One year after a massive tsunami ravaged the east coast of Japan, much attention is focused on the bottles, refrigerators and other debris washed out to sea and its pending arrival on the U.S. West Coast -- endangering ships, seabirds and other wildlife along the way.
Some experts, however, are more concerned about the debris we may never see but that might still pose a threat to human health.
"Over long periods of time, big plastics degrade into smaller and smaller particles, and these may create an additional route of exposure to certain chemical contaminants," said Courtney Arthur, a scientist with the National Oceanic and Atmospheric Administration's Marine Debris Program.
As sunlight and waves break down plastic materials into pieces the size of fish food, new research suggests that fish may mistakenly eat the so-called microplastics and subsequently absorb chemicals into their bodies. Polychlorinated biphenyls (PCBs) and dioxins, among other toxins, could then travel up the food chain and onto our dinner plates.
These pollutants have been linked to everything from hormone problems to neurological disorders to cancer in humans.
So far, microplastic debris -- generally defined as particles less than one millimeter wide, or about half the head of a pin -- have turned up in every ocean on the planet, including samples recently collected from Puget Sound, Chesapeake Bay and San Francisco Bay. Species along the entire length of the marine food chain have been found to ingest the tiny particles: sharks, sea turtles and krill, among others. It may not necessarily be the seafood we eat that has consumed the plastic, but rather the marine life in our food's diet. As chemicals move up the food chain, they can accumulate into larger and more toxic concentrations.
Last year, researchers discovered that about 80 percent of the plastic they collected along shorelines was in the form of small particles. Other studies have linked the amount of plastic in the guts of seabirds to the levels of PCBs in their body tissues, and research has found that microplastics fed to mussels can actually relocate from the gut to blood cells.
"It appears quite likely that contaminants migrate from plastic into the organism," said Chelsea Rochman, a doctoral student studying the toxicity of marine plastic debris at the University of California, Davis. She added that it is still too early to say with certainty that the contaminants from microplastics are absorbed by body tissues, but she hopes her research will get closer to an answer. Rochman recently collected fish and water samples in the South Atlantic to measure contaminant levels and is awaiting results.
Many of the chemicals added to plastics during their manufacture, including flame retardants and bisphenol A, are known to be hazardous. Plastics also attract a "toilet bowl" of pesticides, oil and other runoff from land and boats, said Rochman. The smaller the particle, the more relative surface area to soak up PCBs and other contaminants.
"Some plastic particles can have up to a million times as many pollutants stuck on them than are present in ambient sea water," said Marcus Eriksen, executive director of the nonprofit 5 Gyres Institute. "They become a toxic little pill."
The million-plus tons of plastic estimated to have been added to the oceans by the Japanese tsunami will expand the swirls of plastic rubbish already present by an estimated 10 percent, according to Eriksen.
Eriksen's 5 Gyres team, along with other marine scientists such as Linda Amaral Zettler of the Marine Biological Laboratory in Woods Hole, Mass., are collecting samples from the Western North Pacific Gyre in hopes of determining the fate of plastics from the tsunami debris -- and whether microbes may actually be helping to degrade plastics. Emerging research suggests this is the case, although Amaral Zettler noted that it's not yet clear whether the microbes mobilize potential toxins, making them more harmful, or if they actually keep the toxins from entering the food chain.
Research into microplastics is still in its very early stages and there is a lot yet to learn. Just how many of the little plastic bits are out there? To what extent do they they threaten marine life and human health? All of these questions are now of personal importance to Eriksen. He and his wife, Anna Cummins, are anticipating the arrival of their first child.
Cummins, co-founder of 5 Gyres, knows that she can pass on hazardous chemicals to her developing baby. So she is being careful to avoid foods packaged in plastic, and when she does eat fish -- important for a fetus' brain development -- she chooses the smaller varieties that are lower in the food chain, and are therefore less likely to contain high concentrations of pollutants.
"I'm not personally worried about the levels in my body," she said. "But I follow the precautionary principle as a pregnant woman and stay away from the top predators."