Date of Graduation

Spring 2019

Degree

Master of Science in Biology

Department

Biology

Committee Chair

Ryan Udan

Keywords

zebrafish, environmental toxicology, herbicides, heart inhibitors, morphological deformities, development

Subject Categories

Biology | Developmental Biology

Abstract

Environmental contaminants are chemicals of anthropogenic origin that are found in water, soil, and air, and are harmful to a wide variety of organisms (ORD US EPA, 2018-a). One common group of contaminants are herbicides. Though herbicides are used to control unwanted vegetation in agriculture, aquatic organisms and humans may be exposed to these herbicides through run off into streams and rivers, by drinking contaminated water, by consuming treated crops, by direct exposure, or through bioaccumulation. Thus the effect of these herbicides on animals needs further investigation. In this study, I sought to determine whether six different herbicides, which have had minimal testing in animal studies, have teratogenic effects. Thus, I exposed zebrafish embryos (from the blastoderm stage to 4 days post fertilization) to the herbicides, and assessed the effects of each herbicide on embryonic development. My results indicate that all herbicides tested, with the exception of nicosulfuron, led to some form of toxicity, cardiac dysfunction, or other developmental error. For example, exposure of zebrafish embryos to high concentrations of glufosinate-ammonium or thifensulforon-methyl resulted in some embryos exhibiting cardiac dysfunction. However, due to variation in the results at different concentrations, the LD50 (lethal dose 50%) of these herbicides could not be identified. Quizalofop-p-ethyl exposed embryos displayed cardiac dysfunction at the LD50. However, at concentrations slightly higher than the LD50, embryos exhibited a general toxicity that led to 100% mortality. Mecoprop treatment led to variability in mortality at different concentrations. However, within the suspected LD50, mecoprop treated embryos exhibited cardiac dysfunction, as well as a host of other abnormalities: shortened body axis, micropthalmia, curved spine, tail malformation, lack of motility, and abdominal edema. At a range of concentrations, hexazinone treatment resulted in cardiac dysfunction as well as defective pigment cell alignment, shortened body axis, micropthalmia, tail malformation, lack of motility, and abdominal edema. The results of this study provide evidence that one herbicide, nicosulfuron, appears to be safe for zebrafish embryonic development and survival. However, many of these herbicides have teratogenic effects that need to be explored further.

Copyright

© Kayla Ray King

Open Access

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