Research Stories

by Melissa Crytzer Fry

Lakes and rivers can appear calm and serene on the surface. But they are also the site of a deadly underwater game. The daily struggle for survival is never ending. Aquatic organisms will eat or be eaten.

The food web binds these aquatic creatures together. That web is a topic that interests ASU civil and environmental engineer Yongsheng Chen. He works on the frontier of nanotechnology's environmental implications.

Chen has led two EPA-funded projects. The goal of one project was to evaluate the interaction between aquatic organisms and nanomaterials, and to determine the resulting impact on the food web.

"Nanomaterials don't degrade. As a result, they can be absorbed or ingested by low-level organisms, and then transferred to larger organisms," Chen explains. This process of pollutant retention is called bioaccumulation.

For example, contaminated algae are eaten by daphnia, a tiny aquatic organism. The daphnia is eaten by fish. The fish are eaten by humans.

"We are only at the first stage. We are investigating each organism," Chen says. "We have proven that nanomaterials can be bioaccumulated through algae. Eventually we will want to use the bioaccumulated algae to feed the daphnia. Then we will use bioaccumulated daphnia to feed the fish.

The scientists want to know if the bioaccumulation factors increase or decrease. "If they increase, that means the nanoparticles can be bioaccumulated through the food chain," Chen adds.

Chen works in collaboration with ASU researchers Yung Chang, Qiang Hu, and John Crittenden, and with other scientists from Nankai University in China. The researchers expose each organism to water that contains nanomaterials. They then microscopically evaluate each organism.

In one study, they exposed carp to a solution containing arsenic and nano titanium dioxide. After a few days, the scientists tested the fish for arsenic concentration. To do that they analyzed fish skin, gills, liver and gut.

"We found that the fish had a 160 percent higher level of arsenic in their systems than fish exposed to arsenic alone," Chen says.

This means that nanoparticles can enhance toxic pollutants in aquatic systems. Chen found the same results using nanoscale cadmium.

"Arsenic or cadmium concentrations in the water are usually very low," he continues." But if you have nanoparticles there as well, twice as many pollutants are bioaccumuluated."

Whether or not these types of interactions will impact food webs remains to be seen. The impact on humans is also unknown.

"We need to have enough evidence and data to evaluate if nanoparticles are toxic to human beings," says Chen. He hopes his work is leading researchers one step closer to the answer.

Read more about the environmental effects of nanomaterials in "Too small to see."