Date of Award


Degree Type


Degree Name

Master of Science (MS)


Health Sciences

Committee Chair

Jennifer Freeman

Committee Member 1

Ellen Wells

Committee Member 2

Wei Zheng


Tungsten (W) is a refractory metal that is used in a wide range of applications. Initially perceived as immobile in the environment, tungsten replaced lead and uranium in munition and military applications. Recent studies report movement and detection of tungsten in soil and potable water sources increasing the risk of human exposure. In addition, experimental research studies observed adverse health effects associated with exposure to tungsten alloy, raising concerns on tungsten toxicity with questions surrounding the safety of exposure to tungsten alone or in mixtures with other metals. Tungsten is commonly used as an alloy with nickel (Ni) and cobalt (Co) in many applications to adjust hardness, thermal, and electrical conductivity of tungsten products. In this study, the zebrafish model was used to assess the effect of Co and Ni on W toxicity. First, zebrafish embryos were treated immediately after fertilization with either W, Co, or Ni, then survivability was monitored every 6 hours till 120 hours post fertilization (hpf). A concentration with no effect on survival was then used to study the interaction of the mixture. Three concentrations of each metal were used to prepare the mixtures. Zebrafish embryos were exposed to one of the metal combinations immediately after fertilization. The toxicity of the mixtures was assessed by monitoring the survivability and hatching rates every 6 hours until 120 hpf. Behavioral analysis using the visual motor response test was performed at 120 hpf. Morphology measurements of body length, head length, head width, and brain length were recorded of zebrafish larvae from selected mixtures at 120 hpf. Mathematical models were used to predict the interaction relationship of the W-Ni-Co mixtures and compared to the observed outcomes. The results revealed that 10,000 parts per million (ppm; mg/L) W, 100 ppm Ni, and 100 ppm Co caused a decrease in survivability. The W/Ni/Co mixture exposure showed that 5,000 ppm W-based mixtures may have a synergistic interaction on inhibition of the survival rates compared to control (p<0.05). The 1000 W-10 ppm Co showed acceleration of hatching rates compared to control at 60 hpf (p<0.05). No significant differences in survival rates were observed with the exposure to 1000 ppm W-based mixtures. A decrease in locomotor activities of 120 hpf larvae was observed with the exposure to 10 ppm Co and 10 ppm Co-based mixtures (p<0.05). Morphological abnormalities were observed in zebrafish exposed to the 1000 ppm W-1 ppm Co mixture at 120 hpf (p<0.05). The results of this study highlight the importance of studying the toxicity of multicomponent mixtures as a single unit and not as individual components. According to the concentration addition model, the interaction of the lower concentrations of the W/Ni/Co mixtures is additive but the mixtures did show potential synergistic interaction at high concentrations. The independent action model revealed that the interaction of the three metals is additive.