A Dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Medicine University of the Witwatersrand Parktown, Johannesburg, South Africa June 2017 / Atrazine, an extensively used herbicide is amongst the commonly detected herbicides in groundwater. Atrazine concentrations as low as 0.01μg/l have been implicated to affect frog populations, thus much attention has been placed on its use and safety. Several studies have examined atrazine effects on reproductive organs, immune systems and population fitness of adult Xenopus laevis species and we found no studies on the effects of atrazine on the liver and kidney. This study investigated biochemical and histopathological effects of chronic exposure to atrazine on livers and kidneys of adult Xenopus laevis frogs, post metamorphosis. Forty male frogs were randomly divided into four groups (A -D) of 10 frogs each, housed in stainless silver tanks with 60L of water and atrazine concentration of 0μg/l A: control, B: 0.01μg/l, C: 200μg/l and D: 500μg/l respectively, for 90 days. Liver (ALT, ALKp and AST) and kidney (urea, creatinine) biomarkers, malondialdehyde, an indicator of lipid peroxidation, histopathology, melanomacrophage percentage area and fibrosis were examined. Significant increases of ALT and creatinine were observed at 200 and 500μg/l (P<0.05). Malondialdehyde was significantly increased at 500μg/l (P<0.05). Histopathologically, the liver showed disorganization in the arrangement of hepatic cords, hypertrophied hepatocytes, hepatocyte vacuolization, vascular congestion and dilation, infiltration of inflammatory cells and apoptosis and/or necrosis, with the highest atrazine concentration causing the most adverse effects. The kidney showed glomerular atrophy and degeneration, tubular lumen dilation, vacuolization and degeneration of thick loop of Henle tubule epithelial cells. Melanomacrophage percentage areas were significantly decreased at 0.01μg/l and 500μg/l and significantly increased at 200μg/l (P<0.05). No significant fibrosis was observed in all treated groups. The results suggest that very low and high environmentally relevant doses of atrazine have the ability to adversely affect organs of amphibian species and potentially related aquatic organisms. / MT2017