The tiny critters had seemed so content, swimming around under the microscope.
Scientist Shirley Tang was studying how living organisms might be affected by nanomaterials. These minute particles assembled from just a few molecules offer great promise but also pose a lot of questions - and can cause surprising and unpredictable harmful effects.
In an effort to understand those effects, Tang had just exposed some protozoa to nanoparticles. The one-celled animals promptly absorbed them, ejected them, and then carried on.
"They seemed happy," said Dr. Tang, a chemistry professor at the University of Waterloo in Ontario.
"They would eat bacteria as normal. We didn't see any mortality to the protozoa."
But a closer look showed they weren't happy at all. Sure, they'd eat bacteria, but instead of absorbing their prey, they'd simply excrete it.
"Now they can only digest 40 per cent, 20 per cent, 10 per cent of their food."
Why couldn't the protozoa digest properly after their exposure? Nobody knows. It is one more unknown about nanomaterials, which are now found in hundreds of consumer products from condoms to hockey sticks.
Nobody knows how nanomaterials interact with ecosystems, whether they're capable of entering a food chain or whether they would concentrate higher up the chain.
Nobody knows how to detect them in the environment.
Nobody knows if or how they can be absorbed through the skin.
Nobody even knows what makes them toxic.
"We know almost nothing about environmental exposures," Jennifer Sass, a Canadian toxicologist with the Washington-based Natural Resources Defence Council, said in an interview with The Canadian Press.
Modern physics, chemistry, biology and engineering are now able to manipulate ordinary materials in particles only a few billionths of a metre across - an extraordinarily tiny scale where even the laws of physics are different.
The new rules are mysterious. What we do know is sobering.
"(Nanoparticles) tend to persist," Dr. Sass said. "If they get into the environment, they don't degrade or go away. They do tend to bio-accumulate (and) stay in the organism."
The same property that makes nanoparticles so useful also makes them dangerous.
"They can be highly reactive, and the kind of reactivity we are concerned about is the generation of oxidants," said pathologist Agnes Kane of Brown University in Providence, R.I.
Such oxidants react with chemicals in the cell and can even alter DNA.
"If they damage our DNA, then there's a possibility of generating mutations that can accumulate and lead to cancer," Dr. Kane said.
Her latest paper examines evidence that carbon nanotubes, the basic cylindrical building blocks of many nano structures, could act like carcinogenic asbestos in human lungs. It concludes that there are significant similarities.
And some products, such as the nanosilver already used to deodorize products such as socks, are simply toxic. Some worry about workers in factories who handle such nanomaterials.
Nanoparticles do hold out much environmental promise.
The same reactivity that makes them harmful in the body also means they can break down dangerous chemicals in toxic waste - or anywhere, for that matter. And their use in electronics drastically reduces power demand, which could cut greenhouse gases.
But scientists in the field readily concede that developments on the engineering side are a generation ahead of research on environmental impacts.
A recent paper summarizing studies found only 50 reports on the topic, Dr. Tang said.
"This is nothing," she said. "This is almost zero."
By comparison, thousands of papers are written every year on creating and using nanoparticles.
University of Alberta biologist Greg Goss is hoping to change that.
He has just been awarded a three-year, $3.3-million federal grant to help create a research group, headquartered in Edmonton, that will focus on environmental issues arising from nanotechnology. The centre will involve 13 scientists, five universities, three government departments and two national research institutes and will co-ordinate with similar centres recently created in the United States and Europe.
The challenge is huge.
There are tens of thousands of different nanoparticles and even slight variations can have radically different properties.
Size matters, too.
Some materials benign at normal dimensions become toxic at nanoscale.
"The greatest challenge is simply just trying to understand what the fundamental mechanisms of toxicity are and being able to predict them," Dr. Goss said.
The trick will be to get at the root of how nanomaterials act in individual cells.
"If we know the reason why they're toxic, then we can start to design materials which still retain the properties that we want but have limited or no toxicity. It's really impossible to imagine that we will be able to test every nanoparticle."
New uses for the minuscule particles appear weekly, but the actual quantities used are still relatively insignificant. Researchers have time to learn what their impacts on the environment could be before they happen.
"We know that history is filled with things that are produced en masse and integrated into our system," Dr. Goss said. "Most are non-toxic but every now and then we'll have PCBs.
"With nanotech, we have the first chance to actually get in on the ground floor with the new manufacturers (and ask), 'Can we be green in our approach toward integrating new materials into our lives?"'