Worms Lead Way to Test Nanoparticle Toxicity
Rice University study validates low-cost, high-throughput technology
Jo-Carolyn Goode | 2/2/2015, 1:41 p.m.
HOUSTON – (Feb. 2, 2015) – The lowly roundworm is the star of an ambitious Rice University project to measure the toxicity of nanoparticles.
The low-cost, high-throughput study by Rice scientists Weiwei Zhong and Qilin Li measures the effects of many types of nanoparticles not only on individual organisms but also on entire populations.
The Rice researchers tested 20 types of nanoparticles and determined that five, including the carbon-60 molecules ("buckyballs") discovered at Rice in 1985, showed little to no toxicity.
Others were moderately or highly toxic to Caenorhabditis elegans, several generations of which the researchers observed to see the particles' effects on their health.
The results were published by the American Chemical Society journal Environmental Sciences and Technology. They are also available on the researchers' open-source website.
"Nanoparticles are basically new materials, and we don't know much about what they will do to human health and the health of the ecosystem," said Li, an associate professor of civil and environmental engineering and of materials science and nanoengineering. "There have been a lot of publications showing certain nanomaterials are more toxic than others. So before we make more products that incorporate these nanomaterials, it's important that we understand we're not putting anything toxic into the environment or into consumer products.
"The question is, How much cost can we bear?" she said. "It's a long and expensive process to do a thorough toxicological study of any chemical, not just nanomaterials.” She said that due to the large variety of nanomaterials being produced at high speed and at such a large scale, there is "an urgent need for high-throughput screening techniques to prioritize which to study more extensively."
Rice's pilot study proves it is possible to gather a lot of toxicity data at low cost, said Zhong, an assistant professor of biosciences, who has performed extensive studies on C. elegans, particularly on their gene networks. Materials alone for each assay, including the worms and the bacteria they consumed and the culture media, cost about 50 cents, she said.
The researchers used four assays to see how worms react to nanoparticles: fitness, movement, growth and lifespan. The most sensitive assay of toxicity was fitness. In this test, the researchers mixed the nanoparticles in solutions with the bacteria that worms consume. Measuring how much bacteria they ate over time served as a measure of the worms' "fitness."
"If the worms' health is affected by the nanoparticles, they reproduce less and eat less," Zhong said. "In the fitness assay, we monitor the worms for a week. That is long enough for us to monitor toxicity effects accumulated through three generations of worms." C. elegans has a life cycle of about three days, and since each can produce many offspring, a population that started at 50 would number more than 10,000 after a week. Such a large number of tested animals also enabled the fitness assay to be highly sensitive.
The researchers' "QuantWorm" system allowed fast monitoring of worm fitness, movement, growth and lifespan. In fact, monitoring the worms was probably the least time-intensive part of the project. Each nanomaterial required specific preparation to make sure it was soluble and could be delivered to the worms along with the bacteria. The chemical properties of each nanomaterial also needed to be characterized in detail.