WHOI Theses

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https://hdl.handle.net/1912/1172

WHOI's educational role, at the graduate level, was formalized in 1968 with a change in its charter and the signing of an agreement with the Massachusetts Institute of Technology for a Joint Program leading to doctoral (Ph.D. or Sc.D.) or engineer's degrees. Joint master's degrees are also offered in selected areas of the program. Woods Hole Oceanographic Institution is also authorized to grant doctoral degrees independently.

New theses are added as they are published.

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Browsing WHOI Theses by Author "Aluru, Neelakanteswar"
  • Thesis
    An assessment of the biodistribution, persistence, and health impacts of microplastics and nanoplastics in fish
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2024-02) Pitt, Jordan A. ; Hahn, Mark ; Aluru, Neelakanteswar
    Microplastics have been found in a diverse range of organisms across trophic levels. Although organisms are continuously exposed to microplastics (1 μm - 5 mm) and nanoplastics (< 1 μm), the risk of these exposures are not understood. A risk assessment for microplastics and nanoplastics is urgently needed, but first more information is required on the biodistribution, persistence, and subsequent health impacts of microplastics and nanoplastics in organisms. My thesis addresses these key knowledge gaps through a combination of environmental measurements and laboratory experiments. I first reviewed the microplastics literature to determine the state of knowledge regarding the trophic transfer, bioaccumulation, and biomagnification of microplastics and nanoplastics. I found that in most of the literature there was clear evidence of trophic transfer, equivocal evidence for bioaccumulation, and no evidence for biomagnification. I drew upon these noted knowledge gaps to guide my measurements of microplastic abundance in Atlantic killifish (Fundulus heteroclitus) captured near Falmouth, MA. I found that microplastics were both more abundant and diverse in the GI tract, compared to those in the muscle. Small microplastics, which are often not analyzed, were the most abundant, and I found evidence that these small microplastics may bioaccumulate. Following this, I compared the impact of the route of exposure on the biodistribution and persistence of polystyrene nanoplastic particles (50 nm and 500 nm) in zebrafish (Danio rerio). I found that exposure routes other than an oral exposure (i.e. dermal, respiratory) contribute to nanoplastic biodistribution, and that the nanoplastics were not persistent in tissues 2 days after exposure. I then examined the impact of a 50 nm polystyrene nanoplastic exposure on cardiovascular development and function in larval zebrafish. Larvae exposed to high concentrations of nanoplastics had significant defects in cardiovascular function. Altogether, my research indicates that nanoplastics and small microplastics might be slightly bioaccumulative in tissues, but that 50 nm polystyrene nanoparticles are not hazardous except in high concentrations; however, nanoplastics and microplastics are diverse. Future work should focus on expanding our knowledge of the toxicity of different types of plastic. This work lays the foundation for future risk assessments for microplastics and nanoplastics.
  • Thesis
    Assessing the impact of domoic acid exposure on the zebrafish (Danio rerio) brain across life stages
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2024-06) Hidayat, Alia S. ; Aluru, Neelakanteswar
    Domoic acid (DA) is a neurotoxin produced by diatoms in genus Pseudo-nitzschia. DA accumulates in seafood and can affect the health of humans and wildlife. DA is a structural analog of glutamate - an excitatory neurotransmitter - that activates ionotropic glutamate receptors leading to excitotoxicity and ultimately neurobehavioral defects. While current seafood regulations prevent acute toxicity from high-level exposure, low-level exposure can still have effects on brain development and function. Developmental stages are particularly sensitive to low-level exposure. This thesis assesses the impact of DA exposure on brain health in both development and adulthood, and investigates whether developmental exposure to DA has persistent effects. In the first data chapter, I employed microarray analysis to demonstrate that exposure to an asymptomatic dose of DA significantly altered gene expression patterns in the adult zebrafish brain. These changes were distinct from those resulting from symptomatic exposure, suggesting that low levels of DA could affect brain function in unique ways. In the second data chapter, I investigated the effect of developmental exposure to DA on immune cells in the brain (microglia). Microglia have critical roles in brain homeostasis, development, and the response to injury or infection. Using transgenic zebrafish (Tg(mpeg1:mCherry)), I characterized developmental windows of microglial sensitivity to DA exposure. Developmental exposure to DA (0.1 ng/embryo) at 2 days post-fertilization (dpf) resulted in microglial reactivity without permanent gross morphological defects. These findings suggest that microglia may be an understudied target of DA toxicity. My final chapter investigates the effects of developmental exposure on later-life behavior and sensitivity to subsequent exposures. I exposed larval zebrafish to 0.1ng DA at 2 dpf and raised these individuals to adulthood, where they received a second exposure to DA or vehicle. Fish exposed to DA in early life showed no significant changes in survival or sensitivity to a second dose of DA. Furthermore, there was no effect of developmental or adult treatment on behavior in novel tank or Y-maze spatial discrimination assays. This thesis contributes to our understanding of neurodevelopmental effects of DA exposure during developmental and adult life stages, emphasizing the potential for microglia as a target of DA.