Earth and Environment
A nanoparticle that can help clean water of cadmium becomes toxic once taking in the metal. But research finds that organic matter, in this case from algae, reduces that toxicity.
Nanotechnology plays an important role in removing toxic chemicals found in the soil. Currently more than 70 Environmental Protection Agency (EPA) Superfund sites are using or testing nanoparticles to remove or degrade environmental contaminants. One of these—nano-zero-valent iron—is widely used, though its effect on organisms has not been examined.
“We’re developing new technology faster than we can predict its environmental impact…”
In a recent experiment, a team of scientists tested the effect of sulfurized nano-zero-valent iron (FeSSi) on a common freshwater alga Chlamydomonas reinhardtii). They found that FeSSi picked up cadmium from a watery medium and alleviated cadmium toxicity to that alga for more than a month.
“However, when FeSSi was doing what it was designed to do, we found it was up to 10 times more toxic when bound to cadmium than without,” says lead author Louise Stevenson, a postdoctoral scholar in University of California, Santa Barbara’s ecology, evolution, and marine biology department.
“The current standards for what is an acceptable concentration to use are based on data from the particle itself unbound to the contaminant. Our work suggests that those allowable limits potentially could be huge underestimations of the actual toxicity,” she says.
To simulate a precipitation event in which toxic material from soil washes into water, the researchers dosed C. reinhardtii with the cadmium-laced FeSSi and waited an hour before taking measurements.
They found that organic material the algae produced as a byproduct of photosynthesis mitigated the toxicity of FeSSi and allowed the nanoparticle to remediate up to four times as much cadmium.
“The organic material makes the FeSSi particle less toxic, which allows a greater zone of remediation and increases the cadmium concentrations that can be used,” Stevenson says.