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Leeches Coated in Arsenic Thrive in Montezuma Well

Sonoran Desert NPS

A leech occupies the top spot in the food chain at Montezuma Well near Camp Verde. Surprisingly, its body contains the highest level of arsenic ever recorded in a living organism.

Montezuma Well is a limestone sinkhole in the Verde Valley. Arsenic seeps naturally from the rocks, which makes the water toxic to most living things. A research team at Northern Arizona University discovered the Montezuma Well leech has a unique way of dealing with arsenic.  

The leech feeds exclusively on a type of shrimp, and the arsenic consumed in the shrimp is then stored in the leech’s body. Richard Foust, lead author of the study and former NAU chemistry professor, says, “The other thing that’s interesting is the arsenic seems to be moved from the gut of the organism up to the skin or surface of the organism. We don’t know what that mechanism is.”

In other words, the leeches are coated in a slimy toxic skin. Foust says this is probably how they protect their internal organs. Other top predators in Montezuma Well metabolize the toxin and get rid of it. Unlike the leech, they have lower concentrations of arsenic than their prey.

The study appeared in the January issue of Coordination Chemistry Reviews.

Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.
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