Effects of Pollutants on the Endocrine System of Tadpoles

Environmental contamination of aquatic ecosystems by pollutants is among the major causes of the decline of amphibian populations. At all life stages, amphibians are highly sensitive to contaminants due to their semipermeable skin. Amphibian larvae are particularly susceptible to aquatic contamination as they are limited in their capacity for habitat selection. Furthermore, as most tadpoles are omnivorous, feeding items could also allow pollutants to enter the tadpole’s body by ingestion, in addition to absorption through the skin. Many pollutants are known to affect the endocrine system through inhibitory or stimulatory action, which might lead to profound effects on tadpoles, since growth, development, and metabolism are controlled by hormones. Any imbalance of these physiological processes during the events leading to metamorphosis might impair amphibian health, performance, and survival in later life stages through carry-over effects and contribute to significant population declines. Besides common aquatic contaminants such as pharmaceuticals, agrochemicals, industrial chemicals, and heavy metals, habitat acidification, road salt exposure, and microplastics pollution have also been identified as potential disruptors of endocrine processes in amphibian larvae. This chapter reviews the endocrine disruptive effects of wide-spread pollutants on amphibian hormonal pathways associated with metamorphosis and discusses interactive effects of multiple pollutants and stressors in the face of global change.