial systems are a likely sink for manufactured nanoparticles. The fates of these nanoparticles once released into the environment and the potential for transfer of NPs to organisms higher in the food web (e.g. birds and small mammals) are open questions. This investigation will utilize nanoparticles with a chemical fingerprint to track the fate of NPs in soil and the potential for uptake and transfer to higher-level organisms using the earthworm Eisenia fetida. Earthworms are in constant direct contact with soils and are an important potential entry point into the terrestrial food web where bioaccumulation of NPs can occur in higher-level organisms. The fingerprinted NPs in this study will be readily discernibly from other sources of Zn in the soil and the earthworm. The behavior of the fingerprinted NPs in a soil system will be compared with other non-nano forms of Zn (bulk ZnO powder and ZnCl2) over time to evaluate the impact of soil ageing on the bioavailability of the different Zn forms. This general approach will be used to test the following hypotheses; 1) There will be no difference in the uptake or elimination of Zn by E. fetida among all three forms of Zn, indicating that zinc NPs are easily eliminated by E. fetida and there is no potential for transfer via earthworms to the terrestrial food web and, 2) There will be no difference in the uptake or elimination of Zn by E. fetida among the three zinc treatments after 42 days of ageing and that these treatments will not differ from the initial experiment.
Broader Impacts: An understanding of nanoparticles' fate in soil systems and their impact on the wider environment, which ultimately impacts the quality of our lives, is of prime interest to our society. There is a critical need for scientists trained to understand these types of emerging systems. This project will provide educational opportunities at all levels. Minority students with an interest in working on this project will be identified and recruited through an active NSF STEP program "Towson Opportunities in STEM" (TOPS). All involved students will work as part of a multi-disciplinary research team over the course of the project. Results from this investigation will be disseminated by students at the Towson University Research Expo, at appropriate professional conferences as well as through the peer-reviewed literature.
The increasing use of nanomaterials, dimensions of 1-100 nm, in many fields of manufacturing (cosmetic, solar voltaics, rubber, paints, etc.) has expanded the potential for release of metal nanoparticles (NPs) into environmental systems. Specifically, manufactured ZnO and TiO2 NPs are known for their light absorbing and light scattering properties and are major components of sunscreens and are some of the most popular metal nanoparticles produced and studied. Metal nanoparticles can enter the environment through many different pathways: landfills, incineration, leaching through sewage treatment plants, and soil and surface waters. The toxicological effects of metal and metal oxide nanoparticles are important areas of study for three major reasons: the potential release of free metal, their ability to interact with, and produce harmful substances from, surrounding media (adhesion), and the potential to adversely interrupt biological processes at the molecular level. Expressly, as NPs enter terrestrial environments they tend to agglomerate, or cluster together. Agglomeration increases persistence in the environment and this persistence can lead to the potential for NPs to enter food webs through uptake in lower trophic species like earthworms. To date, there is limited information on the long-term behavior of NPs in soil systems where NPs are deposited when biosolids from waste water treatment plants are applied to fields as fertilizer. Earthworms are an ideal organism to evaluate the fate and effects of NPs in a soil system since they directly process soil through their digestive system making them susceptible to changes in the chemistry of the soil environment. As earthworms are an important food source for other terrestrial organisms, earthworms may represent a critical entry point into the food web for trace metal pollutants associated with NPs. However, because earthworms are able to regulate Zn, tissue body burdens may not reflect the uptake and elimination of Zn from NPs in terrestrial systems. In order to overcome the challenges associated with evaluating Zn uptake and elimination rates, we synthesized isotopically-labeled 68ZnO NPs to investigate their transformation in soil and the rate of turnover of Zn associated with NPs in the earthworm Eisenia fetida. We exposed E. fetida to three treatments of isotopically-labeled zinc (68ZnCl2, bulk 68ZnO, and 68ZnO NPs) amended to topsoil for 21 days followed by 21 days in a clean topsoil to assess uptake and elimination rates. The Initial exposure was repeated following a 21 day soil-aging period. Changes in Zn isotope ratios in worms over the first 21 days of exposure to 68ZnO NPs and 68ZnCl2 amended soils was similar and much greater than occurred in worms exposed to bulk 68ZnO amended soils. Aging of amended soils decreased differences in uptake of 68Zn among particle types. Elimination rates were similar among 68Zn particle types before and after soil aging. Our results suggest that Zn associated with NPs is particularly labile (easily dissolved) in soil environments and that results from investigations using ZnCl2 are applicable when assessing the risk of ZnO NPs in the soil environment of terrestrial systems. This project provided training opportunities and support for one female graduate student in the environmental science program at Towson and two male undergraduate students in the physics program at Towson. Student participants represent both underrepresented groups and disciplines in STEM. All students involved with this project were also provided with several professional development opportunities in the form of presenting their results at local, regional and national professional meetings as first authors. The graduate student is also currently preparing a manuscrip for submission to a peer-reviewed publication.
