Chapter 6: Adult African Toads as Bioindicators of Environmental Xenobiotic-induced DNA Damage and Systemic Toxicity Provide Insight into the Decline of Amphibian Populations

Xenobiotics are regularly being released into the environment due to increasing human exploitative activities. Individual actions and/or complex interactions among these xenobiotics, e.g., radiation, chemical contaminants, parasites/pathogens, toxic metals, climate change, among others, adversely affect amphibian populations. These xenobiotics are stressors that either kill or induce sub-lethal effects on amphibians. In this chapter, the use of adult African toads as bioindicators of xenobiotic-induced geno- and systemic toxicity is considered. Some xenobiotics also generate reactive oxygen species that elicit systemic toxicity and genotoxicity. Also, xenobiotics can directly induce sub-lethal toxicity in the organ systems. Alterations in body biochemistry, haematological indices, body morphology, and histopathology were common findings in systemic toxicity-affected African toads. Micronucleus and abnormal nuclear malformations were the common biomarkers of this anomaly. Damage induced by xenobiotics may also lead to pathophysiological, inflammatory, and genotoxic disorders, while reproductive abnormalities and morphological deformities are present as well. These alterations may incapacitate the toad and eventually lead to its death. These factors constitute a threat to amphibian health and are the hallmarks of population decline. However, there is a need for a better understanding of the causal relationship between environmental toxicant impacts and the decline in amphibian populations.