Date of Award
Spring 2024
Document Type
Thesis
Degree Name
Master of Science (MS) in Biology
Department
Biology
Committee Chair
James Rayburn
Abstract
Amphibians play critical roles in the environment's wellness. Fluoride (F) is a widely existing environmental pollutant. It is commonly known for being added to drinking water and as a topical dose on teeth. Selenium (Se) can be found in organic and inorganic forms in nature. Many different fertilizers, pesticides, insecticides, and fungicides contain sodium selenate in them. The range selenium has between deficiency and toxicity is narrow, meaning excess exposure could cause various adverse effects in aquatic organisms. Xenopus laevis is a standard model for developmental toxicity due to being minimal maintenance, cost efficient, and having transparent embryos. Xenopus makes an acceptable model for estimating the developmental effects of chemicals on native amphibians. Ambystoma maculatum is a non-endangered native species to Alabama making it an acceptable salamander to compare to Xenopus. The objective in this study is to determine the interactions effects on developmental toxicity of sodium fluoride, sodium selenate, and 3 mixtures combinations on amphibian embryos. The assay uses serial dilutions to expose various concentrations to frog embryos. The assay lasts 96-hours holding 20 embryos in small petri dishes per replicate. Assays for Ambystoma lasted 12-days holding 10 embryos in large, deep petri dishes per replicate. Assays were also performed to determine the developmental effects to different exposure times and lengths to 100 mg/L sodium selenate. Mortalities were counted for each day. Mortalities and malformations were counted on the last day of the assay and embryo length were measured. Means, standard error, probit analysis (LC50 and EC50(malformation)), ANOVA and Bonferroni’s post hoc test were calculated using Systat. The teratogenic potential was calculated using the formula LC50/ EC50(malformation). Isobole diagrams were used to determine if the chemicals showed synergism, antagonism, response addition, or concentration response. In Xenopus, the overall LC50, EC50 for NaF and Na2SeO4 was 603.37, 819.42 and 30.41, 15.13 respectively. The mixtures showed a combination of response addition and synergism at different combinations. In Ambystoma, the overall LC50, EC50 for NaF and Na2SeO4 was 540.39, 862.26 and 53.06, 69.21 mg/L respectively. The mixture showed response addition. In both Xenopus and Ambystoma, malformations such as stunted growth, edemas, loose gut, hemorrhages, bent notochords, and kinked tails were seen in both selenate, fluoride, and mixtures. Overall, these assays show the usefulness of the Xenopus embryos as model species for native amphibians. Xenopus embryos showed to be more sensitive to 100 mg/L sodium selenate at different developmental stages than accumulated exposure.