Springfield — River otters collected by DNR in recent years are telling an interesting story of how insecticides may be affecting the state’s wildlife food chain – and ultimately humans.
In other words, while the otter stages an amazing comeback in the state, the furbearer has simultaneously become a sort of “canary in a coal mine.”
This new label comes as researchers at the University of Illinois and the Illinois Natural History Survey report that they have found concentrations of banned insecticides – specifically dieldrin, along with industrial and commercial chemicals like polychlorinated biphenyls (PCBs) – in the livers of otters.
Incidentally, PCBs are a major factor in the fish consumption advisories that are released for many Illinois rivers each year.
“We feel that it is important to understand more about the exposure of fish-eating mammals, including humans, to dieldrin in Illinois,” Samantha Carpenter, a wildlife technical assistant at INHS, said.
At the center of the research are 23 river otters DNR acquired between 2009 and 2011. There was not yet a statewide trapping season for otters, but the specimen otters had been hit by automobiles or accidentally caught by trappers trying to catch beavers. DNR sent the otter carcasses to INHS and the University of Illinois’ Veterinary Diagnostic Laboratory for analysis. Scientists studied the otters for various diseases by conducting autopsies.
Toxicology tests were then done at Michigan State University.
Otters were a popular choice because their diets are similar to many other wildlife in the state. They eat mostly fish from the state’s lakes, rivers and streams.
“They [otters] are basically at the top of the aquatic food chain and act as biomonitor of the health of other fish-eating mammals, including humans,” Carpenter said.
The research team was surprised to discover average concentrations of dieldrin in the otters under current study exceeded levels of river otters previously collected between 1984-89. At the same time, concentrations of contaminants in the otters collected between 2009-11 ranged widely. One male had a concentration of PCBs in its liver of 3,450 parts per billion, while another had only 30 ppb. Dieldrin concentrations ranged from 14.4 to 534 ppb.
Since the otters were collected from counties all over central Illinois, the findings could indicate that some watersheds have a worse contamination problem than others, researchers noted.
“This is a red flag,” Carpenter said. “We need to understand more about what humans and wildlife are being exposed to in different watersheds.”
The researchers do not know why the male otters in the study carried a heavier burden of PCBs than the females, Carpenter said. It may be simply that the males are larger. They may range further than the females, picking up more toxins as they go.
More than 2,000 Illinois otters were trapped during the 2012-13 trapping season – the first open season in many decades.