How does one persist in contaminated waters?

Why do some amphibians persist while others disappear from wetlands carrying decades of heavy metals?

Tadpoles, southeastern US wetland

Amphibians are among the most rapidly declining vertebrate taxa on Earth.

Contamination-driven disruption of immune function, reproductive success and genetic diversity is central to understanding why.

Spotted salamander

Amphibians as early warning signs for the environment

Amphibians possess highly permeable skin, making them acutely sensitive to changes in water chemistry and contaminant load. This, combined with their dual life histories spanning aquatic and terrestrial environments, positions amphibians as powerful bioindicators of ecosystem health.

Cypress swamp with lily pads and Spanish moss

Aquatic environments accumulate high levels of contamination

Runoff and atmospheric deposition carry a complex mixture of agrochemicals, heavy metals, and industrial byproducts into freshwater systems. Many of these compounds interfere with hormones or damage the nervous system, and they accumulate over time, reaching concentrations well above those of the original inputs.

Warmer, more unpredictable weather can also cause plants, algae and microbes to release more natural chemicals into the water. This changes the chemical environment in which amphibians develop. In some cases these metabolites can have direct effects on development and survival.

Toad, southeastern US

Many small stresses add up

Population declines rarely stem from a single stressor. Exposure to contaminants, or secondary metabolites, may not kill animals outright, but can disrupt hormonal signaling and weaken immune defenses. Detoxification and immune responses also use up energy that could otherwise go to growing and breeding. Together, these stresses leave populations more likely to be hit hard by new diseases or more pollution.

Toads in the field

Lessons beyond the pond

Studying amphibians under environmental stress matters beyond conserving susceptible species. Amphibians sit at the evolutionary transition between aquatic and terrestrial vertebrates, so their systems for managing contamination, infection, and physiological stress are versions of those found across vertebrates, from fish to mammals.

How heavy metals, agrochemicals, and secondary metabolites disrupt hormones and immunity, are also central questions in human medicine. Amphibian physiology and sensitivity allow researchers to study these questions in ways other model systems cannot.