First posted on 10-16-2013
Researchers in Illinois discovered something very disturbing: river otters have been exposed to dangerous chemicals and pesticides that were banned decades ago. In some cases, the concentrations of chemicals in the otters’ livers exceeded otters examined before the compounds were banned.
The Illinois Department of Natural Resources gathered the remains of 23 river otters that had been killed by cars or accidentally caught in traps between 2009 and 2011. They then passed those otters on to the University of Illinois Veterinary Diagnostic Laboratory for examination.
Liver concentrations of PCBs and a derivative of DDT were as high as in an earlier survey. However, dieldrin—a widely used insecticide that was banned in 1987—was found in higher concentration in the 23 otters than had been the case in 8 river otters studied from 1984 to 1989.
Dieldrin was commonly used to kill termites, mosquitoes and crop pests, especially in the Midwest’s agricultural belt. Over 15 million pounds of the substance was dropped on farm fields alone each year until use of the chemical was finally banned.
“The PCBs, dieldrin and DDE were the contaminants that we detected in highest concentration, in terms of average concentrations,” according to Samantha Carpenter, from the Illinois Natural History Survey, who helped lead the study. “And male river otters had significantly higher concentrations of PCBs compared to females.”
PCBs—today classified as “probable human carcinogens”—were once used as coolants and insulators in large electrical systems. PCBs were banned in 1979. Even today, some states have fish consumption advisories attached to some streams because of PCB contamination.
DDT was widely used as an insecticide in rural areas and in cities, but its use was stopped in the 1970s. In aquatic environments, DDT and its breakdown components are toxic to fish and macroinvertebrates. The insecticide also causes thinning of the eggshells of many bird species. Hormone functions and genetic disruptions result in mammals exposed to DDT.
“Some studies [of dieldrin] exposure find links to cancer, Parkinson’s disease and Alzheimer’s and some do not,” Carpenter said. “But perhaps most concerning is that both dieldrin and PCBs can act as developmental neurotoxicants, meaning that developing fetuses can be harmed at concentrations much smaller than those that can impact the health of adults.”
Concentrations of contaminants in river otters ranged widely. One male had a concentration of PCBs in its liver of 3,450 parts per billion (ppb), while another had only 30 ppb. Dieldrin concentrations ranged from 14.4 to 534 ppb.
River otters were collected from several counties, so Carpenter speculates that the team’s findings might be an indication that some watersheds suffer more contamination than others.
“For many of the contaminants we did detect a large range,” she said. “This is a red flag. We need to understand more about what humans and wildlife are being exposed to in different watersheds.”
The researchers did not say where the contaminants originated, and it may be that they linger in the environment and in streams for many years. The team said that more study is necessary to understand the factors that contributed to the exposure levels seen in river otters.
The team also said the did not know why male otters carried more toxins than females. Carpenter said it could be that the males are simply larger animals, or that the males might range more than females. The females could also pass some of the toxins on to their offspring while nursing.
“We don’t know enough about how these contaminants behave synergistically,” Carpenter said, especially since “the cocktail of contaminants that we’re exposed to here in the Midwest differs from what humans and wildlife are exposed to in eastern or western North America.”
Information from a University of Illinois press release was used in this article.
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