This article is from the In-Depth Report Chemistry for a New Era

Swimmers, Hoppers and Fliers: How Do Toxic Chemicals Move around the Planet?

Toxic chemicals created by human activity reach unusual concentrations in the Arctic, among other places

NOAA Office of Ocean Exploration

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Editor's Note: The following is an excerpt from Elizabeth Grossman's  book Chasing Molecules.

Even hundreds of miles from the nearest industrial or agricultural activity, the sea ice, ocean, and Arctic plants and animals regularly yield evidence of elemental and synthetic chemical contamination. This contamination includes not only herbicides, fungicides, and pesticides—chemicals that are used in open air, may have washed directly into rivers or are released from factories—but also metals, among them mercury as well as flame retardants and water repellants, among other substances that are, at least in theory, incorporated into the materials of the products they’re designed to enhance.

Among the errant compounds now found regularly in the Arctic, for example, are brominated flame retardants, including those known as PBDEs (polybrominated diphenyl ethers) used widely in upholstery foam, textiles, and plastics. Also routinely recorded in the far north—some at remarkably high levels—are perfluorinated compounds (PFCs) used as stain repellants, waterproofing agents, and industrial surfactants (think Scotch-guard, Teflon, Gore-Tex, and the slick coating on paper used in food packaging such as pizza boxes, candy wrappers, and microwave popcorn bags).

These same compounds are now being detected in animals and people all over the world. A network of more than forty sampling sites has found evidence of synthetic chemicals that do not break down into nontoxic components—a mix of pesticides, fossil-fuel emissions, and industrial compounds—virtually everywhere it looked, from Antarctica, North America, Australia, and Africa to Iceland. A recent five-year study conducted in U.S. national parks across the American West and Alaska found these same contaminants in the majority of its snow, soil, water, plant, and fish samples.

It’s not known when the first persistent synthetic chemical contaminants arrived in the Arctic, but this kind of pollution has been detected there on a regular basis since the 1960s. “Everyone thought the Arctic was pristine, so we were taken aback to find such high contaminant levels in top predators,” says Gary Stern, a senior scientist with Canada’s Department of Fisheries and Oceans. But “anything released in the mid-latitudes travels rapidly north.”

Long-lasting synthetic chemicals are often referred to as “persistent organic pollutants,” or POPs for short. Used in this way, “organic” means that the chemical compound contains one or more carbon atoms and not all organic compounds are toxic or persistent.

Public awareness of POPs such as DDT, PCBs, and dioxins has been growing. By 2001 concern about the environmental and health impacts of POPs had risen sufficiently to prompt the United Nations Environment Programme to formulate a treaty called the Stockholm Convention aimed at curtailing the use and release of these chemicals. “Exposure to Persistent Organic Pollutants (POPs) can lead to serious health effects,” writes the organization that administers the Stockholm Convention, “including certain cancers, birth defects, dysfunctional immune and reproductive systems, greater susceptibility to disease, and even diminished intelligence.” (The United States has signed, but as of 2009 had not yet ratified, the Stockholm Convention—so it has not been a full participant in its meetings and decision making, and its use of chemicals is not yet formally bound by the Convention’s regulations.)

By taking samples at numerous study sites over extended periods of time, scientists have discovered that some contaminants travel entirely by air—these are what Frank Wania of the University of Toronto calls fliers. Some—the swimmers—stay in the water, circulating with ocean currents. Most are hoppers, though; they make their way north in what’s been dubbed the grasshopper effect, a series of air- and waterborne hops, moving toward the Arctic with cyclical and seasonal patterns of evaporation and condensation.

“Chemicals have several ways to be present in the atmosphere,” explains Wania. Depending on temperature and weather conditions, as well as the size, shape, and the elements that make up the molecule, the same substance can be found dissolved in water, as a gas, or as a particle. The smaller the molecule, the more volatile it typically is, and therefore the more likely to be swept along with atmospheric currents as a gas. These gas phase molecules— the fliers—can move in several meters per second, making the trip from their points of origin to remote locations like the Arctic in days or weeks. At the opposite extreme, the waterborne swimmers can take years to reach the same destination.

The hoppers, intermediate-sized molecules that can move between gas, liquid, and particle phase, may take days, weeks, or even years to reach the Arctic after their initial release. These hoppers may be present in liquid water, but as temperatures warm they will evaporate to gas phase but then condense and return to join water when temperatures cool. They’ll repeat this cycle over and over again, rising and falling—or hopping—with daily and seasonal patterns of warming and cooling. It’s in this way that many persistent chemicals move with clouds and precipitation as storm systems and ocean currents circle the globe, and why temperatures so strongly influence how and where pollutants travel.

“Persistence and mobility is what makes something troublesome,” says Wania. “It’s a very difficult, laborious, and time-consuming process to prove toxicity, and by the time you have evidence it may be too late.” If a substance is “persistent, highly mobile, and can’t be contained, you have a problem you can’t rectify."

Another major influence on the movement and deposition of persistent pollutants is precipitation. Put simply, the more it rains or snows the more likely these contaminants are to wash out of clouds and be deposited on land, lakes, rivers, and oceans. In a recent paper Wania and colleague Torsten Meyer note, “Real substances affected by changes in rain rate include lindane, aldrin [both highly toxic and persistent pesticides], highly chlorinated PCBs, PBDEs, and some currently used pesticides.” When it’s warmer, more of these substances will tend to evaporate again and join the cloud layer, and from there the cycle of condensation and precipitation begins again. When present as aerosols, the contaminants may even accelerate precipitation as water droplets coalesce around the tiny solids.

Whatever affects atmospheric and ocean circulation clearly plays an important role in where environmentally roving persistent pollutants end up. The big hemispheric wind and ocean patterns known as gyres and oscillations all play a part—as do more localized storm systems and currents. “These routes all seem to force contaminants released in Europe to the Arctic,” explains Derek Muir, a senior scientist in aquatic ecosystems research with Environment Canada who specializes in contaminants. “Think about Chernobyl,” Muir says by way of illustration. “The radioactivity there ended up in western Scandinavia where a lot of reindeer were sacrificed as a result. Other contaminants follow the same pathway north from Russia.”

What happens once pollutants reach the far north is very much influenced by where there is ice. Ice typically stabilizes contaminants and holds them in place until they’re released again when temperatures rise high enough for melting to begin. Greenland, which Muir describes as “a big block of ice 3,000 meters or more thick,” appears to be acting as a source of contaminants in the Arctic as well as a sink.

On the east side of Greenland and across the Greenland Sea on the remote Norwegian islands of Svalbard that reach all the way up to 80 degrees north—in the path of air and water currents coming off of Greenland and the European mainland—levels of PCBs, PBDEs, and perfluorinated compounds have been found to be particularly high. Svalbard’s polar bears have contaminant levels higher than bears on the west side of Greenland or in the Canadian Arctic, says Muir, largely because of increased melting.

When pollutants are released within range of the Atlantic Gulf Stream or get picked up by northerly air currents that also blow east, North American pollutants can also be transported across the Atlantic toward Europe. Similarly, air masses may travel a northeasterly path from Asia across the Pacific to North America. Thanks to the trans-Pacific air currents, pollutants released in China make tracks across the north Pacific and cause local air pollution health problems in Japan and Korea. Dust from China can reach California in as few as four days and makes a regular contribution to formation of Los Angeles smog.

The chemistry of some contaminants—those that are heavier and less volatile—causes them to drop out of the atmosphere into the northern Pacific Ocean where they may move slowly through the water or be taken up by fish and marine mammals. Persistent pollutants that include PCBs, brominated flame retardants, and perfluorinated compounds have been consistently found in fish, seals, whales, and fish eating birds along the Pacific coast over the past decade. “Fish can become their own transports of contaminants and fish-eating birds are known to excrete contaminants,” says Robie Macdonald, a research scientist with the Canadian Department of Fisheries and Oceans. “Migrating animals are not a huge transport mechanism but it’s focused, because they take the contaminants to where they feed and hatch their young.”

Lipophilic literally means “fat loving,” and this term is used to describe chemicals that have an affinity for and are soluble in fat. Materials with this property are also often persistent—that they are fat- rather than water-soluble makes them resist environmental degradation. And they are “bioaccumulative”—when they lodge in fat cells they can accumulate in plant or animal tissue as part of the fat reserves being stored for energy. When an animal burns fat for energy—this happens in people as well as in birds and fish—the fat cells release their contaminants.

There are multiple ways people may absorb a particular lipophilic chemical, however, which is one reason figuring out sources of human exposure to these contaminants is tricky. For example, people are exposed to brominated flame retardants through household dust but also through food they eat that has accumulated these chemicals in its fat. In the Arctic—where contaminants are aggregating and animals that are staples of the traditional Northern diet have large stores of fat—the region’s top predators, polar bears and humans, have some of the world’s highest exposures to these pollutants.

Monica Danon-Schaffer is a chemical engineer at the University of British Columbia who is investigating how and why these kinds of chemicals are ending up in water in the Canadian Arctic.

Danon-Schaffer sketches for me a series of molecules—PCBs, PBDEs, a couple of perfluorinated compounds, and another kind of chemical called a short-chain chlorinated paraffin (used as industrial lubricants and coatings, among other applications). The PCBs and PBDEs are markedly similar: strongly bound carbon ring structures with either chlorine or bromine atoms attached. The chlorinated paraffin and PFCs also bear a striking resemblance: Both are made up of long, branching chains. These molecules are strong and don’t easily give up either their structure or its linked chemical activity. The very structure that makes these substances effective in squelching fire, effectively flexible, or adept at resisting moisture, Danon-Schaffer explains, is what makes them so persistent. And this is also what them makes them incompatible with, or toxic to, some vital biological systems.

While these substances resist degradation in the environment, because they are added to—mixed in—rather than chemically bound to the materials they’re used to modify, eventually they become separated and leave the finished product. This is part of what makes it so difficult to keep track of these chemicals. For one, exactly how much of each substance is produced is not precisely known. Nor is it known exactly how much goes into each product, let alone how much can be expected to separate out and when or where this happens. The mixtures of these chemicals used commercially are typically not 100 percent pure and so may contain other synthetics that finished products may also shed. Then there’s the fact that, in the environment, many of these problematic synthetics break down into smaller molecules that may be more persistent or more toxic than their larger cousins.

The methods for detecting particular chemicals in any form—gas, liquid or particulate—are very specific. While the same sample of ice, water, or air may yield an entire suite of contaminants, how one kind is detected may not be compatible with measuring another. As Tom Harner, a senior scientist with Environment Canada who specializes in hazardous air pollutants, explained to me, “Every persistent organic pollutant is different and unique. Every chemical is a different story. Because each chemical is unique, we can’t investigate for a range of chemicals—we really have to do one at a time and look at each chemical’s diversity of properties.”

“We are seeing these chemicals in people and in biota where they shouldn’t be,” continues Harner. "Some of these compounds almost have two personalities. In one phase they can be hydrophobic—resist water and prefer to partition or attach to fat—and so accumulate in fat tissue, soil, and plant cuticles. In other phases they can be hydrophilic—be water-soluble—and be transported that way.” In other words, some compounds can hop, swim, and fly—behavior that is influenced both by the chemicals’ structure and the physical landscape and atmospheric conditions that surround them.

Asking questions about how a chemical’s structure will determine its behavior under various environmental conditions is a prerequisite of green chemistry. Had such questions been asked about PCBs or PBDEs— or had more attention been paid to the answers and their implications— they might not be turning up in birds cruising the northernmost fjords of Norway.

From Chasing Molecules: Poisonous Products, Human Health, and the Promise of Green Chemistry by Elizabeth Grossman. © 2009 Elizabeth Grossman. Reproduced by permission of Island Press, Washington, D.C.

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