Searching for the unseen
Amy Ringwood shucks oysters for a living. But instead of prying open an oyster shell and popping the juicy morsel into her mouth, she takes out its guts.
Ringwood, an environmental toxicologist at UNC Charlotte, studies how trace levels of chemicals in seawater affect the health of oysters and other filter-feeding organisms at a cellular level. She collects oysters and strips them of their gill tissues and functional liver, or hepatopancreas, to search their insides for pollutants such as heavy metals, organic compounds, and more recently, the nonliving microscopic pieces known as nanoparticles.
Though she got her Ph.D. when "most environmentalist types were just considered to be those weird environmentalist types," ecological awareness continues to crop up to embrace her work.
"The work we do has relevance not just to oysters and not just to marine organisms, but to more fundamental cellular questions as well," Ringwood said. She notes that low levels of pollutants rarely kill but instead act as chronic stressors that eventually impair organism health.
Over the past 20 years, Ringwood has learned a thing or two about how cells respond to metals and other pollutants. She now uses those cellular responses to gauge the potential toxicity of nanoparticles. Scientists know little about how cells take in and handle newer-field players such as nanoparticles.
Ringwood worries that filter feeders such as oysters, which sift through everything seawater offers, may be picking up nanoparticles and tucking them away inside their cells. Biologically, she says, organisms do a good job of tolerating certain levels of toxins, but at a certain point, there's bound to be impaired growth and reproduction. It's this careful point that Ringwood searches for and hopes to identify.
Ringwood partners with David Carroll, director of the Wake Forest University Center of Nanotechnology, to study how nanoparticles affect marine organisms and what makes some of these particles more toxic than others. Though scientists know how to integrate these particles in everything from LCD screens to toothpaste, they don't yet understand what happens once particles leave these products and spiral away into the environment and into animal diets.
"Right now, we are as a society finding a lot of new technological applications for these things [nanoparticles], and that's great, exciting stuff," said John Ferry, an environmental chemist from the University of South Carolina who is not involved in the study. "While we do that, we have to ask ourselves if there are unintended consequences of their use. Of course, there always are."
And some nanoparticles may have more cellular consequences than others, he says. Nanoparticles' size and shape affect whether cells open their gates to allow these mini-molecules inside. If let in, the particles can cause chaos, scientists find, either as intact nanoparticles or as split-open nano pieces. Depending on the molecular makeup, nanoparticles can sneak by the body's defenses; for instance, a basketball-shaped molecule may be invited inside, while a tripod-shaped one may be sent packing, Carroll said.
"There's dozens of different ways to make a nanoparticle," Carroll said, "all of them leaving different chemicals attached to the outside of the particles, which act differently when they go into cells. It's all about choosing the right synthesis," he said, emphasizing that it's the building process that largely determines toxicity.
The seemingly infinite array of shape and size possibilities makes it nearly impossible for scientists to identify and pinpoint which nanoparticle constructions are toxic. To compound the problem, it's hard for manufacturers to make a uniform batch of like-sized particles when they're assembling molecules smaller than grains of pollen.
Wake Forest's facility builds specific silver nanoparticles for Ringwood, pain stakingly predetermining consistent size and shape characteristics. With measurements preset, she can study a nanoparticle of one specific size and shape at a time and thus learn which, specifically, are more toxic.
"People say nanotech is the next scientific revolution," Ringwood said. "It's exciting, but on other hand, we're presenting to organisms a whole new class of manmade products. How will organisms respond? They [nanoparticles] might have unique characteristics that cause toxicity in a different way than the other toxins."
Since oysters remain cemented to a solid structure in a single location, filtering seawater their entire lives, they're excellent organisms to use to monitor levels of pollutants in an area. In her field-based pollution studies along the Carolinas coasts, Ringwood collects oysters and then takes the cellular analysis back in the lab, peeking into cells to see which and how much toxins are present.
Her nanoparticle lab studies are much the same. Ringwood releases silver nanoparticles, at a concentration similar to trace levels found in the environment, into a beaker with an oyster. Later, she gives the oysters the equivalent of a doctor's visit, using routine diagnostic tests such as an antioxidant level check, to see if they're sick.
So far, Ringwood has noticed a change in cellular responses and protein expression. Carroll says Ringwood's lab has seen negative effects in shellfish embryos, as well as cellular toxicity in oysters.
"We need to find out what makes nanoparticles really a problem," Ringwood said. "If we know that these certain size and shape characteristics make them most toxic, let's focus on developing products that minimize toxicity rather than using just any nanoparticle."
The team's work is funded by a $500,000 Environmental Protection Agency STAR grant, part of an initiative to learn the behind-the-scenes dirt on nanoparticles whose presence continue to rise in the technology sector.
"We're trying to track what's going to happen," said Carroll, adding that scientists need to learn more about nanoparticle impacts on marine organisms and ecosystems. "One thing's for sure: You really don't want nanoparticles in your seawater."
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