Researching Heavy Metal Contamination in Arctic Whales

For decades, that's been a message on bumper stickers and a cry of environmentalists. In recent months, the number of reports raising serious concerns about the health of the oceans and their inhabitants has only increased. Human dependence on the oceans has been well documented; therefore, the benefits of cleaning up these waters globally and protecting all that dwell therein seem obvious. Courtesy of James Kaysen Although the bowhead whale is an endangered species, it is recovering at a rate of 3.2 percent a year, and the Eskimo are allowed to take a limited number. Surfacing in the wake of new research presented at the International Whaling Commission annual meeting earlier this year, however, is yet another reason to heed the call. It just may be that the whales have much to offer to the future of humans. In a study that began about three years ago, scientists have harvested brain, liver, and kidney tissues from the bowhead whale (Balaena mysticetus) during annual subsistence hunts by the Inuits (Eskimos) and found high levels of heavy metal contamination. Though the same high levels could significantly impair the function of terrestrial mammals, so far the whales are not exhibiting any adverse effects. Investigators hypothesize that these cetaceans have some sort of protective mechanism, according to a report being prepared for review. "How [the whales] can have these levels [of metal contamination] and apparently be healthy is quite intriguing; we're interested now in the mechanisms they've developed to handle these high levels without showing any apparent gross or histologic adverse affects," says Barrow, Alaska-based veterinarian and toxicologist Todd M. O'Hara. O'Hara, of the North Slope Borough Department of Wildlife Management (DWM), is one of a team of researchers that also includes scientists from NASA and Tulane University Medical Center's Environmental Astrobiology Center. The highest levels of cadmium, a very toxic metal, were found in the kidney and were most elevated in larger whales, presumably the oldest.1 The average level for cadmium in the bowhead whale kidney tissues was 20.5 parts per million (ppm) wet weight, placing it well within, for example, the high range of 5-36 ppm wet weight for cattle.2 Although the bowhead whale remains an endangered species, it is recovering at a rate of 3.2 percent a year, O'Hara points out, which is why the Eskimo are allowed to take a limited number each year. "Just for the record, they're not killing these whales to mount them on walls, but to eat and live as [the Eskimo] have for thousands of years," adds NASA astronaut and veterinarian Rick Linnehan, co-principal investigator. "They make use of every piece of carcass .... It's a very, very small harvest, and it's the only opportunity to study these animals." This effort is important to the researchers for a number of reasons. First and foremost, the Inuits consume the meat. Moreover, the apparent ability of the bowhead whales to tolerate high levels of cadmium and the researchers' ready access to fresh tissue has made this species a model for the study of resistance to the toxic effects of heavy metals. Indeed, NASA became involved so it could study the mechanisms that evolved in these whales. "We want to discover if it's possible to adapt this mechanism ... to do tests in space to determine what heavy metal toxicities humans may be exposed to, and if it's possible to produce the substance ... [to] protect people against heavy metal toxicity," explains Linnehan, who, prior to joining NASA, conducted marine mammal research for the Navy. "Discovering how these marine animals are able to ameliorate the effects ... and determining if this can be adapted to terrestrial life is something we really need to [do], because we're getting ready to put people into closed environmental systems for long periods of time to travel and work in space," elaborates co-principal investigator Thomas J. Goodwin, manager for biotechnology flight definition and three-dimensional developmental biologist at NASA's Johnson Space Center. "How [the whales] can have these levels [of metal contamination] and apparently be healthy is quite intriguing; we're interested now in the mechanisms they've developed to handle these high levels without showing any apparent gross or histologic adverse affects." --Todd M. O'Hara During the course of research, the team has already succeeded in accomplishing a number of things. For starters, associate professor of medicine and nephrology Timothy G. Hammond and colleagues at Tulane's Environmental Astrobiology Center have found the metallothionein (MTH) protein--the binding site for heavy metals and some other toxins--in the bowhead to be homologous to the human MTH protein (mammalian, not marine), a novel discovery. "It turns out that metallothionein is a carrier for cadmium, copper, and some other lead-carrying proteins, so when you get cadmium and copper toxicity and buildup, ... it circulates in the blood in MTH, which is then thrown into the kidneys and is taken up in the proximal tubule; so the kidneys become the storehouse for the toxins," Hammond explains. They have also cloned the bowhead MTH protein for the first time and logged the sequence with the National Gene Bank. In addition, at NASA's Johnson Space Center, Goodwin, also for the first time, has established in culture the brain, liver, and kidney tissues from the bowhead, which, he says, "are now growing robustly in my laboratory." Although the bowhead whales do appear healthy on examination and in comparative research, Hammond has found marked fibrosis in the kidney tissue. "We got wild samples [collected in subsistence hunts 10-15 years ago] from William G. Henk, associate professor of veterinary anatomy and cell biology at Louisiana State University (LSU), who has worked with these whales for years," says Hammond. "Lo and behold, there was no fibrosis in 1986, whereas today the kidneys of these whales are heavily fibrosed." Where's It Headed? Does that mean these whales will eventually get sick? That's a question that, for now, remains debatable. "They can't take in this much toxicity and not ever get sick," proffers Hammond. "The best analogy is a smoker. Smokers damage their lungs every day, but all they're doing is using up their reserves, and it's only right at the end that they get into trouble. [I]t's only if they have some other disease that puts another stress on their lung capacity. It's the same with heavy metals. Simply put, yes, these whales are being exposed to toxic levels, and yes, they are at risk." O'Hara, however, is not entirely convinced. "Renal fibrosis can be an aging-related change," he says. "The bowhead may live to be 150 to 225 years of age, and it could be a normal aging change. Cadmium accumulation in the bowhead is significantly correlated with the age of the animal, so you can see the dilemma--when we see elevated levels of cadmium, they tend to be or are always in the older animals, so how do we differentiate that? We can't do that when we're just examining the animal." They can, however, study the impact of cadmium in vitro. "We have the ability now to look at the binding process in situ in a tissue culture, and we can study that binding process," says Goodwin. With NASA's state-of-the-art rotating wall vessel, all three tissues have been established as three-dimensional cultures. Presently, Goodwin and colleagues are immortalizing the tissues, exposing them to transforming agent SV40 (simian virus 40). Next, Goodwin says, "we'll begin looking at binding." Courtesy of James KaysenIn an extreme environment, a custom thousands of years old comes into play with the need for biological research. In the meantime, is there any way to alleviate the whales' exposure to these heavy metals? The cadmium, says O'Hara, is coming from the krill and other lower life forms that make up part of the bowhead diet. While the assumption tends to be that most of these heavy metals are coming from industrial activities, O'Hara notes, "There are papers in the literature that indicate that most of the cadmium would be from geological or natural sources." Still, no one is denying that a tremendous amount of heavy metals emanating from municipal waste and melting processes, among other things, is getting into the oceans, Arctic waters in particular. "The complication with these metals," adds O'Hara, "is that they do occur naturally in the sediments of the ocean and the water column of the ocean, and we just don't know what portion of the cadmium, or mercury or lead, has actually come from human activities." In a related study, O'Hara has found human-produced organochlorines and pesticides in the beluga whale population.3 "Even though there's no apparent evidence of significant heavy metal contamination from industrial activities, there's clear evidence that organochlorines that are only produced by humans are accumulating in these whales," maintains O'Hara. "The levels don't seem to be high enough to affect the whale or jeopardize the people who eat the meat of the whales, but they are something we want to continue to monitor to make sure the trend is that they'll go down. We have important issues with regard to contaminants up here. Even things that were banned in the 1970s--the PCBs [polychlorinated biphenyls] and DDT [dichlorodiphenyltrichloroethane]--are still present in the whales today. But we're careful not to be alarmist." Corroborating Evidence Courtesy of James Kaysen Research and coordination of efforts require a team approach. O'Hara's findings correlate with numerous others. During the last several years, environmental contaminants, in fact, have been viewed more and more as potential serious threats to marine mammals. Thomas J. O'Shea reviewed data and summarized literature on the results of residue surveys from more than 13,000 samples of marine mammals in a chapter in the recently published book Biology of Marine Animals.4 The book offers an overview of the state of knowledge on marine mammals and the possible impact of organochlorine compounds and toxic elements. "Interpreting the significance of the presence of contaminants in marine mammal tissues is a difficult and sometimes controversial area," he writes, but "the presence of metabolites of DDT in marine mammals throughout the globe is fact." The trend for PCBs also appears to be rising. "Despite the marked cessation in their production and sale, most PCBs are still contained in systems for which they were originally designed [such as transformers and other machinery] and have not yet reached the environment," O'Shea points out. "As these systems leak, degrade, and are disposed of, the quantities released to the environment will increase .... PCB concentrations in the environment, and in the tissues of marine mammals in particular, are projected to increase for many years to come." Another overview, in Science last summer, examines the rise of mass mortalities in ocean-dwelling plants and animals due to disease outbreaks and cites pollution, human activities, and global warming as factors.5 The study surveys 14 different sets of findings, including morbillivirus in dolphins and porpoises, Pfiesteria in Atlantic coast fish, and the connection between cholera and plankton blooms. It theorizes that the emergence of new diseases is aided by a long-term warming trend, extreme El Niño-type events, and human activities. The authors also suggest that many "less-apparent" species may be disappearing without notice, while other overstressed marine life may be losing natural ability to fight disease. Yet another report from last summer posits that acoustic pollution from ships, oil exploration, military sonar, and other sources may be degrading the habitats, threatening whales, dolphins, seals, and other sea creatures by wreaking havoc with their natural communications systems and forcing the animals to deviate from their normal migration routes, as well as perhaps inducing physical harm.6 Writes O'Shea: "Marine mammal populations with high exposure to organochlorines are also likely to have been subjected to numerous other forms of human-induced stress, such as other contaminants, noise pollution and disturbance, habitat deterioration, or changes in food quantity and quality. ... There is mixed evidence for linkages with increased susceptibility to disease, and the complex study of biochemical and physiological effects in marine mammals is in its infancy. Although there is a lack of absolute scientific certainty in linking the presence of specific organochlorine contaminants to detrimental impacts on marine mammal populations, the body of indirect, circumstantial evidence ... continues to grow." Everything humans make and manufacture on the planet eventually winds up in the oceans. All researchers agree that the big picture is clear: The oceans are in trouble. And more research is urgently needed to get a strong status baseline of the oceans and the marine life. "No matter how you look at it, we are beginning to establish what looks to be a global pattern of different kinds of contaminants getting into marine mammals," says Goodwin. "We're beginning to see a pattern that's really scary. This is a wake-up call. We've got to stop and think about what it is we're doing to our planet. These whales are at the top of their food chain, and they're picking up these contaminants from what they're eating--krill, shrimp, plankton, and all those things, some of which we eat." So how does this relate to humans? "Are we generating an excess of contaminants in the terrestrial environment and letting them run off into the oceans, and is that food chain picking them up, the lower food chain, some of which we eat, [and] are we then ingesting the contaminants through them?" Goodwin asks. "It would be my suspicion there's a high probability that that is happening." "It is pretty eye-opening when you go to a pristine area like the Arctic and the Antarctic and still find very high levels of organic contaminants in the fish, the mammals, and all the way up the food chain--and when you find that, it's eventually going to biomagnify in humans," says Linnehan. "The Inuits are concerned about that, which is why they're looking at their environment and helping with the funding of these projects." As for the bowhead whales, says Hammond, "It's hard to know how to [help] the whales, because what can we do? Put a chemical in the Pacific Ocean?" "We can figure out where the contaminants are coming from and begin closer monitoring of runoff," suggests Goodwin. "We have to begin to clean up our own backyard." O'Shea notes, "Marine mammals in areas with generally high organochlorine inputs, such as near-shore waters close to coastal industrial and agricultural centers, tend to have higher concentrations of organochlorines in tissues." Next Steps The bowhead whale team would also like to study the Inuit population that is consuming these mammals. "The next step for me would be to look at the children, and see if they're at risk," says Hammond. "Heavy metals are associated with expression of fibrosis of the kidney in very specific genes and proteins, such as fibroblast specific protein 1, decorin, and the ratio of collagen 1 to collagen 4," Hammond explains. "Since all the corpses from that area that go for autopsy go to Anchorage, we could get a nice control group of similar age, size, and sex who don't eat that traditional diet in Anchorage with ones who do eat a traditional diet in the wild and look at very specific markers and measure the heavy metal levels. Now that wouldn't tell you about the children necessarily, but it would tell you if you have a population at risk." The bowhead investigators hope to expand their research to beluga whales next summer. "In the belugas, the liver is going to be the organ of major interest with regard to how it's handling mercury and selenium," offers O'Hara. "But ... mercury and selenium accumulate with age, and there is a chance the belugas are accumulating the selenium ... to protect from the effects of mercury. If we can get these tissues in cell culture, that could be tested." Beyond the search for the whales' protective mechanisms, says Linnehan, "the fact that of the species of animals on this planet, cetaceans are the closest to living in microgravity, ergo a neutral buoyancy environment, because they are suspended in a column of water" is something that intrigues NASA. "This may or may not relate to what it's like floating around in zero gravity," Linnehan admits, "but it's as close as you can get on this planet, and so there are similarities there that are interesting, and we'd like to take some of these genes up in space. It's really exciting stuff, though everyone is really just taking baby steps right now," he says, pausing. "If we're able to do nothing we are able now to grow these cells and bank them. And now scientists will have access to this species, maybe forever." A.J.S. Rayl (ajsrayl@loop.com) is a freelance writer in Malibu, Calif. References 1. J.C. George et al., "Age and growth estimates of bowhead whales using aspartic acid racemization," Canadian Journal of Zoology, in press. 2. R. Puls, "Mineral levels in animal health: diagnostic data," Sherpa International, Clearbrook, B.C., Canada; p. 238, 1988. 3. T.M. O'Hara et al., "Organochlorine contaminant levels in Eskimo harvested bowhead whales of arctic Alaska," Journal of Wildlife Diseases; 35:741-52, October 1999. 4. T.J. O'Shea, "Environmental contaminants and marine mammals," J.E. Reynolds, S.A. Rommel, ed., Biology of Marine Animals, Washington, D.C., Smithsonian Institution Press, 1999. 5. C.D. Harvell et al., "Emerging marine diseases--climate links and anthropogenic factors," Science, 285:1505-10, Sept. 3, 1999. 6. Proposed Undersea Noise Tests Threaten Marine Life, New York, Natural Resources Defense Council, 1999.

Researching Heavy Metal Contamination in Arctic Whales

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