DEFINING DEVELOPMENTAL TOXICITY OF THE AGRICULTURAL HERBICIDE ATRAZINE IN THE EXPOSED AND SUBSEQUENT GENERATIONS USING ZEBRAFISH
thesisposted on 02.08.2021, 11:57 by Janiel K Ahkin Chin TaiJaniel K Ahkin Chin Tai
Atrazine (ATZ) is an agricultural herbicide. The US Environmental Protection Agency has set the maximum contaminant level at 3 μg/l in potable water, though concentrations can greatly exceed this amount depending on the time of year. Epidemiological studies report associations with developmental health outcomes with potable water exposure. Studies in model organisms identify ATZ as a neurotoxicant and endocrine disrupting chemical. The zebrafish model system was used to test the hypothesis that developmental ATZ exposure has immediate health consequences as well as in the subsequent generation. It was first hypothesized that developmental ATZ exposure generates metabolites similar to those found in mammals and alters morphology and behavior in larvae. In the exposed generation, targeted metabolomic analysis found that zebrafish produce the same major ATZ metabolites as mammals. The visual motor response test at 120 hpf detected hyperactivity in larvae in the 0.3 ppb treatment group and hypoactivity in the 30 ppb treatment group. These findings suggest that developmental ATZ exposure generates metabolite profiles similar to mammals leading to behavioral alterations supporting ATZ as a neurodevelopmental toxicant. In the subsequent generation (F1), it was hypothesized that parental ATZ exposure altered protein expression leading to modifications in morphology and behavior in developing progeny. Proteomic analysis identified differential expression associated with neurological development and disease and organ and organismal morphology, specifically the skeletomuscular system. Head length and the ratio of head length to total length was significantly increased in the F1 in the 0.3 and 30 ppb ATZ treated groups. Craniofacial morphology was assessed based on molecular pathway analysis and revealed decreased cartilaginous structure size, decreased surface area and distance between saccular otoliths, and a more posteriorly positioned notochord, indicating delayed ossification. The visual motor response assay showed hyperactivity in the F1 of the 30 ppb treatment group for total distance and time spent moving in the F1 of the 0.3 and 30 ppb treatment groups for all phases. Collectively, these results demonstrate persistent ATZ developmental toxicity in this multigeneration study.