Casey Lindberg recently graduated with a Ph.D. from Duke University’s Integrated Toxicology and Environmental Health Program. She received a North Carolina Sea Grant/Water Resources Research Institute Graduate Student Research Fellowship, which supported the work she explains here. She also has received funding from the Duke University Superfund Research Program and the Triangle Center for Evolutionary Medicine.
Can fish tolerate living in severely contaminated or degraded ecosystems? What problems arise when they face more than one potentially lethal change in their environment simultaneously? My North Carolina Sea Grant/Water Resources Research Institute Graduate Student Research Fellowship provided an opportunity to address these questions along the Cape Fear and other impacted estuaries.
The Cape Fear River Basin is one of the most industrialized regions in North Carolina, comprising several towns and cities, including Greensboro, Chapel Hill, Fayetteville and Wilmington. The high level of human activity, both currently and historically, has resulted in EPA designations of several regions along the Cape Fear as “Superfund Sites” — polluted areas that require a long-term response to address hazardous contaminants and remediation strategies.
In 2010, the EPA added a new site, Kerr-McGee Chemical Corp., to its National Priorities List. This site had been highly contaminated with creosote, a complex mixture created from coal tar and used primarily in the wood preservation processes.
The primary chemical components of creosote, polycyclic aromatic hydrocarbons (PAHs), can persist in aquatic environments for decades. They are present in other coal and oil-based products naturally and can form during the burning of products like wood, cigarettes, and even barbequed meats. Individual PAHs and complex PAH mixtures — like creosote and crude oil — are carcinogenic to humans and wildlife. They also can cause severe heart defects, as well as learning and memory deficits.
Surprisingly, even with severe contamination at the Kerr-McGee site, the habitat still supports populations of Atlantic killifish, a small, common marsh fish. These fish usually spend their entire lives within a 100-yard radius; despite living in levels of creosote and PAH contamination that should quickly kill them at any life stage, they have survived.
As it turns out, after many decades of exposure, these fish have evolved and adapted to be able to withstand exposures to creosote. However, while creosote-tolerant killifish can handle the toxicity caused by PAHs, they are often more vulnerable to other types of stress. This can include such environmental challenges as rapid changes in temperature and salinity.
For my research, I was able to capture killifish from creosote-contaminated sites and expose them to another common stressor, environmental hypoxia — a condition in which the oxygen content of water is less than what animals need for survival and development.
There were very interesting, albeit unpredictable, interactions between PAHs and hypoxia during exposures. For example, killifish exposed both to PAHs and hypoxia were unable to hatch as well as those exposed to either stressor alone. In one population of killifish, the co-exposure caused such severe effects that none of the embryos hatched at all.
Work like this highlights the importance of not only looking at multiple different types of stressors at once, but also the importance of identifying the most susceptible species or life stage that may be affected by these exposures. Because of the support from North Carolina Sea Grant and WRRI, we are spearheading new projects at Duke that follow up on the energetic requirements of fish exposed to multiple stressors, as well as how different genes react to such exposures.
We hope that this work will not only inform policymakers about hazards to humans and wildlife caused by climate change and environmental degradation, but that it also will inform regional fishermen about issues they may face with local brood stocks in the years to come.
photo: Atlantic killifish, courtesy of NOAA