CHAMPAIGN — River otters, those furry brown swimmers that have staged a comeback in Illinois watersheds in recent decades, are being exposed to pollutants banned more than a quarter century ago, a University of Illinois study has found.
UI researchers detected concentrations of widely used and long-banned insecticides, particularly dieldrin, along with industrial and commercial chemicals called polychlorinated biphenyls, or PCBs, in the livers of river otters collected by the Illinois Department of Natural Resources in recent years.
Because Illinois is a "hotbed" of the historical use of Aldrin, the pesticide from which dieldrin derives, "it's important to understand more about the exposure of fish-eating mammals, including humans, to dieldrin in Illinois," said Samantha Carpenter, a wildlife technical assistant at the Illinois Natural History Survey at the UI's Prairie Research Institute.
Once abundant in Illinois rivers, otters became rare by the turn of the 20th century because of hunting and habitat loss. By 1989, there were fewer than 100 otters in the state, according to the Illinois Department of Natural Resources. Thanks to a reintroduction program in the 1990s, their numbers have climbed, perhaps up to 15,000.
"They are all over the state and in every watershed in the state," said Nohra Mateus-Pinilla, a wildlife veterinary epidemiologist with the survey and principle investigator on the study.
Mateus-Pinilla said researchers were interested in evaluating diseases in Illinois river otters and learned that because DNR staff collected otters that had been killed by cars or traps, they would be able to access samples for analysis. Researchers obtained a total of 23 otters from 2009 to 2011. Autopsies were conducted at the College of Veterinary Medicine's diagnostic laboratory, and toxicology tests were done at Michigan State University.
Researchers zeroed in on otters because other wildlife also are being exposed to what otters eat — fish, mostly.
"They are at the top of the aquatic food chain, and they act as biomonitor of the health of other fish-eating mammals, including humans," Carpenter said.
Scientists screened liver concentrations for 20 different organohalogenated compounds. What came back in the highest concentrations were dieldrin, the breakdown of Aldrin; DDE , the breakdown of the pesticide DDT; and PCBs. With dieldrin, they found the average concentrations were higher than those found in otters back in the 1980s.
Millions of pounds of Aldrin were applied to crops, especially corn, in the Midwest every year, as well as to control mosquitoes and termites. The United States banned the insecticide in 1987 because of its harmful effects on humans and wildlife. DDT and PCBs were banned in the 1970s.
"They are known as persistent pollutants, so it's not surprising that they are still in the environment," Mateus-Pinilla said.
Studies about the effects of dieldrin have had mixed findings, Carpenter said. Some have linked dieldrin exposure to breast cancer, Parkinson's disease and Alzheimer's, and some studies do not, she said.
"However, dieldrin can also act as a developmental neurotoxicant. It means it can influence the development of the brain of a fetus. The optimal brain development of a fetus requires a really complex movement of and communication between neurons, and if a neurtoxicant interrupts that process, there's little potential for repairs," Carpenter said.
Some states have issued advisories about consuming fish caught in certain rivers because of dieldrin exposure. Illinois has fish advisories related to PCBs, mercury and other pollutants, but not dieldrin, Carpenter said.
In order to better understand how contaminants are accumulating in some of the otters, Mateus-Pinilla said, there are several areas where researchers could continue investigating. They want to better understand otter movements, how far they go, how long they stay in one area, what types of areas they frequent, population dynamics and population health, reproductive status and more.
"Otters have a very good ability to move and to travel long distances," she said. That means it's not easy to determine in which watershed the otters were exposed to the compounds.
"We also recognize this is a very different species. Sometimes it's not that simple to extrapolate from one species to another," she said.
The research team included, in addition to Carpenter and Mateus-Pinilla, UI animal sciences Professor Jan Novakofski and analytical chemist Andreas Lehner with Michigan State University's Diagnostic Center for Population and Animal Health; UI pathobiology Professor Kuldeep Singh; wildlife diversity program manager Robert Bluett with the Illinois Department of Natural Resources; and postdoctoral research associates Damian Satterthwaite-Phillips and Nelda Rivera, both with the Natural History Survey.