3 days ago
Cicadas emerge on Cape Cod after 17 years underground. Why researchers test them for mercury.
After 17 years underground, cicadas are emerging on Cape Cod. The noisy bugs will spend the next four to six weeks above ground as part of their life cycle. When underground, they feed on nutrients and pollutants from nearby trees. The Woods Hole Oceanographic Institution (WHOI) is capturing the insects to test them for heightened mercury levels.
"We are looking at the base of the tree to see any if cicadas are climbing up from the bottom," said Corinne Richard, a WHOI research assistant. "The first thing we need to do is find a tree with holes around the bottom."
Mercury levels in cicadas
Mercury is everywhere from the ground to the air to the ocean. Scientists at WHOI want to see if the mercury levels in the bugs are getting higher, and how much of it is natural versus manmade.
Assistant Scientist Laura Motta is out collecting cicadas, but typically she is working on zooplankton in the ocean. She calls them the bugs of the sea. Often, she sees mercury in plankton as well as the fish we eat.
Cicada on Cape Cod
CBS Boston
"The cicadas are a cool analogue of what happens out in the ocean," said Motta. "What we are trying to figure out is how they get it, through time and anthropogenic emissions increases? How are we polluting our forest?"
Motta and Richard have been collecting cicadas as well as their molts and the leaves they are near. When the molts land on the ground, they will decompose and potentially reintroduce that mercury to the soil. The mercury can also be passed onto their offspring.
"What we are trying to figure out is where does it end up, and how does it accumulate and become a public health problem?" said Motta.
The insects are placed into bags depending on their gender. It's easy to figure out which one is a female.
"They don't have the ability to sing," said Motta, putting a live cicada up to her ear and shaking it. "If you get really close, you'll be able to tell female or male."
How cicadas are tested
After they collect a cicada, they give them a quick bath with a water bottle to clean off any excess mercury on their body. The bugs are later frozen at extremely cold temperatures before they are freeze dried and smashed into a powder. The powder is then tested for the mercury levels.
"A few years ago, someone did a study to show that cicadas have quite a bit of mercury," said Motta.
Now, researchers at WHOI will compare the new data with the study from 17 years ago to see if the mercury levels are rising.
